35 Johnson overheating

sinkhole

Seaman
Joined
Aug 23, 2012
Messages
58
I Just purchased a Johnson 35e77c short shaft together with a seized 35e77 long shaft. Between the two I have got the short shaft running keeping it a short shaft,130psi. Problem is it has serious overheating issues, laser gun shows 2oo deg .plus on upper head and exhaust discharge water is too hot to touch. water comes out of the tell tale only at an rpm higher than normal idle, cold coming out of holes on back of lower leg. Thermostat was broken. I replaced but that made no difference also ran motor without thermostat same result. I have removed water jacket and head cover plate cleaned water passage ways and flushed up and down water tube with garden hose got good water flow out of all openings. On my last attempt I sealed the water pump wear plate with gasket sealer (gaskets not available) and removed thermostat. It still ran not quite as hot but too hot to use. I noticed that when increasing the RPM not only did tell tale pump a good stream of water but the temperature dropped to a working level. I was contemplating using the wear plate from the spare motor as it seems to have less wear, but i noticed that the cutout on top of plate for the water to enter the pump housing is smaller .Would this create more pressure? Will wait for any comments before taking apart again. Thanks for any advice.
 

ThomW

Chief Petty Officer
Joined
Aug 8, 2016
Messages
615
I would definitely pull the lower unit and check the impeller. Sounds like you may have a impeller that is breaking apart and missing fins--therefore it only pumps enough water when it is really turning at higher RPM's.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,446
Perhaps the Water Pump Housing and Plate are worn and need replacement.
Was the old Impeller intact, or were pieces broken off?
Are the Water Inlets on the Gearcase clear of Debris?
 

Ronniewhite

Petty Officer 2nd Class
Joined
May 26, 2022
Messages
199
My motor was doing the exact same thing would on cool when higher rpm. My impeller was still intact but had a few cracks on the fins. Installed a new impeller and it was good to go.
 

Ronniewhite

Petty Officer 2nd Class
Joined
May 26, 2022
Messages
199
My motor was doing the exact same thing would on cool when higher rpm. My impeller was still intact but had a few cracks on the fins. Installed a new impeller and it was good to go.
But I guess if you put a new one in and it didn't work its not that. Someone on here will no what is up with it.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,815
A 2 cylinder model might have water diverters in the block.-----A 3 cylinder does not have those.
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,612
Clean/scrape water passages. Hacksaw blade works well around the cylinders.
 

sinkhole

Seaman
Joined
Aug 23, 2012
Messages
58
11 & 12 If I pull down water tube to check grommet will grommet come down with tube? How hard is it to replace grommet?
 

909

Chief Petty Officer
Joined
Jul 19, 2021
Messages
537
Rebuild the water pump with an OEM kit and replace everything.

Increase your idle speed to 725 rpm.
 

sinkhole

Seaman
Joined
Aug 23, 2012
Messages
58
Perhaps the Water Pump Housing and Plate are worn and need replacement.
Was the old Impeller intact, or were pieces broken off?
Are the Water Inlets on the Gearcase clear of Debris?
Impeller almost new, inlets clear .I'm attempting to take apart and reinstall pump making sure water tubes are inserted properly in grommets.
 
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