Well, I finally picked up my "new" 2008 Tribeca (i.e. it's new to me). Sorry, long posting to follow. :)
Now, I'm debating between various forms of rust-protection. Subaru Canada is heavily promoting electronic rust protection, where they put anodes/cathodes around the car body, and draw some battery power to keep the body powered up constantly. I think it's a gimmick. They claim this is the method that's been used to keep ocean-going ships from rusting. I'm sure it is, but who cares? I'm not floating my car in the ocean. Also the idea that this device draws power from the battery constantly gives me worries that it'll drain the battery out in the coldest days. It's already hard enough to start a car on those days, without having this drain around too. Also why is it necessary to keep the body powered up all of the time? Rust only occurs as you drive around in the salty roads, when you're parked it's not absorbing any salty water. They say it's good for 7-10 years. They are promoting this because it costs $1000, obviously.
Then there's the traditional chemical protection. Subaru offers the traditional underbody coating. They don't even call this rust-protection anymore, they call it "sound absorbent spray, which has some rust-protection benefits". That doesn't sound good to me. Also, because my car is 4 years old, they won't give any additional warranty with it, they said the cut-off value for warranty extension is 3 years old. A couple of different dealerships are offering this between $400-$700. I suppose if they aren't offering any warranty with it, then I might as well also shop around for similar work at independent body shops.
Then there's the other option of going with nothing. My previous 2000 Outback, had no additional rust protection. About a couple of years ago (2010), I got a chance to look at its underbody after getting its clutch repaired. The mechanic was showing me around underneath it, and I noticed that there's little to no rust on it, even the mechanic noted that. That was just 2 years ago. Starting last year, all of a sudden, rust just began all over it: lower body, upper body, even on the roof! I.e. in the space of 1 year, all of the rust began! I guess the Subarus are guaranteed against rust for 10 years, and they really know how to time that perfectly right, the rust began on the 11th year. :)
This time, before I bought the Tribeca, I took it to a mechanic and he showed me underneath it. This one showed a lot of rust underneath it, especially on the exhaust system. My assumption was that original equipment exhaust systems are supposed to be stainless steel, so why should they rust? So I called a Subaru dealer and asked them if this was normal. They explained that it was, saying that rust is only "surface rust" and assuring me that it doesn't go all of the way inside. They said, this rust occurs as a result of driving short distances where condensation forms on the exhaust but due to the short distances, the heat from the exhaust doesn't have enough time to boil away the condensation. This seemed reasonable to me as an explanation, but still it concerns me. My Outback's original stainless-steel exhaust lasted 9 years before I had to fix it. The replacement mufflers are not stainless-steel, they are aluminum, and they corrode much more easily than the original ones. Once the original exhausts are gone, replacement is a much more frequent thing afterwards. So I'd like to make sure this one's original exhaust system lasts much longer. However, they said that no-one coats the exhaust pipes with the anti-rust chemicals as they would start to burn on the hot pipes. My main concern is the exhaust rust. Any way of protecting the exhaust without chemicals?
They are a gimmick and a way to lighten your wallet. A good non-hardening oil-type rust-proofing is the most effective - needs to be redone on a regular basis. My 16 year old Ranger was done by Crown when new, and annually touched up antill 2008 and the truck is totally rust free - in central Ontario - with 306,000km on it.
Daughter's 98 Neon - was my sisters before that - had the electronic gizmo on it and it was pretty rusty when we got rid of it 4 years ago. Several engineer friends - including a chemical engineer - claims the premise the electronic gizmos are supposed to work on is badly flawed.
A friend of mine has been in the under-car oiling business for a couple decades and uses a mixture of oil and lanolin - applied hot - sprayed into body cavities as well as on the underbody surface - and it has proved to be quite effective even on older cars - and it slows down rust even on vehicles where rust has started (but not perforated)
They are "aluminized steel". Stainless replacements ARE available for extra cost.
I don't know any practice but in theory it is the only efficient way to fight corrosion. Rusting does occur *every time* your car sees metal ions and oxygen. In fact, keeping your car in a warm garage after driving on salty North American roads is the best way of promoting rust. So if I were to be dead set to not have any rust *and* if I were to trust that the implementation is done right, I'd splurge.
IMHO, a waste of money. Most of what can be done well, is already done on a new car. Benefits beyond that are marginal.
