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Gas in the Oil!
I have a 390 FE stroked to a 410 that was rebuilt maybe 10 years ago but has had only 2k mi put on since then. Before we started the engine in the "donor" truck before pulling it, we noticed that there was gas in the oil. What would have caused this and what should be done to fix it? The oil was changed before we started it but when I took the oil pan off last night it still smelled like gas. Will the gas do any damage to anything internal? I also took all the plugs out to see how they looked and all looked normal except for one that looked brand new. There was no carbon buildup what so ever. I am replacing the oilpan and carb so what else should be replaced?
Thanks Ed |
A couple of suggestions:
1. You may have a bad or dirty carb needle and seat. In that case, gas may leak past the needle and seat after the car has been turned off. The gas will flow into the cylinders and then seap past the piston rings. 2. Your fuel pressure is too high causing problems similar to no. 1. 3. Are you running a fairly radical cam? If so, the idle vacuum may be less than the rating of the power valve in your carb. That will cause the power valve to be open at idle. Most people compensate by opening the carb butterflies so the engine gets more air. That prevents the engine from dying at idle but it will cause it to run very rich and it will allow fuel to work it's way past the piston rings. This is easy to fix. Hook a vacuum gauge up to figure out how much vacuum you have at idle. Install a power valve that is rated 1.5-2.0 inches greater than your measured vacuum. Good luck. Chris |
Running excessively rich will wash the lubricating oil off the cylinder wall and ruin your rings. The gasoline ends up in the crank case and yes it can do alot of damage. Gasoline is just like pouring mild acid in your motor. I'm sorry to admit that I am speaking from experience. The motor is out of my car undergoing an overhaul right now.
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If you are running the stock fuel pump, it could be leaking into the oil pan. I had that happen on my 1965 390 and the dealer told me something inside the fuelpump had split and was letting gas through. I didn't notice any difference in how it ran, just when I checked the oil I had gas in it. Fortunately I check my oil almost every time I drive so I had no damage from the gas.
Ron |
Thanks for your input. I couldn't get much info on the engine from the guy I bought it from. He did say that it had a "wild" cam. The engine was sitting for a few months. After the oil was changed it started right up. It had a nice lope to it. It idled fine but stepping on the gas, it bogged down. The guy who pulled it said that the carb needed to be replaced. Could that be why that one plug was clean? It was soaked in gas? I think that it was #1 plug. Could it be the fuel pump? Should I go ahead & replace that as well?
Thanks Ed |
Ed,
If one plug was soaked with gas, it most likely wasn't firing for some reason. And if the engine bogged down when you stepped on the gas, you could have a carb problem. Especially if it does have a wild cam. Try to find out as much about the cam as you can, as that could lead to problems later on. Also the cylinder with the gas soaked plug could be where the gas got into your oil pan from. If the plug isn't firing, then the gas that went to that cylinder has to go somewhere. I would first make sure that there is fire from the distributor to that cylinder. Check the plug wire and the distributor cap inside terminal that feeds juice to that cylinder. If you have a good spark through the wire then try replacing the plug anbd see what happens. If the carb has set for a long time and the guy you got it from said it needs to be replaced, that may be a good place to start. Until you get this straightened out, I wouldn't worry about replacing the fuel pump. Ron |
Ed,
All of the points above are good ones....the diaphragm in the fuel pump could have a leak and it would allow gas to pump into the oil pan. If you can not find out any specs on the Cam you can get a degree wheel, take off the valve covers, turn the engine over by hand and see where the intake/exhaust valves open and close. That would tell you very specifically how wild/mild the cam is. One clean or one bad plug is more than likely an ignition problem. Tony R. |
Leak/crack/hole in fuel pump diaphram would definitly pump fuel into crankcase. Top of fuel pump should have a "pee" hole (small
hole) that wil shoot a small stream of gas when the engine is running so you can be alerted to the problem. Check to see if your pump has this hole, and that its not plugged. Sounds like the engine wasn't run much, so gas varnish build-up is a prime suspect. This will cause the needle to stick in the open position and flood the engine with gas which of course adheres to the law of gravity, and heads straight to the oil pan. Also, if this thing has a holly carb. the accelerator pump check ball will be stuck shut, causing the " bogging" when you try to accelerate. Only two ways to get gas in the pan: Carb flooding and leaking fuel pump diaphram. |
Well, I already have a new carb to go on top so I guess that I'll get a new pump as well.
Thanks Ed |
Be sure
To take off a few crank bearing/connecting rod caps and at least one main cap and check to see if there's damage. Then re-torque to specs. Also might want to do a compression test.
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I agree with B n B.
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If it had that many miles on it and it's ran all that long excessively rich, then it's not good for it at all.
I built my engine last year and the car hasn't been on the road yet, but I sometimes fire it up to test headers/sidepipes or let my buddies listen to it. Sometimes it gets a gassy smell in the oil from just firing it up and not letting it warm up all the way....so I just go ahead and change the oil in it even when it wasn't been ran that much. But it hasn't been subjected to 2000 miles of being excessively rich. |
Me too!
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Who's post are you "me too'ing" Rob? :)
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