Regular unleaded where premium is required?

[Alex Franke]

I know someone here will be able to help me with this.

The gas stations here in NC are starting to get fuel again, and in Chapel Hill only a few actually ran out (as opposed to other parts of the state). But the problem now is that the only new fuel they're bringing in is 87 octane... and my car's engine requires 91+.

Now we have only about 2 gallons left in our tank because we can't find premium fuel anywhere...

So, how bad is it to use 87? Will it just knock more, or can it cause damage? Is there an additive that can bump up a tank of 87 to 91?

[jziegler]

Check your manual and see what it says. When I had my Maxima, it said premium reccommended, not required. It said that 87 is OK if you need to use it. Most newer cars will have a knock sensor and make adjustments to avoid knocking.

Jim

[pelligrini]

Most of my experience is with 30yo, carbourated, V8s.

From everything I've read, a newer vehicle should be OK with the faster burning fuel. It shouldn't knock. Most every computerized fuel/ignition system that is out today can deal with different octaine fuels. Even the numbers on the pumps aren't always what you're getting. There are tolerances for them. It also varies per which method used to measure the octane.

There are additives, mothballs will work too.

[dbhost]

I don't know the specifics of your car, but assuming it is a modern automobile, with computer controlled ignition timing, the computer will adjust the mixture, and retard or advance the timing as necessary to avoid the knock. If however you are running a 1967 Pontiac GTO with the 389 Tri Power high compression engine, you should just park it until premium comes back into the market...

Yes there are Octane Boosters on the market that will get your car to run right on regular unleaded. There are a lot of them on the market. The bigger name brands you would recognize have established products and a name to protect, like...
Octane Booster Reviews generally hold STP to be the most effective for the cost. HOWEVER, you will need a LOT to get the effect you want. I think the article shows a 20:1 ratio to get 87 octane up to 93. So if you have a 20 gallon tank, you would need 1 gallon of octane booster. I believe the standard size bottle is a pint, so you would need 8 bottles to a 20 gallon tank to get your octane up... Read the Volvospeed article, it should give you better information than I can...

I know mid grade, and premium are both all but missing here in the Gulf Coast as well... But it doesn't impact me as I don't use anything but regular unleaded.

[Uncle Cracker]

I just read somewhere where the auto makers had recently been put on the spot on this very issue, and all of them were forced to admit that any of their vehicles which were "required" to use higher octane fuel would run on regular unleaded without any ill effects, other than some nominal loss of performance... I personally have been running mid-grade in my "premium only" Lincoln for years, without any problems.

[JeffG78]

It all depends on the car. Most will tollerate 87 with just a slight performance hit, but some do really need premium. This is usually on boosted engines. Turbocharged or supercharged engines are much more sensitive to octane and cannot handle regular without the possibility of detonation. The knock sensor will usually hear the knock and back off the spark, but if it fails to hear the knock, bad things can and will happen. I worked on a vehicle that was supercharged and didn't even have a knock sensor because the knock was muffled by the supercharger. It would knock with anything less than 91.

Also, if your car is European, be sure to check the owners manual again to be sure it doesn't require 91 RON. This is NOT premium, it is 87 octane! We average RON and MON to get our ratings. Europe only uses the RON which is a higher number. If you look at any fuel pump, it will say (RON+MON)/2 method.

[MilDoc]

Performance and MPG hit only. Go for it.

[just started]

I used to have an Esclade that required 91+ and they meant it. I tried 87 & 89 and there was a very noticeable reduction in performance and about a 2-3 mpg hit, but it didn't do any damage to the engine. My mom has a Jag that also says 91+ but runs on 89 with no difference although 87 does give it problems.

[newood2]

I just read somewhere where the auto makers had recently been put on the spot on this very issue, and all of them were forced to admit that any of their vehicles which were "required" to use higher octane fuel would run on regular unleaded without any ill effects, other than some nominal loss of performance... I personally have been running mid-grade in my "premium only" Lincoln for years, without any problems.

Yep saw that report too. I,ve been running my 1994 Toyota(reguire 91) on 87 for last 2 years without any noticeable side effect. I say go for it.

[mpc]

Just buy a couple gallons of the low octane stuff... enough to tide you over until the better stuff is stocked again. Engines that really do require the high octane stuff (as was already noted: high compression ratio engines or turbo/supercharged engines mainly) will survive if you don't accelerate hard while running the low octane stuff. And most modern engines will "adapt" by retarding the ignition timing if the low grade fuel really is a problem - leading to less power and less MPG. If you go back to the high-octane stuff, it may take the engine a lot longer to re-adapt... most engines are faster at reacting to "bad gas" than to "good gas."

mpc

[JeffG78]

It does not apply in this case since he cannot get premium, but many new engines that recommend premium fuel will actually get better fuel economy on premium as well as better performance. It is usually enough of an improvement that it more than makes up for the price difference of the higher octane fuel. With 87 at $4.00 per gallon, for example, and 93 at $4.20, there is less than 5% difference in cost per gallon, so if we add 5% to the fuel economy of a 20 mpg vehicle (on 87), anything over 21 mpg is a better deal overall. This isn't always the case, but it will become more common as direct injected engines become more common.

[Alex Franke]

Well, after days of getting denied premium at over a dozen gas stations (and being a lot more diligent about taking the bus), we finally got to the point where we needed to fill up the talk lest we be stuck without a car if a real emergency occurred. So my wife made a drive out toward a gas station what was near an auto parts store so she could pick up some octane booster. And -- exact opposite of everywhere else -- they had only premium gas.

Thanks for all your advice on this!