over heating problem

[ky-donzi]

Got a friend that has a older boat that over heats at low rpms but at high rpm runs at about 160 F. The engine is a 3.0 4 cyl. merc. with a drive that simply says "4" on it. I would guess the the boat is a 85ish model.

1. Sound like a water pump impeler?

2. is the water pump in the lower unit like a alpha?

Thanks in advance

[MOP]

Yes the pump is in the drive, before pulling it apart check for air getting into the cooling water. Normally if the pump goes it get hot at all speeds, but an air leak at the drives water tube grommet will give you a low speed over heat. Many a pump has been changed only to find that you need to tear into it again. Put a clear hose in place of the feed hose to the manifold, run the boat and watch for air bubbles in the water. It may only be a fine trail of bubble but that is all it takes! It is still worth at least changing impellers and housing as you will have it apart anyway.

[ky-donzi]

MOP

Would the boat need to be in the lake to test it, or can I test it with muffs on? Do you think the muffs would make air bubbles falsely appear?

BTW what is this outdrive called?

Thanks Reid

[MOP]

MOP

Would the boat need to be in the lake to test it, or can I test it with muffs on? Do you think the muffs would make air bubbles falsely appear?

Thanks Reid


It has to be in the water the muffs pressurize the system keeping any air out, plus it can be hard to diagnose an over heat on the hose. Another thing that should be checked is the hose from the gimble to the shield, it can be starting to collapse. At higher speeds it can open enough to cool things down. Ask when he did a pump last, if it has been awhile just do it and replace the gimble hose they only last a few years.