Gas in Motor Oil (1 Viewer)

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Feb 10, 2014
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Need help with finding out how gas is getting in the engine oil. I have a 1976 40 with 2F motor and Holley carb. I have replaced the fuel tank, clean the fuel lines, replaced the fuel pump (not OEM), replaced fuel filter, rebuilt the fuel side of the carb.

Current status is low oil pressure on factory gage, increased fluid in the oil pan which to me smells like gas, no fuel leaks in or around the carb (that I can see), starts and idles better than it ever has, gas smell might be more than normal and running rich. Carb is adjusted to max vacuum.

I would appreciate any help or advise I can get. I have been stalking this forum for many years. It is unbelievable the amount of knowledge in this community. If I can't get it sorted out I may be asking for a good mechanic in the Houston area. I need to find one that is not booked out with work for months in advance.
 

pb4ugo

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Running rich? Gas could be washing down the cyldr walls, or fuel leaking out of carb into the intake. Possibly bad new fuel pump pumping fuel into the crank case. If the oil level is noticeably rising id look at the fuel pump more closely. Im not a fan of holleys either.
 

RWBeringer4x4

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I’m not sure if Holley’s had similar leakdown issues as quadrajets but Welch plugs, needle seats, sunken floats etc all have a tendency to leak on a lot of carburetor models. That said, if you’re getting enough fuel on the oil to raise the fluid levels and drop the pressure, you have a MASSIVE leak and I suspect the truck would be running huge rich as a result. If the fuel gets too hot it could be boiling and percolating out of the bowl after the engine is shut down and can’t burn it off - but even that is a relatively short term phenomenon and not something I’d expect to thin out your oil too rapidly - this would be more of a risk of washing the oil off your cylinder walls.

I too would investigate the fuel pump again to see if it’s leaking into the crank case. This can dump a lot of fuel into the oil in pretty short order if it’s leaking internally and there’s no opportunity for the engine to burn it off. It’s also worth confirming that the fuel pressure the pump produces is in line with the holley’s requirements. Again, I’d expect the engine to flood/stall if it was pumping way too much gas but it’s another variable to consider.

My 40 has a 350 in it so I’m not a 2F guru but on a 350 there’s only two ways for fuel to get into the oil - through the pump or through the intake.
 
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Need help with finding out how gas is getting in the engine oil. I have a 1976 40 with 2F motor and Holley carb. I have replaced the fuel tank, clean the fuel lines, replaced the fuel pump (not OEM), replaced fuel filter, rebuilt the fuel side of the carb.

Current status is low oil pressure on factory gage, increased fluid in the oil pan which to me smells like gas, no fuel leaks in or around the carb (that I can see), starts and idles better than it ever has, gas smell might be more than normal and running rich. Carb is adjusted to max vacuum.

I would appreciate any help or advise I can get. I have been stalking this forum for many years. It is unbelievable the amount of knowledge in this community. If I can't get it sorted out I may be asking for a good mechanic in the Houston area. I need to find one that is not booked out with work for months in advance.

You say “which to me smells like gas”. You don’t seem very sure about this. If there was gasoline in your oil, you would know it by the smell.
 
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As said: check to make sure it’s not a fuel pump leak.
Also, depending on which Holley you have, if the floats are adjusted too high, they will run rich because fuel is bypassing the circuits as the fuel inlet needle isn’t closing off the fuel supply so the bowl is flooded. So, you park it and have 6psi fuel pressure, etc. and the needle isn’t closed so all that pressure pushes fuel out of the carb and into the intake where it trickles down on top of the valves (if closed) or past the valve (if open) into the cylinder. Rings have a gap so this fuel runs past the ring gap and into the crank case.
 
Joined
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Thanks to all for the advise. The fuel pressure is bouncing around 4.5. I think this a little low but that part seams to work OK. I have insulated the line to help with the vapor lock and have a installed a inline glass filter to keep an eye on it. It has been a problem in the past.

In regards to the oil. I changed it a couple of months ago and filled it to the middle of the hash marks. It is now above the full mark. I don't think it is water. It is very clear and not milky. I am just assuming it is gas (sense of smell not to good anymore).

My course of action: order and install a new OEM fuel pump, replace the fuel bowl float and adjust, drain and replace oil and try again.

One other piece of history is I let it sit for over 3 years without much attention. I know that jacked up a lot of little problems. I have been putting off a complete carb rebuilt hoping to get something better in the future. But, I welcome comments on whether or not a rebuild might help. The fuel side has been done. That was the quick way out.

Thanks again for the help
 
Joined
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Is it a Holley carb with a sight glass in the fuel bowl? Float height is an easy and free change.
It is an old Holley carb with a solid overflow plug. I did pull just to confirm and just a small amount came out. Just enough to wet the fingers. Also been sitting for a couple of days and shows 0 PSI on the line going into the bowl. (no back pressure?????)
 
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I’d run it and let it idle, then pull that plug and see. I usually set them so fuel is right at the bottom of the hole. Just so you give the vehicle a wiggle and a dribble cones out.
Even if it’s right on, still doesn’t mean it’s not a bad float or needle/seat.
 

pjohnson

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I wouldn't run it unless I was certain the oil was not thinned by fuel. You said your dipstick read over full after previously reading between the marks. Do you know why? Was it fuel contamination?
 
Joined
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Also if you drain the oil into a clear container, often the gas and oil will separate to form layers due to the different densities - just an easy way to confirm if you have something contaminating the oil.
Just to be on the safe side I an going to change the oil and filter this morning before I start it again. Cheap insurance. I like your idea about the clear container and separation. I am going to give it a try. I did try to ignite a small amount of oil/gas?? that I had gotten of the dip stick. It did not work.
 

hobbes

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I doubt your main issue will have anything to do with a return line, however it can increase the likelihood of vapor lock. Easiest way to remedy is add a fuel filter with a return function on it. See photo below. They’re sitting on the shelf of your local auto parts store. This will give the warm (expanding) fuel a place to go...


1611766619818.jpeg
 

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