Overheating

[jreau]

1994 Mercruiser 5.7 overheating. Remove thermostat and it runs cool. New impeller, thermostat, whole system is pumping water. Marina put clear hoses on at all hose positions and there is good flow. They checked everything and as soon as you put the thermostat in it ramps up over 200. They are running out of things to try. Any ideas?

 

[Bt Doctur]

clogged therm housing. , with the exception of the SS housing.Or the engine circ pump has a broken shaft

 

[NHGuy]

Drill 2 or 3 small holes in the stat to allow a little water through. This allows the water through the block which allows engine heat to get to the t stat. In some cases it's been alleged the outside water flowing past the thermostat keeps it closed and keeps the cooling water from passing into the block.

 

[redneck joe]

New to you boat or did this just start?