Does high octane gas matter?
July 23, 2009 6:47 AM   Subscribe

I have recently acquired a 1988 Toyota pickup with 126k miles. Is it worth it to use higher octane gas?

It's been a while since I've had a car of this vintage. Will it make a noticable difference if I use better gas?
posted by youcancallmeal to Travel & Transportation (13 answers total)
occasionally, maybe, for the detergent additives, but the higher octane is for higher knock potential. That thing isn't gonna knock if you hit it with a wrench.
posted by notsnot at 6:49 AM on July 23, 2009 [1 favorite]

Yeah, most vehicles are designed to work with a single grade of gasoline. Higher octane gas can operate at higher compression ratios than the lower octane stuff, but since compression is set by the engine, using more expensive gas won't actually get you anything other than poorer.
posted by valkyryn at 6:58 AM on July 23, 2009 [1 favorite]

How long are you planning to keep it? If the answer is 'forever,' then I think it's worth it for the detergents (I like Shell gas).
posted by box at 7:09 AM on July 23, 2009

An '88 w/126k? If the answer is not 'forever,' keep me in mind when you sell it.
posted by box at 7:12 AM on July 23, 2009

Do some research, or have a mechanic check, if the engine needs it: I don't think Toyota was known for high-compression engines, but my '91 Chevy van needs the high octane to run right. While it gets horrible mileage anyway, it gets really bad and doesn't run well when I use the cheap gas.
posted by AzraelBrown at 7:17 AM on July 23, 2009 [1 favorite]

According to my dad, older engines do need a higher grade gas these days IF you live somewhere that there is a significant (say 10%) amount of ethanol in the gas, particularly if you are looking at a carburetor rather than a fuel injection system. This is apparently doubly true for small engines like weedeaters and leaf blowers. (My dad is retired now, but was a professional car repair person for the entirety of his adult life.)
posted by Medieval Maven at 7:17 AM on July 23, 2009 [1 favorite]

Octane is octane, regardless of whether it comes from straight gas or an ethanol blend. Use whatever octane the manual (or the sticker on the gas flap) says to use. Using a national brand (like Shell) might get you a better mix of detergents and whatnot. However, all gasoline sold in the US has to have a detergent mix.

Occasionally using a gas additive like Techron can help clean the fuel system, as well.
posted by Thorzdad at 7:42 AM on July 23, 2009

Older engines, Toyota or lesser, do tend to knock under load, especially if the outside temperature is over 90 degrees. If you hear knocking, that would be the time to consider filling up the tank with 89 octane gasoline. Otherwise, just have the fuel injectors (assuming EFI) cleaned every 30k miles or so.
posted by Burhanistan at 7:42 AM on July 23, 2009

Only put high octane in if you get a knock or a ping under acceleration. Yeah, some old cars might require high octane, but only ones that are old enough that they predate unleaded gas. Your Toyota does not.
posted by Jon-o at 7:53 AM on July 23, 2009

If it has the 22R engine (the 4, not the V6), you could pretty much run it on a mixture of half 7-11 gas/half water, and it would wheeze out its whiplash-inducing 97 horsepower just fine.

But the detergent gasolines (detergent and octane rating are unrelated) are nice for keeping fuel systems clean, as other posters have observed.
posted by M.C. Lo-Carb! at 8:22 AM on July 23, 2009

The straight dope on gas octane measures. Answer: you shouldn't need premium.
posted by autojack at 8:58 AM on July 23, 2009

posted by gribbly at 9:13 AM on July 23, 2009

My mechanic just the other day told me some stuff about how this stuff works, most of which I was unaware of.

He says the engine is set to take a certain amount of time to burn gas, and once that burn time is done, it ejects whats left and moves on - it doesn't know if the gas finished burning early, or if there is more left to burn. So if the engine hasn't burned all the gas, there is gas in your emissions.

Secondly, he says higher octanes take longer to burn, not shorter, as I had for some reason assumed. So in my mid-90's econo-car, and likely in your car as well, where the timing is set for lower octane gas, high-test is just going to lead to there being unburned gas in the exhaust and maybe some gunk in the engine after a while.
posted by [@I][:+:][@I] at 7:42 AM on July 24, 2009

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