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1983 75hp Evinrude odd cooling issue

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btasler

New member
I've got a 1983 75hp motor that in neutral, the tell-tale pees out a nice stream of water, but the moment I shift into either forward or reverse it starts blowing steam. Motor is in terrific shape and is in no way a piece of junk. I think it got a little warm but I don't think I cooked it too bad.

I put a new impeller on it at the beginning of last year before it needed it. I know there is a thermostat and some poppet valves in there but don't yet know how they all work together. I bought a service manual but for the life of me I can't find it.

Anybody have any ideas before I commit to wrenches?

Thanks in advance, Bryan
 
Interesting problem, what is the engine RPM when you put it in gear? Is the cylinder head discolored from overheating?
Maybe someone else will come along and help out.
 
Btasler.... You've said nothing about a warning horn. Did it come on and sound constant and steadily, and if so, did you shut down the engine quickly? The warning horn comes on before the engine is hot enought to do any damage, hence the terminology... "Warning".

To check the horn, have the key in the ON (not running) position, then ground the TAN wire at the cylinder head out to the powerhead. This completes the warning horn circuit and the horn should sound off steady and constant. If it does not, find out why as this is the only warning you'll receive should the engine start to overheat... the next warning is the engine powerhead turns brown and seizes up solid! (Too Late)

The thermostat and poppet valve assemblies are located at the top area of the cylinder head. The thermostat opens at approximately 143 degrees. The poppet valve opens if/when the water pressure exceeds a certain point to bypass the thermostat should you his a rpm high enough before the thermostat opens... keeping it simple.

Even though you installed a new impeller last year... that could have failed 30 minutes later. Drop the lower unit and inspect the pump assembly. I strongly suggest that you install a complete water pump assembly as a new impeller in a slightly pitted housing etc is a poor fix! So it may be a $100 fix instead of a $30 fix.... what's the engine worth?

If you've never changed the thermostat, it would be a good idea to change it... and inspect the nylon poppet valve as they've been known to fail/melt somewhat. Best to be sure.

Check the compression and the head bolt torque. Compression should be 100+ psi and even on all cylinders )or close to it). Bolt torque should be 18 to 20 foot pounds and tightened in the following sequence as follows whereas each number is a head bolt.

13..14
9....10
5.....6
1.....2
4.....3
8.....7
11..12

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
 
Last edited:
joereeves said:
Btasler.... You've said nothing about a warning horn. Did it come on and sound constant and steadily, and if so, did you shut down the engine quickly? The warning horn comes on before the engine is hot enought to do any damage, hence the terminology... "Warning".

To check the horn, have the key in the ON (not running) position, then ground the TAN wire at the cylinder head out to the powerhead. This completes the warning horn circuit and the horn should sound off steady and constant. If it does not, find out why as this is the only warning you'll receive should the engine start to overheat... the next warning is the engine powerhead turns brown and seizes up solid! (Too Late)

The thermostat and poppet valve assemblies are located at the top area of the cylinder head. The thermostat opens at approximately 143 degrees. The poppet valve opens if/when the water pressure exceeds a certain point to bypass the thermostat should you his a rpm high enough before the thermostat opens... keeping it simple.

Even though you installed a new impeller last year... that could have failed 30 minutes later. Drop the lower unit and inspect the pump assembly. I strongly suggest that you install a complete water pump assembly as a new impeller in a slightly pitted housing etc is a poor fix! So it may be a $100 fix instead of a $30 fix.... what's the engine worth?

If you've never changed the thermostat, it would be a good idea to change it... and inspect the nylon poppet valve as they've been known to fail/melt somewhat. Best to be sure.

Check the compression and the head bolt torque. Compression should be 100+ psi and even on all cylinders )or close to it). Bolt torque should be 18 to 20 foot pounds and tightened in the following sequence as follows whereas each number is a head bolt.

13..14
9....10
5.....6
1.....2
4.....3
8.....7
11..12

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
Click to expand...

Joe, thank you for your reply. I appreciate it much :)

Just to follow up, I took it apart this weekend and found the thermostat and poppet valves full of silt. I cleaned everything real good and tested the thermostat in a pot of water and it works good so I put it all back together and it works perfectly.

Until I got a close look at it I was sweating it a little but it was real real easy to get open.

ETA There was no warning horn. I don't think I cooked it real bad.
 
btasler said:
There was no warning horn. I don't think I cooked it real bad.
Click to expand...

Then, to repeat myself........
To check the horn, have the key in the ON (not running) position, then ground the TAN wire at the cylinder head out to the powerhead. This completes the warning horn circuit and the horn should sound off steady and constant. If it does not, find out why as this is the only warning you'll receive should the engine start to overheat... the next warning is the engine powerhead turns brown and seizes up solid! (Too Late)
-----------------

The horn is normally within the control box but can also be found under the dash attached to the engine to instrument wiring harness if a console type mount is used. It is strongly suggested that you put that horn (any horn), or even a bright light that would get your attention, back into the circuit to avoid future like problems.
 
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