Car presented with engine making a moderately loud tapping noise, and via OBD-II a fault code was found to be stored for the variable engine valve timing solenoid. Upon inspection the technician noted that engine oil pressure warning light wire was disconnected. We connected wire and engine oil pressure warning light came on. A check of engine oil pressure with mechanical gauge showed pressure to be very low at idle, about 5 PSI, gauge is unsteady and flutters. During extended idle the reading will nearly drop to nearly zero at times. The low and unsteady gauge reading indicates possible cavitations in oil pressure.
Volvo has a somewhat common problem of defective oil pump pick up seals. These small rubber sealing rings serve to connect the engine oil pickup, located in the oil pan, to the engine block where the actual oil pump is located. After several years and thousands miles of engine heat, these seals become hardened and allow air to enter into the oil pickup system, preventing the oil pump from drawing the proper amount of oil. Early symptoms are a oil pressure light on at idle, or an engine that sounds unusually loud, often a tapping noise, at idle.
The correction for this involves removing the engine oil pan, cleaning and inspecting the pan sump and pick up tubes. The small rubber o-ring seals are then replaced on both the oil pick up and engine oil cooler. It is important to inspect the sump, and clean any oil sludge or debris from the oil pan area. As the 850 and S/V70 series engines use a two piece crankcase, you can not easily remove the main bearing caps for inspection, nor are the rod bearings readily accessible. The best test of the engine condition after this service is to use the mechanical gage again to verify pressure readings. On the car in question the engine oil pressure went from nearly zero at idle, to 35 PSI warm, and nearly 75 PSI at speed. This pressure in indicative of a engine in good condition, not having experience any wear in the bearing surfaces. Given the exceptionally low oil pressure, it is a testament to the robust design of the Volvo engine that no damage seems to have occurred.