Thermostat closing position

[3ric]

Good morning. I have a 2012 Mercury 115 efi. I changed the oil the other day and noticed some water in the oil. Not a whole lot, but enough for concern. From my reading, the thermostat could be the culprit if it’s not closing completely. I installed a new thermostat last year when the boat was new to me. I’ve used it about 3-5 hours since then.

I pulled the thermostat and tested it in water, it does seem to be moving, but when installed, the valve never really fully closes. It seems to be perpetually open about 1/16” (but will open further when heated). I can put it under the faucet and water flows through almost freely. Apparently this thermostat is only sold with the housing and is $80, so I am looking to you all’s experience and familiarity before I just buy a new one. Should my thermostat be closing all the way when cold or is some flow appropriate? Is my thermostat faulty?There is a little notch intentionally in the valve that would let a little water by.

I would like to figure this out before I start investigating more costly sources of the water in the oil. Thanks in advance

 

[Texasmark]

I know nothing about your engine except that the water and oil circuits don't touch each other. Your water in the oil is probably condensation from humid areas and temperature changes. It happens in farm equipment all the time.

Possibly the engine design needs "some" cooling under all operating conditions....hence the permanent open condition. Agreed that most engines don't move water until it reaches the stats opening temp.

 

[Scott Danforth]

all marine thermostats are used as mixing valves and not true shut-off valves. in the outboards, there is constant flow

 

[3ric]

So you’re saying that it is not supposed to close all the way?