engine overheating

[michaelfagan]

I am a first year boat owner of a 1985 Chapperal with a 170 hp mercruiser I.O.. I changed the thermostat and the impeller and still same problem. It is a intermitten problem sometimes I can pull a tuber for hours, then suddenly the temperature just jumps up and won't go back down. I noticed right before the temperature is about to get out of hand the sound of the boat changes to almost a gurgling sound coming from the exhaust almost like extra air coming from it. I appreciate any suggestions.

 

[KaGee]

Re: engine overheating

Fresh water or raw water cooled??

 

[Manipulator]

Re: engine overheating

I have a 5.7L with the OMC 800 series in fresh water. Mine does the same thing. Few years ago it ran a little hot so the previous owner had a new impeller installed. <br /><br />I don't know if it could be my gauge or what. I put a new thermostat in and I also replaced one of the risers which was cracked and leaking. When doing that I checked out the manifold and they were clear. Actually the exhaust manifolds were replaced 3 years ago. Someone told me that if air gets into the system it will cause this problem. They said something about getting some clear tubing and installing it temporarily to see if air is indeed getting in there. Anyone heard of this?

 

[michaelfagan]

Re: engine overheating

My system has a heat exchanger. Yesterday I tore everything apart and made sure there was no obstructions and found in the heat exchanger some pieces of my old impeller restricting water flow, hopefully this cures the problem. Thanks.

 

[michaelfagan]

Re: engine overheating

Well it didn't clear the problem. I pulled a tube for about a half hour then the temp started to soar to about 200 before I cut the engine. I'm going to give the heat exchanger a closer look but I noticed when the heat started to go up the engine got a little sluggish, but this could have been from the weeds. Does anyone know if there is a really good heat exchanger on the market. To help the engine cool while I'm sitting there I would start it and let it run for about 30 seconds then let it sit for 3 minutes and repeat a few times and that brought down the temp a lot quicker than just sitting there would of. Thats why I'm thinking a better heat exchanger might do the trick.

 

[vipzach]

Re: engine overheating

Have you gone through the rest of it and made sure there isn't any more pieces of the old impellar lodged somewhere else, maybe in the drive restricting water flow.

 

[rbezdon]

Re: engine overheating

You mentioned weeds, maybe you have a second problem (or a new one) where the water inlet is cloffed from lake gunk and weeds. If there were weeds where you were then it was shallow too.

 

[michaelfagan]

Re: engine overheating

The searching continues....<br /><br />I took every hose off of the fresh water system and found no blocks. Took the heat exchanger out and it is clear. Checked the intake and it has some sedement built up on it, I don't think enough to make a big difference, but I cleaned it anyway. I'm going to take the lower unit off again and back flush it and check further in the intake. I installed a clear tube from the voltage regulator to the heat exchanger so I can see if any air is getting in there. <br /><br />I wonder if my overheating problems could be from a combination of small factors culminating into a overheating engine, I don't think this boat was very well taken care of.<br /><br />Does anyone know how much flow I should have? gallons per minute etc... from the fresh water pump.

 

[Bondo]

Re: engine overheating

I don't remember the years involved,......<br />But,.... Just after the 470s were introduced, there was an Over Heat problem,.....<br />And Merc.'s way around it was to Up-grade to a 4" exchanger, rather than the 3" that was the Original offering.........

 

[michaelfagan]

Re: engine overheating

Thanks for the response Bondo,<br /><br />I put a clear tube on the intake to the heat exchanger and saw some air bubbles coming from the impeller, I think thats why its overheating. Of course this is in my driveway with a hose on it. What do you guys think?

 

[michaelfagan]

Re: engine overheating

Anyone?

 

[trebor0301]

Re: engine overheating

Did you blow a head gasket?check your oil for anti-freeze or water.Doubt it though.How about doing a pressure test on the freshwater side?If the pressure is lower than it should be I believe you would overheat.Good luck and let us know what you find.

 

[michaelfagan]

Re: engine overheating

What should the pressure be?