Gas odors

[Mr Jody]

Originally Posted by DanEC

...Suspiciously, it seems that my oil level has increased slightly too - can't be sure as I may have just overfilled it slightly when I changed it.

I'm running a mechanical pump....

Dan – I experienced a similar gas smell on a passenger vehicle of mine, and it was the mechanical fuel pump. The diaphragm inside the pump can develop a hole, and the fuel can indeed get into the crankcase from there. Fuel will leak through this hole from the fuel side of the diaphragm with the fuel inlets and outlets, to the mechanical side with the cam operated actuator and thus into the crankcase (and of course these “sides” are actually the top and bottom of the pump, separated by the diaphragm in between).

On my particular pump, there was what I will call an ‘evidence hole’ manufactured in on the actuator side of the pump exterior. If there is a leak in the diaphragm, then fuel will be coming out of this hole when the engine is running. Best time to check this is when everything is cold and you first crank it so the fuel will not be immediately evaporating. In my case, it was easy to see, as fuel was squirting out of the evidence hole and not just leaking out. The smell went away with the fuel pump replacement.

I never saw an obvious rise in my oil level, so maybe most of my gas leak was exiting through the ‘evidence hole’, although I can’t help but think that some gas did get into the crankcase, so an oil change would be prudent. You may want to take a good whiff of your oil to see if you can detect a gas smell (although I would think that some evaporation occurs through the breather as the oil heats up). If you do a little googling on mechanical fuel pump leaks, you will probably see where one of the symptoms is a rising oil level.