1989 Mercruiser overheating problem

[JohnMercruiser]

Hello all, I have a 1989 Maxum 2300 w/ a 5.0L Mercruiser motor. Last year I had to get the hull fixed. After about a month of being in the shop I finally got it back and took to the lake. My buddies and I hung out in the water while the boat ran (idling) to allow charging of the batteries. The overheating alarm went off and I got in the boat and took off. The motor cooled down. This went on for about another 2-3 weeks then summer was over and I put the boat up. This yr I get it out and replace the Impeller as I figured that was the problem. Took to the lake and it ran hot again. I then replaced the Thermostat, checked all the hoses for blockage, checked the water pump and everything seemed to be fine. Even replaced the Water Temp sender. Went out this past weekend and the boat seem to be running fine. Temp guage dropped from around 180 to about 120. Seemed strange but it didnt stop me. We finally stop the boat after running for 25-30 mins and heard loud popping sounds coming from engine area. Anyone have any idea what that was? I took off the engine cover and small amts of smoke was coming from air hoses that run up to air filter. Checked oil and it was fine. Cranked motor up and it ran ok but I was too worried so we went back to dock and loaded up. Got home and checked the Exhaust risers and they were clean as could be. Any ideas?

 

[Olds Eddie]

Re: 1989 Mercruiser overheating problem

I am not sure about the popping sounds but a little smoke(oil vapor) from the crankcase vents could be normal depending on the age and condition of your motor. You say you checked the water pump, are you talking about the circulating pump or the one in the lower end of your outdrive that supplies water to the engine. It sounds like time to replace the impeller to me.

 

[JohnMercruiser]

Re: 1989 Mercruiser overheating problem

Yes the water pump on the front of the motor. I have already replaced the lower unit impeller.

 

[Olds Eddie]

Re: 1989 Mercruiser overheating problem

You may have to replace the whole pump as the housing and bottom plate get grooves in them. Also all it takes is for the impellor to run dry one time to damage it.

 

[Hook Line & Sinker]

Re: 1989 Mercruiser overheating problem

You can check the raw water flow from the leg by removing the hose from the lower unit (looking from the front of the engine compartment, it would be the hose on the front r/h side of the thermostat housing) and firing up the engine. You should have full stream of H2O coming out of this hose at idle.

 

[JohnMercruiser]

Re: 1989 Mercruiser overheating problem

I checked that and I do have a full stream of water. Could it be a cracked head?