Overheating while in gear

[yimmyb]

Have been having a problem with overheating of my 1980 alpha 1. I replaced the water pump on the motor and the lower unit. When the boat is in neutral it does not overheat but when it is in gear it starts to overheat with barely any water flow.

 

[CamaroMan]

in gear in water? that means load, maybe the impeller is spinning on the inner bush. Trace the incoming water pipe from lower unit to upper circulating pump. with motor cold - disconnect and start her up, even on muffs u shd see water coming up.

Repeat test with thermostat removed.

Can remove lower unit (put shifter in fwd), reverse flush via the incoming water hose - might have corrosion/impeller blades stuck there).

Make SURE impeller is not spinning on the inner bush AND it has the lock tab holding it in place and that it is installed in the CORRECT direction - (fins/blades pointing right when looking into housing where it sits). Some impellers are directional, ie they need to go in a certain direction in relation to the wear plate (Stainless plate it spins on) -

 

[yimmyb]

Ran boat in driveway for 25 minutes in neutral after water pump and impeller replacement. Temperature ran about 140 degrees and had good water flow the entire time

 

[tpenfield]

It sounds like you were not overheating with the hose and the ear muffs running in the driveway, then got to the lake and the boat overheated . Just wondering if you idled the engine at the lake if it did or would overheat?

The hose and the ear muffs puts pressure in the water inlet which can create enough flow through the engine to cool it at idle. At the lake there would not be the pressure, and the impeller has to do the job. So, I would be re-checking the impeller installation, etc.

As an aside, based on numerous threads over the years, it seems that boats really run great in the driveway.

 

[Bt Doctur]

the boat is in neutral it does not overheat but when it is in gear it starts to overheat with barely any water flow.

If this happens on land your:
just forcing the water thru the motor from hose pressure but if the water stops flowing when shifted into gear the impeller is not turning at this point.
If this happens on the water the upper gearset may be bad or the coupler is bad

 

[yimmyb]

Removed lower unit again. disassembled water pump housing. Inspected and everything looks great. Reassembled and installed lower unit. Placed lower unit in tub and ran it. Temperature went to 155 but no higher. Had good water flow out the exhaust for about 15 minutes while it was in forward. Water flow stopped at that point but temperature did not increase. Also now have oil dripping out of the water inlet on the lower unit.

 

[CamaroMan]

perhaps u have a cut in the water pipe by the bellows.. it would pump water up and straight back down past gimbal indicating that water is going up/down when its not - just going as far as the bellows and coming back down - although I dont think ud see water coming out exhaust but then you wouldnt since ur in a tub..

Locate and disconnect the incoming water hose in the engine bay - run motor for 15-30 seconds on the hose and see if the water flow "INCREASES" as compared to sitting on the hose (not running).. that will tell u immediately if the water is making its way up via the impeller or not at all.. A block filled with water not working might not heat up too much because of heat dissipation - just a possibility