My choice. Today's cars are incredibly good with regard to the rust protection. Our 2002 Forester still has nothing visible (WI winters, driving in puddles of salty water after every snow). If experience with
17 years old Impreza is of any indication, various minor problems past 15 years quickly become dominating before the car develops any significant rust. And even when it does, replacing a body part is still a lot cheaper than paying for rust protection over the years.
Thanks, that helps seal that decision. Forget the electronic crap.
What is a good place to get it done, namely cheap but effective? The Subaru stuff is supposed to be good for 5 years, but I suspect a yearly application is a more effective protection. Do any of these guys still drill into the car to apply this stuff anymore?
Yes. using the right steel grades that will on average survive the rust through warranty (a decade for FHI as you noted). That is the FHI job, not yours.
Your job is giving the makers of low grade aftermarket exhaust crap pipes zero dollars zero cents.
As for the undercarriage coatings I'd guess if the undercarriage is pounded by gravel with any regularity it might have some merit. On the other hand tribeca is not a race ready sound deadener stripped Evo IX so it's up to you. Me thinks you want to go undercarriage washing, thorough drying and spray yourself route to save money.
I think that is partially right but the wrong way around. As I understand it, after startup the hot exhaust gasses as they pass through the cold exhaust condense and form a corrosive liquid INSIDE the exhaust system. because of the short running the exhaust system never gets hot enough to 'boils off' that liquid. So it sits there corroding the system from the inside out.
Everyone brings joy into your life, some by coming in, and others by leaving!
Most of the aftermarket rust-proofing guys I've talked to have said that they all require drilling into the car body to apply their product. Is there any that doesn't require this?
Subaru itself says that its "Sound Deadening" doesn't require drilling into the car.
On Wednesday, September 19, 2012 11:46:01 PM UTC-4, Yousuf Khan wrote:
rry, long posting to follow. :) Now, I'm debating between various forms of = rust-protection. Subaru Canada is heavily promoting electronic rust protect= ion, where they put anodes/cathodes around the car body, and draw some batt= ery power to keep the body powered up constantly. I think it's a gimmick. T= hey claim this is the method that's been used to keep ocean-going ships fro= m rusting. I'm sure it is, but who cares? I'm not floating my car in the oc= ean. Also the idea that this device draws power from the battery constantly= gives me worries that it'll drain the battery out in the coldest days. It'= s already hard enough to start a car on those days, without having this dra= in around too. Also why is it necessary to keep the body powered up all of = the time? Rust only occurs as you drive around in the salty roads, when you= 're parked it's not absorbing any salty water. They say it's good for 7-10 = years. They are promoting this because it costs $1000, obviously. Then ther= e's the traditional chemical protection. Subaru offers the traditional unde= rbody coating. They don't even call this rust-protection anymore, they call= it "sound absorbent spray, which has some rust-protection benefits". That = doesn't sound good to me. Also, because my car is 4 years old, they won't g= ive any additional warranty with it, they said the cut-off value for warran= ty extension is 3 years old. A couple of different dealerships are offering= this between $400-$700. I suppose if they aren't offering any warranty wit= h it, then I might as well also shop around for similar work at independent= body shops. Then there's the other option of going with nothing. My previo= us 2000 Outback, had no additional rust protection. About a couple of years= ago (2010), I got a chance to look at its underbody after getting its clut= ch repaired. The mechanic was showing me around underneath it, and I notice= d that there's little to no rust on it, even the mechanic noted that. That = was just 2 years ago. Starting last year, all of a sudden, rust just began = all over it: lower body, upper body, even on the roof! I.e. in the space of= 1 year, all of the rust began! I guess the Subarus are guaranteed against = rust for 10 years, and they really know how to time that perfectly right, t= he rust began on the 11th year. :) This time, before I bought the Tribeca, = I took it to a mechanic and he showed me underneath it. This one showed a l= ot of rust underneath it, especially on the exhaust system. My assumption w= as that original equipment exhaust systems are supposed to be stainless ste= el, so why should they rust? So I called a Subaru dealer and asked them if = this was normal. They explained that it was, saying that rust is only "surf= ace rust" and assuring me that it doesn't go all of the way inside. They sa= id, this rust occurs as a result of driving short distances where condensat= ion forms on the exhaust but due to the short distances, the heat from the = exhaust doesn't have enough time to boil away the condensation. This seemed= reasonable to me as an explanation, but still it concerns me. My Outback's= original stainless-steel exhaust lasted 9 years before I had to fix it. Th= e replacement mufflers are not stainless-steel, they are aluminum, and they= corrode much more easily than the original ones. Once the original exhaust= s are gone, replacement is a much more frequent thing afterwards. So I'd li= ke to make sure this one's original exhaust system lasts much longer. Howev= er, they said that no-one coats the exhaust pipes with the anti-rust chemic= als as they would start to burn on the hot pipes. My main concern is the ex= haust rust. Any way of protecting the exhaust without chemicals? Yousuf Kha= n
Dealer treatments are high profit items and usually not necessary. Don't know details on Subaru but cars are normally made from one sided galv= anized steel and when assembled are dipped in a corrosion proofing bath fol= lowed by an corrosion proof epoxy coat before painting. We have a lot of winter road salting here and I've never seen any rust on m= y Subarus.
