pwanghk

Greetings:

At almost $2 a gallon, I am trying to justify my 93 Octane purchase for my 04 4Runner. I've been told that even though it doesn't bring better performance for the engine; however, it makes the engine burn more efficiently, cleaner e.g. have less impurities and deposit in the valve. Is this true?

Thanks in advance for your insight thoughts.

My99

High octane prevents pre-detonation which is bad for an engine. It has a higher... i forget what it's called... flashpoint maybe? Anyway, my point is, is that if you run low octane in an engine that needs high octane, and it causes a "pinging" to occur, this is pre-detonation. What is happening is the fuel is exploding before the piston reaches TDC and before the spark ignites it (sort of like a diesel, no spark plug needed to ignite the fuel). This is bad. This is harmful for an engine b/c you are basically trying to burn the fuel in the cylinder and push the piston in the opposite way it is currently moving. HOWEVER, if your vehicle does not ping and the manufacturer doesn't call for a higher grade gasoline than regular, by all means, use regular. It's all the same stuff as far as cleanliness goes.

WATRD

If you are normally aspirated you should run whatever the owners manual recommends, usually 87, unless you have pinging problems. Higher octane is just wasted and can result in higher emissions It's like setting fire to your money.

If you are supercharged, 92 is the order of the day, higher if you can find it.

pwanghk

Thanks a lot for your explanation and help. I will switch to regular, since the manual doesn't specify that my truck requires 93 Octane.

amusement

If you have mods like a free flow air system or a super charger or turbo (as WATRD reported) then it's time to increase octane. But the majority of us aspirated engines just need 87. It's almost cheaper anyway to buy 104 octane from your local auto store than buy premium at a gas station.

4RUNR

Bet 3rd Gens would run ok on 85, and older even 83 Abroad they run DPC ratio of like 1:1.

kyle_22r

even my '79 recommends 87 octane

lee

i run 89.. was told that was what the previous owner ran so i stuck to it. is switching now (50+k on 89) bad (to 87)?

4RUNR

Not if you switch to synthetic oil at the same time or else your blinker fluid will boil out.

02Runner

That must have been what happened to me. I switched and ended up with a broken seal to my blinker reservoir.

Poul D'eau

How much did that seal cost??

My99

I know that i've noticed on my dad's 3rd gen when we went out west a couple years ago that it ran like crap (missing and all) and even turned on the CE light whenever he ran gas that had ethanol in it. And the 85 makes them kinda run rough to. At the same time, my dad said his 87 he used to have ran great (better than w/out the ethanol) whenever he was out west and used that stuff with ethanol in it on the 22RE. I'm not exactly sure what properties it contains. Not even sure why they offer 85 anymore, it seems all cars require 87 or higher.

Henryv

Really? So if you were running a higher octane, then switching it to a lower one and you have a good amount of miles then you have to switch to synthetic? I always thought that didnt matter much cuz the octanes werent that different. I got mine used so I dont know what was the previous owner used, but since I got it I've always used 89 but just very recently I switched over to 87 to try it out since prices were so high. For some reason, maybe its in my head, it seems to be running better with 87 so I'm going to stick with it. I got my runner with around 55k and have run 89 for over a year and am at around 68k now when I switched to 87. Do I really need to switch over to synths?