0W-40 in 1970 Cadillac Eldorado

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I don't think it would be a good idea to pour Techron into the crankcase. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Which is WHY I reccomend AGAINST mixing types and brands of oil.Use that solo can for something else.

I don't think motor oil has a great shelf life. I'd be leery of using it in a good engine. It breaks down. Ever see gasoline that has sat around in a tank for a long time?
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do you really want to take mechanical advice from a guy who purchased his education online?
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do you really want to take mechanical advice from a guy who purchased his education online?
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Why won't this myth die after 30+ years of synthetic oils that are COMPLETELY compatible with all seal materials used since the 50s and all conventional oils????
As for the original question- you might join the forums on bobistheoilguy.com and bring it up there. I think the general consensus is that the Mobil "0wXX" oils have a very good base oil stock and are typically higher viscosity index (thin less as they get hotter) than the "5wXX" and "10wXX" versions (whether XX be 30 or 40). So I'd say give 0w40 a try if you want to. There is a subset on there who think Mobil is overpriced and will recommend Pennzoil Platinum or Castrol Edge... but any of the 3 are interchangeable in my book. I've had a longer history with Mobil 1 personally.
If it were me, I'd also seriously consider Shell RotellaT Synthetic 5w40. Its a diesel (really "heavy duty" is more accurate- it also meets all the gasoline ratings) engine oil and works very well in torquey, slow-turning engines like big-block v8s. And interestingly, the Subaru guys who autocross their WRX turbos also love it. I know for a fact that it doesn't thin out at high temperature as much as Mobil 1 5w30 does, having tried both in one of my old Mopar 440s. I've been using RotellaT for about 2 years now.
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Completely? That's going overboard. Generally compatible. The POINT is that when you have been using regular oil there is NO benefit in switching to synthatic. The fault isn't in the synthetic oil, which is VASTLY superior to regular oil, but when you have 50,000 miles on an egine that has used conventional oils you already have the internal parts varnished. Synthetic do nothing for you. WHen you go from a buck something a quart to 6 bucks a quart it's stupid.

If you had followed this discussion several of us have suggested Shell Rotella and Texaco Havoline.
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krp wrote:

No, just true. > The POINT

Yes, there is. Synthetic oils can let you extend your oil change interval even further than you can with conventional oil.

50,000 miles is a drop in the bucket, and if you have varnish or sludge at 50k you must either a) have a Toyota, or b) have found a stash of 1940s non-detergent oil. Good conventional oils don't "varnish" anything.

The difference between 1 buck for oil you'd damn well better change every 5000 miles, and 6 bucks per quart for oil that you change every 9000 miles is NEGLIGIBLE in comparison to the other costs of operating the vehicle. Especially for a rarely-driven car like this which needs the better acid buffering and moisture tolerance of a top grade oil.
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Not long enough to make up the price difference.

The guy has a 70 Eldorado. Not sure how many times this car has seen 5K, or this engine. I suspect more than once. I have a new Honda CR-V and use Castrol Edge. Never used anything but synthetic oil since I got it. The engine will never see anything else. All conventional oils DO leave some varnish. Now Pennsylvania oils leave SLUDGE. I'd only use a Pennsylvania oil in a Russian car that I HATED. Like a LADA (Fiat) or a Muscovitch. Doesn't make any difference what you use in those damn things.
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krp wrote:

Suffice it to say, you're reguritating myths and legends that are 30 years old. Today's "dino" oils are highly refined. Even the most basic Group II base stocks are so refined that it really doesn't matter where the original crude came from, the waxes and other contaminants are long since removed before it gets put in a bottle and sold as motor oil. Group III+ oils are synthetics derived from petroleum that has gone through multiple refining steps that basically dismantle the molecules and put them back together in a very consistent way. Group IV synthetics are synthesized from natural gas. The idea that there is something different about "Pennsylvania" motor oil is just a myth, Pennzoil and Quaker State may have been pretty crappy oils back in the 70s, but today both of them (even the low-end lines, not just Q or Pennzoil Platinum) consistently yield some of the best used oil analysis results reported.
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Quaker State and Pennzoil are paraffin based. Other oil companies are asphalt based. Pennsylvania oil is not the idea for today's engines. Which is why both companies are now heavy into synthetics. Have you see Castrol's latest data on testing oils? Edge versus everything else?
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krp wrote:

False.
Pennzoil "yellow bottle" is not synthetic, yet it consistently yields superb oil analysis results. I used to be a Pennzoil hater too, but the facts today say its among the best conventional oils out there. Welcome to this century, quit living in the previous one.

I could care less about any oil company's self-test results. What impresses me more is that Castrol Edge does well on independent tests too. Edge, Pennzoil Platinum, Mobil 1, Valvoline SynPower, etc. are all very comparable.
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Well those that aren't synthetics. That's what both companies packaging says.

Actually not. SHell Rotella and Taxaco Havoline are considerably better.