Perhaps what they are really doing is eliminating or reducing electrolysis. That is where 2 dissimilar metals are involved and an electrolyte. The different metals have different electrolysis voltages which causes a current through the electrolyte. The DC current leaves one metal to travel to the other metal. The higher voltage metal material migrates to get deposited on the other. Another term is galvanic corrosion. I'm assuming the vehicle is destined for a region where they spread salt (the electrolyte) to deice the roads.
I haven't bothered investigated if Subaru is bonding dissimilar metals together in their car bodies but I strongly suspect that happens. Aluminum alloys are good for lightweight but steel is needed in places for stronger support. The reverse electrolysis is probably not to prevent rust along the body panels but where they connect to dissimilar metal supports. The galvanic corrosion weakens the joint between the 2 metals. Once metal migration has occurred, the polluted metal will experience accelerated rusting even when coated. Electrolysis is used to remove the ions from the corroded metal before coating rather than grinding down the corroded metal.
The HCl continues attacking the impregnated metal via reaction 1. The process stops when the iron, water, or chloride gets depleted. You can try to clean the impregnanted metal but cleaning may not be complete plus (CL ions are in joints, crevices, under the surface) and it is going on under the paint job with flaws (during application or later due to damage). You can grind the material (which requires removing the impregnated metal and recoating), or you remove the CL ions impregnated into the metal (via reverse electrolysis). Electrolysis can be chemically induced, like using sodium carbonate (often found in powered laundry detergents) but may affect the surface of the treated metal plus it won't permeate under and throughout the affected metal under a compromised coating, or an alkali bath (which isn't something doable with a coated surface) which eliminates hydrogen embrittlement or etching of the unrusted metal. The techniques used to neutralize rust mentioned above are obviously rather catastrophic repairs (to prep the affected metal for treatment) as they cause damage that then needs to be repaired, like repainting the metal, so these techniques are those employed by body shops or enthusiasts willing to expend the effort.
Rust is caused by electrolysis. I suspect Subaru is applying a voltaic differential to equivalence the potential differential in galvanic voltages for joints made of dissimilar metals to eliminate or reduce the electrolysis in the first place. They're trying to lengthen the time for when you have to take your car into the body shop to perform the more destructive methods of removing and treating rust. Subaru has already performed the chemical rust protection at the factory and obviously something you cannot do except as a repair job for damage incurred later. Whether they do or don't use galvanic equalization doesn't preclude them from still performing their chemical protections in manufacturing their product. While galvanic equalization probably protects mostly the joints, how well it protects the surface of your body panels is another matter. There would have to be a circuit for the current to flow, not just a potential difference between the metals. At the joints, there probably are circuits within the connection but rust somewhere at the center of a body panel would require your car to be wet. Well, if it's winter and they're spraying salt on the roads to melt it then the wet salty spray is coating your car to lengthen the circuit.
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Here they are looking at only the chemical reaction rather than galvanic corrosion beween the joints of dissimilar metals. Rather than the exposed metal getting corroded by having its electrons depleted, the electric field provides those electrons for the chemical reaction. The chemical reaction with the electrolyte will occurs (it gets electrons) but the metal isn't depleted of those ions. I doubt that this eliminates surface corrosion but would help alleviate the deeper corrosion that pits out the metal and result in having to grind it down or replace it. So you could buff the rusty coating and repaint without having to sand down the metal or replace body panels or doors.
