I have a 91 940 SE turbo that the oil light will come on and stay on at idle (750-1000 RPM) after it gets to operating temp. I use 20w50 oil and change it every 3000 miles or 3 months religiously. Can this be a weak or failing oil pump or should I be thinking something else? Can the oil pressure be checked and how? (I might add it has approx. 500,000 miles.) Love this car.

 

The simplest way to check the o.p. with a gauge is to remove the oil sender from the block and screw in an actual mechanic's gauge. It is possible either the oil pump or the oil pump seals are failing. The seals are rubber and will always eventually fail but with 500k I'd be planning on replacing main and con rod bearings. To check/replace the oil pump and or seals, the oil pan has to come off. That's the time to spec the bearings. The oil light from the factory trips at 7 p.s.i. so I'd certainly keep an eye on it. Volvo says it's acceptable for the light to flicker at idle when warmed up but it's definitely telling you something needs some TLC. For the time being, you could switch to 30W oil; the increased viscosity may keep the light from staying on...it's not a cure but can help in the short run until you decide what to do.