1961 75HP Johnson cooling issues

[vess]

Still having trouble with my 1961 75 HP Johnson, cooling trouble. It is a V4AL, and when idling in the bucket it is overheating. I replaced the vernatherm, impeller and gaskets. It appears to be cylinders 1&3 that are too hot to touch. 2&4 are cool enough to lay a hand on. I am going to pull the head to look for blockage in the cooling passages, unless you think I should start somewhere else. I do have the repair manual, so getting it apart and back together isn't an issue. Any ideas?

 

[R.Johnson]

Re: 1961 75HP Johnson cooling issues

On an engine that age, pulling the head would be a good idea, Check the head gasket, and water passages. Did you just replace the impellor, or the entire pump?

 

[vess]

Re: 1961 75HP Johnson cooling issues

I only replaced the impeller, as that was all I could find for parts online. I even had to cut some gaskets manually, as the dang impeller didn't come with a gasket set. I will pull the head off today to see if there is something obstructing the flow of water. I had the heads off last year to fix one helicoil, so I know that the rest of cylinder looks OK. Well, looked OK last year anyway. Is this common, where one side of engine will overheat while the other side stays cool? Before I changed the impeller, both sides were overheating- couldn't hold a hand to either head. Thanks for responding- will let you know what I find.

 

[R.Johnson]

Re: 1961 75HP Johnson cooling issues

The pump housing on that engine was cast aluminum. Only the impellor plate was stainless steel. I would think it is very well ready for replacement if it still has that style pump.

 

[F_R]

Re: 1961 75HP Johnson cooling issues

Get it out of that stupid bucket and put it on a boat in the water and see what happens before you start tearing things apart. They were not made to run in a bucket.

 

[vess]

Re: 1961 75HP Johnson cooling issues

You are correct about the housing. In fact, the steel plate has some grooves in it where the impeller spins- nothing major, but probably should be replaced. I shudder at how much it will cost to get a new assembly.
I have had this boat and motor for 4 years, and never had an issue testing it in the tank, though I do know that the muffs don't work on the water pickup. In fact, when I put it up this winter and fogged it, it was running and cooling well in the tank, so that is why I am stumped. I will give that a shot, FR, if you that may be the issue.

 

[Evinrude Boater]

Re: 1961 75HP Johnson cooling issues

Is the water level in your test bucket above the the water pump? Are you sure you put the impeller in the right way? If you don't know the difference then you should check to make sure. My '64 75HP Evinrude runs a few degrees warmer on the bottom two cylinders. The touch test is good for the experienced but you should get an infrared thermometer to be sure what the temperature is. Mine ran at about 125-130 F in the test tank.

 

[vess]

Re: 1961 75HP Johnson cooling issues

Just wanted to update on the cooling problems- pulled the heads off, and cleaned the carbon deposits off the cylinders. Replaced with new head gaskets and reassembled. I checked the water flow from the heads by letting the pump push water and watching that it flowed out the hose that connects to the thermostat housing. It ran great, no overheating this time. Thank you all for the help on this one. I am sure I will have more questions in time.

 

[ladoga76]

Re: 1961 75HP Johnson cooling issues

is your 61 electric shift i have 62 that is and im getting ready to put impeller in it any info from someone who has done it would be great thanks

 

[ladoga76]

Re: 1961 75HP Johnson cooling issues

does your 61 smoke alot what fuel mix do you use i have been told 32/1 is ok help on these old motors is hard to come by so i like to ask alot of questions thanks

 

[vess]

Re: 1961 75HP Johnson cooling issues

I know we will hear differently from others, but I have used 50:1 since I bought it, per previous owner of 16 years.
Mine isn't electric shift, thankfully. I hear that they are more of a pain to service. The impeller was easy. Dropping the lower unit isn't difficult. It helps if you can see a video of it first- I saw one that was posted here as a link awhile back, but I don't know what it is now. I will post if I can find it. You will need to disconnect the shift linkage to get the lower unit to drop, although with your electric shift that may be different. Get a seal kit, although I have trouble finding parts online, and they are expensive now as they are so old. But you can find them. Check your manual. That was the best 50 bucks I spent when I got the boat, as I have used it many times on the old girl. And there is a good description how to change impeller in it also. Let me know if you have other questions- I will try to answer best I can.

 

[Evinrude Boater]

Re: 1961 75HP Johnson cooling issues

Two stroke engines will smoke since the lubricating oil is burnt. It doesn't matter if it's a trial bike, Lawn Boy or a boat motor, they all smoke. There's no way around it unless you want to buy a four stroke engine. Using less oil to reduce smoking is just exposing your engine to more wear. It won't smoke at all if you use straight gas....for about five minutes.
I run a 1964 Evinrude Speedifour and I want to keep it running for years to come. I suspect it's still running 43 years later because the proper oil was used. The recommended ratio is 50:1. You be the judge.

 

[skybobber]

Re: 1961 75HP Johnson cooling issues

Still having trouble with my 1961 75 HP Johnson, cooling trouble. It is a V4AL, and when idling in the bucket it is overheating. I replaced the vernatherm, impeller and gaskets. It appears to be cylinders 1&3 that are too hot to touch. 2&4 are cool enough to lay a hand on. I am going to pull the head to look for blockage in the cooling passages, unless you think I should start somewhere else. I do have the repair manual, so getting it apart and back together isn't an issue. Any ideas?

Where did you find a Vernatherm? is there a substitute?

 

[yorab]

Re: 1961 75HP Johnson cooling issues

Vess, I have an extra pump plate from a 1963 75hp. Should work fine in yours. Brand new, still in OMC envelope. I somehow ordered two for my rebuild. Let me know if you want it and we'll work something out. You won't be able to find only the plate on iboats nor many other places for that matter.

 

[lindy46]

Re: 1961 75HP Johnson cooling issues

Guys, this thread is over 3 years old.

 

[yorab]

Re: 1961 75HP Johnson cooling issues

D'oh! Lesson learned...