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Can higher octane gas hurt?


Old 07-06-2002, 12:52 AM
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Can higher octane gas hurt?

I have read post after post disputing the benefits of higher octane gas in our engines - I don't want to go there with this thread.

In my case my '01 5.4 pings a little under load so I began to put mid-grade in it. The ping is gone but now I read in another thread that higher octane fuel can cause carbon build-up:

Originally posted by hcmq
the number one reason for that year engine is a dirty EGR system (Not just the valve)

have you been using a higher octane gas than your owners manual calls for? If you have you probably have a bad carbon build up in the cylinders.

find a shop that has either a BG or Snap On carbon depletion machine.

my .02
Any other opinions?
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Old 07-06-2002, 01:44 PM
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I could see damage long term. The higher octane burns at a higher temp. Your lower octane designed engine doesnt get that hot so some of the fuel would not burn properly.

But at the same time, higher octane fuels also have more cleaners and detergents that may offset this problem.
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Old 07-06-2002, 02:22 PM
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For what it's worth, I started using higher octane for about a 2 or 3 month period a couple years back. I stopped when my buddy who was driving behind me noticed puffs of black smoke coming out of the tailpipe everytime I wouls "get on it".

Sure enough I had someone else drive and I followed . . . yup, lots of black smoke. I assume it was from the higher octane and "build up".

I stopped using it and haven't noticed anything since . . . it only occured when i was using it. So for me it's good ole 87 until the Superchip shows up

p.s. I didn't notice any difference in mileage or performnace when using it either.

1997 4.6, 4x4 EC SB
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Old 07-06-2002, 03:57 PM
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If it burns at a higher temp then it should make less deposits,not more deposits. Manufactures rate the engine for Minimum octane requirements, not Maximum octane requirements.
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Old 07-06-2002, 04:15 PM
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I see where you are coming from Ltruck, but if the fuel does not have complete combustions, other by-products within may not burn off either.

Have you ever put a beer can in a very hot campfire? Melts. Now ut a beer bottle n the same camp fire. Doesn't melt. Solid matter left over in the pit.
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Old 07-06-2002, 04:51 PM
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Higher octane fuel doesn't burn any hotter than lower octane. If that were the case it would cause detonation. Higher octane fuel has more resistance to break down into elements that can start the combustion process from the heat in the cylinder, and not a controlled spark.

Higher octane fuel has the same flame front speed as lower octane, there are slight differences, however they are too small to even be a factor.

Gasoline when vaporized/heated starts to degrade into seperate flammable elements, including free Hydrogen, and elements containing Hydrogen. These can burn with much less heat to start them off. What happens in the cylinder is as this uncontrolled flame front burns, it creates more heat in the cylinder, causing the remaing fuel to degrade and auto ignite, the gasses create more pressure as they expand,and are compressed by the piston. More pressure, makes more heat, and the visous cycle continues. Detonation.

High octane fuels have stronger(chemical) Hydrogen bonds, and don't give up free Hydrogen as easily. And they resist breaking down. Heat can come from compression, left over spent gasses, even a burr or piece of carbon on the head or on a piston.

A Ignition spark that comes too early in the cycle, causes the fuel to start it's burn, heat is released as the piston is still compressing the air/fuel mixture, it rapidly degrades from heat of the burn and compression(from the piston, and expanding gasses) , then auto ignites(explodes) and you hear a "knock". This is pre-ignition.
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Old 07-07-2002, 12:48 AM
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When your engine detects knock, it retards the spark. Some engines retard 18 degrees or more.

By reducing the propensity to knock, you reduce the chances of ECM-issued spark retardation.

Where poor gas mileage is the result of retarded ignition spark timing, moving up to a grade of gasoline which eliminates the knock can result in seemingly-irrational improvements in gas mileage.

Spark knock also tends to wipe oil from the inside of the cylinder walls due to the multiple flame-fronts -- and the result is oil consumption. In such cases, elimination of spark knock causes an immediate reduction in oil consumption.

Try a tank of Gasohol Regular -- my non-scientific tests suggest that around here, it has greater knock-resistance than do other Regular gasolines.
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Old 07-07-2002, 12:55 PM
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Stepping up to a mid-grade octane level to eliminate spark-knock is good for your engine. You shouldn't see any ill-effects from a higher octane. Spark-knock over time will cause engine damage. Only thing bad about going to a higher octane is the higher price.
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Old 07-08-2002, 12:38 PM
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Here's some good info on fuels although its not about cars it gives good info on what fuel does and doesn't do. I run 87 octane in my car and truck without problems but I run 108 octane race fuel in my bikes the higher octane makes a big difference in my modified bikes there's much less carbon buildup and my engine runs cooler but I don't see the need for higher octane fuels in a stock car, if your truck doesn't run properly under normal driving conditions with 87 octane I would have it ck'd out to find out why. assuming your truck is basically stock. ck it out
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Old 07-24-2002, 11:57 AM
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I don't care who tells me that I should use 87 octane, I'd never use it. It is cheaper for a reason and makes engines ping everytime. I use only 93, always have. It is not much more money and the engine will always run cleaner and never detonate. I think that the real reason Ford "recommends" 87 octane is so that they can justify selling you that ridiculous "INJECTOR CLEANING SERVICE" at 15,000 miles. With 87 octane, those injectors will be clogged up by 15k miles. Just my 2 cents.
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Old 07-24-2002, 12:34 PM
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As far as I know the only place higher octane hurts is in the billfold. Ignition knock will definitely hurt your engine. There are a lot of posts on persistent ignition knock in some engines. If you can eliminate it with 89 octane fuel then go for it.
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Old 07-24-2002, 02:24 PM
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Go to the computer chip forum and read many of the post there by Mike T as he has answered the ? many times in there and he can go into detail more than anyone else can.
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Old 07-24-2002, 11:05 PM
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Back in the 60's, SUNOCO gas had a variety of octanes available. You dialed your own at the pump. I ran the highest they had, burned two valves in short order. I believe the higher octane burned longer or something like that. Any way, use a quality 87(cheveron) and your engine will probably not ping, Just my .02
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Old 07-25-2002, 12:12 AM
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Oil companies love you octane sensitive guys. But hey its your money.
My 99 F 150 has only been fed 87 octane now knocks here.
Maybe im just lucky ???

Last edited by BEC308; 07-25-2002 at 12:14 AM.
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Old 07-25-2002, 02:43 AM
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I run 91 octane ( new for california).

With today's high quality gas standard, there should be no worries for carbon build up.

An old remedy, take your truck for a good run. Take it on the freeway for a nice journey. These are V8's.

Techron or Redline SI-1 are very good cleaners if carbon is ever a prob.

The probs. arise when we use the cheapo gas, like Arco. ( made from corn.)
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