Operating temp Yanmar 3GM30F

[skunther]

I took multiple readings of temp on my engine, and they ranged from 134 to 214. I’ve read these engines should be operating <180.
Am I taking these readings correctly? Are they within range? I took one at the sensor (169), one at the oil pan (214), and one at the mixing elbow (134).

 

[RoyS]

The reading you took at the temperature sensor is appropriate, the others are not. If your engine was just idling then that may explain the lower than expected results. Your engine thermostat regulates the engine coolant temperature so as to not exceed its setting. The coolant will travel through a by pass pipe until the thermostat comes into play. Try taking another reading at the sensor (as above) or at the thermostat housing when the engine is being worked harder, say, pushing the boat at hull speed for a while. Should that result still appear lower than the thermostat setting value, then you could remove the thermostat and test it in a pot of heated water to see when it opens. At idle, particularly with a water heater, your engine may never reach full operating temperature.

 

[Scott T-Bird]

I have the same engine and my temp gauge never goes above 165 under load. There was an explanation that I can't remember exactly - something about the sensor not being located in the optimal location, I think. Previous owner explained that with an infrared thermometer he consistently measured 180 at the thermostat housing (or the heat exchanger outlet - I don't recall exactly). As long as I read 160-165 on my gauge, I never worry about it. The temp at the oil pan has no relevance (I think) and it's definitely going to be lower at the mixing elbow.

 

[skunther]

The reading you took at the temperature sensor is appropriate, the others are not. If your engine was just idling then that may explain the lower than expected results. Your engine thermostat regulates the engine coolant temperature so as to not exceed its setting. The coolant will travel through a by pass pipe until the thermostat comes into play. Try taking another reading at the sensor (as above) or at the thermostat housing when the engine is being worked harder, say, pushing the boat at hull speed for a while. Should that result still appear lower than the thermostat setting value, then you could remove the thermostat and test it in a pot of heated water to see when it opens. At idle, particularly with a water heater, your engine may never reach full operating temperature.

The engine was running at 2700 for around an hour when I took those readings. Seems perhaps the thermostat isn’t opening properly? Any other tests I should do before removing the thermostat?
It may also be time for a coolant change. I’ve had the boat 2.5 years, and am not sure when it was last changed. Is it possible to check if the coolant is still any good?

 

[Scott T-Bird]

Testing the thermostat is relatively easy but you would remove it for placement in heated water. The temperature of the water would be monitored while observing how the thermostat opens and closes. You can read about test descriptions. It's just as simple (and pretty cheap) to replace the thermostat. After 20 years of service, I replaced mine. Temp gauge readings are the same before and after, but now I have a spare thermostat.

I'm not sure why you are questioning the operating temp. It doesn't sound like you monitored temp at the right location if you haven't monitored the thermostat housing yet. If you have any question about the coolant, by all means, replace it ... but I have my doubts that older coolant would affect the operating temp. You can run water through the system with the same results. The purpose of coolant (AKA antifreeze) is to prevent the liquid from freezing at extremely low temps, boiling at high temps and it prevents corrosion. Other than that, it doesn't affect the operating temp of the engine. If you aren't running the engine under load (driving through the water) you may not even be heating the engine fully simply by raising the rpms in neutral. But I suspect that you are simply reading coolant system temps in areas where the coolant is cooling down, not where the temp is highest. Like I said, the temp sender is not located where the circulating coolant is the most heated.

 

[Alan Gomes]

The engine was running at 2700 for around an hour when I took those readings. Seems perhaps the thermostat isn’t opening properly? Any other tests I should do before removing the thermostat?
It may also be time for a coolant change. I’ve had the boat 2.5 years, and am not sure when it was last changed. Is it possible to check if the coolant is still any good?

FWIW, I find that when I shoot temp at the oil pan/oil filter it is noticeably higher than in other places. Checking it at the thermostat housing seems to give a more reliable reading. Personally, I doubt you have a problem here.

 

[sailcapt340]

I remembered your post yesterday while I was maneuvering through the marina. About 1.5 hours of running time. Same engine as you, 3GM30F.
I didn’t remember the exact places you took measurement, so I just took a few around. This was also running at <1500 rpm and up to 2000 rpm.
I hope this helps in some way, different areas, but it gives you a comparison to see.
One is of the oil filter, but that was my own curiosity. One was of the thermostat, but it didn’t come out clear at all. I’m not the best picture taker. The temperature was 170.

 

[kloudie1]

Thermostat spec is to start openiing at 160 F and be fully open at 185 F. if you measured 170 on the thermostat housing, that sounds fine. A measurement on a rubber hose will not be accurate for the internal temperature since rubber is a much better insulator than iron/steel/aluminum.