Yanmar 4LHA-HTP Marine Engine - Running cool - is too cool a problem?

[OdyRoad]

My Yanmar 4LHA-HTP Marine Engine recently had heat exchangers and engine block waterways cleaned. It now runs at 70 degrees Celsius (158 F), even under load ..... is there potential damage to the engine temperature?
Three new Thermostats have been tried and and each of the thermostats have been bench tested and they meet their specs. Thanks

[OdyRoad]

Is there potential damage to the engine running at this low temperature? Temperature taken with heat gun which matches temp gauge

[GreenWave]

What percent of WOT have you taken it to? Try 80% for five minutes and see what happens, but do this after you have warmed the engine up (meaning run it for at least 20 minutes at lower rpm). I suspect your thermostat should open around 175-180 degrees. Is that what you saw with your bench test?

[skipperpete]

How and where are you reading the temperature? The sender or gauge could be reading incorrectly.

[OdyRoad]

Originally Posted by GreenWave

What percent of WOT have you taken it to? Try 80% for five minutes and see what happens, but do this after you have warmed the engine up (meaning run it for at least 20 minutes at lower rpm). I suspect your thermostat should open around 175-180 degrees. Is that what you saw with your bench test?

Hi - Thermostats (all 3) opened at 71 degrees Celsius (160 F). Ran for 4 hours at at 2200 rpm (with some fouling growth on the bottom), not sure what WOT this was ....

[OdyRoad]

Hi - tested the temperature with a heat gun on the Thermostat - results did match the gauge

[skipperpete]

Just a guess here…. but it sounds like the temp it might run at if the bypass was constantly open, are the thermostats you tested fitted with the disc that covers the bypass when the thermostat opens?…..