1991 Passat Wagon 2.0L/5speed

Hello All,

I came into possession of a 1991 Passat Wagon. I have a quick question that hopefully somebody here can answer.

Does anybody know what fuel octane VW recommended back then for these cars? The fuel door sticker is long gone and I didn't get an owner's manual either (of course!) Right now it seems to be running on 87 and my machanic tells me that it has knock sensors and will run on anything

-- but I've read stories about messing up parts (the O2 sensors seem vulerable?) by running below recommended octane.

Should I be putting the good stuff (93) in this tired old baby or does it not really matter? Given the lack of a manual and fuel sticker I have no way of knowing what was recommended back then. Hopefully someone here does :) If there's anything else I need to know about this type of beast please share that as well.

Many thanks in advance!

Reply to
Timothy Barbeisch
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I think your mechanic is right in that it will run fine on US (M+R)/2 87, but I am not presenting this as an authoritative answer. I believe that with lower octane fuels, the knock sensor retards the timing. I expect the engine to have more power and/or use less fuel with higher octane. I have watched for people who do regular long commutes to do a mileage test to see what happens in real life, and I have not seen results posted. Now if there was a car pool commuting and the test was a blind test, that would really be good.

If you are just going for economy, it would seem that there would be a price differential that would make the switch make sense. My

*feeling* is that the more expensive the fuel on absolute terms, the cheaper premium is on a percentage basis. So if fuel is expensive, I tend to opt for the premium.

If I am taking a long highway trip with constant engine loads, that may call for a different analysis than if I am doing urban driving.

I don't know how much the effect is. Am I paying 8% more for (M+R)93 premium to get 2% better mileage?

Reply to
Tom's VR6

In my opinion, with few exceptions almost all cars will do just fine with 87 octane - making higher octane fuels just a waste of your money. In fact, I've never owned a car that really required anything other than 87 octane. The 87 octane has been used in my '95 Buick Roadmaster V-8 since the day I drove it off the showroom floor, and I've never experienced any engine problems. I also use it in my '88 VW Cabriolet Convertible (1.8L 8V) 4 cylinder engine. No problem there either.

However, don't take my word for it. A quick telephone call to the nearest VW dealership should answer your question about the type of fuel recommended for your '91 Passat.

Reply to
Papa

that engine has 10:1 compression and you will get the best performance from premium fuel, but the ECU will adjust for 87 if needed.

Reply to
Lost In Space/Woodchuck

My Roadmaster V-8 (Corvette) engine has a compression ratio of 10.5 to 1. The engine has never pinged in over 125,000 miles of driving, and not a drop of anything other than 87 octane has ever been in the tank. Putting premium fuel in my car would not aid performance at all, and would be just money thrown away.

Reply to
Papa

You take that on faith, I assume.

Reply to
Tom's VR6

But the newer VW 1.8t & 2.8L V6 engines require premium, but run fine on 87 with slightly less power! I know. I own a 99 GLX Passat and only run 87 most of the time. You gota LOVE computerized engine systems..

Reply to
Lost In Space/Woodchuck

Well I vote that you try to find what your engine likes. My 91 Passat Sdn auto trans likes premium for performance and seems to get slightly better mileage with premium too. Your manual trans should net you around 30 mpg while my auto trans keeps it closer to low 20s. :-( Of course being cheap I try to use regular gas and it runs fine on that too. lol

Experiment and post your results here! :-)

later, dave (One out of many daves)

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Reply to
dave AKA vwdoc1

It seems to run on 87 but it doesn't seem to like it very much. Small hills that I could take (at speed -- 65-70mph) with 93 octane just fine seem to require a downshift to maintain speed with 87. I"ve only tried

89 once and couldn't see much of a difference from 87. Passing performance seems to suffer as well.

I guess what I was looking for was somebody with roughly the same car to tell me what's on that missing fuel label :) I think I'll wind up running with 93 from now on. It seems to get by with 87 but the performance really suffers (oddly enough the MPG doesn't change much one way or another). I also found some archived messages in this group of somebody that a had an O2 sensor fouling problem with 87 -- though that could have been unrelated.

Your 91 Passat only gets ino the low 20s with an auto? My avg is about

29.5 and that was before my latest tune up. Gotta love the 5 speed! :)
Reply to
Timothy Barbeisch

GRRRR Yeah I would love a 5 speed! ;-)

I believe that the ECM has two fuel maps in it. When the ECM sees pinging then it will revert from the default High Octane fuel map down to the Low Octane fuel map. Bye Bye max. power. lol

Feed it the good stuff then! I personally HATE that mid-grade stuff and recommend either low or high octane.

later, dave (One out of many daves)

91 B3 Sdn auto

Reply to
dave AKA vwdoc1

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