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Gasoline grade

I have a 2003 Mercedes SLK320. The owner’s manual states that I should use high octane gas, but I was always told that if the engine doesn’t ping (i.e. pre-ignition) with a lower grade gas, then it is OK to use such gas. So why should I use the higher grade gas as long as performane is OK?

If it says premium is ‘required’, I’d use premium.

Even if you don’t hear any pinging, it is building up carbon in the heads. Why buy and expensive car and cheap out on the gas? If you ever have engine problems, Mercedes will probably deny the warranty claim because of the low octane gas use.

It will say one of two things and they don’t mean exactly the same.

Premium REQUIRED:  In this case failure to use premium could result in engine damage.

Premium RECOMMENDED:   In this case you can use regular without fear of damage to the engine, but you will likely suffer some reduction in power and mileage.  It might even end up costing you more in the long run.  

Using premium in a car that does not require or recommend it is a waste of money and can acturally cause problems.  

 You paid a lot of money for your car, don't cheap out a few cents now.  If you wanted less power mileage and reliability, you should have bought a car that did not need premium.

If you want to use cheap gas, trade-in your Mercedes for a Honda Civic.

Does your owner’s manual say high octane gas is recommended or required? If high octane gas is required, it is a no-brainer. Use the required fuel. If high octane gas is recommended, you can get away with cheaper gas, but you probably won’t save any money due to decreased engine performance.

your SLK is supercharged,right?i wouldn’t chance detonation in a boosted engine.you could probably get away with it if you drive like a grandmother,but if you do a lot of accelerating(like on a highway on-ramp,etc.)i’d only use premium.your pistons and valves will thank you for it!i have a non-supercharged engine in my VW,but it has really high compression(11.3/1)i tried using 89oct,instead of 93 last year when fuel was $4/gal-i didn’t even get out of the parking lot,before the pinging started.

Don’t listen to a lot of what you are told. About octane, you will be told everything but it is mostly something taken out of context. I’m happy to tell you that the owner’s manual is always the winner. People are built to read the instructions and then try to do something else. You are just acting normally.

This is the v6, not supercharged.

Octane rating has nothing to do with carbon buildup other than lower octane might ping just a little bit and prevent carbon buildup.

If the gas is not so poor that you notice it, or the ECU notices, then don’t worry about it. All engines ping just a little bit, just below your ability to perceive. GM published a paper way back (1980?) when knock sensors started to become standard equipment stating that not only did a little ping do no harm, it did good.

Is most probable the ECU will detune the engine. You should monitor MPG to see if it changes. If MPG drops enough then premium fuel may be cheaper.

Engine computer reduces timing due to knock due to low gasoline octane. Reduced timing results in carbon build-up.