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Volkswagen GTI Engine Problems

82 messages,  Last post on Jun 08, 2011 at 10:34 AM

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What is this discussion about? Volkswagen GTI, Engine, Hatchback

Messages Page 6 of 9

#46 of 82 Re: 2007 GTI - Fuel Requirements [geeteeeye] by 600kgolfgt

Jun 08, 2007 (7:05 pm)

Replying to: geeteeeye (Jun 08, 2007 4:52 am)
Your GTI will run fine on 87 octane gas
 
I beg to differ (based on my 25+ year mechanical background), and the experience of many master VW mechanics, engineers and technicians that I have worked with over the years. The manufacturer specifies (requires) the use of premium fuel on a given engine for a reason.
 
The GTI's engine incorporate two knock sensors. A knock sensor monitors noises in each cylinder and "listens" for any signs of knocking. When a knocking condition has been encountered (or is about to occur), the knock sensor sends a signal to the engines computer, or electronic control unit (ECU). The ECU automatically retards the engine timing of that particular cylinder in small increments until the knoocking condition disappears. Retarding the engine's timing will exact a power and fuel economy penalty. This issue is much more critical with forced induction engines (turbocharged or supercharged) engines than with naturally-aspirated engines.
 
I have performed this experiment on two of my cars:
 
1) 1997 VW Jetta Trek - 2.0 Liter 8-Valve, normally aspirated engine with a 10:1 compression ratio
 
2) 2003 VW Jetta Wolfsburg Edition - 1.8 Liter, 20 Valve turbocharged engine with a 9.5:1 compression ratio (pretty high for a turbo).
 
I ran each car with regular until empty, took note of the mileage/amount of gas used, and repeated the process with the cars running on premium.
 
Each car averaged 3-5mpg higher running with premium than regular. Keep in mind that VW recommends regular for my 1997 Jetta - but with a high 10:1 compression ratio, it runs much better on premium. As for the 2003, you are playing with fire by running a turbocharged engine on anything but premium.
 
Direct injected, turbocharged engines like the current GTI don't change that equation - it only allows turbocharged engines to run at a higher compression ratio than normal.
 
When in doubt - go with the manufacturer's specfications. The only current engine that VW recommends the use of regular fuel is the 2.5 liter 5-cylinder engine. All others require either diesel or premium.
 
You may run regular if you like, but my parents have a saying:
 
"Those who won't hear - must feel"...

#47 of 82 Re: 2007 GTI - Fuel Requirements [eldaino] by geeteeeye

Jun 10, 2007 (6:10 am)

Replying to: eldaino (Jun 08, 2007 11:05 am)
Yes, octane is an additive and not a measure of a gasoline's purity. Actually, modern gasolines are relatively impure compared to before it was reformulated to reduce harmful emissions.
 
The manual for my 2007 GTI recommends 91 [(R+M)/2] octane, but requires an octane rating of only 87.
 
If you live at higher altitudes, gas stations offer lower octane gasolines because a car is less likely to knock due to lower atmospheric pressure.
 
Actually, octane won't be the only additive used to increase the "octane" (or Anti Knock Index) of a gasoline. In almost all cases it is a mixture in which iso-octane is a component. There's really nothing special about octane, it is simply a flammable chemical that burns at a higher temperature than gasoline. This helps reduce gasoline's tendency to ignite before it's supposed to. This is the cause of knocking. The octane measurement is not an indicator of how well your car will perform, just how likely it will detonate (explode) at a certain temperature. High performance engines are more likely to knock and therefore require a higher octane gasoline at full throttle only.

#48 of 82 Re: 2007 GTI - Fuel Requirements [600kgolfgt] by geeteeeye

Jun 10, 2007 (6:30 am)

Replying to: 600kgolfgt (Jun 08, 2007 7:05 pm)
Actually, I agree with just about everything you said.
 
However...the only instance where an engine will run less efficiently on a lower AKI gasoline is a high compression engine under load where, as you correctly stated, the engine's computer retards timing (and decreases the air/fuel ratio) to a point where the knocking disappears.
 
But this instance is relatively rare (depending on your driving habits) and almost non-existent on flat highway driving.
 
I would never run anything less than 93 octane in my '71 Datsun 240Z because it knocks with even the slightest load on the engine and because there is no computer to make the knocking disappear.
 
But modern engines don't have this problem. This is partly the reason that it is rare that a manufacturer actually requires the use of a high octane gasoline instead of just recommending it.

