I have a Universal M-18 in my 1984 Catalina 30. The engine has about 1200 hours on it, and I have had the boat for 4 years. The engine starts and sounds great and runs at 700-800 rpms at initial starting idle and will max RPM at ~3200 under no load and 2600-2700 under load. There is no smoke coming from the steady stream of exhuast water. I replace the Racor and Universal filters every 200-300 hours with an oil change. I use the specified oil and oil filter as per the owners manual for the M-18. I replace the zincs yearly. I hose out my stock heat exchanger several times a season. (By removing the end zinc and cover and spraying water through it until it run clean.) I can do ~5.5 knots under power. (Which I believe is normal.) The engine will run between 185 - 200 degrees when hot. It almost never passes 200 degrees, and if it starts to I stop the boat and have always found the cause was something starting to clog my raw water strainer. The bottom line is that everything seems to be running the way it should, HOWEVER when I run the motor in excess of 1 hour (essentially bringing it up to 200 degrees) if I should bring down the idle ABRUPTLY, the 2 alrms on my panel light up and BUZZ. (ALARM and OIL) In this case the RPMS seem to be less than 800 (600-700). If I raise the RPMS to around 800, the problem goes away. I have purchased a new Thermostat, Water Temp Sending Unit, and Oil Pressure Sending Unit but have not installed them yet. Has ANYONE encountered this? I believe that the problem is not really that I am running with low oil pressure, but that the engine IDLE RPMS at ~200 degrees are too low to maintain the ALTERNATOR OUTPUT and OIL PRESSURE required. ANy feedback would be great. Thanks, Bill Bettini "Kilgore" 1984 Catalina 30 Hull # 3650
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Seems Normal
Bill, From everything you describe, it sounds like your engine is working perfectly, if maybe a little warm. When it has been under load for a while, and then you suddenly drop the RPM's real low, the oil pressure pump (mechanical), and the raw water pump (mechanical) just don't have enough flow thru them to do their job. I think that's why the alarms go off. If raising the RPM's didn't make the alarms go off, I would be more concerned. I don't think your alternator has anything to do with the symptoms you describe. Just my thoughts.
Bill, From everything you describe, it sounds like your engine is working perfectly, if maybe a little warm. When it has been under load for a while, and then you suddenly drop the RPM's real low, the oil pressure pump (mechanical), and the raw water pump (mechanical) just don't have enough flow thru them to do their job. I think that's why the alarms go off. If raising the RPM's didn't make the alarms go off, I would be more concerned. I don't think your alternator has anything to do with the symptoms you describe. Just my thoughts.
Oil Pressure
Your problem sounds like low oil pressure to me. When your engine is hot the oil is at its lowest viscosity. The clearances in your oil pump are such that low viscosity oil can seep back to the low pressure side causing low oil pressure at very low idle on a hot engine. Of course you have no load on the engine so it is unlikely that any damage is being done. You would know more if you had an oil pressure gage rather than a warning light/buzzer. The pressure probably drops down to around 20 psi at low idle hot but gets back up to operating pressure (usually around 40 psi) when revved up to normal idle or beyond. Nothing to worry about as long as the problem doesn't get worse. You say you have purchased a new oil pressure sending unit. Is this just a switch for the warning light/buzzer or will you have a real pressure gage? The latter is much more helpful in diagnosing engine troubles. But keep the light/buzzer because, if you're like me, you never look at the pressure gage until the buzzer goes off.
Your problem sounds like low oil pressure to me. When your engine is hot the oil is at its lowest viscosity. The clearances in your oil pump are such that low viscosity oil can seep back to the low pressure side causing low oil pressure at very low idle on a hot engine. Of course you have no load on the engine so it is unlikely that any damage is being done. You would know more if you had an oil pressure gage rather than a warning light/buzzer. The pressure probably drops down to around 20 psi at low idle hot but gets back up to operating pressure (usually around 40 psi) when revved up to normal idle or beyond. Nothing to worry about as long as the problem doesn't get worse. You say you have purchased a new oil pressure sending unit. Is this just a switch for the warning light/buzzer or will you have a real pressure gage? The latter is much more helpful in diagnosing engine troubles. But keep the light/buzzer because, if you're like me, you never look at the pressure gage until the buzzer goes off.
