regular gas + octane booster= ? RON

jay4500

I work for a rental car company , and I am a mechanic , we have several cars that takes premium fuel , bmw,infinity and I don't think rental car companies use premium fuel , and the cars run just fine, no problems from running regular fuel. the ecm compensates for the fuel.

essixx

The ECM will change spark advance to compensate for different octane gas. Never heard that the Knock sensor will fail if you use different octane gas. I'll have to research that one, Thanks!

bvl

If the sensor fails and it cannot detect knock...bad things can happen sure.

Not sure about the specific car, but knock sensors often are simple electric/acoustic devices. The sensor detects noise and the system filters out knock regulal engine noise levels. Knock is typically a huge spike in that noise floor and easy to see from an algorithm perspective. They don't touch fuel and they are not effected by what fuel you use.

All of this is moot if you simply use appropriate octane fuel and not 'rely' on the safety systems of the car because you are too cheap to use the right fuel.

Rental cars do have that problem: a few times I have rented a car with premium fuel and I would bet 9/10 renters don't top off with premium. I did top off with premium just because its the right thing to do. The extra $1 didn't hurt me.

Since rental cars are new, you would hope things all work and the car has retarded timing and lower power levels due to this. Is it good for the car? I would say no. Do you care? Only if you are the poor sap who buys that car once the rental car company is done with it. I always wonder if people who buy them are fully aware of their use history.

- b