Low Operating temperature Yanmar 4-JH3-TE

[bendriver]

I recently bought a 13 year old boat with low diesel hours - 900. I now have 1100. Engine - Yanmar 4-JH3-TE - runs well. No blue, black or white smoke. It hits or nearly so max RPM ( 3200 of possible 3600)when Autoprop is cleaned. My worry is low engine temperature. Motor never exceeds - even with full load - 105-110 F. That is Fahrenheit! I can literally sit on motor after long tip with no burns. It is freshwater cooled installation with transmission cooler and 40L engine heated hot water heater.

My questions are has anyone experienced same with Yanmar and what are possible effects - if any - of low operating temperature.

Thanks
Ben

[Crew of Turning]

Normal setup with a raw water cooling system. In salt water you will not get separation of crystal salt in your cooling system leading to plugged water channels in your engine.

[Privilege]

I am also interested in the responses. I too have a 4JH 3ce and my port engine hardly ever shows the faintest sign of warming up. Changing the thermostat made no difference. It runs well and the only time the temp has risen is when I caught a plastic bag and the alarm went off.

[a64pilot]

My 4-JHE runs about 165F if memory is correct, and I think that is thermostat temp.
It should run right at thermostat setting temp, if your getting HOT water out of the water heater, I'd suspect its running hotter than 105 F, cause that would be at best, warm water.

[sailorboy1]

My 4jh3e runs at 175-180 once fully warmed up and the potable hot water it makes will take your skin off.

If your engine runs "cold" it almost certainly is the thermostat. But make your gage is not reading wrong before getting carried away it seems they all go bad somewhere around 10-15 years

[bendriver]

Engine heats hot water to warm not hot. I may misunderstand thermostat but was under impression thermostat is closed when engine starts then opens and stays open when operating temperature is reached. If it did not open, motor would overheat; if it stays open always, it takes longer to reach operating temperature but will eventually. How can thermostat be problem especially in hot climate? I believe someone here is saying it will never reach operating temperature if open'always?

[a64pilot]

You have the operating principle figured out, thermostats can fail open and often do, in fact I'd say that is the preferred failure mode, they can also as they age begin to operate incorrectly.
The operating principle I admit confuses me a little, they work apparently by wax melting inside the thing.

Here read this,
https://en.wikipedia.org/wiki/Wax_thermostatic_element

A Yanmar I believe uses a "double valve' Thermostat

They are so easy to replace, I'd pull the one out of spares and replace it and see if that helps, long term it is not good to run an engine too cool, they form varnish and the oil doesn't cook off moisture that forms acids etc. It won't kill an engine right away, but will prematurely wear one

[a64pilot]

OK, no if stuck open the engine will never likely reach operating temp, when fully open there is an excess amount of cooling capacity or an engine would overheat if run wide open for example, a thermostat will partially open to control temps, its not an on or off type of thing.
You have to have excess cooling capacity, or anytime your cooling system was anything less than perfect, your engine would overheat. There are very, very few perfect cooling systems in boats.

[a64pilot]

I'm learning reading that article, now I understand how they work, I didn't know wax expanded when it melted, but I cut and pasted the how it works part, this is it

"While the thermostat is closed, there is no flow of coolant in the radiator loop, and coolant water is instead redirected through the engine, allowing it to warm up rapidly while also avoiding hot spots. The thermostat stays closed until the coolant temperature reaches the nominal thermostat opening temperature. The thermostat then progressively opens as the coolant temperature increases to the optimum operating temperature, increasing the coolant flow to the radiator. Once the optimum operating temperature is reached, the thermostat progressively increases or decreases its opening in response to temperature changes, dynamically balancing the coolant recirculation flow and coolant flow to the radiator to maintain the engine temperature in the optimum range as engine heat output, vehicle speed, and outside ambient temperature change. Under normal operating conditions the thermostat is open to about half of its stroke travel, so that it can open further or reduce its opening to react to changes in operating conditions. A correctly designed thermostat will never be fully open or fully closed while the engine is operating normally, or overheating or overcooling would occur."

[bendriver]

Thanks for the explanations. Clearly I need to change out thermostat. I did not realize it was dynamic process; I though it was either closed or open.
Ben