1980 johnson 4.5 low rpm overheat

[merclund]

Hello I boat experts

I have a 1980 Johnson 4.5 model #J5RHCSS. The motor at low rpms overheats and water no longer comes out the tell tale. At anything above a low idle the water will come out the tell tale and the motor will cool properly. I have replaced the water impeller using an OEM complete kit and still have the same results. Just wondering what my next course of action should be. I'm not sure if I should remove the exhaust cover or head gasket and inspect or try another water pump. Just looking for some ideas, the motor runs really well, but I would like to use it for trolling also. Any help would be great. Thanks in advance.

 

[sutor623]

Re: 1980 johnson 4.5 low rpm overheat

I always run a waterhose up to the water input line before I slap the lower unit back on, so that it clears the water line if necessary. I had 2 of these motors and both of them had enough garbage in the water lines that I had to break the block apart and clean out all of the water passages. But they were saltwater, so most of it was corrosion. Anyways, both of them ran hot at idle and cool at higher rpms, until I cleaned them up. Has the paint on the cylinder head started to turn red? If so that means this motor has been a little on the hot side for some time.

So in short, I believe that you have some sort of blockage in your block or water line.

 

[sutor623]

Re: 1980 johnson 4.5 low rpm overheat

Here's what I was talking about. http://forums.iboats.com/johnson-evinrude-outboards/coolant-passage-issues-532341.html

 

[merclund]

Re: 1980 johnson 4.5 low rpm overheat

Thank for the reply. No the cylinder head is still white, a little paint is flaking off the exhaust plate. I rarely run the motor at very low speeds to avoid the overheating. With what you said about breaking the block apart, what would be the order of operation to do that? Is it better to inspect from the exhaust plate or the cylinder head first? Thanks for you help

 

[sutor623]

Re: 1980 johnson 4.5 low rpm overheat

Well if you have paint coming off the exhaust plate that is another possible sign of slight overheating. I wouldn't start with breaking the block apart but I would drop the lower unit again and make an adapter hose to fit over the water feed tube. Also check te copper line for damage. Did you change the grommet that goes from the waterpump housing to the input line?

 

[merclund]

Re: 1980 johnson 4.5 low rpm overheat

suter623
Yes I did change that grommet at the housing. I do have adapter I made last year when my 9.9 Johnson had a bad upper water line grommet. My first thought with this 4.5 was maybe the same problem, but my manual doesn't say anything about a upper water grommet. I guess I can start first with the water feed and see what happens. Unfortunately I live in Minnesota and will have to wait till nicer weather to use water outside to check it. If you or anyone else has other tips to check on I really do appreciate it. Have a great day.

 

[sutor623]

Re: 1980 johnson 4.5 low rpm overheat

Man our like the only other guy on her tht I know that ha to change the upper water line grommet. Suck because you have to remove the powerhead.

Anyways I have an older 4hp that uses the same block that is torn apart. Ill go check an see if it uses an upper water grommet

 

[sutor623]

Re: 1980 johnson 4.5 low rpm overheat

No grommet up there.

Evinrude Exhaust Housing Parts for 1980 4.5hp E5RLCSS Outboard Motor

 

[oldboat1]

Re: 1980 johnson 4.5 low rpm overheat

think back flushing as sutor623 suggests is the way to go. need to remove the t.stat if there is one, and put the cover back on. I regularly do this back flushing (granted, a summer project for those of us up north), and use a combination of rubber and plastic hosing to fit snug on the motor's water tube. It doesn't take much to block passages, and it's easier to clear them out by back flushing if you can.

 

[merclund]

Re: 1980 johnson 4.5 low rpm overheat

Thanks guys. I will try that once the weather warms up and I will report back.