1988 85 hp overheating

[force fan]

Motor was bought new in 1988. Replaced impeller last year (1st time) and used the boat multiple times with no problems. Hooked it up to the garden hose before last outing and ran it for several minutes. Went skiing for a good run, got back in the boat and continued up river. Overheat alarm went off. Engine runs cool at slow speed and allowed me to limp back to ramp. Overheat alarm went off everytime I went to high speed. Good water flow out exhaust at low speed but diminishes at high speed. Thermostat checked out, but will be replaced due to age (original). Haven't pulled water pressure relief valve yet but plan on doing so. Ideas?

 

[Frank Acampora]

Re: 1988 85 hp overheating

Some impellers last longer than others. Before you go crazy, pull the lower unit and check the condition of the pump and impeller. also be sure that the lower plate has not corroded under the SS plate and gasket. If this corrodes badly enough, it lets water short circuit back to the intake side, reducing the amount that is pumped up to the block.

 

[force fan]

Re: 1988 85 hp overheating

I just pulled the pressure relief valve and it looked okay. Nothing appeared stuck or too gunked up to keep it from working. I'll replace the valve anyway along with the thermostat and see how it runs before yanking the water pump. I can't believe that I could run the original impeller for over 17 years and the 2nd one fails in less than 2! But if the engine overheats again, then I have no alternative but to pull the pump.

 

[rudedude]

Re: 1988 85 hp overheating

Might be a good Idea to change the impeller and check the pump out BEFORE you get stranded .

They dont make things to last like they did 17 years ago.

 

[force fan]

Re: 1988 85 hp overheating

Update: The thermostat checked out okay. The local dealer looked at my high pressure relief valve and said it was okay. There may have been some gunk or scale keeping it from popping open but I can't be sure since the opening is difficult to see to confirm.

I replaced both gaskets and reinstalled. Did not replace impeller. Took it to the ramp and ran it at 4500-5000 rpm for many minutes (on the trailer just in case the impeller was bad). No overheating. Full water flow. Power head ran warm but never hot. Force manual suggested that the high pressure valve may have been stuck since overheating was only at high rpm. Looks like they were right.

1988 Blue Fin/85 hp Force