Overheating issue 1987 90HP

I have replaced therms and still have heat problem on starboard side. I have not changed impeller/water pump yet but was going to do it anyways as a precautionary measure. I feel I still will have a problem since port side is nice and cool as other side gets hot. In other words the impeller is not the problem. Am I presuming too much ?

My thought is to get to the water jackets and replace the DEFLECTORS.Are they usually the CULPRITS ??? Why do they list the CHECK VALVE ASSEMBLY under the same number ( 10 I think)? What is it ? In some other post somebody mentioned PRESSURE RELIEF VALVES for similar issue. What are they ?

Re: Overheating issue 1987 90HP

Are you sure you have a overheating issue? Are you getting an alarm? The head should NOT be nice and cool under operating conditions. Both heads should be hard to touch for more than a 3-4 seconds. Is it possible you have a relief valve stuck open from debree on the cold side?

Re: Overheating issue 1987 90HP

they are all part of the same system, in the same area, it really sounds like a deflector problem. you won't know till you get there. on a 1987, i would plan on replacing it all. why have to go back.

Re: Overheating issue 1987 90HP

The pressure relief valves (item 76) are the spring loaded white nylon plugs located next to each thermostat in the housing. When on plane, the higher water pressure forces them open and floods the powerhead with extra cooling water. You would have seen them when replacing the stats. The rubber deflectors in the powerhead need to be in good condition and properly placed to properly cool the cylinders. Check for any debris in the cooling passages when you have the head off. I'd try to borrow a laser temp gun and check the head temps after warmup. Should be in the 145 to 155 range. If it still overheats after a new impeller, new stats and new deflectors, I'd pull the cyl head cover on the starboard side and see if you have any debris in it.

Re: Overheating issue 1987 90HP

My warning horn is bad. I am trying to put in a big order so as to save on shipping and time.

Can I rule out the Impeller ? I still am going to replace this but want to figure this problem out and ORDER THE PARTS.


TD - I replaced ENTIRE THERM ASSEMBLY (therms, gaskets, valves, springs) Sorry for confusion. "REPLACE ALL" - what is all ? I was thinking DEFLECTOR and WATER JACKET GASKET and might need to replace some/all screws.

Re: Overheating issue 1987 90HP

If It Is A Open Deck Block Than Water Passes By The Cylinders And The Cylinders Head But Not Going Into The Chambers In The Head. I Would Check And Make Sure There Is Not A Water Block In The Head From Corrosion. I Would Clean It Out Real Good If There Was. Try Running It Without The Thermostats Also Like What Most Offshore Fisherman Do. That Way The Flow Of Water Wont Be Restrictive. Good Luck

Re: Overheating issue 1987 90HP

not too sure about the advice about offshore fishermen running without thermostats!! no one should be running without them, end of story!