We did not realize and used 87 octane for a year in our mini. Did it damage the engine. The dealer has said the worst is carbon buildup on the valves? Help

 

Did it damage the engine? No. The engine computer is able to adjust the ignition timing to accomodate the low octane.

Will you have carbon buildup on the intake valves? Yes. But take heart: Even premium gas will produce carbon buildup - that's just how these engines are designed. Without much effort, you can find a great deal of discussion here on NAM about fuel grades and carbon buildup. Changing to premium fuel will most likely give you a bit better fuel economy and perhaps a bit more power too.

 

I use a product called Sea Foam in all my motors . Look for it at any auto part store and follow the directions . The stuff works great .

 

Here's a good search for Seafoam - folks seem to have strong but divided opinions.

Although expensive, the shell blasting services now offered by many dealers would strike me as a less risky alternative.

But it's not clear to me that you have an issue - just a question. I completely agree that 87 octane would not damage the engine due to detonation, as the ECU does adapt by pulling timing if it hears any pinging. If the gas was of poor quality (and I've read reports of carbon buildup associated with various octane levels) then carbon might be accumulating, but a bore scope or other inspection from a mechanic should be able to confirm or deny this.

Cheers,

Charlie

 

The REAL answer is maybe.

While the ECU can and will pull timing when it detects engine knock or pinging, or detonation. There is only so much it can do. If the ECU pulls as much as it is designed to do and the condition persists, you can damage the engine. The check engine light will come on if the problem is severe.

If the CE light isn't on, you are probably ok.

As for octane, using low octane should provide you with slightly better mileage, because the engine is pulling timing and reducing power when it detects knock. Less power uses less fuel= better mileage. Lower octane gas is also easier to burn in the combustion chamber.


All direct injection engines seem to have carbon buildup issues. It's the nature of the system. In a regular port or throttle body injected engine, gas is sprayed into the intake air stream, and the gas helps clean the intake valves. In a direct injection engine, the gas is injected into the combustion chamber, (direct injection), and there is nothing to clean the valves. It also doesn't help that the positive crankcase ventilation systems lets a lot of oily vapor be sucked back in. The oily vapor gets baked onto the hot intake valves, and that's what carbon buildup is. An oil catch can greatly reduced the amount of oil in the vapor, and thereby reduced the buildup.

ANY method of removing the carbon from the valves will work.

 

Good answers above. I just got back from New York working for FEMA after Sandy. No gas anywhere except for first responders [fire, ambulances,police and fema all 87] the only differance I could tell was a slight decrease in mpg. I drove home to FL [1238 miles] and put in 93 will change oile tommorrow.