The tar coatings and other coating type of rust protections are just to add more layers to avoid a compromise (exposure) of the metal underneath. Well, we all know those will fail eventually due to accidents, flying stones, flex, degradation over time, etc. Applying an electric field to the metal tries to avoid severe chemical electrolysis when the metal *does* get exposed to an electrolyte. Since galvanic equalization is likely not what Subaru is targeting to accomplish, my guess is they are just trying to eliminate the deep corrosion (pitting) caused by chemical corrosion. Some electric (not really electronic) rust prevention gadgets only have 1 contact to the body but I would think more contacts would be better to ensure no loss of electric field to a body panel due to loss of electrically connectivity by the part wherever the other contact was made. While water doesn't conduct electricity very well, salt water does so there may be some drain on the battery when driving your car in a salty splash but the circuit path (and its resistance) might be too long to care.
While the electric field method to reduce electrolysis has thoeretical merit, I don't know that it has practical merit. Even if put on a car, I'd still want the coating methods (e.g., tar [antiquated] or wax & oil- based undercoats) used to protect the metal from rusting as a first line of defense. I have a burglar alarm in my house but I still use the door locks. For the outside surface, probably rinsing your car after a trip with a solution that neutralizes the salts and using touchup paint on every nick would probably end up doing as well for protection as these electric field methods but then that doesn't help underneath where you can't wash and where you are relying on the coating (tar, neoprene) to not get penetrated or crack over many years. After all, all this rustproofing effort is so you can keep your car in good condition over MANY years of ownership.
How long do you plan on keeping your Subaru? I keep mine until the repairs exceed the value of the car (the value to me, not the Kelly Bluebook value). How much do you pay for insurance every year? Well, over the number of years of ownership you expect for the vehicle, how much does the electric anti-electrolysis kit cost you per year? Do you water your lawn before it goes yellow or after? Watering beforehand means it won't go yellow but then maybe it'll rain and you didn't need to water. It's like all protection measure: you're hoping the expense now will eliminate a greater expense later. Do you perform preventative maintenance on you vehicle for gradual expense or do you wait until your vehicle requires catastrophic repair and high expense?
This isn't really a new scheme. I've read forum posts where users posting back 6 years ago were reporting mixed results from using the old [impressed current] cathodic protection. Most of the old schemes relied on electron transfer under a moist environment; i.e., your car gets wet a long (rain, snow melt) and not under a dry environment and yet dry salt sitting on your dry car still causes rust due to absorption of water from the air. That cathodic method eliminated rust at the surface where the electrolyte was extracting ions from the metal. Apparently there is some "capactive" or electrostatic methods that work lower within the metal to help avoid the pitting, too. I don't know what method Subaru is using. The traditional method was used on buried cables, [sea] boats, and the bars in reinforced concrete where they are in buried or submerged (wet or damp) environments to provide an ionic path, not for free-air environments. I really doubt Subaru would be using that antiquated and inappropriate method for electron substitution. Cathodic protection works when there is a complete circuit for electron flow and that circuit is always there when the conditions for rust are there. Almost every article that I've seen debunking electronic anti-rust devices are arguing against the cathodic protection method (so they're out of date with recent methods). See Michael's much shorter description of the capactive method at
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If you're really good at always rinsing off your car after being on salty roads or after a long trip, periodically cleansing and waxing/coating your car, touching up every nick and scratch (with real paint and not some wipe-over or dab-on coating) and even plan on re-coating the underside of your panels and body after around 5 years (which is usually pricey) then I don't see the need for an electronic gadget that has had few stats compiled by a sufficiently large *user* base (not by sellers) to determine the efficacy of the electric method. Of course, all that protective maintenance costs money, too. That Subaru is offering this option seems to lend some credence to this method of rust protection. While the sellers always have their success stories and proof-of-concept articles lauding their products, consumers really haven't seen such remarkable results. Of some dealers of traditional anti-rust coating products that have tested these electronic devices to evaluate their efficacy, the results have been negative; see
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Just remember this is areview from a biased reviewer (they have an interest in selling theirown traditional method than recommending a solution that doesn't involvemoney going into someone else's pocket). I can't see that such devices have exemplied an ultimate anti-rust solution. For me (when I was younger), I'd probably skip it when buying a new car. The dealer markup and having to pay for their (or mfr) installation just makes it too pricey. I'd rely on the traditional coating protections for awhile and then sometime later decide if I wanted to install myself one of these kits. These typically have you run just 1 or 2 wires to the body but then there's the problem of electrical continuity (grounding) between body frame, panels, and other metal parts so you might have to run shorty jumpers between these metal parts to ensure they actually do receive the charge. That's why it's probably better to get a kit that has multiple contact points instead of just 1 or 2. Of course, that means getting under the vehicle to run the other contacts to the rear of the vehicle (versus a mfr-installed kit that probably runs through their wiring harness). I don't know if Subaru's offering is a manufacturer-installed kit or an add-on or after-market install. Now I'm too old, too lazy, or too picky to bother working on anything under the car myself so now I'd probably get the kit from the mfr or dealer or have a shop do the install sometime later.
