1987 Johnson 90HP Crossflow Overheating question

[etracer68]

The motor ran fine all last year, and no over heating problems. The water pump was done two years ago. This year the only thing I did was disconect the vro line, and mixed 50:1, because I just didnt trust it. I plugged the oil line, and pulled off the gas line going to the carbs, and pumped the fuel until I seen the new mixed fuel, and reconnected it. I didnt undo any wires, because the alarm didnt work anyway.

I started the motor on muffs after work today, and it started right up. After about 2 min I felt the heads, and they were getting warmer them normal, also the tell tail was getting hot, I also felt the back water cover, and it was getting hot too. I shut it off. I did notice the tell tail was strong. I let it cool down about 20 min, and restarted it. The back water cover got cold right away, then in about 30 sec it warmed up and got hot, also the tell tail water was hot. I then shut it off again. The heads were hot, and back cover. I was getting water out of every where, but not the two higher 1/2" holes. Does this sound like a thermostat problem? If so, is it common for both to not open, at the same time? It looks like the bolts for the T stats are a pain to get at too. Any help is welcome. Thanks

 

[itsaboattime]

Re: 1987 Johnson 90HP Crossflow Overheating question

As a rule of thumb, I replace my waterpump assembly every 2 years. I have an '87 'Rude 110.
The fact that the exhaust cover cooled off right away shows that the waterpump is working. It's pumping fresh water into the powerhead.
I can't tell you if t-stats fail in pairs, I have always replaced them when I replace the waterpump. Have you ran this motor on muffs before? Did it get this warm then? Did the temp alarm sound or did you shut it down prevent it?
My advice is go pick up a infrared thermometer. Reletively inexpensive at an autoparts store. Run the engine and take a reading. Generally the operating temp should be around 140 degrees.
Try this and let us know what you get.

P.S. The bolts ARE a pain on my 110 and I'll bet they are on your 90 too.

 

[etracer68]

Re: 1987 Johnson 90HP Crossflow Overheating question

Yes, I have run it on muffs, and it didnt get this hot. I could always keep my hand on the heads or exhaust cover. I have a temp gun at work, and will bring it home tomorrow. I think water is getting in the motor, but not getting out through the T stats, only the tell tail. I will have more info tomorrow. Thanks for your input.

 

[emdsapmgr]

Re: 1987 Johnson 90HP Crossflow Overheating question

Very possible one or both of the stats are acting up. When idling on the hose, the block should heat to 143-150 degrees. Your laser temp gun will give you a good indication. Much over that and that's a sign of a problem. An overheat horn will signal if the heads get to 212 degrees. You can overheat due to stuck stats, even if you have a strong water flow and good impeller. If the stats stick shut, they prevent cooling water from exiting the block, and it will overheat.

 

[etracer68]

Re: 1987 Johnson 90HP Crossflow Overheating question

I was looking on IBoats for a complete kit, Gaskets, Thermostats, springs, valves, and grommets. Can someone point me in the right direction. I see they have parts, but didnt see a whole kit. I figure if im in there, might as well replace everything. I purchased the boat, and motor last spring, and owner said the water pump was replaced the summer before. I will be replacing that also. I have a factory manual, and I will do the work myself. Thanks for the input again.

 

[DargelJohn]

Re: 1987 Johnson 90HP Crossflow Overheating question

I had this exact problem with my '96 Johnson 88SPL. Overheat and back cover would get hot. Wish I could give you an exact cure, but I tried several things at once.
Rebuilt T Stats, rebuilt back cover and chased out the threads with a tap, replaced the T Stat hoses.

Look closely at the two hoses that connect the T Stat housing to the heads. One of mine was slightly kinked. Apparently it does not take much of a water pressure imbalance to upset the powerhead cooling. When I replaced those hoses, I think that was the ultimate cure. Good Luck

 

[etracer68]

Re: 1987 Johnson 90HP Crossflow Overheating question

Ok, I ordered, and received the thermostat kit. Whats the trick to compress the two springs, and try and get every thing together? In the sevice manual it shows the power head off.

 

[DJ]

Re: 1987 Johnson 90HP Crossflow Overheating question

Ok, I ordered, and received the thermostat kit. Whats the trick to compress the two springs, and try and get every thing together? In the sevice manual it shows the power head off.

The trick is having three hands with eight fingers on each.

All kidding aside, you just have to be patient. You can give yourself some additional room by removing the band at the top of the mid section and dropping the lower pan/cowl about three inches.

 

[boobie]

Re: 1987 Johnson 90HP Crossflow Overheating question

Get a 2"x1/4-20 thread bolt and cut the head off and make a stud out of it. Put that in the center mounting hole and use it for a guide. Push the thermo assy on and when seated insert the outer bolts and tighten loosely. Remove stud and install the last bolt and torque all three to specs. 1/4" drive tools work best for this. Been there and done it.

 

[etracer68]

Re: 1987 Johnson 90HP Crossflow Overheating question

Thanks, will drop the lower cowl. I like the idea of the 1/4-20 stud too. I have threaded rod, and will cut a piece of that and use it.

 

[wayneo99]

Re: 1987 Johnson 90HP Crossflow Overheating question

I just changed mine and the local old school dealer who has been working on the old engines since he was a kid got me all the parts. He also said forget the stock bolts and gave me what he called a shoulder bolts. basically the same thread but with a 3/8 head and kind of a built in washer. it allows the use of a universal 3/8 socket and small extension and you can compress the spring and thighten the bolts at the same time. He also had me change the plastic housing and 2 hoses.