1976 mercruiser 233 Overheating

[johnmorgan]

I have been working on this boat for awhile now so far I have changed the coupler ,gimbal bearing ,impeller (fixed a quarter inch hole in brass tube) put new bellows on and new water hoses. Still can't get it to run at 160 with new t stat. The motor has a heat exchanger on it I took the end caps off and cleaned the tubes. Not sure what else to look at.

 

[Scott Danforth]

What temp are you running?
did you verify with an IR thermometer?

 

[johnmorgan]

Temp gauge says 190 I don't have a ir thermometer. It's definitely hot though

 

[kenny nunez]

Marine gauges are not the most accurate. Does the engine stay at a constant 190* . If it does not get any warmer at cruising or WOT then I do not think you have a problem. 351s run around that in vehicles and you have coolant not raw water.

 

[johnmorgan]

Yea it stays around 190

 

[kenny nunez]

Being able to run at that temperature with coolant is why it has lasted this long.

 

[Lancer76]

I run the same year mercruiser 233. Mine is raw water cooled. Spent a long time chasing down an overheat issue last year. It turned out to be old chunks of impeller lodged in the water tube just on the outside of the transom.

Regarding operating temp, now that I have corrected the issue it runs steady at just a hair below 150* F as measured on gauge and IR at the temp sending sensor. If memory serves, my t-stat is 140*F.

 

[johnmorgan]

Seems to be pumping a lot of water anyone know how much water should be flowing at idle. That being said it doesn't start getting hot until 3300 Rpms.

 

[johnmorgan]

I'm going to get a 140 thermostat maybe that will help

 

[wahlejim]

Check your exhaust shutters. If they are partially fried, they may allow some water through that keeps you good through the 3300 rpms, but may be restricting the water flow needed to keep up with cooling beyond that point.