Engine/Transmission (1994 - 1998) temp gauge problem?

[WDixon27]

i thought i was having a cooling system problem till i finally got to shoot it with a temp gun this morning, and the thermostat housing was only 185-190 with the ac on and fresh off the road unloaded and the lower hose was in the 120s, but the gauge is probably 220-230 (even after idling 5 minutes while tempgunning it) it's always run at 200 when up to temp which i thought was a bit high but it was stable, it's started this reading high stuff in about the last week with the arrival of near 100* afternoon temps, anybody have any ideas? common gauge problem? i am leaving on a 2300 mile round trip to va pulling a single car trailer thursday and would love to know if my motor is melting, when i thought it was actually getting hot i pulled the fairly new cummins thermostat and put in a motorad and if anything it got a tad higher and started the gauge swinging again. i unfortunately won't have time to search the board for answers till late this evening

 

[Howard Durand]

I would guess that the first thing to check would be the temperature sensor. If you can't find it, it is located at the upper rear corner of the engine block on the driver's side. First of all, make sure the connection is tight.



You can check it in the engine with an ohm meter.

With the engine completely cold, if the ambient temperature is 75 degrees, the sensor should read between 9200 and 11,000 ohms. At 100 degrees, it should be between 5000 and 6000 ohms.

The most accurate test would be to remove it and put the end in a pan of boiling water, (212 degrees). It's resistance should fall between 640 and 720 ohms.



If you can't do the tests, I would try a new sensor.

 

[WDixon27]

i have a new sender coming from dodge tomorrow and we shall see what it does, i didn't feel like pulling it out and screwing with it as it's in such a wonderful dark little hole and figured it's got 310k miles on it, it's due, i am just happy i don't gotta shell out $238 for a new radiator

 

[Howard Durand]

It could still be something else. If the new sensor doesn't solve the problem, I would have the engine and radiator flushed out.

Even though the temp gun is giving good readings, there may be some blockage preventing a good flow through the motor and around the sensor.

Try to get some fluid out of the block when you remove the sensor.

 

[WDixon27]

when i did the head gasket a month or so ago i cleaned to the fur off of the sensor and out of the head, plus i blew about a pound of crap out of the fins of the radiator, it looks fairly clean inside and doesn't seem to have any cold spots on it like they get when they clog/collapse, i am reasonably sure it's running a normal temp, i checked it again after a hard run home from the shop with the ac on and ambient temps running in the high 90s and it looked good



i had to do the gasket due to a crack in the gasket at the front corner in the usual spot, no milkshake involved