overheating merc 3.7 need help

[terrylittle]

ok i had my boat on muffs just changed impeller seems to work, but the temp gauge went to 3/4 and it seem to stay there. so i took it out to the lake was driveing for 5-10 min it got to 3/4 and just keep going so i shut it off and then it was overheating. i dont know what to check when i was driveing the boat ran great lots of power but why is it overheating? is there a thermastat on these. if so where? i dont know what to do or where to start. please help me out guys.

 

[nola mike]

Re: overheating merc 3.7 need help

Did it overheat prior to the impeller change?

 

[stonyloam]

Re: overheating merc 3.7 need help

#12 right here: http://www.mercruiserparts.com/Show...EXHAUST+MANIFOLD+AND+EXHAUST+ELBOW+(ALUMINUM) Opens at 155-162, fully open at 182.

 

[Bt Doctur]

Re: overheating merc 3.7 need help

Follow the flow: from the impeller thru the connecting hose(kinked internally), thru the PS cooler(clogged internally , old impeller pieses), thru the heat exchanger, out the riser(clogged water outlet ports).
Other cause is commpression gasses entering the cooling system from a bad head gasket,
Being A/F cooled you will be running 170 ish ,constantly

 

[terrylittle]

Re: overheating merc 3.7 need help

yea it did overeheat before i changed the impeller. so i changed it, and the old impeller was wreaked, every spline on it was cracked but they were still there not broken off.

 

[oilydogg]

Re: overheating merc 3.7 need help

what year is the engine? i would check the exhaust riser/ reservoir. as the get old and crusty inside they tend to diminish flow. careful how many times you allow this engine to over heat. you may end up with more problems than you can stomach.

 

[terrylittle]

Re: overheating merc 3.7 need help

it is an 86 i think. what is the ps cooler i blew out all the lines i think, i only have the muffs that the hose goes only on 1 side could that make a diffrence it keeps heating up to 3/4 i cant figure it out i checked the thermastat in boiling water it opened, so that works. its spiting out water but not a lot and it is hot. any suggestions. how do i check the exhust riser/resovore

 

[terrylittle]

Re: overheating merc 3.7 need help

can the exhust bellow that runs off the top of the motor inside my boat make it overheat if there is a little hole in it, does this exhust bellow need to be completely sealed?

 

[bucnon75]

Re: overheating merc 3.7 need help

I have the same situation with a 470. My engine was sitting for a long time when I got the boat.
I'm going to flush out my cooling system this weekend. It sounds like you could have corrosion or junk stopping the flow of water from the exhaust. Keep us posted. It's recommended that the coolant system be cleaned out every 2 years, so I know I'm due.

 

[terrylittle]

Re: overheating merc 3.7 need help

how do u flush your system is ther a easy way to do this?