94 Johnson 140 V4 overheating at higher speeds

[FreddyB]

Hey all! New to the forum as of today!
Sorry in advance for the lengthy post, trying to include as much info as possible!
I'm was hoping I could get some help with my overheating issues on my 94 Johnson 140 V4.. It's sitting on a 19 foot center console. I just bought this boat one month ago, and the previous owner showed a receipt from a boat mechaninc in Riverview FL. The receipt lists;
(5/11/2011)
2 143 deg. T stats
2 diaphragm cup
1 water pump kit
2 gasket t stats
4 spark plugs
4 carb kits
1 trim motor
1 stator 9 amp
2 shift shaft o rings
1 hose gasket for 55 housing?

Also previous owner removed oil injection tank, so I just premix with Johnson 2 stroke oil, 50:1
I also just did a compression check my self and found 135 psi on 3 cylinders, while port side top was at 130 psi.
Also had 2 fuel hoses that were loose, tightened up, starts immediately, runs great! Smooth, quiet, shifts nicely.

Now for the problem... When running at higher speeds, I usually like to cruise at anywhere from 4-5000 rpms.
I run in salt and freshwater.

When running at higher speeds, after 10-15 min the high temp alarm comes on, as well as the slow feature. I'll back the throttle off, anchor, sit for 5-10 min and it re sets. The alarm will not come on at slower speeds or idle. I have noticed though when at idle the pee hole stream is fairly hot. This afternoon I will attempt to back flush.

The intakes are clean, I will look inside the impeller housing to make sure there's nothing inside of there as well.

Any other suggestions/comments would be greatly appreciated!

Thanks

 

[FreddyB]

Re: 94 Johnson 140 V4 overheating at higher speeds

Progress report;
Dropped the lower unit to inspect impeller and housing. A pinch of sand in there but nothing major. Impeller blade looks new still. Cleaned lower unit. Took off thermostat housings, no evidence of any debris or clogged water passages. Ran water from impeller pipe with hose, t-stat covers off and had a nice steady stream coming out. I'm going to go ahead and replace the thermostats for the heck of it even though they were replaced last year, they look beat up. This is where I left off as the sun is now going down, and I have a long day tomorrow!
When I have time this week I'm also going to pull the heads off and have them checked out, and then put new seals on just to be extra cautios.
I have heard of a pressure relief valve that is supposed to help the t-stats out at higher speed.... Anyone know if this motor has one and where it would be?

Would greatly appreciate some input!

 

[OutOfControl]

Re: 94 Johnson 140 V4 overheating at higher speeds

Freddy,
Just went through the over heating thing myself. I tested my T-stats on the stove with a pan/pot of water and a candy thermometer and I got some debris and fine sand particles in the bottom. I also flushed the motor through the thermostat openings with the garden hose for a few minutes.
After reinstalling the thermostats I ran the motor for a few minutes in a trash barrel with a few gallons of vinegar and water while diverting the telltale water flow back into the barrel. You have to be careful not to run for too long as the water will become too hot. I waited a few hours and repeated, have not had the over heat problem since.

 

[FreddyB]

Re: 94 Johnson 140 V4 overheating at higher speeds

Glad to hear you fixed your issue! I will definatively take your advice and do the same with mine! I will report back hopefully this coming weekend after a test run, and thanks for the post!

 

[FreddyB]

Re: 94 Johnson 140 V4 overheating at higher speeds

Btw the "pressure relief valve" I was told about is actually the pressure relief spring on the t-stat... My mistake. Also a buddy of mine suggested flushing out the engine in the can with the t-stats out, then re-install after flush is complete. Again thanks for the post, nice to have re-assurance!

 

[FreddyB]

Re: 94 Johnson 140 V4 overheating at higher speeds

Today I ran the vinegar through the motor in a 55 gallon drum cut in half, t-stats out, motor never even thought about getting hot. That's wHat I wanted to see. new t-stats on order.
Did however notice small amount of oil in the drum.. Any thoughts?
It's not from the gear case as I just changed the oil, oil looked good with not a drop of water.
Cooling system seems to be accounted for, as I today probably found the real culprit.
Found a loose hose on the fuel pump, cut it and re zip tied. Fixed.
Then I primed it again, to have fuel drip from the carb bowl gaskets.. New gaskets on order. I'm assuming the air pockets in the fuel filter which I'm also replacing, caused the high speed temp alarm.

Only questions I now have;
Oil in the drum, is it un burnt fuel? If indeed will check spark. Motor does not seem to be misfiring though.
Pee hole tell tale was flowing steady with the stats out, but not hard, was that because there was no pressure from the t-stats pressurizing the system?

Any help is welcome! Thanks!