Idle Overheat?

[Aubrey]

I looked through the stickied links and didnt find anything relating to my problem so i hope u guys dontr mind this question.

My engine was overheating the other day and i chekced to see the problem and it was only my water pump. I changed it with new one and installed a new thermostat at the same. All is well and there is no coolant leaking anywhere now.
The problem is when my truck is running, the engine stays at a cool 100 degrees but when its idling at a light, stop sign, whatever... it starts climbing towards the 125 degree mark and doesnt cool down unless i turn the heat on HIGH or start rolling again?

I havent checked any of the sensors yet light the thermostat, coolant temp. sensor or anything before i know i have to. Anyone have a quick and easy answer as to whjat the problem might be before i jump into it.


Thanks for your time, its appreciated...
p.s. - No error codes came up on the OBDI diagnostic check

[JeepFreak91]

whats that in US degrees

[Boneguru]

similar sitch in a 93 4.0, ended up having burned the sensor, finally replaced it and all was well, worth a check. was overall unhappy with heat management, put on a rocket city cnc oversize thermostat housing and a 180f thermo to get the cooling I wanted (AZ heat)

[Thayer]

Originally Posted by JeepFreak91

whats that in US degrees

Yeah, I was confused too. I'm guessing he's in Celsius, so 100C=212F and 125C=257F. I'd guess the aux fan or mech fan clutch is not working.