Reply To: Evinrude 90HP 1999 “NO OIL” ALARM

[Don]

Well yes, there is a pressure switch on the vacuum/pressure driven oil pump. There were never and big issues with the pressure switch, but surely the pump can get worn, perhaps the diaphramn is just worn out causing weak performance at idle. You mention the “no oil” alarm activates, does the check engine light come on as well? Does this happen usually at low speeds after running for awhile? If so, you might try the following the next time it happens. Don’t shut the engine off, prime the oil bulb while the engine is running. If the light goes out after priming, it is safe to guess there is some sort of oil pressure issue. Keep in mind that these alarms stay on for a bit once triggered, so allow the alarm to stay on long enough so the horn shuts off but the “no oil” light is still illuminated. The engine is running at idle, you won’t damage it letting it run while this alarm “times out”.
Another thing to consider is that these system check gages were notoriously unreliable back in the day, so it could be a problem with the tach/gage as well. Like others have said, perhaps there is a restriction or air leak in the oil line/pick up causing the pressure issue as well. When was the last time you replaced the pick up filter. Not a bad idea to clean out the oil tank every once in awhile although this is a messy job indeed. Sometimes the oil gets gelled up a bit with time and may be causing a flow issue. Just be sure to bleed the oil line before restarting the engine to purge any air that got in during the cleaning process.
Keep in mind that this oiling system is a two part deal. The vacuum/pressure pump supplies the oil the the electric oil distribution manifold. Problems with the oil distribution manifold system may trigger a “check engine alarm”, not the no oil alarm. You will need the laptop and software to investigate and codes stored by the “check engine” alarm.
I’m “guessing” that there is an issue with the oil pick up pump triggering the low pressure switch, but please check everything else first. I agree with you, don’t just start throwing very expensive parts at this issue only to have it remain. Keep in mind that this oil pick up pump is driven by pressure/vacuum pulses from two different crankcases. Perhaps there is a leaky pressure/vacuum hose. An internal problem in one of the crankcases could cause this issue as well, you may want to do a compression test on the cylinders. Yes, I realize that a compression gage is not going to tell how well a crankcase is being sealed, but low/erratic reading could indicate a problem.
Again, let’s stick to simple things for now and avoid the urge to throw big money at it by replacing expensive parts. I wish you could just replace the diaphragm in the oil pick up pump, but I don’t think they offered repair parts for it.