Gasoline in Crankcase

Anteek29

Anteek29

Well-known member
In my '41 p-u would a hole in the fuel pump diaphragm cause raw gas to drip into the crankcase? I suspect the diaphragm may have deteriorated as a result of the corn gas here in CA? The truck ran fine otherwise but the problem needs resolution and the oil changed before driving again.
 
Would it still pump gas to the carb if there was a hole in the diaphragm of the pump? My fuel pump on the Merc is at least 40 years old and still seems to work as it should.
 
sounds like your on to it you need alcohol rated diaphragm after all ethanol is just good old fashion Moonshine
 
I have seen many cars run just fine with the fuel pump leaking gas into the crankcase.
After changing the fuel pump and oil and filter you should change the oil again after a few minutes of running.
I have also known of new car dealers telling the customer that the gas in the oil is caused by a crack in the block. I have never seen that proven, always a fuel pump problem.
I have had a couple of fuel pumps spit gas out the vent instead of going into the crankcase.
 
Are you running the mechanical only? or an electrical pump through the mechanical pump? A hole/ripe in the diaphragm won't pump real well. But a electric pump running through it will certainly fill a crank case with gas quick.


Fix it and oil change. Gas in the oil will wash bearings.
 
Tinker said:
Are you running the mechanical only? or an electrical pump through the mechanical pump? A hole/ripe in the diaphragm won't pump real well. But a electric pump running through it will certainly fill a crank case with gas quick.
Fix it and oil change. Gas in the oil will wash bearings.
Click to expand...


Mechanical only - no electric.
 
Kind of interesting to note. When I rebuilt my '46 mechanical pump, it was the (under)side that does not come in direct contact with any gas that was deteriorated. I rebuilt it before it failed. The (top)side that comes in direct contact with gas appeared fine visually but the other side was cracked right up. This pump only tasted gas with ethanol in its later lifetime.

If you rebuild it, be sure to save and reuse the old spring.

(top)Side contacting gas directly.
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(under)Side contacting crankcase vapor/fumes
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Side contacting crankcase vapor/fumes
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Will,
The underside is exposed to high heat, while the topside is cooled by the fuel. Apparently, it may have been replaced prior to being attacked by ethanol?
 
ford38v8 said:
Will,
The underside is exposed to high heat, while the topside is cooled by the fuel. Apparently, it may have been replaced prior to being attacked by ethanol?
Click to expand...

Yeppers, the deterioration definitely looks to be from heat and age. You could be right about the ethanol. I've read allot about ethanol deterioration and figured I'd rebuild before being stranded.

From what I've seen, ethanol tends to expand rubber not dry it out. When I rebuilt my pump, I put the rubber O-ring from the glass bowl into a jar of gas thinking I would prevent it from dying out and shrinking. To my surprise it grew/swelled allot. It gained about 1/2" to its circumference. No longer fitting, I set it out to dry out before I could reuse it. This could be a result of other additives in the fuel but I was using PetroCan fuel which is known to have the highest ethanol content in Canada. Its no E85 but greater than 10% ethanol.
 
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