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Is Premium Gas Really Necessary?

Is there really that much benefit & engine safeguard to using 92 octane vs. 89 gas? Is premium worth the extra $0.10/gal?

It all depends. If your owner’s manual says that premium is REQUIRED then you should use it.

If the owner’s manual says premium is only RECOMMENDED then you don’t need to use it unless the engine starts to knock/ping (sounds sort of like marbles vibrating in a can).

If the owner’s manual says nothing then there is no benefit to higher octane.

More to the point, have you actually done the math? For most driving habits the extra does not add up to very much. You have a mercedes - and you want to quibble about $.10 per gallon? Maybe you should just change cars.

I believe all MB products except the diesels require 91 octane or better. You bought a high end car, expect to use high end fuel.

Why is it that people driving “premium” cars are the ones who always ask if they really need to buy premium gasoline?

As far as I know, all MB cars, except the diesels, require premium. The MB engineers specified premium, and they know what they’re doing. If you don’t buy the correct gas you the engine will suffer in the long run.

But you won’t have the car in the long run, will you? You’re not going to keep this car for 10 years, correct?

You’ll use the less expensive gasoline, and the poor sucker who buys your C-class as a used car will pay for the damage you caused.

You’re driving a Mercedes Benz, but you’re worrying about and extra $0.10 per gallon. What’s wrong with this picture?

I hear a little bird, singing, “Cheap, cheap, cheap.”

“Is there really that much benefit & engine safeguard to using 92 octane vs. 89 gas? Is premium worth the extra $0.10/gal?”

The real question is, “Can I buy an expensive car and use cheap fuel?”

The answer is - Only if you don’t care much about your car.

Does your manual say premium is required or recommended? If it’s required, use it or you risk engine damage. If it’s recommended, then you can get away without using it (assuming your knock sensor never fails), but the timing will be retarded, probably reducing your miles per gallon and likely cancelling out any financial benefit.

What you should really be asking is whether 5 octane points (87-92) can possibly make a life or death difference in ANY engine…Depending on the compression ratio of the engine and a few other factors, the 5 missing octane points MIGHT cause a little “ping” and it might not. Luxury cars typically recommend or require “Premium Fuel” because it reinforces the perception the car is something special and linking it to anything “premium” helps promote that image. That being said, ten years from now, the third owner is very unlikely to spend .30 cents a gallon extra for premium fuel. The cars themselves don’t seem to mind, or at least are able to tolerate, the missing 5 octane in their sunset years…

My last wife was the opposite, she used preminum in a car that didn’t require it. Even me being a professional auto mechanic could not convince her she was wasting money. She had this streak of not admitting to making a mistake, probably good quality when you are an officer in the U.S. Army (rank of Major)but not a good quality to make a marriage work.

This my 3rd MB, so I am well aware of the cost to run & maintain this type of car. My question was not relative to being cheap, but to generally try & understand what is the mechanical reason some engine types would run better on premium. It doesn’t appear you have the expertise to answer my inquiry as it was stated.

For every 10,000 miles you drive it will cost you an additional $45. The car is designed to run at its best with premium gasoline. It’s worth every penny of it.

Gee, I’m the only person you replied to. Guess I must have struck a nerve.

High performance engines, such as the one in your C-class, require premium gasoline to prevent pre-ignition, aka “detonation,” “pinging,” “knock,” or “spark knock.”

In the old days, before computers controlled the engine, you could hear this “knocking,” or “pinging,” in the engine, especially when the engine was under load, such as going up a hill. It would rattle like a tin can full of stones. Hearing this is rare with newer cars.

Modern computer controls, especially knock sensors, minimize and hide the noise, so you don’t know it’s happening. But it’s still happening.

Some people claim the computer will adapt, and running regular in an engine that requires premium will result in reduced performance and lower gas mileage, but nothing more.

These are the people you want to believe.

Others, however, have shown that, over time, using lower octane fuel than specified will cause significant damage to the engine.

Worst case scenario? Holes in the pistons.

But, as I suggested earlier, you’re unlikely to own the car when this becomes evident, so fill your tank with whatever grade of gasoline you choose.

It’s your car.

For now.

The owner’s manual will tell you if premium is recommended, required, or neither.

If required, not using premium could damage the engine.

If recommended, not using it will reduce power and mileage. It may actually cost you more per mile using regular.

If it does not say, then don’t waste your money, it will not give you better mileage, longer engine life or more power.

“My last wife.”

How many wives have you had?

Just curious.

Is 3 a bad sign?

Regular gas is just as good as premium gas as far as “cleaning the fuel system”. All fuels have sufficient cleaners.

As far as octane, that depends on the car. Cars with “knock sensors” reduce the ignition timing to avoid any engine damage from using lower octane fuel. These cars are “premium recommended” as per their owner’s manuals. Other cars are set up for premium fuel and NEED it to avoid damage. These cars are “premium required” and often give a specific octane number that is a minimum, often 91 octane.

The answer for your car is in the owner’s manual. A MB is a precision car and likely has a high compression ratio. If it says “required” in the manual I’d use premium.

Both premium recommended and required cars will perform slightly better and get a bit better mpg when using premium fuel. The differences might be hard to feel but it is there.

Cars set up for regular, run the same or slightly worse on premium. Buying premium for a car that requires regular fuel is just a total waste of money.

That’s a blanket statement and an incorrect one at that. There are certainly cars today that will indeed suffer damage if the incorrect fuel is used. We had a guy with a Lightning pickup threaten bodily harm to a service writer when warranty claim was denied because the guy had been using 87 octane in the truck when 91 octane was required. The pre-ignition caused by the 87 octane resulted in a hole a piston. Automakers don’t recommend premium fuel arbitrarily.

If the vehicle runs fine with no loss of performance and fuel mileage and most importantly, no pinging while the engine is warm and under a load then there should not be a problem with running 89.

My opinion is usually at variance with many others because this issue, like many, is not black and white and there’s some gray area involved.
If the state of tune is fine, the EGR system is operative, no restrictions in the converters, etc. then it just flat may not matter.

Assuming everything is fine as to performance/pinging, etc. the final answer would lie in installiing a new set of spark plugs and re-examining the tips after several hundred miles.
The plug tips will be the final, true indicator of what’s going on inside the engine.

Yes. Yes.

I’ve been running 89 octane in my '89 190E 2.6 for years without a problem.

The OP is not going to benefit from any more input on this subject.