Use of regular gas in european automobiles

We have a 2003 Mercedes C230 car. It now has 77,800 miles, and for the third time, we have low compression in the #3 cylinder. The valve springs were replaced at 49,000, and the head was replaced at 51,000. The dealer now tells us the head must be replaced again. He told us it is because we have been using regular gas, instead of premium as recommended by the manufacturer. I seem to recall you guys have held the position that premium gas was a waste of money, and a con-job. In fact, you both convinced my wife and me that there was no advantage in using regular. Now what do we do? How do you feel about using premium gas in a car like our Mercedes C230?

I think you need to follow what the owner’s manual says. If Premium gas is not recommended, dont use it. But if it is recommended, then you almost have to.
I still dont understand the relationship between the gas grade and your specific problem. It looks like there is some problem with the quality of the engine.
A wrong grade of gasoline should not cause a problem with the head IMHO. I will wait for others to comment on this.

It sounds like your problem is valve related, as in “burned valves”. This is not related to gasoline octane. The cause is usually a improperly adjusted valve, a defective valve or a vacuum leak which causes a “lean burn” condition that can burn a valve.

In any case, replacing the head is seldom required to repair the problem. A “valve job” usually cures it. But replacing the entire head is quick, easy and VERY profitable for the dealer…Tell the dealer you would like to keep the original head as a paper-weight and have an independent shop examine it and give you a repair estimate.

Or, tell the MB service manager you are going to take the old head to an Automotive Machine Shop and get a second opinion as to repairability and repair cost. Confronted with that, they may have second thoughts about their diagnosis…

If you are paying for this out of your pocket, I’d get the heck away from that shop and go to an independent shop. Three strikes, and that dealer is out!

According to Mercedes-Benz website, your car REQUIRES premium fuel, (91 octane minimum). Even if the car can adjust to using regular, your obviously not doing yourself any favors. Is saving roughly 6.67% using regular vs premium worth all this hassle? I think just the last few repairs have cost way more than the gas savings alone.

If the information Busted found is correct, using low octane could be your problem. If the manufacturer says it requires premium it would be a very foolish thing to ignore that. The cost of using regular will be far more than the extra cost of premium. If they “recommend” premium than it seem foolish not to use it as you likely will loose some power and mileage and may not end up saving anything due to the reduced mileage.

That said, I agree with Caddyman.

So the question I have is this. You state that “for the third time, we have low compression in No.3 cylinder”.

So if regular gas is the problem why is it picking on No. 3 cylinder only and why in the world is anyone replacing valve springs?

To add an additional question: Has the engine been clattering on you for all of those miles, and if so, why did you keep on going?

A relationship between failed valve springs and fuel used would be unlikely to state it mildly. When combustion occurs, the valves are closed and the valve springs would not know what is happening in the combustion chamber. Further, the valve springs are isolated from the combustion process. You might want to question your dealer extensively about why the valve springs had failed. I would be so hot that I would want to get Mercedes involved to get this question answered. My gut feel is that you were cheated regarding the valve springs. Ask your dealer for the service bulletin related to this repair. Possibly he can supply you with it. In that case, I retract my view.

I don’t know if your valve/head issues are related to using the incorrect fuel, but your engine requires higher octane fuel so there is no reason not to use it.