1971 18HP Evinrude HELP!!

[Blake Hearn]

My 18hp Evinrude is not cooling correctly. It lets some water through and the water pump is new but it is still not cooling like it should. I really need a diagram of the cooling system as far as where the water goes through the engine so i can check for blockage. It does fine at low speeds but when you give it enough gas it will burn your hand when you put it to the block. The thermostat is fine. Any help appreciated.

 

[oldcatamount]

Re: 1971 18HP Evinrude HELP!!

Take the lower unit off, and take the thermostat out, rig up a hose to the copper pipe in the lower unit and flush the motor with water. How do you know the t-stat is ok?

 

[boobie]

Re: 1971 18HP Evinrude HELP!!

If you replaced the water pump, was the old one broken up in pieces or what ?

 

[HighTrim]

Re: 1971 18HP Evinrude HELP!!

I would follow Oldcatmounts advice, pull the lower again, ensure the intake area is clean of debris, ensure that the water line is not pinched, remove the t stat and both flush/backflush either water or compressed air through the system to ensure it is clear. What is the compression on the motor? You didnt forget something silly like the key did you? lol Is the whole waterpump new or just the impeller?

 

[Blake Hearn]

Re: 1971 18HP Evinrude HELP!!

The reason i said the t-stat was ok is because i took it off the engine and it still overheated, so i ruled that out. The water pump was rebuilt with new impeller and case and cover. The old impeller was very chewed up so i thought i may have a piece of it somewhere in the line. Ill include a picture of the old impeller. I have tried blowing the line with compressed air but still think something may be stuck in there stubbornly. I have not checked compression but it seemed to run good when it was running.

 

[HighTrim]

Re: 1971 18HP Evinrude HELP!!

Not to be rude, but that is not the best test for a t stat. If you want to truly test it, you should do by placing it in a pan on the stove in water and ensure that it opens when it should. Heat it slowly.

Regarding that old impeller, it is really missing alot of rubber, which Im sure is lodged somewhere along your cooling circuit. Drop the lower unit, pull the impeller, and flush the water line from the water pump to the t stat housing, then backflush from the t stat housing to the water pump. Do this numerous times to ensure good flow. Also ensure the water intake is clear of debris.

Let us know how it goes.

 

[F_R]

Re: 1971 18HP Evinrude HELP!!

The water from the pump goes up the tube to the powerhead. Hard to plug that up, put possible with a hunk of rubber. You will have to pull the powerhead to see. Once it gets to the powerhead, it first goes through the exhaust covers on the side. So that is the nest place to look. You have to pull the powerhead to get them off, so see first comment. After the exhaust covers, it goes two routes through the cylinder block and head. So, pulling the head is next. Pay attention to the thermostat bypass channel of the head gasket area. From there it is out the blowhole in the backside. But first, it goes through a plastic restrictor, which may be melted from overheating. It is also below the powerhead.

Um.....did I mention pulling the powerhead?