Why is my boat over heating? its a 120hp 1982 mercruiser?

Question

motor is in good cond

Answer 1

The impeller in the lower unit has sheared off its blades.

or

Bad thermostat

Answer 2

If it's an outboard, It's most likely the water pump needs re building. As for east wood's answer, the impellar is in the waterpump. It's what you replace when you rebuild the water pump.

If it's an inboard/ outboard, it has two water pumps. One on the engine and one in the outdrive. To check the one in the outdrive, make sure the outdrive is submerged in water, remove the hose going from the outdrive to the engine at the thermostat housing and start the engine. If it spews water the outdrive pump is working. Replace the hose and remove a hose from one of the exhaust mainfolds and start the engine. If it spews water, the engine pump is working. And you probably have a clogged exhaust riser elbow. 1 or both. If that's the case the clogged elbow(s) need replaced.

Answer 3

either the impeller has sheared off all its blades or the water intake is clogged up on it,or the main delivery tube is leaking inside the prop,or the thermostat is bad in it,i wouldn't run it until i found the problem with it,those are good engines but when they get hot it does a lot of damage to them,mostly on the heads,been there and done it,good luck on it.

Answer 4

This might not be the water pump it might be the impeller. If it is not spittin water out of the spitter hole on the side of the lower end.this might be the problem (less costly) than water pump.hope it helps!!!!

Answer 5

Water pump is out .......hard to work on sobs