Should I be using Premium Gas?

[Degnol]

Degnol: Wouldn't higher octane fuel mask the symptoms you refer to? So it's possible that some folks experience pinging/knocking due to timing problems and "solve" the problem by running higher octane fuel?

Exactly. If your compression is stock, ie <9:1 and your timing is not too advanced(I know many time their engines a little advanced over the stock specs) and your pistons are not all carboned up.....you don't need anything higher than the recommended ocatane rating spec'd by Toyota.
Now the post by Living in the past stumped me because I have never heard of Toyota specifying anything greater than 87 octane for F or 2F engines, but then again, I don't have an owner's manual for a '76. There are at least a couple of recognized ways to calculate octane ratings and I think both were used routinely in 1976. So, does 1976 90 or 91 octane = today's 90-91 octane? Dunno.


Ed

 

[Living in the Past]

I agree it sounds strange that a 2F would need 90 octane or better. But when I was checking out the manual I remember it being higher than I thought it should be, that's why it caught my eye. I know a US spec 2F will probably be different than most other parts of the world just because of our emission requirements. I've got a 78 owner's manaul but it's probably stored out of town too, but I'll check tonight. Somebody should have a late seventies owner's manual laying around.

John

 

[74fjsemistock]

If it get's you in and more importantly...get's you out.run it .Pull a jeep while you're at it cause more trails are being closed from trash than tread.

 

[Degnol]

Copied from the link......


in most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).


Ed

 

[Degnol]

If it get's you in and more importantly...get's you out.run it ..

Well, engine knock is nothing to be ignored. Left unchecked it will burn a hole in the top of pistons.


Ed

 

[MOfj40]

Copied from the link......


in most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).


Ed

My 06 suzuki sportbike had a factory sticker on the tank to only use 91 or higher octane. Most riders I've talked to assumed this means (U.S.) Premium. Howver if you stop to read the user manual, it states that they are referring to RON. The manual lists the (R+M)/2 equivalent as 87. I would assume the Toyota manual refers to RON as well.

As stated, higher octane will mask detonation due to advanced timing. It will also mask dieseling, which is a symptom of timing, rich mixture, incorrect plugs, carbon buildup, etc.

If your mix and timing are correct, the only advantage to running premium (in a F/2F) will be the higher additive percentage- not worth the increased price. You come out ahead by running 87 and adding a can of STP, Lucas, etc Fuel System Cleaner every couple months.

 

[bsevans]

That could also be a result of you running an HEI/DUI that is not curved for your motor and is providing too much mechanical advance.
Ed

The DUI HEI in my 40 was curved specifically for my engine by DUI based on my input (type and style of driving). Having said that, the issue of pinging at high altitude occured while running a factory dissy set to FSM specs.

 

[Degnol]

The DUI HEI in my 40 was curved specifically for my engine by DUI based on my input (type and style of driving). Having said that, the issue of pinging at high altitude occured while running a factory dissy set to FSM specs.

Asked and answered....................at ease

So, as an engineer, what do you think caused your pinging problems? I realize you are not necessarily an automotive engineer, but the same logic applies. Do you have higher compression? Or rather, DID you when the pinging occured?



Ed

 

[crushr]

The only noise that higher octane (premium) fuel would reduce is pinging. Your (tractor) engine should not ping on regular fuel unless its compression ratio has been increased, or your timing is excessively advanced. Pinging can cause engine damage, so you should determine the cause, and consider running premium until its fixed.

Don't equate "premium" (higher octane) fuel with being higher quality. The only difference between regular and premium fuel at any given station is very likely to be the fuel's octane rating, which is in no fashion a measure of the fuel's quality. Calling a fuel "Premium" does not indicate superior cleaning attributes, fewer deposits, etc.

 

[cpratt]

I have to run premium. The engine is a pretty high compression SBC though. I tried running plus for about a 2 weeks and my idle dropped about 200 rpm, it smelled like crap, and didn't sound good when I put my foot into it. A few miles after refilling with premium, all was good again.

like I said, it's a high compression SBC though.

 

[fj40forlife]

I drop my dirt bike 110 gas and seem to run better lol

 

[MOfj40]

Don't equate "premium" (higher octane) fuel with being higher quality. The only difference between regular and premium fuel at any given station is very likely to be the fuel's octane rating, which is in no fashion a measure of the fuel's quality. Calling a fuel "Premium" does not indicate superior cleaning attributes, fewer deposits, etc.

Actually there was a discussion a month or two ago in the FJC section that has some info you might want to check. Some members with firsthand knowledge of the oil industry weighed in with opinions that there is a difference in detergents (cleaning power) between brands and between grades.

https://forum.ih8mud.com/showthread.php?t=141163

 

[Rick '79 FJ40]

I worked for a large oil products pipelein for 20 years, and the only real difference between brands is the additives. Many times the gas is the same between brands unless they add things to it after it has been shipped to their local tankage. Most of the "off-brand" stations use the same gas. The only differences may be when grades mix in the pipe and a higher octane fuel has to be down-graded because it does not meet the minimum octane requirements for that grade. In that case you could actually get a higher octane in an "off-brand" station than you do in a name brand station. The name brand stations are going for consistancy between batches and the "off-brand" stations will buy gas that could be a few points higher than the minimum and call it the lower grade...

Does this make sense?

 

['74 UA FJ]

Let's just keep the terms straight for people who might not know. We aren't talking about "engine knock" as some have said. What they meant was "spark knock" or pinging or predetonation.

 

[Doug_S]

I have the same problem with the engine pinging. When I run premium (92 octane) fuel, the pinging stops. My mechanic says that the pinging is just a byproduct of lower octane fuel. 'm going to try and retard the timing a bit and see what happens. Right now it's set right on 7 degrees advanced which is what Toyota calls for.

 

[projektdotnet]

The cause of pinging is essentially the same effect as a diesel but instead of the gas being injected during detonation it is already in there. What octane does is keep fuel from a Compression Detonation (exploding due to excess compression). The amount of compression determines how much octane to run. I have an 89 Saab 9000 CD Turbo and even it runs on "regular" according to it's owners manual so I know that unless you've serioulsy increased your compression that your pinging is probably NOT caused by the fuel you run but as stated earlier by another problem inside the engine that needs to be addressed.

 

[fj4o]

My 1977 FJ40 was running like crap, then I put a full tank of premium in it and a can of seafoam and she reacted positively. I have only had her for about a month but man I am in Love with my FJ40. I don't think I will ever sell it, it is so F ing fun to drive!

 

[Ali Ali Ali]

You're not driving a Ferrari or other high performance engine. It's a tractor engine, it'll probably run on dirty water!!

 

[ToyotaMatt]