Problems using lower octane?

pacers1994 · Jul 8, 2004

Hey BITOG Team!

My 2000 Acura TL owner's manual recommends premium fuel with an octane of 91 or better. Gas is getting pretty pricey. What happens if I use 89 octane mid-grade? I know it's only a couple of bucks saved per tankful on a car that cost quite a bit new, but I am commuting 100 mile per day and it is really adding up. Thoughts?

k1xv · Jul 8, 2004

The higher the load on the engine, the less it will tolerate lower octane than recommended without losing efficiency. Also, the higher the ambient temperature, the higher the minimum octane requirement.

Thus, in hard driving in summer (and stop and go city driving is harder than open road cruising) with A/C use, going with lower octane does not save much, if anything. However, in winter driving with light engine loads, you are better able to get away with it.

cweed · Jul 9, 2004

I'll be honest, I didn't read any of the previous responses so I may be repeating others, but please don't use a lower octane, if you do your car's computer might see some ping/knock, retard your timing and degrade your performance. The manual tells you 91 because that is what the car was tuned for, since we're all oil geeks, its like using a 5w-20 where your manual clearly states 10w-30.

I've tuned a couple of supercharged cars and know first hand what lower octane can do to your engine, that's why i never ever even consider anything lower than 93. Just dont do it, the car may run fine on it, but it may also ping and knock, why risk your engine to save a few cents....

rpn453 · Jul 9, 2004

quote:

Originally posted by berge:
I've got the exact same situation with my 92 Legend. My car has knock sensors so I assumed it wouldn't really be an issue other that slightly reduced horsepower and torque.

I thought they used a distributor on those? Maybe just the older Legends though.

For the little bit of extra cost, I'd stick to the recommended fuel unless Honda says it's OK.

pacers1994 · Jul 9, 2004

Thanks Everyone.

I think I am sufficiently scared straight. I will pop for the good stuff.

eljefino · Jul 9, 2004

Use a credit card that rebates 3-5% of your gas purchase price. Justify to yourself that you're getting premium for near the price of regular.

seotaji · Jul 9, 2004

Acura released a statement saying that it was fine to use lower octane fuel at the cost of reduced performance. I thought it was in the manual too.

I've been running regular 87 in my TL without complaints. I might jump up to midgrade 89 since it is the summer and all. If you drive hard at all, I'd stick with premium.

TL's on average get 22mpg mixed driving (using regular 87). EPA window sticker says 19 on premium 93. I don't notice a difference btw. 87 or 93 MPG wise.

Hope that helps.

berge · Jul 9, 2004

I've got the exact same situation with my 92 Legend. My car has knock sensors so I assumed it wouldn't really be an issue other that slightly reduced horsepower and torque.

Steel Blue Wind Rider · Jul 9, 2004

Reading the responses on this forum on FP, I would think that it's possible to run 89 octane with 1oz of FP for every three gal of gas. I also know the vehicle manufacturer recommends higher octane for a good reason, the car was built to run on a minimum octane which is stated in your manual. My thoughts are short term it would be OK. Long term I have many doubts. No one is going to guarantee your vehicle will run without problems either now or later on down the road using fuel with an octane rating lower than what the vehicle manufacturer recommeds, even with FP. Even the folks at lubecontrol say it doesn't specifically increase a fuels octane rating. I hate to say this but I'm thinking your on your own. The few pennies extra using premium fuel might hurt, but what would new injectors cost?

Kestas · Jul 9, 2004

This issue was addressed some time ago by Car & Driver. Assuming your engine has a knock sensor, it'll adjust the timing to optimize for whatever gas you'll put in. Gas with lower octane will burn less efficiently, so anything you save with lower octane will be lost through inefficiency. It's a wash.

Now, if you DON'T have a knock sensor in the engine, use the lowest octane you can get away with before the onset of pinging. Any more octane than necessary is abjectively wasted.

T-Keith · Jul 9, 2004

The best way to tell is to scan your car for knock or knock retard with the lower octane.

You really don't want the computer to pull the timing because it means that there has been knock.

-T

VaderSS · Jul 9, 2004

quote:

Originally posted by Kestas:
Gas with lower octane will burn less efficiently, so anything you save with lower octane will be lost through inefficiency. It's a wash.

I seriously doubt that reducing octane will drop fuel economy by 5-7% which is what you typically save by going to midgrade. I'd go ahead and run 87 unless you are hard on the car, in which case I would not run 89 either. Take it easy and you should have no problems.

XS650 · Jul 9, 2004

quote:

Originally posted by VaderSS:
I seriously doubt that reducing octane will drop fuel economy by 5-7% which is what you typically save by going to midgrade.

Right you are. Most normal driving is at relatively light throttle where there is little to no knock induced timing change.

rjundi · Jul 9, 2004

quote:

Originally posted by pacers1994:
Hey BITOG Team!

My 2000 Acura TL owner's manual recommends premium fuel with an octane of 91 or better. Gas is getting pretty pricey. What happens if I use 89 octane mid-grade? I know it's only a couple of bucks saved per tankful on a car that cost quite a bit new, but I am commuting 100 mile per day and it is really adding up. Thoughts?

You are only going to save $0.40/day or $2.00/week assuming 25 MPG if you use midgrade vs premium, why bother?

Problems using lower octane?

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