Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Will Octane Booster damage my cars engine?

We have a 2000 Mazda MilleniaS 6cyl turbo.

approx 78000 miles.

The users manual recommends 91 octane gas -however, it is hard to find and I have been using 90 octane and having problems with the check engine light coming on. When we add the STP Octane Booster to the gas, the check engine light goes out.

Would it be hardful to my engine to continue adding this to each tank of gas I purchase?

thanks, Mazda Mom

I read that your light is out now,get the history codes read or when the lights on get the code read. I am having a hard time connecting a check engine light and a 1 point difference in recomended 91 octane and the 90 you are using.

Where do you live that 90 is the highest? In the mountains, perhaps?

I think the engine needs some checks performed which we can’t do over the Internet. There may be something marginal which a good mechanic can uncover. Just because the check engine light goes off, doesn’t prove that everything is fine. If the spark plugs are several years old, it’s about time to change them. With this car’s mileage, other routine maintenance is due, such as air filter, fuel filter, pcv valve, and the etc.

Does this car have the Miller Cycle engine? If so, you should be aware that, because that technology was unique to Mazda, and because not very many Millenias (hmmm…plural of a plural) were ever sold, many mechanics have never worked on one. If you do have the Miller Cycle engine, I would suggest taking it to the dealership, as they may be the only ones able to properly work on it.

Also–lion9car makes a good point. If 90 octane is the highest that is sold in your area, that would suggest that you live at a high altitude, and if that is the case, your car’s octane needs are actually reduced from what would be required at sea level. All-in-all, this sounds like a job for the dealership.

Have someone check for any stored codes. That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

I doubt if the CEL and the octane issues are related. I agree with the others that it does sound like you are in a high area.

I agree with the others that it sounds like the car has a minor issue of some kind, and adding one point to the octane is just making the symptom less noticeable. Fixing the problem would be better than hiding it.

The answer to your question of whether octane booster will hurt your car - I am not familiar with your particular engine but I think I can say with confidence that No, mixing in octane booster at the recommended, rate will not hurt the engine at all. It will put a little wear and tear on your wallet, but it won’t hurt your engine.