Overheating mercruiser 120?

Question

I recently bought a 1983 boat with a mercruiser 120 and an alpha one outdrive. I just installed a new impeller. When I put the garden hose on the muffs and hooked it to the motor after about 10 minutes the engine reaches a temp of about 220 and steam begins to come out the exhaust. I checked the impeller by unhooking the incomming hose from the outdrive on the thermostat housing and cranked it and it pumped water. The engine runs perfectly fine and doesnt run rough, starts right up but get gets hot. Is this normal because im using a garden hose and the low rpms arent getting enough water to the engine or what? I havent had a chance to see if it stays cool at higher rpms yet but it has me worrying. Any suggestions ?

Answer 1

check the water hose inside the gimbal housing it is a 3/4 in diameter.gimbal housing is in the back of the boat where the outdrive is mounted.if the outdrive is up you can see this water line.make sure you check it for cracks.the impeler sucks water and flows to this water line and to the water pump.this could be your problem

Answer 2

How about a bad thermostat?

Answer 3

Garden hose, not the best way to check overheat problems. Your boat sounds small enough that it should be no problem to take it to a ramp and just put the drive in; that way you know that you are getting water from the pump & not trying to force it through the engine with water pressure. You may have stuck thermostat as was said before. Next step would be to go to the hardware store and buy some clear reinforced hose to replace some of the black hose. You only need to put a short piece in, say about a foot. Put the clear hose in a few different spots in the cooling system.What you are looking for are bubbles which are normaly exhaust gas; big problem! Diffently buy a repair manuel they are plenty cheap with good advice.