I was speaking to the independent tests.. It performs much better than the other synthetics. Remember,"Edge" is not Castrol's only synthetic, nor is Mobil One Mobil's only synthetic. Head to head, Edge is the best.
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krp wrote:

I did read the thread. I saw multiple references to Rotella T (conventional) 15w40, which is too heavy for anything but a worn-out beater gasoline engine or an air-cooled gasoline engine. Which is why I SPECIFICALLY mentioned the synthetic 5w40 version, which gets down much closer to the 0w40 that the OP asked about. IMO, Rotella synthetic 5w40 will provide all the cold flow he's looking for, but the high VI of the synthetic Rotella base oil will also protect an engine like a Cad 500 just fine in Death Valley heat if necessary.
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Not from ME. Rotella OIL straight weights were made for SEVERE engine use. (Trucks etc) and are great on cars with high revving engines. I have my own opinions of what weight to use. Depending on climate. In Wisconsin where I grew up 10 weight in winter and 30 weight in summer. I don't really believe in multi-weight oil. We could get into a hot debate on that. I used to work for Texaco and had fun arguing with the refinery engineers and making them agree with me that THERE IS REALLY NO SUCH THING. You see, all you do with multi-weight oils is change the clock. The amount of time it takes to change the viscosity from what it is at the ambient temperature to run hot. The oil is still the same - ALL fluids change when heated and cooled. You can't escape that, just fudge with how long it takes to get from point A to Point B.
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krp wrote:

Its obvious that you don't really understand what a "multi weight" oil means. "The time it takes to change viscosity" doesn't even come into play at all. All measurements are made with the fluid fully cold or fully hot.
Yes, all oils change thickness with temperature. But grossly oversimplyfing- the AMOUNT (not the speed) that a fluids thickness changes with temperature varies a huge amount from fluid to fluid. The way that you qualify a fluid to be a "multi weight" oil is to have a very high viscosity index- meaning that the viscosity change with temperature is low. A low viscosity index means that thickness changes greatly with temperature. So whereas a "straight 30 weight" oil may be as thick as honey at 0 degrees F and as thin as water at 212 F, a 5w40 will be as thick as room-temperature maple syrup at 0F and as thin as lukewarm syrup at 212F. IOW it doesn't change thickness NEARLY as much, even after its fully heated or fully cooled and allowed to come to equilibrium.
Example time: How much does the thickness of honey change when you take it from 40 degrees F to 180 degrees F? A lot. Honey has a low viscosity index over that temperature change. Now, how much does the thickness of water change when you take it from 40 degrees F to 180 degrees F? Hardly at all, in fact not enough to measure without sensitive instruments. Water has a high VI over that temperature range. You want your engine oil to behave more like water (although it needs to be thicker) than you want it to behave like honey.
Making an oil have a high VI used to be done primarily with viscosity modifiers- long-chain polymers that coil up tightly at low temperatures letting the fluid flow easily, then uncoil and "tangle" at high temperatures to thicken the fluid. VI modifiers are used far less these days since base stock oils are now made with much higher inherent VI. This is another good reason to use a synthetic in any engine- Rotella T Synthetic for example is made using Shell's XHVI base fluid (a group III+ hydroprocessed slack wax derivative) which has a viscosity index much higher than most conventional oils, and in fact higher than many Group IV PAO base oils. This means that it can flow easily when cold and stay thick when hot WITHOUT adding the long coily polymers, which themselves do not lubricate and in fact contribute to deposit formation when they break down. This USED to be a good argument for sticking with a single-grade oil. No more.
These characteristics (high VI base oil, combined with less need for VI improving polymers) are a good reason to consider a synthetic or semi-synthetic for any vehicle regardless of age- ESPECIALLY given the OP's desire for an oil that both flows in cold and protects in heat.
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Sure I do. It deflies the LAW of fluids. Look - ther FACT is that at any given temperature the fluid is constant as far as thickness and lubrication potential is. It gets thicker when it is cold and thinner when it is hot. ALL fluids behave that way. All that molecule chaining does is to change the curve of the change. It modifies time. In other words it stays thicker longer at higher temperatures.

ALL fluids get thicker when they are cold and thinner when they are HOT. That includes motor oil. What you do when you screw with the chemistry is you change the RATE of change over time.In simple terms a multi-weight oil takes longer to get thin when the engine gets hot, but thin it gets. The FACT is also that when you deal with a "straight weight" oil - say 30W - technically it doesn't STAY 30 weight, it THINGS out. But it stays thicker than a 20 weight. Thinner than a 50 weight. a 10 W. 30 oil supposedly acts like a 10 weight when hot and a 30 weight when cold. In reality it doesn't act all that much differently than a 20 weight.
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Not really, no.
Look at the viscosity curve. It doesn't have time on any scale. Yes, many people measure viscosity as a rate of flow through a fixed size hole, but that doesn't mean there's a T in the definition.

No, not all fluids do this. Some fluids aren't even Newtonian at all. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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I had this argument with a refinery engineer almost 30 years ago. We did measurements together. ALL fluids behave the same way. They get thinner when they are heated, and thicken when they get colder. It's a law of physics.

Actually it is a measure of the specific DENSITY ot the fluid, and how it changes at various temperattures.

Name one that doesn't. ON THIS PLANET.
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No, density and viscosity are related but they are not the same thing.

Atactic polypropylene. The molecule is a little ball, but when it gets hotter, the ball unrolls and the molecule turns into a long straight string. A solution of the stuff gets thicker when you heat it up, because the resistance to flow of the unrolled molecule is greater than the rolled up one.
Typical multigrade motor oils use this principle, although more popular now are proprietary ester polymers that form corkscrews that unroll instead of balls. VI technology is pretty nifty stuff. --scott
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"C'est un Nagra. C'est suisse, et tres, tres precis."

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wrote:

Not strictly a "fluid" in the technical sense.
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