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Mercruiser 5.7 two problems or are they related

J

Jim@PineSt

New member
I am new to the site and looked for answers prior to posting. If I missed a post that would be helpful please direct me there.

I have a 1998 Bayliner Ciera 2452 Express Cruiser with a 5.7 Mercruiser engine. We were out boating and lost oil pressure. Limped back to the dock with the kicker motor. Oil levels were good and no sign of water.

Two months later when I found time to troubleshoot I replaced the oil sending unit and pressure unit. Pressure came up to 40 psi and ran great. The next day I went to start it and it would only run for 45-60 seconds then cough and die. No oil pressure again. When it starts it runs great (for 20-30 seconds) but then dies. So... is it an oil pressure problem or bad gas or both? I completely tore down the fuel system (two water seperators, fuel line check, and fuel pump check) and everything seems okay.

IDEAS AND SUGGESTIONS APPRECIATED!

Thank you,
Jim
 
If you have an electric fuel pump there is an oil pressure switch down on the port side of the engine block that puts power to the fuel pump while the engine is running.

The fuel pump is powered directly from the starter solenoid while cranking, this oil pressure switch is there to shut off the pump in case of stall condition.
 
Hi Chris, thanks for the quick reply. I replaced the oil pressure switch and the sending unit on the lower port side. They were a son of a bitch to pull out and get back on. Is there anything else that could be?
 
Jim@PineSt said:
Hi Chris, thanks for the quick reply. I replaced the oil pressure switch and the sending unit on the lower port side. They were a son of a bitch to pull out and get back on. Is there anything else that could be?
Click to expand...

Yeah, the switch you installed.That is what you need test. Jump out the switch and see if the pump stays on. If it stays on the switch is not activating.
 
Seriously, you need to temporarily install a mechanical oil pressure in the circuit and see what's really going on. IF the engine is truly loosing oil pressure, it could be stuck open check valve in the oil pump. Hope not.

Jeff
 
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