Re: Yanmar Oil Pressure Pegged
When troubleshooting anything try to split the system in half and isolate the problem to one side (of the half) or the other. In this case the problem could be in the engine that the pressure IS too high, maybe caused by blocked passages? Or, it could be indicating too high caused by the pressure monitoring system (sending unit or gauge, etc.). I'd split the system between those to systems, the engine and the monitor. As stated above, get a mechanical pressure gauge and put it in where the oil pressure sending unit was. if you get the same indication, you know it's in the engine. If your nearly due for an oil change I'd start there though. Or if the problem showed up right after you did one, replace the oil filter (may be a defective pressure bypass in the filter).
What did the pressure used to be? Used to be 55 then dropped to 20 after 5 min? In other words is it a 30 PSI even gain? If so I'd look at wiring, might be getting extra resistance into the monitoring system from a poor connection.