OIL PRESSURE

[Guest]

I HAVE TWIN 165 VOLVOS DIESELS IN MY BOAT ALWAYS SERVICED, BOTH LESS THAN 900 HOURS , BOTH START PERFECT AND DONT SMOKE BUT MY STARBOARD OIL PRESSURE HAS DROPPED TO 30 PSI ON TICK OVER BUT WAS 60 ASTHE PORT ENGINE STILL IS, REV IT UP AND GOES BACK TO 60, THERS NO NOISES , ENDS OR MAINS? OR IS THERE A PRSSURE RELIEF VALVE IN THE OIL PUMP, ANY HELP?

 

[colinroybarrett]

60psi at tick-over?

I think you are lucky here.

We must assume that both gauges and sender units are in top order first, then those tick-over speeds are similar, and/or close to the manufacturer's specs?

Typically the oil pump produces both pressure and flow, well in excess of that required lubricating the engine. The pressure relief valve seems to be set and opening at 60psi OK on both engines. This is located either in the pump body itself, or in the main oil gallery, excess oil being dumped back into the sump, or sometimes squirted up under the piston crowns to assist with the cooling effect.

At tick-over the pump will be running much slower and with a partly worn engine, often cannot make the relief valve pressure, hence the drop-off seen on your gauge, which I would say is relatively normal for a hot engine.

I had an old mini that was so worn-out, the oil pressure light would flicker at tick-over (about 4psi) but it ran on for many years like that. Check that your oil is not too thin, on the affected engine, if a diesel, it is possible that the injector spill rail or even a water-cooler, is leaking into the sump and diluting the oil?

Otherwise, assuming it doesn’t get rapidly worse, I would suspect that both engines will eventually exhibit similar low-pressure signs and that this would be perfectly normal behaviour.

Cheers, CRB

 

[Guest]

Re: Oil Pressure

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[eddieperkins]

Chris,
For difinitive advice go to www.boatdiesel.com and post the question. For what its worth though it may be resistance in the wiring connections that is causing the reading.
Regards,
Eddie

 

[Guest]

Re: 60psi at tick-over?

You are right it is normal to be below pressure on start-up and at tick-over, but half normal? This sounds a bit extreme to me, and definitely a warning of poor lubrication.

But since the normal pressure is reached, it is hard to blame either the pressure relief valve or the oil pressure gauge. Your suggestion to check oil level, grade of oil, possible water contamination sounds good. But if that is all OK, I would start wondering about whether the oil pump is badly worn or leaky in one engine, and so slow to achieve the right pressure until the revs are raised. It might be worth taking a look at it if there is access to the sump.