3.7 gets hot while idling

[RoadKingClassic]

Was out with my sons today in his boat with the 3.7 mercruiser. He bought of a buddy of mine who took good care of it. Changed impeller last year. It gets up in temp if you idle for too long. Today the water temp was 65 degrees. The engine was running warm. Then noticed she got up to 200 after idling for 15mins. I put it in gear and got it moving. It came down to 180 quick. Got it going faster around 3000 rpm and it came down to 160 fairly quick. Question . Is this normal for that motor to get hot if you just idle for that period?

 

[Scott Danforth]

You have a flow issue. Fix it before you loose the head gasket. Running the 470 to 200 will spit the head gasket

 

[Scott06]

Did u use an oem or aftermarket impeller last year

 

[RoadKingClassic]

Did u use an oem or aftermarket impeller last year

Not sure. New one was installed before buying the boat. Runs cool. 160 when moving

 

[Scott Danforth]

Not sure. New one was installed before buying the boat. Runs cool. 160 when moving

I would find the issue and fix it before using the boat. the open deck, iron head and aluminum block mean that the motor will spit its head gasket with a mild overheat. and on that motor, 190 is too hot.

 

[Dubed]

My 3.7 runs at 150 - 155. If I ever see it approaching 170, shut it down immediately!
Why did the impeller get changed? Did the last one come apart and all the little bits are still in the system? Was the impeller installed properly? Was it run in the driveway without muffs even for a couple seconds?

 

[Chris1956]

I had that exact issue on my 4.3LX Mercruiser Alpha. The bottom of the impeller was damaged slightly so it did not pump sufficiently at idle.

If your impeller is new, and you did not suck up some sand to damage it, you may have a different problem.

 

[Scott06]

Not sure. New one was installed before buying the boat. Runs cool. 160 when moving

As mentioned by others this engine is very sensitive to slight over heats. Not sure if you have the upgraded heat exchanger or not?

If it were my boat I would start with replacing the impeller including the base and housing as they are plastic. Check the water tube is not collapsed and you are getting good supply inside the boat as the supply tube from bellhousing to transom can kink.

Also would look at exhaust elbow is not clogged with corrosion and might be worth popping the heat exch to see if tubes are clear

 

[ROY WILLIAMS]

Not sure. New one was installed before buying the boat. Runs cool. 160 when moving

The 3.7 engine of the year ? the water exchanger ? the 3.7 engine of the coolant 140F .....
the outdrive is inspecting it the new impeller and the damaged it new ....

 

[Bt Doctur]

most likely a clogged/restricted exaust elbow