43GL low pressure alarm

"Can someone help me diagnose

"Can someone help me diagnose my problem? I have received a low oil pressure alarm on 2 occasions. Both have been on very high temperature days (>105*F air temp), and both after skiing/wakeboarding (so the oil is hot), then idling in gear. On each occasion the problem it always at idle, and is intermittant. This makes me suspect a bad oil pressure sensor, but I'd like other opinions.

Here's what I know: The boat is a 2001 Four Winns 180 with the Volvo-Penta 4.3GL sterndrive; ~200hrs. Oil and filter are changed annually - by me. The first time this happened, I was concerned that it was my selection of an automotive oil (Mobil 1 10w30), so I changed it to the Volvo-Penta 30wt synthetic. (Oil level is within the hashmarks on the dipstick) That appeared to have fixed it, at least until the next 100*+ outing over the weekend.

So I looked closely at the guages to see what was happening. When the ignition is turned on, all of the guage needles sweep the guages, then return to zero - except the oil pressure, it stays put. Then when I start the motor, the oil pressure jumps around a bit, then settles in at or near the red (there are no numbers on my guages.) Sometimes I get an audible alarm, and the oil light. When I put it in gear and rev the engine, the oil pressure quickly moves to the mid-point on the guage, and the alarm and oil light go out. When back to idling, the problem does not always return, but the pressure seems to be consistently near the red.

I'm a reasonable automotive mechanic, and have a Clymer's manual for the boat (which I haven't yet consulted for this problem.) Any suggestions?"

"As a reasonable automotive me

"As a reasonable automotive mechanic, you probably know that oil viscosity changes with heat: the hotter the oil, the lower the viscosity; and the lower the viscosity, the lower the pressure. Also, since the engine uses an attached gear oil pump, the oil flow is minimal at idle. Therefore, lower flow and low viscosity is a sure recipe for low pressure.

Additives in multigrade oils can compensate for the viscosity change to a point. However, marine engines work many times in very hot conditions and, unlike in a car, there is no flow of air around the oil pan. In those cases, the viscosity drops regardless the use of additives. To go around this problem, some engines are provided with oil coolers, while others do use a high viscosity oil. For example, some VP applications use oil coolers, while Mercruisers use 25W-40 oil in the same base engines where Volvo uses 10W-30.

In any case, low lubricating pressure at lower RPM is usually not due to a faulty oil pressure sender or gauge, but rather to too thin oil due to high oil temperature. To go around that problem, I have used for many years 15W-40 mineral both in 4 cylinder OHC engines as well as in V-8 Volvo Pentas (Fords and Chevs) that I have owned. It may give a marginally lower fuel economy, but my oil gauge tells me that I have sufficient oil pressure at idle not to damage the crankshaft."

"Inspired by a search on this

"Inspired by a search on this forum, I decided to check the oil level. I placed a level on the valve covers, and adjusted the trailer tongue height - turns out I overfilled the crank with oil by about +3/4 of a quart! I've probably done so previously, since I never took the time to check the level of the engine.

Assuming I was whipping the oil with the crankshaft, I'm not sure why keeping the engine speed above idle would create sufficient oil pressure, though. I guess I need to put a reliable gauge in and check actual pressures instead of relying on the stock gauges.

Any other insights are still welcome."

"put a mechanical guage in the

"put a mechanical guage in there, and see what's really happening."

"My gut feel was right - I fou

"My gut feel was right - I found that the oil pressure sensor (mounted to the block just above the dipstick tube) was disconnected.

But this brings up an interesting dilemma - how was the oil pressure gauge ever registering if the sensor was disconnected? The plastic-encased plug was in close proximity to the sensor, held in place by a hose, but there was no physical connection between the wire and the sensor - the plastic sould have insulated it...

And, now that I have plugged the sensor back in, I get the low oil pressure alarm and light every time I turn the ignition on, even before I start the engine (it turns off after starting.) I purchased the boat used, and it had never given this alarm before starting - but this sensor was probably always unplugged. Is this normal?

Thanks for the help.

Craig-o"

"Somehow, I think you have two

"Somehow, I think you have two sensors: a transducer for the oil gauge, and a pressure switch for the alarm.

And maybe (only maybe) the alarm sensor was disconnected either by accident or because the previous owner didn't like its noise. Nevertheless, I think it is good that the noise is there once you turn the ignition switch on, for either you start the engine or you turn it off if you want the noise to go away. Distributors (either with points or with electronic modules) don't like to be powered for long periods while the engine is not running."