Gas in the Oil

The engine is sucking gas into the oil pan. It is detectable buy the smell of gas on the dipstick and the oil viscosity is thin. What could the cause of this be?

We are doing our first valve job and found about a cup of oil and gas mix in the right-hand valve cover. There is definitely gas in the oil … we have been told to replace the fuel pump, also that the carburetor may be at fault.

The usual cause of fuel in the oil is the fuel pump diaphragm starting to leak. Usually replacing or repairing the pump fixes the problem (and of course changing the oil). If you pull the pump and the undersides are fuel wet, or the grease in there looks runny rather than sticky, then you've almost certainly found the problem.

DON'T run the engine with fuel in the oil for any length of time - the fuel dilutes the oil, resulting in increased engine wear, and there is always the danger of the fumes from the evapourating hot fuel that you'll end up with a fire.

A faulty carburettor won't leak fuel into the sump in any quantity -- it will just result in a rich or lean fuel mixture, which is burned, not drained into the sump at all. The only way fuel from the carburettor could get into the sump would be past very badly worn valve guides, or badly worn piston rings, and either would result in the engine blowing a LOT of smoke -- you'd certainly notice it. Even then, the leaked volume of fuel in the oil would be very small (in comparison to a leaking fuel pump).

The valve cover area on the VW engine is arranged so almost all the oil in those areas drains back to the sump via the push rod tubes. When you take the valve covers off, there is usually only a few drops of oil clinging to the inside -- nothing like a cup full.

The only way I can see any volume of oil (oil/gas in your case) being in one cover is that either -

1. The car was sitting at an angle, so the oil could not drain back to the sump, or
2. The push rod tubes are bent or blocked, once again preventing normal flow back to the sump.

Of course with gas in the oil the oil level would be much higher than normal, and so it would be easy for a slight angle on the car to result in the gas/oil mix to drain to the valve cover on one side via the push rod tubes.

So have a good look at the push rob tubes first. If they are straight, then get the fuel pump repaired/replaced, and drive the car, checking the oil level after a few miles to make sure it's not getting more fuel in the oil. If the oil is OK, then check that side valve cover again just to make sure it's not filling up again. If it's OK, then it was probably just an overfilled sump problem.