1991 Mercury 115 thermostat Question

yukonpaul

Recruit
Joined
Mar 14, 2010
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1
I've got a 1991 Mercury 115 that runs great, but I need a confirmation on something.

Had it running in the driveway using a large barrel with water being circulated using a garden hose, air temperature was about 50F, water temperature about 40F. Noticed no water coming out of the tell tale, took the engine cover off and felt the exhaust cover which was air temp or cooler, and felt the cylinder block cover and it was about the same temp.

Continued running at high idle for a considerable amount of time (45 mins) and water coming out of the exhaust ports on the lower leg started to get warm, but never hot. Continued checking the exhaust cover and cylinder block cover and they never got warmer than air temperature. Which makes me believe that the water was pumping adequately through the block.

Shut down the engine and heard the water draining from the power head, and as soon as the water was no longer in the cooling jackets both the exhaust cover and cylinder block became warm to the touch, though not so hot that I couldn't leave my hand on them.

So after checking my shop manuals and doing a search on iBoats I found, or so I believe, that this model of motor has the tell tale after the thermostat and that there won't be any stream of water until it opens. I've checked and the tell tale isn't obstructed by any bugs, dirt or anything.

So given all this is it safe to assume that at high idle and without a load on the motor that there was just not enough heat produced to cause the thermostat to open?

Thanks
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: 1991 Mercury 115 thermostat Question

Snake a piece of weed wacker line back thru the P hose to rod it out, then give it a shot of compressed air or water from the garden hose to be double sure that it is cleared.

My 115 4 cyl P hose comes off before the stat and flows immediately.
 

Craig-

Petty Officer 1st Class
Joined
Jul 25, 2010
Messages
316
Re: 1991 Mercury 115 thermostat Question

Plugged up, should flow all the time.
 
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