As for draining the battery, the electrostatic or capacitive devices draw very little power, probably around what your radio clock draws to maintain its memory of preset stations. Some also look to be pulsed capacitive coupling. They aren't keeping the body charged all the time but only to pulse when the charge gets too low. I've not read a complaint against the capacitive units of someone saying it drained their battery. They're meant to be powered all the time.
My opinion: Don't buy and wait. Subaru's $1000 price is a hell of a lot higher than for a kit that you install yourself (or even to have a local shop install the kit). Buy the car without the electronic anti- electrolysis kit but get a good underbody rust coating (see below) and keep the undercoat touched up every couple of years. Sometime later decide if you want to spend your tax refund on this gimmick or to reapply the traditional rustproof undercoating. Meanwhile, baby the paint job on the outside. Then also remember that a lot of what you see for rust doesn't really affect the usability of the vehicle. I've got a
2002 Subie with rusted out rear fenders but that doesn't prevent the vehicle from being drivable.
That's not chemical protection (as in preventing the chemical reaction that causes rust) but barrier protection. If that barrier is breached then the exposed metal will rust. The sound deadening "rubberized" or neoprene undercoatings are not for rust prevention. They are to make an otherwise noisy care more quiet (it partially absorbs the sound). See
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Of course,competitors have their own explanations of why other materials are lesseffective, like
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Obviouslythey don't divulge their ingredients but it sure sounds the equivalentof spraying bar chain oil. The MSDS is worthless to find ingredientssince only hazardous materials need be listed. Their "rust inhibitor"listed as "CAS 72623-83-7" was also found as "Refined Petroleium Oil" at
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and as"Lubricating oil" at
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use a brand and part number to hide their simple ingredients.That's also why such oil-based rustproof treatments have to getperiodically retreated.
It's still iron and unprotected iron will rust. What do you think happens when that shiny surface gets scratched? You get more surface area. You've never had to use polishing compound (contains ammonium) on your stainless steel kitchen sink or its stainless steel drain basket? If you don't mind looking at the rust, you can leave it and it won't penetrate much beyond the surface. Of course, consumers don't like to see rusty sinks. Stainless steel sinks, counters in a deli, and so forth are expected to look shiny.
Stainless steel does not /readily/ rust but it does rust (i.e., it is NOT stain-proof). It is corrosion-resistant, not corrosion-proof. See
To be effective, the car needs to be drilled, and the guy doing it needs to know where to drill. The sound deadnener is aoften worse than nothing, because when it peals off it holds water and "crap" - causing rust. Rubberized coatings are a no-no, as far as I'm concerned.
I'll have to respectfully dissagree - with decades of experience to back me up. A properly done and maintained rustproofing job will at least triple the life of most auto bodies in northern North America (rust belt)
When's the last time you paid a body shop or repairs???????
