1981 ski nautique overheating

[The_Jake_McNasty]

I'm trying to restore my dad's nautique. I've replaced the thermostat, new impeller and impeller pump. Before replacing these parts the boat would cold start and idle fine. After cruising around the lake then slowing down to go through a no wake zone or coming to an idle the boat would shut off and temp would be between 200-220. After cooling down for an hr I could get it back to the dock. It would not over heat when cruising and stay between 140-160. Put the old thermostat in a pot of water on stove and by the time the water temp got to 170 it would fully open but replaced with new thermostat anyways(tested new thermostat and it works as it should. It is a 160° thermostat). One odd thing to note: engine would not shut off when slowing down through a no wake zone or idling if engine cover is removed but still overheats. Past weekend i put a new thermostat and impeller/impeller pump on. Took the boat out to test it WITH engine cover removed again. Same thing still happened though. Would not shut off but when slowing down through no wake zone or idling, temp would still rise. I'm not that mechanic savvy so I'm at a loss as of what to do next. Any help with my issue would be greatly appreciated. Boat has a pcm 351 windsor in it. I've checked the exhaust manifolds and they are rusty on the inside and do need to be replaced but the water channels are not clogged.

[SilentSeven]

Cooling is one the most common issues posted on the board. Frequently the problem is due to air leaks on the raw water side of the pump - the section between the water pickup on the hull and the pump itself. Air leaks prevent the required suction needed to pull water into the system.

Here's the items you should check.

1 / if equipped...make sure the raw water strainer has the o-ring installed, has no housing cracks and the clear section is snugged down (not super tight, just hand tight).
2 / if equipped...the raw water through-hull shutoff valve is fully open
3 / all hose clamps on the raw water feed hose are tight
4 / raw water hose is in good condition

If you pulled the raw water pump off the engine when changing the impeller, you may not have gotten the hose connection to the pump tight. Numbers 1 and 3 are the most common problems.

[The_Jake_McNasty]

Thank you for the reply! Those will be the next things I check

[Jonny Quest]

Over heat issues at slow engine speed may indicate an air leak. Check hoses and clamps. Don’t use a screwdriver on the hose clamps- use a nut driver. Usually 5/16”