57 Continental R6602 Recommended Fuel Octane

Paul.McLean.US

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I apologize if my question has already been answered.... 1000's of posts are hard to read thru... I have a 1957 M55 Diamond T dump truck. I've had it now for several months. What is the recommended fuel octane? I read thru the manuals and it seems like 85 octane, but they don't make that around here any more. I tried 91 octane non ethanol but was worried of engine damage so I went to 87 octane 10%ethonal... After a few rain storms it now runs like crap and barely starts. I am thinking water is the problem. Does anyone see a problem with running 91 octane non ethanol?

And if anyone can lead me to a set of sparkplugs and gaskets, I am thinking maybe I need to change them.... No clue the condition or last time they were replaced... possibly 1991 when the engine was overhauled.
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Karl kostman

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Paul you need to lose the Ethanol right away but I am guessing you have already caused some problems! First off just about any older military truck with a gasoline engine in it was setup to run some pretty crappy fuel hence the very low compression ratios running your truck on regular octane fuel will make no difference what so ever, if your paying extra for higher octane your wasting your money! STAY AWAY FROM ETHANOL!
Here is the problem you are likely dealing with now, Ethanol put into a fuel system that has never had it in before and was never designed for this type of fuel in the first place is going to have problems starting at your fuel tank. The filters in your tank will start to deteriorate and will likely be gone over time. The fuel lines will start to erode from the inside obviously polluting your entire fuel system. Any old residue that you had in your fuel tank and filters etc. will very likely come loose and start working their way through the system and now your truck is running like crap. IMHO you are looking at draining the fuel tank, flushing the fuel lines completely changing all the filters that have to do with fuel and then hopefully only drain and clean the jets on the carb, I say hopefully because you may have to disassemble the carb and go through it and clean everything (maybe, maybe not)!
Good luck and ethanol sux!
 

Paul.McLean.US

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Paul you need to lose the Ethanol right away but I am guessing you have already caused some problems! First off just about any older military truck with a gasoline engine in it was setup to run some pretty crappy fuel hence the very low compression ratios running your truck on regular octane fuel will make no difference what so ever, if your paying extra for higher octane your wasting your money! STAY AWAY FROM ETHANOL!
Here is the problem you are likely dealing with now, Ethanol put into a fuel system that has never had it in before and was never designed for this type of fuel in the first place is going to have problems starting at your fuel tank. The filters in your tank will start to deteriorate and will likely be gone over time. The fuel lines will start to erode from the inside obviously polluting your entire fuel system. Any old residue that you had in your fuel tank and filters etc. will very likely come loose and start working their way through the system and now your truck is running like crap. IMHO you are looking at draining the fuel tank, flushing the fuel lines completely changing all the filters that have to do with fuel and then hopefully only drain and clean the jets on the carb, I say hopefully because you may have to disassemble the carb and go through it and clean everything (maybe, maybe not)!
Good luck and ethanol sux!
Yea I only buy the 91 octane non ethanol from Stewarts Shops for my other vehicles. I put a call into the previous owner asking what type of gas he used. I just put 4 ozs of Mechanic in a bottle in the tank with the 5 gals of 87octane 10% I had in there and it is now humming away down there... tho even way up in the house I can hear it skip a beat or something familiar to that. So do you think it is safe to use 91 octane?
 

Mullaney

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Yea I only buy the 91 octane non ethanol from Stewarts Shops for my other vehicles. I put a call into the previous owner asking what type of gas he used. I just put 4 ozs of Mechanic in a bottle in the tank with the 5 gals of 87octane 10% I had in there and it is now humming away down there... tho even way up in the house I can hear it skip a beat or something familiar to that. So do you think it is safe to use 91 octane?
Paul,

Whatever you do - don't run "ethanol flavored" gas in your truck. It has a tendency to eat the carburetor gaskets as well as all the other horrible things that Karl mentioned. I made that mistake with a 29 Model A and I am still fishing bits and pieces of the fuel tank insides out of the fuel filter a year later. Found a new carb for it after a rebuild kit. It just never ran smoothly after giving that vehicle "corn squeezins".

You can always add octane booster, but honestly I don't think you will need to do that. Higher octane isn't going to hurt the truck.
 
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Paul.McLean.US

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Paul,

Whatever you do - don't run "ethanol flavored" gas in your truck. It has a tendency to eat the carburetor gaskets as well as all the other horrible things that Karl mentioned. I made that mistake with a 29 Model A and I am still fishing bits and pieces of the fuel tank insides out of the fuel filter a year later. Found a new card for it after a rebuild kit. It just never ran smoothly after giving that vehicle "corn squeezins".

You can always add octane booster, but honestly I don't think you will need to do that. Higher octane isn't going to hurt the truck.
Cool thanks. I have not run it very long since I got it... maybe 2 hours tops. I will go back to the 91 octane no ethanol. Just waiting to here back from the previous owner on what type of gas he was using.... by the way his name is Karl too... and the guy he bought the trucks from was named Carl.... :)
 

Mullaney

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Cool. Corn belongs in our bellies not our tanks
Absolutely!! I agree 100% and the farmers aren't making any money on the corn they sell to make gas - and from what I understand - it actually costs more to make ethanol than gas. Not sure that is a cold hard fact, but it wouldn't surprise me.
 

BEASTMASTER

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believe what u want, i 've been running reg gas in my 61 M51 with the 602 in it for 15 yrs now, still runs like a champ. one time it did run like crap after sitting for a while ,and would'nt go over 35 mph, i put in 5 gals of high test and that fixed the problem. been good ever since. good luck.. pull the plugs on the bottom of tanks and check for water . first thing to do.
 

m715mike

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believe what u want, i 've been running reg gas in my 61 M51 with the 602 in it for 15 yrs now, still runs like a champ. one time it did run like crap after sitting for a while ,and would'nt go over 35 mph, i put in 5 gals of high test and that fixed the problem. been good ever since. good luck.. pull the plugs on the bottom of tanks and check for water . first thing to do.
What is “high test”?
 

2deuce

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I saw this old post and just thought I'd add that that engine is the biggest or I guess the second biggest gas hog I have ever owned in a truck. Anyone that can afford to run and work one of these pigs, I guess can afford the extra cost of non-ethanol too. They do make nice power, and sound strong. You don't see many of the R6602, they were swapped out long ago.
 

GopherHill

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Those engines will run on low octane fuel just fine. Avoid ethanol in the fuel unless you drive it enough to use up a tank full every few days. I'm not sure of that time frame.
 

frank8003

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And about that ethanol... It has eaten a lot of carburetors!



and this seems high rated
 

2deuce

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The guy who originally posted was concerned about high octane being bad for his engine. The reality is he would only get better performance/more power/run cooler with high octane. It would have no detriment except it cost more. The problem is the R6602 can't take advantage of the higher octane of premium. The higher the octane the more the burn is controlled. High compression engines need the octane higher to eliminate pre-detonation, the low compression R6602 can run on regular without pinging. The compression is low enough in the R6602 that the spark is the only way the fuel will ignite.
I say run the cheapest fuel you can get, it will burn up a tank before you know it. You can't let ethanol sit in the system anyway....it's bad in a couple months. Drain the tank if you're not using your truck, and run non-ethanol gas in it with a stabilizer(I like 2-stroke at 100 to 1).
 

2deuce

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Ethanol is bad on carbs, even the fiberglass gas tanks on vintage motorcycles. Don't let it sit in your old vehicle that was built before ethanol was introduced. Nothing but problems!
 
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