When i start my engine i have 50psi of oil pressure, But when it gets hot it drops to 0psi and the oil light comes on, If i hold the revs at a higher rev range the pressure slowley builds up, but as soon as it goes to idle i have no pressure.

What could cause this, I have already tried a different oil pump, I was suspecting i will have to replace the engine?

Bit more info would help. Silvertop or blacktop? How long been in car? What oil and when last changed? What filter and when last changed? What sump? Clearance of pickup to base of sump? When did it start? Sudden or gradual? After a trackday, long journey, lay-up? Do you have an oil pressure gauge? What sender? Shared with the warning light?

Sounds unuaual on a modern engine. On old stuff it was a good sign that big ends (or mains, but less likely) badly worn.
Or, is there a pressure bypass valve somewhere on these engines. If that is stuck open can cause those symptoms.
But somewhere the oil pressure is leaking away, assuming the gauge you have fitted is correct.

Has it got a shortened sump, wonder if the pickup pipe welding were its been shorted has cracked and its now sucking up through the neck in stead of strainer?

Cheers

Rich

Its a 2ltr zetec silvertop, It has a shortend sump, I have already checked the welding on the pickup pipe and that is tight.

I have a oil pressure gauge on it and it seems to be working ok as when the oil pressure light comes on it is low in pressure.

Oil filter is off a renault 5 turbo.

I would dump the renault filter, it is m18 thread not 3/4unf. Close, but not clever. I lost a filter off an engine a few months ago, cue reground crank etc

I would pop the sump off and be having a look at the bearings, and any pressure relief valve. Again, I assume there is one, but no idea where.

As an aside, are there any associated rattles/knocks/noises?

[Edited on 19/7/11 by cliftyhanger]

Perhaps as the sump heats up it buckles ( like the biscuit tin lid when you were a kid) and blocks the strainer??

i would say sticky pressure relief valve jamming open

I would do an oil pressure test using a decent workshop pressure gauge before doing anything else, if you still have problems it's engine related and not a faulty gauge or sender. IIRC the oil pressure relief valve is in the pump??? , unlikely to be 2 faulty valves but easy to take out and check.

What about the wrong grade of oil being used?

As there is pressure when cold but not when hot

As ^^. Oil pressure relief valve is accessable from the intake side of the engine.

Haynes manual has pictures IIRC.

HTH

Len.