485 3.7L Mercuiser overheating

[Landon]

My 485 mercruiser overheats within 5 minutes of running it. Heats up past 200f. I have removed the thermostat, flushed the cooling system and refilled it with coolant. I have also changed the impeller as it was completely burnt out, I also checked under the heat exchanger cap for impeller pieces or other depris blocking the water path but there was nothing. Can't figure out what can be causing it to over heat. Also if I rev up the engine when it gets running hot the temperature drops down about 10 degrees for a minute or so until it gets hot again.

 

[Bondo]

Re: 485 3.7L Mercuiser overheating

My 485 mercruiser overheats within 5 minutes of running it. Heats up past 200f. I have removed the thermostat, flushed the cooling system and refilled it with coolant. I have also changed the impeller as it was completely burnt out, I also checked under the heat exchanger cap for impeller pieces or other depris blocking the water path but there was nothing. Can't figure out what can be causing it to over heat. Also if I rev up the engine when it gets running hot the temperature drops down about 10 degrees for a minute or so until it gets hot again.

Ayuh,.... Pull a hose, 'n See if the raw water is pumpin' through....

Have ya got P/Steerin',..?? if so, check the cooler for impeller parts...

 

[HT32BSX115]

Re: 485 3.7L Mercuiser overheating

My 485 mercruiser overheats within 5 minutes of running it. Heats up past 200f. I have removed the thermostat, flushed the cooling system and refilled it with coolant. I have also changed the impeller as it was completely burnt out, I also checked under the heat exchanger cap for impeller pieces or other depris blocking the water path but there was nothing. Can't figure out what can be causing it to over heat. Also if I rev up the engine when it gets running hot the temperature drops down about 10 degrees for a minute or so until it gets hot again.

Howdy,

(Assuming you have VERIFIED your temp gage)


Closed cooling engine overheats are frequently caused by clogged raw water systems and restricted flow either from a defective raw-pump, through the supply lines/hoses, clogged heat exchanger(s) or a clogged (from rust) riser.

 

[cr2k]

Re: 485 3.7L Mercuiser overheating

Did you replace the thermostat? If not do that first. You need a thermostat not only for warm up but without one the water will flow too fast to absorb the heat from the block.

 

[allycat1521]

Re: 485 3.7L Mercuiser overheating

was the water pump base replaced when you replaced the impeller?? in a severe overheat it can warp the base creating havoc on the vacuum/pressure side of the base which could go unnoticed if don't lift the stainless wear plate.