Hi guys,

I'm having a very frustrating low oil pressure problem with my '98 S90. It only happens when the engine is hot, ie. cruising on the highway for over 1 hour and driven aggressively. Took it to the dealer and here's the list of things they've eliminated so far...

- Faulty sender (confirmed via mechanical oil pressure gauge that it is loosing pressure)
- Clogged oil filter (oil & filter changed)
- Oil pickup tube O-ring (replaced with new parts)
- Oil pump & pressure relief valve (replaced with new parts)

Dealer told me when they had the mechanical oil pressure gauge attached, pressure was around 6 bar (87 psi) when cold, 2 bar (29 psi) when hot... then when pushed hard all of a sudden it'll drop off to around 0.5 bar (7 psi). Pressure stayed low even when increasing engine RPM but if the engine is switched off for 2-3 minutes and started again the pressure returns to normal. Also when the pressure is low the hydraulic tappets stayed quiet, they never made noise & complained of low oil pressure.

At first the pressure dropping away suddenly & recovering only after 2-3 minutes of allowing the engine to rest suggested a faulty pressure relief valve. Unfortunately after replacing the pump & pressure relief valve with new Volvo parts the problem still occurs.

So far the dealer suggested it's possibly cracked main bearing or blocked oil galley, but I feel both seems unlikely as it doesn't quite explain the above symptoms, besides my S90's only done 106,500km (66,176 miles).

At this stage I'm totally at a loss as to what else could cause such an unusual symptom. It doesn't happen very often but it'd be nice if it was completely resolved. Any ideas or suggestions please let me know!

 

Problem still unresolved. Anyone know what could be causing such a bizarre oil pressure problem?

 

First off the spec for pressures are about 10 psi at 800 rpm and about 40 psi at 3000 rpm.

You can try engine oil flush like Gunk and drain and oil. I agree with you that blocked oil galleys is not a plausible explanation.

It is sound like either an installation error, or there is a faulty pump / oil relief spring, which is part of the pump.