I just bought an '03 Passat GLS 1.8 turbo (manual). I put regular unleaded in it by accident (out of habit actually, since my 95 Jetta didn't care). Anyway, the car almost didn't start after the second day. I know the owner, and she states that this has never happened before (she always put super in, and I have no reason to disbelieve her).
Anyway, is it possible that the regular is so bad for this car that it would almost not start because of it? Perhaps the turbo has something to do with it?
p.s. The car has 95K miles on it, and has had nothing but expensive dealer servicings since birth. Also, the car has a new fuel pump, new water pump, and new timing belt.
I suspect that was probably some sort of coincidence. Generally speaking any modern car will not run appreciably different between regular unleaded and super unleaded, as the engine management system will just alter the ignition timing to compensate. This can mean however that the car will produce a little less power for every cycle and you will probably hit the accelerator a little more aggressively, so your MPG might actually drop slightly (and negating the cost difference of regular vs. premium fuel). Long term, the altered timing could result in lower combustion temperatures and carbon buildup and that could cause problems. But one tankful shouldn't hurt. Just put the right stuff in next time.
If you run the engine for less than a minute or two from cold then switch off, the next start will be very difficult. Pumping the accellerator won't help, it's best just to hold it wide-open till it fires.
a) Regular gasoline (R+M/2 87) is actually MORE volatile, but contains less energy per ounce than premium gasoline (91 - 93 octane). b) All other things being equal, using regular fuel should make your vehicle easier to start rather than harder, especially under cold-weather conditions.
So, I seriously doubt that switching grades has anything at all to do with your hard-start problem, especially within the realm of a single (or 3) tankful(s) as it applies to octane rating alone.
Then, under starting conditions, the turbo is entirely out of the picture.
Lastly, as this is an EFI engine, throttle position should be dead-closed at starting (Keep Your Foot OFF the Gas Pedal!)... but follow your owner's manual as to whether you set the throttle-positioner based on outside air temperature. Our last VW wanted the gas pedal pushed down ONCE and then let go with outside air temperatures below 32F/0C at cold-start.
So, to address the hard-start issue:
You say the mileage is over 90K. When was the last time:
The fuel filter was changed? The plugs were changed? The plug wires were changed? The air-filter was changed?
I suspect that you are ~30,000 miles (or more) into your present fuel filter. If you make a habit of running down your tank until the little 'reserve' light comes on, you have also likely clogged your filter, especially if you purchase from a low-volume station or when their tanks are near-bottom.
Check your paperwork and mind when the filters and plugs were done. As you are the 'new' owner of the car, it would be a good thing to start with a 'clean slate' on certain things. Change the oil, replace the fuel and air filters and check the plugs and wires. Run a fuel-injector cleaner (Techron or equal) through on your next tank. Betcha this cures the problem assuming that nothing has affected the timing.
Does it "Require" premium fuel: That depends. As long as it does not knock or ping, you will not be doing any immediate damage to the engine... you will crud it up over the long-term if you are not careful. However, your mileage will drop significantly as will overall performance. The engine will run very slightly hotter with poorer-grade fuel... most of which will be handled by the computer. Do understand that were this vehicle under warranty, consistent use of low-grade fuel would void that warranty. But, realistically, as this is a turbo-engine (and not an LPT such as Volvo or Saab), it is designed against a higher-density, less volatile fuel to take best advantage of the turbo. So, you are wasting some of the capacity of the engine using poor fuel, the attached performance losses nearly wipe out the cost savings, and you are causing a potential for crud-up. Stick with mid-grade _at least_ and run premium every 3rd tank or so. If mid-grade is not available, do not try to mix yourself, stick with premium.
The engine is designed against a certain octane for optimum operation. Regular gas will cause the engine to run less efficiently and at the limits of computer response. Any savings in price-per-gallon will be obviated by the losses in performance and possible cruding up of the engine.
Mid-Grade (some engines, some cars, some conditions) is a reasonable compromise where some savings *may* be realized. Running premium every so often reduces the potential for crud.
Not mixing it yourself (if 1/2 @ 87 + 1/2 @ 93 = 1 @ 90, I can do this!) is because conditions and circumstances simply are not good enough for you to be sure. And, if you do the calculations, typically there will be no savings in cost over mid-grade. You will also find that 93 octane is getting harder and harder to find these days what with Ethanol and suchlike. This makes self-mixing even more problematic.
Okay, I wondered if you were thinking about the detergent action. If that's the only reason for wanting to go with premium every now and then, I'd skip it. Run the mid-grade, and if and when some symptom of "crud" appears, then run a bottle of Techron through it. If you use top-tier gasoline, you will probably never have a gas-caused crud problem, even with regular-grade gas.
