1996 Force 120 overheat question

[rhedayi]

Hi gang, I recently bought a 1996 bayliner trophy (20foot walkaround)
Boat ran fine but the water coming out of the telltale was sort of intermittent, especially at idle. However I ran it for 2-3 hours at the lake (65 degrees) and no issues, no overheat. My OCD got the best of me, I swapped the impeller with the quicksilver kit which included the impeller and housing. Still poor ****. I then checked to make sure I got the small metal key in the impeller, replaced the black coupler seal to make sure it makes good seal with the copper tube. Went out and seemed to run fine but **** still a bit anemic at idle and much better at speed. I also installed a fuel water separator and filled the tank with 50 gallons of premix. Today I took it to the lake and water temp was 50. We slow trolled at idle for a bit and the overheat buzzer went off. I stopped the engine, took off cowling and felt the block and it was barely warm. I started it and buzzer was still going and we got up to maybe 1500 rpms and whatever that speed is and it stopped buzzing. SO I am trying to determine, could this be buzzer sensor going bad ? could it be a stuck thermostat ? could it be something about the fuel separator being installed ? just trying to sort this out and how to go about this ? Any input would be appreciated. I would like to add we have good compression and the boat starts up easily and runs great.

 

[jerryjerry05]

Most of the water/exhaust comes out the prop, you won't see it as you run.
Get a temp gun under $20 that way you'll know what the temp really is.

 

[Nordin]

I would suggest you to check the thermostat and as jerryjerry says most water exit under the water and yes buy a cheap infra red gun to check the temperature with.
As you have a late Force there are no idle releaf (poppet) valve on that engine that can be stuck.

 

[rhedayi]

Merry Christmas everyone and Thank you so much for the replies. I have an IR thermometer. Where exactly do you point it to get the measurement?
Also I have been buying quicksilver parts but it seems the gaskets are not in some sort of package and something like this looks to be cheaper. Would this be a suitable kit ? Thanks

For MERCURY F664068 THERMOSTAT KIT FITS 70 75 85 90 120 150 1990 THRU 1999 | eBay

1 X Thermostat 55℃ 130℉. Repair Kit. 120HP 1995， 1999， 2000. Exhaust Bellow. 95HP 1996-97. 90HP 1993-95. 90HP 95HP 120HP SportJet. Sierra ：18-3527.

www.ebay.com

 

[jerryjerry05]

That kit would work.
The best bet is buy products that say Mercury/Force on the package.
China has made so much junk, you never know what your getting.
Measure the temp next to the plug on the head and along the pistons travel or side of the cylinders. Hit a bunch of places and record the results.

 

[topgun3690]

The best bet is buy products that say Mercury/Force on the package.
China has made so much junk, you never know what your getting.

Agree with jerry 100 percent......Sierra would be acceptable as aftermarket brand IMO.....and a little cheaper than Quicksilver. Just look at the brand names in the product descriptions on ebay......the one in the link above states it is "UanOfcn"......sounds very Chinese to me......

 

[rhedayi]

update.....thermostat change did the trick. Boat runs cool now. I installed a faria block temp to the motor and it runs really cool now as measured near spark plug 2

 

[jerryjerry05]

The area next to the plugs runs the hottest.
When checking temps??? check all over the head and sides where the water passages are.

 

[rhedayi]

 

[rhedayi]

That’s the sensor. I found a faria 2 inch temperature gauge with 140 degrees being the center and attached this here. After the new mercury thermostat it runs really cool. Cool enough to touch right there with my battery gang even after wide open throttle. I must admit the lake is only 48 degrees and ambient temp was similar so fairly cold conditions.