overheating

[harleymc4u]

1986 4 cyl mercruiser, 3.7 overheating, where is the theromstat located, it will cool down to 160 at the dock but when you put it in gear it goes to 220 degrees, just bought it and have no clue, supposedly the outdrive has been rebuilt.

 

[Bondo]

Re: overheating

just bought it

Ayuh,..... Sorry to hear that,...
You've just bought the Worst Better Idea to Ever come from Mercruiser.....

Here's a copy of the Factory Service Manual for your motor,...

Good Luck,+ Welcome Aboard.........

 

[Don S]

Re: overheating

Before I would worry about the thermostat, I would check the raw water pump impeller in the outdrive. Too many things can take out the impeller, even in a rebuilt drive.

 

[tide me over]

Re: overheating

We have the same engine and I'm pretty sure we have the same problem. My boat runs very cool at idle or underway in (no wake) 5mph or less but, when I try and cruise she heats up fast. I was guessing the sterndrive waterpump and someone answered my thread as that as well. I can tell you with this engine check and double check you battery connections as the voltage regulator in internal and difficult to replace. I had corroded connections two years ago and as soon as I went to adjust my trim while underway I smoked my regulator. Other than that it has been a good engine and it's great on gas which could not be more important these days.

 

[harleymc4u]

Re: overheating

looks like it is the impeller, thanks to all for info, what check can be performed to know if it is impeller prior to pulling boat out of water??? The lower tank is hot when running, shouldn,t this be cool if impeller is working????

 

[Bondo]

Re: overheating

what check can be performed to know if it is impeller prior to pulling boat out of water???

Ayuh,... None really...
The lower unit needs to be Pulled to Check the Impeller....

 

[Don S]

Re: overheating

Locate the hose that goes from the transom shield to the regulator, then on to the heat exchanger. Disconnect the hose from the heat exchanger and start the engine for a few seconds. you should have a good flow of water out of the hose.