Mercruiser 470 Overheating

[jpugh87]

I have a 1980 Crestliner with a mercruiser 470 with a closed cooling system. I just replaced the impeller and it stays at about 200 degrees at 3/4 throttle on plane but as soon as you get it wide opened it starts climbing. I am under the impression this motor was a piece of @#$% especially since they undersized the heat exchanger on it. Could it be possible that my thermostat is sticking or it be my head gasket any help would be greatly appriciated.

Thanks

Jake

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 470 Overheating

I have a 1980 Crestliner with a mercruiser 470 with a closed cooling system. I just replaced the impeller and it stays at about 200 degrees at 3/4 throttle on plane but as soon as you get it wide opened it starts climbing. I am under the impression this motor was a piece of @#$% especially since they undersized the heat exchanger on it. Could it be possible that my thermostat is sticking or it be my head gasket any help would be greatly appriciated.

Thanks

Jake

Yes and yes.
Mine stays rock steady at 165? no matter the RPM. Check the compression and see if any are low.

You could have impeller pieces that have gotten lodged somewhere. Was it intact when you replaced the old one? Did you ever start the engine even for only a few seconds without water to the drive thru muffs?

Your heat exchanger may need to be cleaned.

More than likely you are looking at a head gasket replacement at those temps.

 

[Don S]

Re: Mercruiser 470 Overheating

If you are seeing 200? at 3/4 throttle and below, it's probably not the heat exchanger size causing the problem. More likely to be a water flow problem through the heat exchanger and out the exhaust elbow. I would check both for plugged passages.

 

[jpugh87]

Re: Mercruiser 470 Overheating

YEah man We cleaned all the impeller pieces out when I put a new one it a month ago. I have never dry fired the motor thats a number one rule with inboards, never start them out of the water. It gets up to 200 and stays there. I was just thinking about putting a head gasket on it, but I have no water in my oil, it starts at the bump of a key, and takes off great. Do you really think I could have a bad cylinder, I would think it would have a dead spot in it when accelerating. How do i clean the heat exchanger is it like back flushing a car cooling system?

 

[jpugh87]

Re: Mercruiser 470 Overheating

HEy Don Would it be possible that if the thermostat housing is melted, that is what is causing this also. I dont know if it is but everything one this boat is factory seals and gaskets i guarantee it. I will try checking the heat exchanger elbow and all of that. Thanks for you help to both of the replys you guys. I just hope i can get it going

 

[Desertsky]

Re: Mercruiser 470 Overheating

Have you replaced the thermostat? The symptoms are exactly what would happen if it is stuck in the partially open state.

 

[jpugh87]

Re: Mercruiser 470 Overheating

Dude I just ordered the thermostat last week and am waiting for it to come in. That is my next move. Thank you