I GENERALLY keep my vehicles 'till they are over 16 years old - I'm selling one now at 10 that was not rustproofed - I bought it at 6 years - and it is rusting severely enough at 10 that I'm not going to hang onto it any longer. My other 10 year old car was rustproofed and is spotless - as is the 16 year old pickup I just bought -also rustproofed.
long posting to follow. :) Now, I'm debating between various forms of rust-protection. Subaru Canada is heavily promoting electronic rust protection, where they put anodes/cathodes around the car body, and draw some battery power to keep the body powered up constantly. I think it's a gimmick. They claim this is the method that's been used to keep ocean-going ships from rusting. I'm sure it is, but who cares? I'm not floating my car in the ocean. Also the idea that this device draws power from the battery constantly gives me worries that it'll drain the battery out in the coldest days. It's already hard enough to start a car on those days, without having this drain around too. Also why is it necessary to keep the body powered up all of the time? Rust only occurs as you drive around in the salty roads, when you're parked it's not absorbing any salty water. They say it's good for 7-10 years. They are
chemical protection. Subaru offers the traditional underbody coating. They don't even call this rust-protection anymore, they call it "sound absorbent spray, which has some rust-protection benefits". That doesn't sound good to me. Also, because my car is 4 years old, they won't give any additional warranty with it, they said the cut-off value for warranty extension is 3 years old. A couple of different dealerships are offering this between $400-$700. I suppose if they aren't offering any warranty with it, then I might as well also shop around for similar work at independent body shops. Then there's the other option of going with nothing. My previous 2000 Outback, had no additional rust protection. About a couple of years ago (2010), I got a chance to look at its underbody after getting its clutch repaired. The mechanic was showing me around underneath it, and I noticed that there's little to no rust on it,
all of a sudden, rust just began all over it: lower body, upper body, even on the roof! I.e. in the space of 1 year, all of the rust began! I guess the Subarus are guaranteed against rust for 10 years, and they really know how to time that perfectly right, the rust began on the 11th year. :) This time, before I bought the Tribeca, I took it to a mechanic and he showed me underneath it. This one showed a lot of rust underneath it, especially on the exhaust system. My assumption was that original equipment exhaust systems are supposed to be stainless steel, so why should they rust? So I called a Subaru dealer and asked them if this was normal. They explained that it was, saying that rust is only "surface rust" and assuring me that it doesn't go all of the way inside. They said, this rust occurs as a result of driving short distances where condensation forms on the exhaust but due to the short distances, the
This seemed reasonable to me as an explanation, but still it concerns me. My Outback's original stainless-steel exhaust lasted 9 years before I had to fix it. The replacement mufflers are not stainless-steel, they are aluminum, and they corrode much more easily than the original ones. Once the original exhausts are gone, replacement is a much more frequent thing afterwards. So I'd like to make sure this one's original exhaust system lasts much longer. However, they said that no-one coats the exhaust pipes with the anti-rust chemicals as they would start to burn on the hot pipes. My main concern is the exhaust rust. Any way of protecting the exhaust without chemicals? Yousuf Khan
galvanized steel and when assembled are dipped in a corrosion proofing bath followed by an corrosion proof epoxy coat before painting.
See a lot of rusty Soobs here in Central Ontario. ANd rusty just about anything els too. Not as bad as in the seventies and early eighties - but still substantial.
Nope - all steel. Some different steel formulations - but still steel
- and the rust very seldom accurs where two peices join. The process works good for re-bar in concrete bridges, and for ships at sea - but a car is totally different.
By the way - the electronic crap is NOT sold by Subaru - it is sold by the dealer. Not made by or for Soob either.
Take a good look at how they are installed. One contact - no circuit
- Snake oil. You are buying an expensive insurance policy with enough loopholes to drive a fleet of hummers through.
Which is why I specified a NON HARDENING coating - also known as "self healing" - which are oil based (or a wax) and NOT rubberized. Tar hardens. Rubber peals off. Oil / grease soaks in and sticks.
Like I said before - this stuff is NOT manufacturer specific or supplied. It is aftermarket - so it does NOT use the wiring harness.
At least every one I've seen - and I've seen hundreds.
Well, in my experience, I found my 2000 OBW to be perfectly rust-free up until its 10th year too. It was in its 11th year that the first problems started, and when they started, they started big time!
You're on your 10th year now with that Forester, so it would be interesting to see if it's still in the same shape in the 11th and 12th years?
I don't like the idea of drilling into a car, as there is a potential of the rust starting at the very spot that they drilled into, thus creating a rust starting location where previously there was none. I know they put extra coating in those spots, but why take the chance with a brand new car? Why can't they just do a mini application only over the outer portions of the car while it's still new?
I'm thinking maybe I'll wait on rust protection until it reaches near its 8th year, when it's natural protection is starting to wear away. I'd also be more comfortable having the car drilled into at that time. Would waiting that long still be effective in preventing rust?