#49 of 82 Re: 2007 GTI - Fuel Requirements [geeteeeye] by eldaino

Jun 11, 2007 (7:53 am)

Replying to: geeteeeye (Jun 10, 2007 6:10 am)
The manual for my 2007 GTI recommends 91 [(R+M)/2] octane, but requires an octane rating of only 87.
 
you see this is what i don't understand. according to the literature that i have on the gti,(its the booklet that comes with the dvd) mentions that 93 octane is reccomended with the 91 being the other choice with reduced performance. Thats the whole reason why this had me confused to begin with, since very few gasoline statins have anything higher than 92 around here; otherwise i'd be good to go if i had a gti, i'd do regular all the time. But something tells me that if i do put regular in it, i'd be in for it in the long run, like golfgt said.

#50 of 82 Re: 2007 GTI - Fuel Requirements [eldaino] by geeteeeye

Jun 11, 2007 (10:24 am)

Replying to: eldaino (Jun 11, 2007 7:53 am)
Look on page 34 of booklet 3 of your owner's manual. It states:
 
"Do not use any fuel with an octane rating lower than 87 AKI or 91 RON. Using lower octane fuel may cause expensive engine damage may occur."
 
Perhaps you are confusing the RON with AKI? RON is a European unit. In the USA we use AKI which is synonymous with [(R+M)/2].
 
Yes, a higher octane fuel will result in better performance of your GTI. But don't confuse performance with engine damage.

#51 of 82 Re: 2007 GTI - Fuel Requirements [geeteeeye] by eldaino

Jun 12, 2007 (7:56 am)

Replying to: geeteeeye (Jun 11, 2007 10:24 am)
ahhh..ok man thanks!

#52 of 82 Re: 2007 GTI - Fuel Requirements [geeteeeye] by eneko

Jun 13, 2007 (12:21 am)

Replying to: geeteeeye (Jun 08, 2007 4:52 am)
I am sorry to disagree, but octane it is not an additive in fuel. Octane is a component of the gasoline, actually octanes are hydrocarbons, not something that you add to fuel. The octane rate is an index to indicate the proportion of different octanes in the fuel. Some of the octanes are less "stable" under pressure and they combust prematurely. Higher octane rate means better performance because the fuel will burn at the right moment and completely.

#53 of 82 Re: 2007 GTI - Fuel Requirements [eneko] by eldaino

Jun 13, 2007 (6:10 am)

Replying to: eneko (Jun 13, 2007 12:21 am)
this is what i thought it was.

#54 of 82 Re: 2007 GTI - Fuel Requirements [eneko] by geeteeeye

Jun 13, 2007 (12:07 pm)

Replying to: eneko (Jun 13, 2007 12:21 am)
You're way off. The only thing you got right is that octane is a hydrocarbon. Don't think of gasoline as a pure substance. It is a blend of many hydrocarbons that are produced through many different processes in an oil refinery plus other synthesized flammable chemicals that are partly petroleum based. The straight, pure, hydrocarbon component of gasoline that you're referring to is usually less than 50% (of which iso-octane is only one example of).
 
Iso-octane (and other anti-knock chemicals) is considered an additive because it is added such that a specific "octane rating" is acheived, unlike the base blend of gasoline in which the specific blend of hydrocarbons is not as crucial.
 
The octane rating of gasoline doesn't mean that the only anti-knock component is iso-octane, just that it has the same anti-knock characteristics of a reference blend of, say, 87% iso-octane and 13% heptane (to refer to an "87 octane" gasoline). This is what you were getting at when you said the octane rate was a reference to the proportion of different octanes in the fuel (but this is incorrect).
 
Also, all gasolines in a high performance engine will "burn at the right moment." But a fuel with the proper octane rating for the engine means that it will combust when the cylinder is at its highest pressure. That's where you get your engine performance. Lower octane-rating gasolines will work fine, because the engine's computer will alter the timing so that it prevents any knocking.

#55 of 82 Re: 2007 GTI - Fuel Requirements [600kgolfgt] by vvk

Jun 14, 2007 (11:26 am)

Replying to: 600kgolfgt (Jun 08, 2007 7:05 pm)
Every car I have owned got 1-2 mpg better mileage on regular vs. premium.
 
I still use premium because a) my BMW requires premium and b) my SAAB engine runs a lot smoother and quieter on premium.

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