vacuum/gasoline pump - does it leak fuel? How to check?

pduske · Post by **pduske** » Wed Jan 08, 2020 3:15 am

Hello Jeep fellows,

the engine of my M38A1 consumed 4 litres of oil on 400 miles - I will build in an overhauled engine next week.

The guy that sold me overhauled engine recommended to make sure that the pump does not bring fuel in to the oil system of the engine - which would ruin the new engine fast.

question 1: Is that correct / does this sometimes happen with this pump?

question 2: how do I check if the pump does leak fuel?

I appreciate your support

Regards
Philipp

Post by **wesk** » Wed Jan 08, 2020 11:45 am

Yes, when the fuel pump diaphragm fails the fuel will leak thru the block opening to the oil. You can smell the gas in the oil instantly on your dipstick. Rebuilding the pumps solves the problem but if you continue to operate the engine on the thinned oil you can damage the engine.

Early fuel pumps of this type had a problem with early diaphragm failure and this was resolved with a Technical Bulletin issue TB 804-11 dated Jul 1954. This bulletin has been complied with long ago in most pumps but you should always check a new pump on installation for previous compliance.

pduske · Post by **pduske** » Wed Jan 08, 2020 3:56 pm

Thank you Wes,
I "tested" by holding a lighter to the dipstick before and after an engine run - no inflammable reaction...

Is that a "valid" test?

Regards
Philipp

Post by **wesk** » Wed Jan 08, 2020 10:44 pm

Yes & No. The flammability of the gas depends on its temperature and the ration of gas fumes to oxygen in the air next to the dip stick. So it is quite possible to have gas in your oil and the fumes to not ignite using your test. Plus you are also introducing the smell of lighter fluid and the open flame which can confuse your nose.

The best test is to simply smell the dip stick. If you aren't sure what smells you should identify take a new sealed bottle of engine oil and open the cap. Wet a finger on one of your hands. Now smell it. That's the smell of engine oil with NO gas in it.

Now open a small container of gasoline and wet on finger on your other hand with it. That's the of raw gasoline.

Now wet the finger on your hand that was wet with engine oil with the gasoline. That is the smell that will alert you to an internal fuel pump leak if you smeel that on your dipstick.

RonD2 · Post by **RonD2** » Thu Jan 09, 2020 10:26 am

Another way to tell for sure, but certainty will cost $28 plus postage.....

https://www.blackstone-labs.com/about-u ... -analysis/

https://www.youtube.com/watch?v=1dC9ZMeUkwI

Post by **wesk** » Thu Jan 09, 2020 10:32 am

God help the poor man that cannot smell the difference between engine oil and gasoline!!!!

$28 !!!!! I get mine done for aircraft piston & turbine engines for $12 + postage $2.

davem201m38 · Post by **davem201m38** » Tue Jan 14, 2020 4:56 pm

Hum. I have my pump off at the moment, the engine is out for rebuild. The pump has been fine so far but we’re now forced to have ethanol 10% and it may be going to 15%. Is there an ethanol tolerant rebuild kit out there your side of the pond?
Thanks, Dave.

4x4M38 · Post by **4x4M38** » Tue Jan 14, 2020 8:34 pm

I believe the diaphragms from current Then And Now are ethanol compatible.

Give them a call or email. They are very helpful.