1992 Force 90HP overheat alarm

[dcar00]

I have a 92 90hp Force with an overheat alarm issue. last year I had the impeller and thermostat changed. Get out on the lake for the first time this weekend. 30 seconds off the dock the overheat alarm sounds for about a minute then stops. ran for another 15 minutes and then the motor quits. wait 5 minutes and start it up again. runs for another 30 minutes no issues.

next day I run for about 1 hour at about 2500 ]RPM. no alarm. Take it out just before nightfall for 30 minutes no alarm. stop for 30 minutes. 1 minute after restart ALARM TURNS ON. stops after 1 minute.

next day run the boat for 1 hour at 2500RPM no alarm. Go to put it on trailer. slip it into neutral and ALARM TURNS ON AGAIN.

new impeller, new thermostat, water is coming in a decent stream out of the 2 exhaust holes. put my hand on the block and could leave it there for about 2 seconds before having to release. I'm stumped.

Any ideas of what to do or check?

Thanks
David

 

[steelespike]

Re: 1992 Force 90HP overheat alarm

Speaking generically.
Temp sensor is a simple switch that completes the alarm circuit to ground if the wire is bare or shorted it could be turning on the alarm.Also the switch could be defective.
The head is a better place to check the temperature.
Should be too hot to hold your hand on but not so hot it burns you.BE CAREFUL TESTING!!

 

[jasonbailey]

Re: 1992 Force 90HP overheat alarm

Check the compression. My 75hp did the exact same thing, turned out to be a blown head gasket.

 

[dcar00]

Re: 1992 Force 90HP overheat alarm

Thanks guys.

I'll check the sprk plugs to see if they are clean due to blown head gasket.

one question, I have the clymer manual. are the temp sensor and thermostat the same thing? I

f I look at the blow up of the power head it actually shows 2 thermostats. the electrical wiring diagram shows a "temp sensor".

Any help would be appreciated.

 

[dcar00]

Re: 1992 Force 90HP overheat alarm

All right. got to the boat this weekend.

1. did compression check(cold, sorry I know not the right way to do it) cyl #1 110, cyl #2 120, cyl#3 120. I guess that is good right? had the throttle in neutral.

2. removed thermostat housing. guess what, no thermostat. I'm guessing the mechanic just took it out instead of replacing it like I asked. so i assume water just flows freely immediately? is this correct?

3. grounded the temp sensor and the alarm buzzed. seems like it works correctly. can't change out temp sensor without removing the head.

4. spark plugs were not clean. all were the same amount of black. a littel carbon deposit on each one.

Can no t-stat cause an overheat alam at low RPMs or soon after starting?