Regular fuel use in cars "requiring" premium fuel

Am engineer friend told me my late model car–which specifies “use Premium only”–will run fine on regular, without harm to the engine, just with less than maximum power. He says all the electronics adjust things so there can’t be “knock”. Is he right?

There’s not a set answer to the question. It can vary by car and there can even be variation amongst the same cars.
The electronics can control things, but only up to a point.
Premium is recommended, not required, for my Lincoln and I’ve been running 87 for about 120k miles with zero problems and no loss of performance or mileage. I’ve even used 85 in the Colorado mountains with zero problems or loss of anything.
It gets 27 MPG on the open road with 91 and gets 27 with 85 so it’s a wash.

The key issues to me would be if the power appears to remain the same, fuel economy is not changed, and most important of all - there is no pinging. The latter can be destructive to an engine.
Forced induction vehicles (turbos/superchargers) will normally require premium anyway, but even that is debateable. It all depends on if pinging occurs when the engine is under a load and in the boost.

There are differents schools of thought on this, but that’s mine.

I’m from the school that thinks “required” means required. I would not run regular in a car that requires premium. If the owner’s manual says premium is “recommended,” that’s different, but if it says “required . . .” Yes, the electronics will compensate to a degree, but many believe there is still detonation occurring, it’s just being masked.

Whenever this subject comes up, I have to ask, “Why did you buy a car that requires premium if you’re not willing to pay for premium?”

Is you car still under warranty? If so, anything you do that is contrary to manufacturer’s requirements will void your warranty.

Your engineer friend is technically correct that it will likely run without detonation, but doing so is not recommneded. Use the gas specified; there is probably some long term negative effect from using regular…And there are possible warranty issues. The nice thing about the feature is that if you are stuck in Twisted Scalp in rural Tennessee, you can gas up with whatever is availble.

Good Point.

I come from the same school. I find it hard to believe that there are many cars out there that indicate that they “require” premium that would not suffer loss of power, mileage and or suffer damage when regular is regularly used.

True for some cars and others no. You cannot generalize.

Can you spare an extra $4? Cause with the price difference between 87 and 91 octane at the pump is only 20 cents. Even if you let a car with a 20 gallon tank(not too many cars have this large a tank anyways) get to running on fumes, you’ll only spend $4 more for that car. If you can’t afford that little bit of extra for your car, you should really reconsider what car you should be driving.

Thank you bscar. Those are exactly my sentiments. A tank a week is still only about $20 a month, and that’s if it has a BIG tank. If you can’t afford the extra $20 a month, find your self a used Yugo.

I have always run premium in my cars that say they REQUIRE premium. Those that say it’s RECOMMENDED have sometimes been filled with regular or mid-grade when premium has been unavailable. Premium USED to be harder to find.

It’s like the mechanic says “you can pay me now, or you can pay me later”.

Is your “friend” an automive engineer? Is he smarter that the automotive engineers who designed your car’s engine? I doubt it.

You might also peruse the part here about “measurement methods”.

Thanks for all for the good responses. I am generally a “follow what the factory says” guy on cars and other products. Only if I concluded it would be foolish or wasteful to do so would I want to not do that–like if everybody but me seemed to know regular was okay. Sounds like the better option here is to use premium if the factory says so. If you’re wrong its by about $20 a month–cheaper than if you’re wrong the other way.

Thanks particularly for the Wikipedia tip–that is a particularly good piece.

Some cars used to run great on unleaded regular until they didn’t. A Chrysler 383 would run great until a hole through the piston made it run bad. Fixing the engine is a lot harder than in 1968. It’s a lot easier to put it back together wrong too. Don’t make me work on your car unless you like walking.