1972 Evinrude overheating

Hello again. I'm also working on a1972 Evinrude 4HP direct drive. It over heated a week ago, and stopped running. I replaced the impeller, but it still doesn't seem to pump much water and overheated again yesterday. Can the cooling channels in the engine be clogged? It is a salt water motor and I haven't been to good about flushing it over the years...What else would make it overheat with a new impeller? Thanks

Hello. Does the engine get seized? Salt water can block the water channels for sure, and also old gaskets which get too old. I know this, because when i was doing my 3hp rebuild work, i cleaned all water passages, and they was full of salt, and old gasket materials. And cleaning all this, was very slow and it takes very long time to get all old gasket material away. Be careful with gasket-surfaces and dont damage them while cleaning old material off. Old gaskets get burn and so it is difficult to remove them. But, all old material must be clean away, because otherwise you cant get your new gaskets to seal perfectly. I hope that your pistons,rings and cylinders are still ok. Also, are you sure that you have right fuel/oil mixture.

Drop the lower unit... Blow some compressed air up the copper water tube to see if it's blocked.

Double check your work on that pump installation.

Remove the cylinder head so as to check and clean the water passages if needed.

Evinrudemen said:

Hello. Does the engine get seized? Salt water can block the water channels for sure, and also old gaskets which get too old. I know this, because when i was doing my 3hp rebuild work, i cleaned all water passages, and they was full of salt, and old gasket materials. And cleaning all this, was very slow and it takes very long time to get all old gasket material away. Be careful with gasket-surfaces and dont damage them while cleaning old material off. Old gaskets get burn and so it is difficult to remove them. But, all old material must be clean away, because otherwise you cant get your new gaskets to seal perfectly. I hope that your pistons,rings and cylinders are still ok. Also, are you sure that you have right fuel/oil mixture.

Click to expand...

Hello. Thank you for responding. I would say the first time it overheated it seized briefly. I was motoring about half throttle, and it just stopped. When I tried to start it with the cord, it wouldn't turn, but I took the cover off and was able to turn it with my hands easily. It smelled very hot. I then replaced the impeller, but it's overheating again. Could I have done some major damage the first time it overheated? It's a tiny motor, low compression......Thank you again

It is possible that pistons and rings have some damage, very sad, but it is possible. Cylinder hone-work can be done at home at it is not big deal, but you need take apart whole powerhead. If you need new pistons, i am sure you can find good used ones, or you need to buy another engine with similar powerhead, and take parts from that. This was how i done, during my project. I think at first step, would be good to check compression in both cylinders. I think your head-gasket is at least burn now and you need new gasket, before compression test.
My project can be seen on here:
http://www.marineengine.com/boat-forum/showthread.php?451657-Evinrude-3hp-1966-rebuild

It's possible, even though the engine did seize slightly, that you might be lucky... worth a shot anyhow.

Remove the cylinder head as mentioned, carefully clean the head and block surfaces and install a new head gasket. torque the head bolts to 60-80 inch pounds in the following sequence whereas each number represents a bolt.

5.....6
1.....2
4.....3

Check for powerhead loose bolts, screws etc... simply tighten as needed.

Let us know how you make out.

joereeves said:

Drop the lower unit... Blow some compressed air up the copper water tube to see if it's blocked.

Double check your work on that pump installation.

Remove the cylinder head so as to check and clean the water passages if needed.

Click to expand...

Hey Joe, Thanks for the help. So I did take off the lower unit and attempted to blow air through it. Nothing. Seemed plugged, so I removed the copper tube and it's clear- I can see right through it. Next step is to remove the head, since I need a new gasket anyway it seems, and clean out all the water passages. Are they all accessible with the head off? Thanks again for the knowledge and help. BTW, it's pumping the same amount of water(very little) through those 8 little holes that is was before I replaced the impeller. Seems like something is plugged...

If that models long exhaust housing (between the powerhead and lower unit) has a series of small holes in the back of it, about halfway down... that's really the water telltale, it amounts to simply just a small spray.

The main water outlet is straight down that tube/housing and the exhaust blast blows some of it out those little holes as a signal of sorts that all is well with the cooling.

Strange that water is spraying out of those holes and you couldn't get air thru the water tube.

Water passages can be found under the head, under the exhaust cover and in my 3hp there are some passages also under the powerhead. So powerhead must be remove to get access these passages. It is best to obtain new gaskets ready, before starting the work. During my project, i didnt put any extra sealer to the gaskets, and there are no leaks. I have short model, and water spray from these small holes is quite strong.

OK, here's the update. I took the head and exhaust covers off and cleaned the water channels. I was ready to start assembling it with new gaskets and I thought I'd give it another look at with a bright light. Glad I did, because there was a tiny -1/8"- hole near where the lower spark plug goes, that was totally plugged. I didn't even see it the first time. I reamed it out and got it opened up, and made sure everywhere else I could access was looking clean. I put the motor together last night and before I put the lower part on,I blew on the copper tube and air went in and came out! WAY better than before when nothing went in! So I'm thinking that was the problem, because I shot some water in the hole with a syringe before I assembled the motor, and it went around the cylinder and came out beneath it. I think water wasn't circulating around the cylinder and that's why it overheated. I'll run it tonight and find out, I guess. In hindsight, looking at the motor, I blame myself, because I've always stored the engine with the pull cord facing up, and the hole was on the bottom of the motor. It's was just a normal thing to be carrying the motor by the handle, and just putting it down. Any water that was still in the motor, and it would be salt water, would just settle at the lowest point, and that's where the hole is. We'll find out tonight..............

SUCCESS!!! Started on the 5th pull, but there was a slight water leak from the exhaust cover. Shut it down while I ran and got a 5/16" wrench. Started it up and slowly went around the cover and slightly tightened each bolt. Water stopped leaking, and I ran it for 15 minutes without any overheating. Even was able to hold two fingers on the sides of the cylinders and it was barely warm to the touch. One little 1/8" hole that was plugged caused me so much grief...Thanks to Joe and Evinrudemen for all the help, knowledge, and encouragement. Now if I could just get that 1985 Johnson split apart I could change that impeller too. Next project...

That is very nice to hear. During driving remember sometimes have a look that water is coming out from the small holes.