M25xp Thermostat

[Chuck]

According to my water temp, mine never gets above 140 no matter how hard I run the engine. I plan to test the thermostat in a bucket of hot water. If everything is ok, does it hurt to run cool? Maybe the temp gauge needs calibrating. Any comments appreciated.

 

[Tim Dranttel]

Thermostat

Chuck,I think you are doing the right thing by checking the thermostat first instead of having blind faith in the guage. Most of mine lie. As far as running too cool I've heard that if the oil does not get hot enough the moisture and acids in the oil do not get burned out. I know a gas motor running cool will foul the plugs and valves over time but I don't know if the same holds true for diesels. At 140 degrees you are just barely on the cool side of normal so, if the guage is correct, I don't know that you are running too cool. That is all I know, which ain't much.Tim

 

[Joe Luciano]

Same problem right now

I'm having the same problem right now. Mine normally reads a solid 160 degrees F and the last time out, it only got to 130 degrees F. I was talking with a diesel mechanic today and he advised me of a couple of things. First, it may be a problem with the oil sending unit which sends the temperature to the gauge from the housing where the thermostat is. A replacment sending unit costs about $12, so this is the easy first step. If the gauge still reads low after replacing the sending unit, the other test he indicated was to get a kitchen type candy thermometer and with the engine at operating temperature, measure the actual water temperature and make a comparison to the gauge reading. This will indicate if the temperature is actually too low, or if the gauge is off. A replacement thermostat for the M25XP is about $60, which is expensive for a thermostat. (You need a housing gasket as well). My mechanic indicated that while the thermostat can fail, it is unusual. I'll be investigating mine this weekend. In terms of problems, running too low a temperature can cause fouling, so you want to run at the normal operating temperature of 160 degrees F.

 

[John C. Bollinger]

I have the same thing after repair

My 1983 C30 usally stays about 120, a few weeks ago it went up tp 140( I thought 140 was high, what did I know) , I had a Universal mechanic look at it and we replaced the old water pump with a new Sherman Pump and I also had a newer "bigger" heat exchanger put on it. We also disconnected the hot water heater from the engine coolant hoping that this would help raise the water temp. In addition we put in a brand new thermastat( maybe the old one was sticking open). I also installed all new hoses on the engine, and had it painted. might as well since we were in there.After all this and $$$$, the temp. is now 140 Deg. The mechanic says not to worry???Jack