Thermostat sticking???

[Mark42]

Toward the end of last season, I launched the boat and while motoring through the marina in the no wake zone, the temp alarm went off (1985 85hp Force). I shut off the motor and weighed my options. After a minute or two, I tried to start the motor, and it fired right up, the thermostat was open, and the motor ran fine the rest of the day, and two or three outings after that event.

Today was the first outing of this season and it happened again. Alarm went off while in no wake zone, shut off, waited a minute or two, then started and went on our way.

I'm afraid that the thermostat will just seize up and not open at all. Do these thermostats die a slow death? Is this typical of an aging Force thermostat?

I read all the threads I could find on removing thermostats with stuck screws, which is my situation too. Grrr.....

Not sure if the thermostat is going bad, is just sticking because of some corrosion and will "work itself out" if used frequently over the next two weeks, or is just reacting slow.

Any thoughts? Comments?

 

[pnwboat]

Re: Thermostat sticking???

Either thermostat or impeller. When was the last time you changed the impeller?

 

[Mark42]

Re: Thermostat sticking???

Either thermostat or impeller. When was the last time you changed the impeller?

I have a receipt from the previous owner that showed the impeller was replaced a year or two before I bought it, so maybe 6 years ago. It pumps water great, so I don't think the impeller is bad. I also installed a tell tale a few years ago, so I can see the water stream.

 

[jaybirddog11]

Re: Thermostat sticking???

DEFINITELY time to change the impeller. They should be replaced a mininmum every 2 years.

 

[mla2ofus]

Re: Thermostat sticking???

I'm going thru the same thing w/ a '98 90 Hp Force. I've tested the thermostat, the over temp sensor and checked the water pump. All OK and I get good strong flow out the top of the block at idle w/ the muffs on. When I idle mine for 10 min or so the alarm goes off. Next time out I'm taking my non contact thermometer w/ me so when the alarm goes off I can get readings off different areas of the engine. My suspicion is the alarm sensor is awfully close to the exhaust collector box and heat builds up in it at idle. I hope my thermometer will help me.
Another member said he solved his problem by enriching the idle mixture about a 1/4 turn. I may come to that if I can't find anything else wrong.
Mike

 

[Mark42]

Re: Thermostat sticking???

DEFINITELY time to change the impeller. They should be replaced a mininmum every 2 years.

Even though it could stand to have a fresh impeller, it is pumping water fine, with good pressure out the tell tale. So even though it is due for a change the water flow is indicating that the impeller is not the problem at this time.

I'm going thru the same thing w/ a '98 90 Hp Force. I've tested the thermostat, the over temp sensor and checked the water pump. All OK and I get good strong flow out the top of the block at idle w/ the muffs on. When I idle mine for 10 min or so the alarm goes off. Next time out I'm taking my non contact thermometer w/ me so when the alarm goes off I can get readings off different areas of the engine. My suspicion is the alarm sensor is awfully close to the exhaust collector box and heat builds up in it at idle. I hope my thermometer will help me.
Another member said he solved his problem by enriching the idle mixture about a 1/4 turn. I may come to that if I can't find anything else wrong.
Mike

I think the 98 Force is the Mercury brand engine, and is not the same as the 80's Force engines from the Chrysler design era.

I did a temp check while waiting for the engine to cool. The head was too hot to touch bare handed for more than a second or two. I know from experience that even after running hard, I could touch the head and thermostat box bare handed for a 5 or 6 count before it was too uncomfortable to touch. After re-starting, it quickly came down to temps I could stand bare handed.

Judging from the "touch test", I think it has a 110 thermostat in it. I don't think the thermostat was ever changed, because paint still covers the edges of the thermostat cover gasket. Although I am unsure if the factory put in a 110 or 130 back in 1985.

 

[pnwboat]

Re: Thermostat sticking???

Looks like it's probably the 110 degree thermostat. I would definitely change it. Not worth cooking the motor.

 

[Mark42]

Re: Thermostat sticking???

Looks like it's probably the 110 degree thermostat. I would definitely change it. Not worth cooking the motor.

Now if the thermostat cover will come off...... I've been unable to get it off in the past, as the screws are probably corroded into the head.

Its not just these old Force motors, it seems every o/b I've worked on had corroded thermostat cover screws. Maybe I'm jinxed.

Anyway, I'm going to order a new impeller and thermostat.

 

[pnwboat]

Re: Thermostat sticking???

You can try one of these. The trick is to find a slotted bit that fits the slot on the screw really tight. The more play you have, the less effective the tool is. The combination of striking the tool with a hammer, and the twisting motion that the tool generates usually works pretty well.

http://www.kk.org/cooltools/archives/000723.php

 

[jason32038]

Re: Thermostat sticking???

take that screw out on top of the head by the thermostat and spray some penetrating oil in there and let sit for a while before using again.

 

[Mark42]

Re: Thermostat sticking???

take that screw out on top of the head by the thermostat and spray some penetrating oil in there and let sit for a while before using again.

I'm not sure I understand this completely. Do you mean to get penetrating oil on the thermostat to prevent it from sticking, or is this a way of getting penetrating oil into the thermostat cover screws so they come out easier?

There is a threaded plug on top of the head near the thermostat cover. Will spraying penetrating oil in there get oil on the piston of the thermostat?

I think your suggestion will help my situation, but I just need to understand better what the purpose is.

Thanks!

Mark

 

[Mark42]

Re: Thermostat sticking???

I sprayed WD40 into head where the tell tale fitting is. Can't see anything, even with a flashlight, but using the straw on the can, got the spray all around.

Later we took the boat out and ran the boat on and off all afternoon. The motor did not over heat. Don't know if it was coincidence, or just because it was the first outing of the season, or what ever. But it didn't over heat and that is what matters.

When we get home next week I will work on changing the thermostat, hopefully without breaking the screws or the cover.

And a new impeller will go in too.

I intended to use this old Force for just a season or two, but with the prices of motors, I think I will keep it a few more years, and give it detailed maintenance.

 

[jason32038]

Re: Thermostat sticking???

No the penetrating oil was to help loosen up the thermostat a bit. Most likely has corrosion on it preventing it from operating correctly. Give those bolts a good soak...good luck with those. If I were you i'd replace those old flat head screws with hex heads.