Lancia Motor Club

Petrol in oil sump. Can this be caused by incorrect valve clearance? Posted on behalf of a LMC Kent member who is not yet registered on this forum.

  

check fuel pump pressure, both at idle and at speed. Too much pressure can push fuel past needle valves and wash the cylinder walls.

I think it's possibly a mechanical pump. High fuel level dripping down ?

Some mechanical pumps use a diaphragm which can fail as I found on our Jowett Bradford about 60 years ago. A sudden "pop" and the dipstick flew out!
What kind of pump is it?

Mike Clark

A diaphragm pump. Would I be correct in thinking that petrol  would enter the oil system only via the piston rings, due to carburettor floats allowing an excessively  high petrol level, overflowing into the piston bores or via the fuel pump mechanical linkage between fuel and oil systems?
 

The Fulvia mechanical fuel pump diaphragm can split  allowing fuel to enter the engine......

...via the pushrod.   Time for an electric pump + pressure regulator conversion?

About £35 for a new pump from Omicron, a fairly easy fit, I have an electric pump that is only used to prime the carburettors , to save all that churning over to drag up fuel, this is turned on by a switch on the dash, and is fitted underneath by the fuel tank.
It's also available to use if the mechanical pump fails.
Belt and braces!
Brian
8227 8)

Pump reported to be ok, but maybe worth replacing the existing mechanical fuel pump as an immediate precaution. A low cost item including the gasket I assume, involving only two threaded fasteners and two hose fasteners . Another oil and filter change being further time and materials. If there is nothing apparently with the existing it could be put in the spares box. Peace of mind with a new item + a spare. Apart from oil contamination the pump could fail to pump petrol if the diaphragm is deteriorating.

  Richard

Just to clarify, when it comes to the oil contamination, valve clearances are an unintentional red herring but obviously correct valve clearances are one solution for  poor compression. £35 mechanical pump sounds reasonable Brian.

 Richard

Fuel in the oil will quickly damage the big ends. Necessary to change oil and filter.

In WW2, aircraft had a system called oil dilution for cold weather operation. Before stopping the engine, when a cold start was anticipated, petrol was introduced into the oil circuit. Depending on ambient temperature, the dilution was up to 30%. When the oil went cold, it remained thin and helped to start a cold engine. While warming up the engine before take-off, the petrol in the oil evaporates.

However, I agree, that it is no good when petrol leaks into the oil sump on a car.

Karl

Richard, I checked online and the Omicron price was better than anyone else, and some were double for exactly the same pump.
Brian

My father who was non mechanical and an ardent VW Beetle fan - the car could do no wrong - , once became very excited that his engine oil level was increasing. He thought it was a miracle......and then I changed the mechanical fuel pump for him, drained the oil and found it was mostly fuel.
Chris

Got to be the mechanical fuel pump diaphragm leaking fuel into the sump. can't be much else. You will have to change oil and filter so take off air filter box and carb trumpets. This gives much better access to the oil filter and fuel pump from the engine bay. No need for crawling underneath. I always keep a spare in the car.
Whilst you are at it you can now give the carbs a quick balance check with a manometer.

70 miles on, and the oil problem hasn't returned yet. What hasn't been mentioned is how the petrol in the oil initially became apparent.  There was a rise in sump oil level and a smell of petrol. This has been attributed to unburnt fuel  ending up in the sump (by an expert, who I am told, reports that the fuel pump is ok according to his gas annalyser).
  Our member is now registered on this LMC forum, so perhaps will be able to confirm his findings, for the benefit of other members.
  My own car has electric fuel pumps, so one less thing to be concerned about,(or should that be two more things to be concerned about)  There is always something.

  Thanks for the replies,

  Richard

I experienced a similar issue with excessive petrol in the oil. Intially it was a split diaphram, new mechanical petrol pump installed and all appeared to be fine. Then several months later the oil was once again smelling like petrol. I took the decision to remove and rebuild the engine, it was something I was planning and winter was around the corner so bit the bullet. After teardown 2 of the bores were found to be heavily pitted/eroded. This was the second leakage path for the fuel.

Did the pitted bores cause a rise in sump level?
  Ok now I expect.
  Richard

It certainly did, with a serious fuel consumption :-\.