Will it hurt the engine if a premium gas is used instead of regular gas? Also, what
happens if you go from premium back to regular gas? (note: premium gas is neither required nor recommended for the car in question).
Thanks for your feedback.
The only thing you’ll hurt is your wallet by spending a couple extra bucks more per fill up.
What’s the problem? Use the octane gasoline stated (whether recommended, or required) by the vehicle maker.
Your gaining nothing but a lighter wallet. Premium fuel has a higher octane rating for high-performance engines that require it. The higher octane actually burns slower to prevent pre-detonation (or early ignition) in engines with higher compression ratios. But, in engines that do not require it, will do absolutely nothing that the less expensive fuel will do. All fuel companies are putting the same additives in the less expensive fuels as the premium fuels, so there is not even a benefit there. Simply put, it is a waste of money. It will not harm the car, and switching between regular and premium will do not harm.
The only time you may want to go up in octane rating for this car is to try and eliminate valve pinging that can develop when the car gets older. Other than that, just a waste of money.
Not quite true. BP regular gas is not equipped with the same additives, so it does not qualify as a top tier gas. It’s high test does have them. This is the only exception I know.
No problem. The fuel req’t is minimum octane req’d.
Many thanks for all your replies 
Fortunately, it has not hurt me financially
that much because the car is not used that much - to give you an idea, it is 10 yrs old
but has only 25K miles on it. Nonetheless, it does not necessarily mean that it will stay
that way for ever…
again, thanks a bunch for your feedback
I have read that higher octane fuel can actually harm an engine designed for 87 octane, over time. I know that knock sensor can tell the computer to lean the fuel/air mixture when higher octane is used, to compensate for the slower burning…however, it can’t lean it out enough to prevent carbon buildup on the valves and cylinder walls…which can cause pinging later in life.
Tell me if this is wrong…
This is backwards. Using lower octane fuel in an engine designed for higher octane will use the knock sensor to prevent the knocking and pinging from happening. The sensor tells the computer to retard the timing, and this will hurt fuel economy. Plus, the lower octane fuel will cause more carbon build-up, causing the pinging problem to worsen.
Using higher octane in an engine designed for lower octane does not cause any problems.
Running a premium/high octane fuel in an engine that doesn’t require it can have damaging effects.
First. Because high octane fuels are harder to ignite and burn slower can result in incomplete combustion of the fuel. This can result in carbon deposits building on the tops of the pistons. When this happens it raises the compression ratio of the engine. So, you started out with an engine that didn’t require a high octane fuel, but end up with one because of the higher compression resulting from the carbon deposits.
Second. Any unburned fuel goes into the exhaust system and into the catalytic converter. This unburned fuel will ignite in the catalytic converter causing the converter to run hotter. This then shortens the catalytic converter’s life.
Tester
I’ve never hear of this “high octane fuels are harder to ignite and burn slower”.
Everything I’ve read says that high octane fuels are the same as regular except that self-ignition occurs at a higher pressure. And that is the only difference. So for the pressure seen in a auto (that requires only low octane) both will perform identically, with NO difference.
So, I repeat what lots of other people say, if you car does not require high octane, don’t use it, there is no advantage. On the other hand, there is no disadvantage to using high octane under these conditions.