what can cause oil to go into fuel tank and fuel in sump ( blb engine )

would like to no what the causes are for above please

from little research i have done i conclude that oil in fuel tank can only be tandem pump
and fuel in sump can only be injector seals

other theory is if i have a crack in cylinder head from fuel into an oil galley

Faulty seals on tandem pump...

I had a 1.9 transporter that did this, I think start with the cheapest fix first. Mine was injector seals ended up at £80 for the seals from vw. Is there some sort of pressure test you can do to help? I remember I was lucky because the van went to rev up and "run away" managed to stall it just intime.

mine was tandem pump i put a pump from working unit and cleaned the tank out
thanks for you input guys

How did you find out?

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Originally Posted by Pimpinthepidge

How did you find out?

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i used a specialist technique basically guessed lol
i ordinarily found the problem when i changed the fuelfilter on service i always put the filters in see threw bags and leave over night to my suprise i found it to have large content of oil
i already had new injector seals so i went after the tandem pump
so i started by cleaning the tank out with electric pump then wiped with rag and put few liters of fuel, i also made a see threw bit or return pipe from return going to a clear bucket and started up with the faulty tandem, fuel went black almost instantly (see threw pipe was a bad idea because it just looks like normal fuel) but bucket showed the oil content as it poured out the return

i had a working tandem pump of another car and switched it done the same as above cleaned filter. after runnig for 20 min no oil so ordered a new tandem pump

nice clean tank and lift pump

engine oil has been changed but will do another one in few days to be 100% sure