Johnson 7,5 HP seems to overheat

[merc20076]

I replaced the water pump impeller + all the tstat kit in this 7.5 HP. Before it didn't have a tstat in the motor.

While running it (in a big 50 gallons barrel), it had good amounts of water coming out from tell tale but nothing from top exhaust ports and it should be I think. And when touching the head, after 5 seconds, my fingers where almost burning and it's cold outside at this time of the year.

Do you think it's a water passage blocked somewhere in the cylinders walls and needs to remove the head cover? Motor has about 90-95 PSI compression in both cylinder but the head is a different white than the rest of the block. Must of overheat before that's why there where no thermostat in before.

Thanks

I will receive very soon a Johnson/Evinrude 2-8 HP factory service manual that I found on ebay for 15$.

 

[HighTrim]

Re: Johnson 7,5 HP seems to overheat

Was it overheating before you made the repairs? Drop the lu, and ensure the intake area is free of debris. Ensure the grommet on the water line is not pinched. Remove the t stat and run compressed air, or the garden hose, to flush and backflush the cooling passage. What was the condition of the impeller housing? Let us know what you find.

 

[merc20076]

Re: Johnson 7,5 HP seems to overheat

Removed the thermostat and it runs like a champ even at idle speed. I can keep my fingers much longer on the head but I still dont have water coming out top exhaust ports. Lots of water from tell tale compare to before the impeller change.

 

[cr2k]

Re: Johnson 7,5 HP seems to overheat

Those ports are relief ports for exhaust at low rpms. Water can/will come out but that doesn't really mean anything.
You need to determine the restriction. Often a small piece of impeller will go up the water tube and plug it or somewhere in the powerhead.
Did you have ALL (every single one) of the pieces of the impeller? Have compressed air? Blow back thru the pee hole with the lower unit off and see what comes out.

 

[merc20076]

Re: Johnson 7,5 HP seems to overheat

Yes I blew compressed air thru the cooling system then put back everything in place but I still found that the head was hot. Water in the barrel is cold, from the tell tale warm to hot. I shut the motor off quickly.

On my Johnson 4.5HP kicker, I can keep my fingers a long time on the head, same thing for my 40HP Lark that has a tstat too.

Those 3 last outboards you see in my signature, got them for real cheap and it shows that it's more work than I was expecting first, but it's fun to learn more in this kind of job!