1999 90ELPO over heat alarm sensor removel and trigger temp?

[mikeneal]

I have a 1999 90 HP ELPO and over the weekend hit some grass and over heated it. It got pretyt warm, steam outta pee stream and started lossing power. I had added a super loud piezo electric siren about ayear ago but it never went off. I shorted the wire from the sensor and it works fine. So either:
a) didn't quite get hot enough to trigger alarm , I dunno what the factory temp is but that seems unlikely. I am off to do a compression test now, ran fine for reminder of the day so fingers crossed.
b) I have faulty sensor. I removed the screws and plastic cover and cant figure out how the sensor is removed from the head, it must electrically tie to the head for grounding, is it epoxied into place?

 

[Texasmark]

Re: 1999 90ELPO over heat alarm sensor removel and trigger temp?

I have that engine basically....a 2002 model. The tstat is set to 143F. The OT alarm is below boiling point of water (212F at sea level....one atmosphere) and per the service manual is set to 190F to open (alarm sounds) and has to drop to 170F to reseat....alarm goes back off. Steam means boiling water....but where is it boiling?

212F isn't that bad a temp on engines. I have a 2011 Chevy Silverado and the engine temp sits at 210 regardless of what I am doing....it has electric fans rather than the belt driven, engine mounted fan of yester-year, and if the temp gets out of control it kicks the fans into the high speed condition. I have let it idle (parked) for 30 minutes or so, in the current Texas drought 100-107F temp (800 Ft altitude) with the sun bearing down on it (granite blue paint obviously absorbs sun's rays) with the AC running at a comfortable level for the occupants.....and I have never seen the temp gauge move from 210. (I am not affiliated with GM and I was a Dodge lover prior to this purchase.....Chev dealer was close to home. I used to hate GM products but it looks like the Fed's takover made them shape up....which they obviously did. Don't get hung up on this....just a point of reference.)

So back to the task at hand. Parrafin oils are good to 230F or so, synthetics to 400F.....my air cooled lawn mower/tractor air cooled engines run around 250F when working......

"I have faulty sensor. I removed the screws and plastic cover and cant figure out how the sensor is removed from the head, it must electrically tie to the head for grounding, is it epoxied into place?"

Yes, it grounds out to the engine block to cause the alarm. If you remove the screw and it doesn't come out it is apparently corroded. Follow the (Tan/Light Blue) wiring back till you get to a male/female connection. Unplug the connection and ground the wiring harness side to the engine block and the alarm should sound. If not, you have a bad alarm or open/corroded wiring somewhere.

Looking back to the sensor, if it is above 190F it should close short circuiting the wire to ground.

HTH,

Mark

 

[mikeneal]

Re: 1999 90ELPO over heat alarm sensor removel and trigger temp?

Update: I checked compression and 105psi all three cylinders (was it was ~3 yrs ago when purchased boat) So that is great news. Still cant figure out how the sensor comes out of the block, the screws and cover are no brainer but the sensor appears to be epoxied or RTVed into the counter bore or?

 

[Texasmark]

Re: 1999 90ELPO over heat alarm sensor removel and trigger temp?

Run a can of Sea Foam in your next tank of gas. May loosen your rings and get you closer to the min 120 psig that Merc recommends in their '97 and on service manual.

Seems we missed something here. After just going out to the shop and checking my engine, the sensor is part of the bracket which is held to the block, sensing the temperature in the exhaust water and retained by two screws. I doubt that you can remove the sensor from the bracket. They are probably sold as an assembly. But you can follow your wiring from it and go back to where you pick up the tan/Lt blue wire and ground that wire to sound the alarm.

The OT sensor, per the book shorts out at about 190F and opens back up at about 175F. If you want to test it you will have to take it out and put it in a pan of water on the stove, measuring for a short as the water temp gets around 190F.

HTH,

Mark

 

[mikeneal]

Re: 1999 90ELPO over heat alarm sensor removel and trigger temp?

I got the sensor out found a fair amount of corrosion in the counter bore. I tested the switch using hot water , ohm meter and thermocouple and it triggers perfectly at 190 and unlatched around 175 , I think the test 5 times in a row, worked perfectly everytime. I think the corrosion was not allowing the ground. I cleaned it all up and re-installed.