In my opinion, the only reason you'd use premium fuel is for the anti-knock properties. And, if the manufacturer recommends it, I'd use it. Not all potentially-destructive pre-ignition is going to be easily detectable by ear.
Both liquids will take up the same volume. The weight (specific gravity) differs. There is more energy in an 8-carbon chain hydrocarbon than in a 5-carbon chain.
Now, *with* additives, except ethanol:
Gasoline, Regular 60 F .680 - .720 (.680 verges on 80-octane aviation fuel, BTW, or "DRIP Brand" in Texas) Gasoline, Premium 60 F .730 - .760
Per the API handbook.
Note that Premium Unleaded E10 Ethanol ranges to a specific gravity of .788, sometimes more. As a point of comparison, Leaded premium (Old-type Sunoco 102 octane) ranges to .728 and up. Tetra-ethyl lead may be added in tiny quantities to achieve a large virtual increase in octane. It acts as a combustion inhibitor (slows it down) but also adds a bunch of potential energy (Pb1C8H20).
Bottom line: Less energy per liquid ounce of lower-grade fuel than higher. Same volume, lighter in weight.
An interesting codicil of this is the reason why putting premium fuel in engines not designed against it is a waste of energy _AND_ possibly damages the engine. There is simply not enough oxygen available to use all the energy present. So, it is dumped out the exhaust unburnt. Two things happen under these conditions... as combustion is incomplete, the engine runs cooler. Unburnt residue can cause carbon build-up. Once upon a time back in the bad old days of carburetors (and early pre-knock-sensor EFI), spark plugs for any given engine were specified in heat-ranges based in part on driving style.... to help address this sort of thing. Now, everything is controlled by sensors.
And why low-octane fuel has a bad effect in a (relatively) high-compression engine: The engine will always average slightly lean (and therefore hot) except under load, when it will run excessively rich... the computer is managing a tight balancing act.
Be careful of believing something just because it is represented as the "Straight Dope". There is a site by this name that simply does not understand that "premium" fuel burns slower and cooler than regular fuel... hence its usefulness in High Compression engines (and you have all heard the term "dieseling"... what happens when regular gas is put in a carbureted premium-fuel engine)... All making sense when one considers that a diesel engine does not have an "explosion" at all (and no spark required either).
Gasoline _will_ deliver the same energy by weight... more-or-less the same amount of carbon and hydrogen will produce more-or-less the same amount of energy when burnt. But you are not purchasing it by weight. You are purchasing it by the liquid measure of your region.
Nope. "Detergent Action" is a wildly moving target. Given that a great deal of the gasoline purchased even from a Brand Name outlet was actually refined by "someone else".
Techron is my additive of choice on a regular basis.
Absolutely on audible engine knock. Follow the manual.
In article "KJ" writes: $I just bought an '03 Passat GLS 1.8 turbo (manual). I put regular $unleaded in it by accident (out of habit actually, since my 95 Jetta $didn't care). [...] $Anyway, is it possible that the regular is so bad for this car that it $would almost not start because of it? Perhaps the turbo has something $to do with it?
The 1.8t engine is designed to run on 87 octane (regular), though they recommend 91 (premium) for higher performance.
As with most other modern engines for which premium is recommended, this engine has knock sensors. Its engine control module has two sets of maps: one for 91 and one for 87. Each time you start the engine, it uses the 91 map. If excessive knock is detected, it switches to the 87 map and remains there until the engine is shut off.
Thanks for all the science and numbers. VW recommend premium but engine will run fine on 87 & 89 with reduced performance, but I doubt it will cause a starting issue. I have run 87 & 89 on my 99 2.8l GLX Passat and can't tell any difference in the way it runs. 93-premium... never even tried that blend. As for keeping the valves clean, well I took many a cylinder head off for broken timing belts and as yet to see any buildup on the intake valve in the last 5 years or so. At least over here in western Pennsylvania. So is the starting issue caused by the gas-don't think so. I would be more concerned if the sparkplugs were replaced at 80,000miles. Also go with the OEM plug and not something fancy like platinum's.
Please excuse the extensive editing. It is just an attempt to be brief, not to edit ideas or content. .
It has been quite a few years (about 40) since my organic chemistry classes. Do you have a reference for the above. (Note: I am challenging it, I would just like to learn more)
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Do you have any numbers (preferably real world with all the messy alcohol and additives mixed in)? I suspect that the difference in purchased (by volume) total energy is very small, but I really don't know.
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