Also I had some problem with roof rust on my previous car. Usually no one coats anything to do with the roof.
I've seen a lot of rusted Subarus, including my own old one. In fact, I see all Subarus of a certain age develop the rust spots almost simultaneously in the exact same areas. I was in Montreal a couple of weeks back and I parked in a parking garage quite coincidentally right next to an OBW of the same vintage as mine, and also with the exact same dark green colour. I realized it was an American Subaru even before I saw its license plate because it had no rust on it.
I think we might be using more salt on our roads up here than most American cities do.
Because the rust does not start on the exterior. It starts where moisture (and salt) sits on the unpainted inside surface of the metal
- cars rust from the inside out - and if you can protect the interior you can prevent the rust. The holes are drilled, the product is applied,nd the hole is plugged with a plastic plug dipped in the product if the guy is doing it right. Really fussy guys will paint the edges of the holes - but that is not very common.
Signigicantly less effective, as the rust has a good head start by that time. It's not through yet - but the cancer is well established.
I was going to do that on my (2002 - purchased used at 5 years) PT cruiser - I had it oiled at age 7, but the front fender blistered through in year eight.
Roof rust is usually due to running with the heat on the floor in winter - the roof stays cold and all the moisture from wet snowy floormats condenses on the rood metal, and runs down the pillars - rusting them out along with the roof corners.
Yep, that's the old argument that addresses the old method of cathodic protection (impressed current) and NOT for the newer capacitive method (which has electron flow but not a "completed circuit" for it). I haven't bothered to investigate the history (of something I haven't used or cared about before) but I believe the capacitive method started getting used or became available around 2006. The cathodic method requires the protected item be submerged (water, wet dirt) so there was a circuit path. Not true of the capacitive method. The electrolytic reaction via voltaic potential difference provided the electron flow, not a completed circuit. Read the provided articles.
So we are in vehement agreement. Okay.
Cracking is the problem, mostly due to flex of the brittled aged tar, which compromizes the boundary protection. A hard coating that remains in place and maintains the seal would work. Bad formulations also had the tar coating dripping off or oozing due to gravity to thin the boundary protection in super hot weather.
Even when it doesn't peel (or YOU peel it off), it isn't a good seal. Water can and often does get trapped between the rubber/neoprene coating and the metal it covered. Later due to this reality, peddlers had to change from calling their product a rustproof or rust-resistant product to just a sound deadening product.
Doesn't really soak in. Put oil in a beaker. Drop in a strip of metal. Remove the metal strip. Squeegee the metal strip to remove the oil. The same amount of oil is in the beaker other than the microscopic portion still residing inside the microscopic pores on the surface of the metal strip. If oil impregnated further than those surface pores, the metal would be unusable for structural use since it would "dissolve" and be too weak.
Metal is still porous on its surface and why we use heatsink compound on heatsinks, like for the CPU in your computer. Filling the surface pores of a metal is not "soaking in". There is no treatment of the metal beyond filling those microscopic pores. The wax & oil blend for rustproof coating just coats the metal (just like tar and rubber). It doesn't soak in or blend into or impregnate the metal. The so-called soaking into the joints or crevices is due to the wetting effect. It's not some intelligent ooze (The Blob) that knows there is some bare metal in a crevice that it has to go cover. That's why the "inhibitor" in these blends is also called penetrating oil.
Obviously if they just used the penetrating oil to coat the surface of the metal then it would be near worthless protection. It would be gone the first time you did an underbody wash, after a few hot days, did some offroading, or just after some time, like storing the vehicle. If it was just did the "soaking in" (wetting) of the oil into the microscopic pores of the metal's surface than that protection would also soon be gone. It's the blending with the wax to hold it in place that makes the oil-based coating of value. But, and as you noted, it does require periodic reapplication to rebuild the boundary and close any breaches that have occured since the prior application.
So, we're in agreement that it is a waste of money to get the electronic rust protection gizmos, that the cathodic method is worthless in a free-air, non-closed circuit environ versus the submerged, closed- circuit environ where it does work, and that the wax & penetrating oil is better than the other undercoating materials. That leaves babying the topcoat (outside) of the metal shell when that side's boundary protection (paint) has been breached.
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