Try a higher viscosity oil...
Oil pressure is created and maintained by the oil pump forcing oil through critical clearances of bearings within the engine. As the engine ages these clearances open up, ever so slightly. That's why when you overhaul and engine you have clearance limits within these bearing surfaces. As these clearances open up it takes less pressure to force the oil through them therefore you see a reduced oil pressure (which is common in older engines). Increasing the oil's viscosity, or its resistance to flow, will inturn increase your engine's oil pressure.
Oil pressure is created and maintained by the oil pump forcing oil through critical clearances of bearings within the engine. As the engine ages these clearances open up, ever so slightly. That's why when you overhaul and engine you have clearance limits within these bearing surfaces. As these clearances open up it takes less pressure to force the oil through them therefore you see a reduced oil pressure (which is common in older engines). Increasing the oil's viscosity, or its resistance to flow, will inturn increase your engine's oil pressure.
Viscosity
While increasing the viscosity of your oil will probably increase the pressure at the pump it may decrease it at the bearing journals where the oil pressure is really needed. The higher viscosity causes a larger pressure drop in the oil galleries leading from the pump to the bearings. The increase in pressure may be only cosmetic. If the problem is poor pressure from the pump, fix the pump. The problem which started this thread was low oil pressure when hot and at very low idle speed. Just get her back up to normal idle and she should be OK.
While increasing the viscosity of your oil will probably increase the pressure at the pump it may decrease it at the bearing journals where the oil pressure is really needed. The higher viscosity causes a larger pressure drop in the oil galleries leading from the pump to the bearings. The increase in pressure may be only cosmetic. If the problem is poor pressure from the pump, fix the pump. The problem which started this thread was low oil pressure when hot and at very low idle speed. Just get her back up to normal idle and she should be OK.
Try disconnecting the sensor's
If you not sure if it's the temp. or oil pressure that's causeing the alarm, next time it goes of just pull the wire off one of the sensors to see which one is causing the problem. I have a Westerbeke 21 in my '77 C30 and it seems to like to idle around 800 RPM. The temp. gauge is rock steady at 180 and the oil pressure gauge ususally reads around 60 - 75.
If you not sure if it's the temp. or oil pressure that's causeing the alarm, next time it goes of just pull the wire off one of the sensors to see which one is causing the problem. I have a Westerbeke 21 in my '77 C30 and it seems to like to idle around 800 RPM. The temp. gauge is rock steady at 180 and the oil pressure gauge ususally reads around 60 - 75.
had the same problem on my M18...
idle rpm was set too low at 650rpm. Raised it to 750 and the alarm has not sounded in 5 yrs at idle. Also changed from 30w to 15w-40 Shell Rotella and found the cold start oil pressure comes up faster and it starts quicker. I think your engine is running too hot. In warm Florida waters, my M-18 runs around 165-170 at 2500rpm for hours at a time. When the temp rises above 170 there is usually a restriction in the raw water intake side or the nipple where the heat exhanger hose attaches to the exhaust pipe is starting to corrode shut. Higher temps thin may the oil a bit, lowering the effective oil pressure. Hope this helps.
idle rpm was set too low at 650rpm. Raised it to 750 and the alarm has not sounded in 5 yrs at idle. Also changed from 30w to 15w-40 Shell Rotella and found the cold start oil pressure comes up faster and it starts quicker. I think your engine is running too hot. In warm Florida waters, my M-18 runs around 165-170 at 2500rpm for hours at a time. When the temp rises above 170 there is usually a restriction in the raw water intake side or the nipple where the heat exhanger hose attaches to the exhaust pipe is starting to corrode shut. Higher temps thin may the oil a bit, lowering the effective oil pressure. Hope this helps.
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