1972 Johnson 65hp overheat

[halfmoa]

I recently replaced the impeller in my 1972 Johnson 65hp outboard. It went so well I posted my pics as a tutorial. First time out it overheated within 2 minutes and left us stranded in the channel. The old impeller came out in a single piece. Actually, it could've been reused it looked so good. Any ideas on what caused the overheat? Thermostat? Any guidance is appreciated.

Half

 

[busted-bayliner]

Re: 1972 Johnson 65hp overheat

did u make sure the copper water tube hooked back up to the water pump housing?

 

[James R]

Re: 1972 Johnson 65hp overheat

As busted said. tube hook up but did you get the impeller blades the right way round by turning the drive shaft clockwise when fitting the housing. Is the tube seal good and did you get a good seal on the housing. Did you get the key located correctly. It could have fallen out during assembly and gone unnoticed.
You should run the motor in a tub to check that the pump is working before taking her out.

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

100% sure the tube is hooked up and the impeller is turning in the correct direction. Also sure the woodruff key is in place. I'm going to drop the lower to check all of the above again even though it took almost a half hour to get the lower to completely seat (and I still don't know why it finally went). Just wondering if it's possible the thermostat froze in place over the winter.

Moreover, I'm concerned about the damage that was done by the overheat....scared shirtless to check the compression.

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

I'm going to check compression and pull the t stat tomorrow. Is checking an outboard's thermostat the same as a vehicle? i.e place in pan on stove and heat water, check opening temp and check full temp? Is 160 degrees the standard opening temperature on an OB?

I've also read that this engine has some sort of bypass valves on either side of the thermostat for high RPM operation. Can anyone shed some light on those, specifically is there a way to test them?

Thanks guys,
half

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

Bump.

 

[James R]

Re: 1972 Johnson 65hp overheat

It is possible that the thermostat is stuck. It is common for crud and corrosion the block up the system at the thermostat. There is a spring loaded pressure relief valve also in the thermostat housing . This too could be stuck due to crud. Take it all apart and clean it out. If the parts and seals are in bad shape replace them. Not worth messing with an old Thermostat it will fail eventually. Yes you can check the thermostat with a pan of boiling water.

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

Thanks James. As soon as the rain stops and my compression tester gets here I'll start testing and posting.

And as soon as my compression tester gets here I'll find the old one, of course...

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

T stat tested fine, going to get a new one anyway.

I got to thinking...my engine has high speed by pass valves. Shouldn't those have opened up at WOT and cooled the system regardless of whether the t stat failed or not??? Thoughts?

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

Removed the t stat, high speed valves and cover entirely. Fired up on mufffs and got not one single drop of water out of the t stat housing.

Any and all input appreciated! I'm at a loss. I can drop the lower and see if everything looks OK there but water DID come out of the vents on the top of the anti ventilation plate....

 

[busted-bayliner]

Re: 1972 Johnson 65hp overheat

Removed the t stat, high speed valves and cover entirely. Fired up on mufffs and got not one single drop of water out of the t stat housing.

Any and all input appreciated! I'm at a loss. I can drop the lower and see if everything looks OK there but water DID come out of the vents on the top of the anti ventilation plate....

pull the lower unit make sure the water tube is hooked up

 

[bullcity101]

Re: 1972 Johnson 65hp overheat

I believe water will come out the vents on top of the plate just from the pressure of the hose on the muffs. I am guessing the water tube as well. I know its a plain but likely find something simple in the lower unit.

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

It seems to me that the water tube isn't seating properly. With the lower pulled, forcing water up the water tube with a hose will make water come out the thermostat housing (with housing removed). Install lower, place guide in place, install lower, run water....nothing out of t stat housing. Is it possible that the tube is too short/been forced up and made too short somehow? It looks like your typical soft copper pipe... a little bent but otherwise just perfectly normal. When I remove the lower the guide is in it's proper place but there's really no way to tell if it's fully seated with the lower installed without xray vision.

Note I also checked the impeller condition and that the woodruff key was in place. Both are fine. Shouldn't matter when pressurized, just covering the bases...

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

I just re installed the lower for the 400th time, hooked up muffs and cranked the motor with the ignition off and water came out of the t stat housing. Time to the the replacement tstat installed and see what happens. Right????

 

[05blastsrt4]

Re: 1972 Johnson 65hp overheat

on my 71 johnson 60, I was experiencing the same problem after an impeller change.
come to find out my plastic guide tubes where sliding up the water line shaft when water was put to it.
I went and bought some orings and placed them on the copper tubes so the guides could not slide up anymore,
and have not had any problems since.

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

on my 71 johnson 60, I was experiencing the same problem after an impeller change.
come to find out my plastic guide tubes where sliding up the water line shaft when water was put to it.
I went and bought some orings and placed them on the copper tubes so the guides could not slide up anymore,
and have not had any problems since.

Thank you very, very much for that insight! I will keep that in mind!

 

[halfmoa]

Re: 1972 Johnson 65hp overheat

I absolutely hate threads with no outcome....so here's my outcome.

I apparently didn't have the water tube placed properly. After removing the lower again and checking to be sure the woodruff was in place on the impeller, ensuring the tube seated, replacing the T stat (and installing a helicoil ) everything seemed fine in the driveway. Took her out today, fired right up like always, ran like she should've and we're back to normal.

Cheers to the guys who guessed water tube out of place! Shame on me for not realizing the big center bolt in the lower is for pushing it back into place and thank God there are no severe problems after the overheat!!!!

Now off to Indiana to get Gramps to get a duplicate title for the trailer, DNR for registration, and the tax man's cut and I'll be ready for real.