Im at wits end here.. lol.. My truck runs cold.. Has since I owned it.. this winter there was very little heat.. I looked around on the forums, and decided the thermostat maybe stuck open or something, and replaced it with the standard 195.. a 195 came out of it.. Still, over cooling.. So I searched some more.. I read somewhere about the fan clutch not working.. So I just finished bustin my knuckles up on that job.. And, its still over cooling! its runs about 150-160 (Take that how you will, its being read from the gauge on the dash, not a technical reading.. I figure its gotta be half correct though.. A bad gauge shouldnt effect my heat being cool... Anyone have any ideas on what ELSE would cause the motor to run cold? Thanks.

 

the bad t-stat was a good first guess. it being stuck open, or opening too soon, is the most common problem of an engine running too cool.

the fan was a bad guess. it could be the cause of overheating (by slipping), but not a cause of over-cooling. it's the t-stat's job to open/close and regulate internal engine temp at 195 or above. its the radiator and fan's job to cool it back down.

the 150-160 on the dash gauge would be about right if you accidentally got a 160* t-stat in it.

so- one or more pieces of your system are not doing what they should.

do you have any way to check the upper hose or radiator temp with a heat gun or thermostat to see if its really 190-ish?

did you check the t-stat in a pot of hot water on the stove to see where it actually opened? you should do this. i think you still have a bad t-stat.

if any test confirms that the engine coolant is actually around 190-ish, then the next step is to replace the temp sensor in the top of the intake, to make the gauge read correctly.

lastly on the heat... the heat in our trucks can really suck, even when the temp is correct. if you haven't backflushed your heater core both ways, you should do that. i cut both my heater hoses out in the middle of the hose, then reinstalled 5/8 plastic connectors with clamps. dorman makes them for very little and it prevents you from breaking the pipes at the heater or water pump and just makes it generally a lot easier.

 

I wouldnt figure both stat's to be wrong, but, I got nothing else! I will do a boil test on it, and no, I havent flushed the core.. I know there is that nasty stop leak in it.. Ill have to flush the radiator before long anyway, so I may as well do as you stated and cut the hoses and flush it to.. I know if it is warm outside, the heat is hot.. but when it got down in the teens, I actually had to get a different ride to take the kids to school.. I can figure out a way to test the actual temp of the coolant.. In fact, I will probably do that first.. Someone had said something about the thermostat in the clutch going out and letting the fan spin all the time.. Im not familiar with the fan operations.. I know electric fans kick on and off, and I dont have one of those.. But, the fan was making some god aweful noises anyway, and needed replacement. Anyway.. I will test the coolant temp, and proceed from there.. Thanks for the help!

 

odds are against it, but either the tstat is bad and opening at too low of a temp, or, the temp sensor is bad and registering low, or the gauge is bad and doesn't register correctly.

by the way, if the pcm sees the engine temp at 160-ish for too long, it should trip CEL code P1281.

you can do a Gauge Test if I can remember how to do it. hold the trip meter in while turning key to on, then release the trip button. it'll do a cluster self test, then sweep all the gauges to about 1/4, then 1/2, then full. not sure what years do this, maybe 98+

 

I forgot about that! My Dakota was an 03 and done the guage test.. Not sure if this will, Ill have to check it! For some reason, Ive had three bad transmission sensors, a bad TPS, and god knows what else and it has NEVER thrown a single code for anything.. I mentioned a bad pcm once, but everyone said thats rarely the case.. So I dunno? I just did a test on my coolant sensor.. Its reading 1300 OHMS at 70 degrees out.. Whats the normal? There was a forum for a car that stated 2200-2700 ohms but I dont know if they are the same per different vehicle. Will the Coolant sensor make the truck run colder, or just send the wrong reading to my gauge? Ill run and do the guage test right now!

 

Just done a Gauge test, all the gauges are working properly, so that's not it.

 

Its reading 1300 OHMS at 70 degrees out.. Whats the normal?
sorry - i don't know. we need hey-you to look this up, he's eats up these tech questions. hey, where are you?

Will the Coolant sensor make the truck run colder, or just send the wrong reading to my gauge?
coolant sensor is just a passive sensor. neither the sensor nor the pcm can actively control the engine temp.

engine temp is a never ending battle between the t-stat trying to keep temp at 195 or above, and the radiator/water pump trying to bring it down.

 

Just to chime in I have read alot were the temp sensors go bad and its not correct.the cts is only for the guage. scan the truck and get the ect temp on a scanner that has a live data connection My truck read around 160 on the guage but the actual temp the ecm was getting was normal 190 ish. Hope this hasnt already been said

 

a heavy coating of scale and sludge can cause the temp sensor to mis-read.

the older models have 2 temp sensors in the intake manifold, one for the pcm and one for the gauge.
the later models, not sure when they started, but including the 00-01 have only one sensor. i'd expect that one sensor to drive the pcm and the gauge to the same result, whether right or wrong.

 

the next low cost moves would be to
interpret the 1300 ohms, there might be a check procedure in the 01 service manual. i have not looked.

temp check the coolant or upper hose with a temp gun.

boil test the t-stat in a pot of water with the wife's cooking thermometer. expected result is that it remains closed up to about 185-190, then cracks open a little, and opens fully at 195.

or blindly replace the temp sensor. iirc they are a bit expensive, seems like $15 or so. i don't want to suggest wasting money.