Mercruiser 5.0L MPI Overheating at idle

[bengaltiger14]

Hello all. I have a 2005 Sea Ray with the 5.0L MPI engine. Took the boat out this week and the overheating alarm went off after 4-5 minutes of idling. Got a tow back and loaded back on trailer. Popped the thermostat out and it appeared to be stuck. I cleaned it up real good and took it home and put it in a pot of hot water. It opened at the correct temperature and closed back after cooling off. I reinstalled the t-stat and removed the water pump and impeller just to be on the safe side. Impeller looked good. I reassembled everything and cranked it up on garden hose with ear muffs. It ran correctly. Engine heated up, t-stat opened and water pressure was normal. Put boat back in water and it runs great as long going 10 mph or more. If I am just trolling or at idle, the engine will begin to overheat. When this happens, I can throttle down and cool it back down fairly rapidly. I understand that the garden hose was likely forcing more water in at a much higher pressure, hence the reason it ran fine on the muffs. While pulling back up to dock after the test drive, I heard a loud squealing sound coming from the engine bay and noticed that the power steering hand stopped working. I popped the hatch and noticed that the serpentine belt had stopped spinning. I shut it off, checked the belt tension and it appeared normal. Cranked back up one time and the belt was spinning again. Any thoughts?

 

[ThomW]

Does that motor have water pump assembly that is run by the belt?

 

[bengaltiger14]

Yes. The water pump assembly is run by the belt.

 

[Fun Times]

Make sure the sea water pump impeller pulley shaft assembly isn't able to slide in and out or move up and down as you may be experiencing a shaft bearing failure. Raw water pump bearing failure... - Boat Talk - Chaparral ...

Sometimes the sea water impeller could get locked into place within the housing stopping the belt from turning.

 

[bengaltiger14]

Ahhh. Thinking back, when I had the impeller housing on the table working on it, I had the pulley facing down on the table. When I initially layed it down, I believe I felt it move in a little. I didn't think nothing of it at the time.

 

[wahlejim]

In addition, change the impeller. You can't tell the condition by just looking at it. Plenty of guys change it annually. The pressure from the water hose on the muffs is enough to force feed the engine, but in the water, your impeller may not be functioning properly. When your rpm's rise in the water, the rubber in the impeller expands, changing the way the water is pumped in and creates more of a centrifugal pump which would explain the pump functioning at higher rpm's but not at idle.

 

[bengaltiger14]

Went back to the boat today to investigate further. Took the serpentine belt to inspect the pulleys further. The water pump impeller pulley had very noticeable movement in the in and out direction. I could push it in and out 1/4-1/2". A little resistance but not too much. The other pulleys seemed, to me, in good condition.

 

[bengaltiger14]

Problem solved!! It was the raw water pump pulley bearing causes all of the issues.

 

[Bondo]

Ayuh,.... Glad ya found the problem, 'n Thank you for the update,.....

 

[Fun Times]

Problem solved!! It was the raw water pump pulley bearing causes all of the issues.

I finally was able to guess one right.:encouragement:

Glad you found and solved the problem and thanks for the update.