Yanmar 4JH3-CE not reaching normal operating temperature

[Privilege]

Do I have anything to worry about?

I have twin Yanmar 4JH3-CE's. Both are correctly propped and are cooled via a heat exchanger. Both engines start every time and run without incident, with no abnormal oil or smoke emissions.

One engine runs at normal operating temperature; just under 175 F but the other, older engine never gets above about 125, even when I run it at higher revs. Normally, it hardly even registers on the gauge but once it has been run for a good while it will creep up to 115. I have replaced the thermostat but it made no difference. The high temp. alarm works fine but has never been needed. The raw water coolant pumps overboard without a problem.

I have the new C-type instrument panel and have tested it plugged into the other engine and it works correctly. I am told that I have the correct sender for the new type panel. The engine has been this way since I replaced the panel 50hrs ago and presumably it was the same before then but I did not have a temp gauge so I cannot be certain.

Do I need to be concerned?

Thanks.

[delmarrey]

Originally Posted by Privilege

Do I have anything to worry about?

I have twin Yanmar 4JH3-CE's. Both are correctly propped and are cooled via a heat exchanger. Both engines start every time and run without incident, with no abnormal oil or smoke emissions.

One engine runs at normal operating temperature; just under 175 F but the other, older engine never gets above about 125, even when I run it at higher revs. Normally, it hardly even registers on the gauge but once it has been run for a good while it will creep up to 115. I have replaced the thermostat but it made no difference. The high temp. alarm works fine but has never been needed. The raw water coolant pumps overboard without a problem.

I have the new C-type instrument panel and have tested it plugged into the other engine and it works correctly. I am told that I have the correct sender for the new type panel. The engine has been this way since I replaced the panel 50hrs ago and presumably it was the same before then but I did not have a temp gauge so I cannot be certain.

Do I need to be concerned?

Thanks.

I would check the thermostat on your cold motor. Maybe even replace both of them for GP and keep the hot one as a spare. Fresh water cooled yanmars should run at 180-190º F.

[Privilege]

I had a mechanic check the thermostat on the cold motor and it seems to be working O.K.

[Ex-Calif]

Originally Posted by Privilege

I had a mechanic check the thermostat on the cold motor and it seems to be working O.K.

This falls into the category of a puzzle. Doing the work myself I would be sorely tempted to swap left and right guages then left and right sensors.

Paying someone is different. Did the mechanic have any advice when he declared the sensor ok?

A dumb sounding question but is the fresh water full on the low reading engine? It is possible to have the water level low and the sensor is not actually reading fluid temp but air temp.

Edit - whoops just reread. You plugged the low reading plug into the normal side guage and it read higher or still read low? Didnt quite understand what you wrote.

[Privilege]

I'm certainly no expert, but I believe that the sensor does not sit in the water resevior. Rather, it is on the top of the engine in one of the hoses so that the moving water will pass it. I am guessing, but I would assume that a low tank would not make a difference. However, I will make sure that the water is topped up just so as to tick it off the list.

[janders]

I am definitely not an expert but I would get both engines warm and take readings with an IR thermometer on each engine. We record baseline temps on our engine at each side of the freshwater pump, freshwater inlet and outlet for the heatex and at each of the injectors.

If the differences in temps between the engines are that high, then you should notice a difference in readings.

[Ex-Calif]

Originally Posted by janders

I am definitely not an expert but I would get both engines warm and take readings with an IR thermometer on each engine. We record baseline temps on our engine at each side of the freshwater pump, freshwater inlet and outlet for the heatex and at each of the injectors.

If the differences in temps between the engines are that high, then you should notice a difference in readings.

Good tool to have with a diesel engine.

[sailorboy1]

on mine it was the gauge itself