1982 Johnson 4.5hp Overheating

I just bought a 1982 4.5hp Johnson, that has seen very little use. It still looks like a new motor. I was told that it was overheating, and needed an impeller.

I took the bottom end off, .... checked them impeller, ... it is perfect. I reassembled it, making sure to put the tube in the water pump properly.

I put the motor in a tank.
The motor starts, and runs perfect, but the temperature climbs quickly. I shut it down at little over 230 degree head temp.(on a temp gun) I have a service manual that says the temp should be in the 160's.

The paint on the head bolts look like they have had a wrench on them. Could someone have put a head gasket on incorrectly, or were they just checking for a blockage!!!

Any ideas would be appreciated. Thanks.

Re: 1982 Johnson 4.5hp Overheating

It doesn't look like your engine has a thermostat, but there is a water deflector in the block. If it looks like someone has had the head off, maybe they removed for some reason. I am not sure about the orentation off the head gasket, no service manual in front of me.

Re: 1982 Johnson 4.5hp Overheating

Thanks;
My plan for tomorrow is to pull the bottom end again & put a hose on the tube. We'll see how the water flows.

Will check the service manual for water deflector location. My guess is that somewhere along the line, the previous owner ran the motor through some mud & plugged something, or ran the impeller dry, blew it, & there are fragments in the system. It's such a simple engine, this should be easy to sort out ...... with patience.!!

Re: 1982 Johnson 4.5hp Overheating

I pulled the bottom end, put a hose on the tube, and couldn't get any water to flow through the cooling system. It seems to be plugged solid.

Next:
1)I blew on the tube and couldn't force any air through it.

2)I pulled the head .... water deflector is in place, and the water passages are clean.

3) I pulled he powerhead, to check the water ... hoping it was damaged. No problem with it, ..... could blow through it with ease.

4) I blew compressed air through the water out passage, and the "in" .... air would NOT flow !!!!!!

Any ideas???

Re: 1982 Johnson 4.5hp Overheating

By the "in" are you talking about the water tube from the pump up through the exhaust housing? If so, it should be a straight shot from pump to powerhead, take a stiff piece of wire, coat hanger, and try to shove it through the tube.

Re: 1982 Johnson 4.5hp Overheating

I think I found the problem. I took the power head off, found that the water tube was fine, but still couldn't blow air through, either way.

I took the head off again, and found a piece of wood, or plastic, stuck in the water passageway in the block. I've been slowly(for the last 2hrs) digging it out a fragment at a time, .... I can at least blow air through it now. It's so hard that I had to use a drill to break some of it up.


Will try to get the rest tomorrow.

Problem solved ..... had to take the exhaust cover off, to get at it, but there was a piece of plastic stick about 2 in long stuck inside the water jacket. I was able to blow it out once the cover was off. Put it back together, and it now runs cool. About 120 per cylinder. Now I have to replace the gasket though. Job for another day!


Thanks for your help.