I currently have a 98 Chevy k1500... It's not going above 150°F and I get horrible fuel mileage from that, and no heat. It has a brand new motor, radiator, water pump, heater core, all cooling hoses, temp gauge, temp sensors, radiator cap, and I've tried 6 different thermostats many different mixes of coolant, the fan clutch is good. I've tried blocking off the front grill to keep the air out and that didn't help, so I removed the fan and the temp still stayed in the 150°f range. I manually tested the temp of the motor with 4 different temperature guns, and probes, and I get the same reading with all of them that matches the gauge.

 

I am as stumped about this as you are. Usually, the engine overheats. That heat has to be going somewhere, but I don't have a clue as to where it's going. You are correct about the 150 F temp being way too low.

 

curious but have you ran the temp gun on the exhaust manifolds to see what their temps are? your cel isnt on? im with oil can im stumped also, i mean even with diesels if you block the rad 75% i will get a little warmer and 100% should run really warm. the only thing i can think of is if maybe not all cylinders are firing or too much fuel causing the engine to run rich but ive never see it make an engine run that cold

 

Have you put a scanner on it? I'd be curious to know if the computer is showing the same temp as the dash gauge.

 

Ya I have put a scanner on it, it all reads exactly as the dash does, pretty close to the reading I took on a temp gun

 

The only thing I can think of is that somehow, the coolant is bypassing all the thermostats you used CR2003, but how that could or why that would occur is a mystery to me.

 

when did it start doing this? im not sure about these trucks but i know some are possible to install the thermostat upside down. and did you install a failsafe thermostat?

 

It's been doing this for a few months now, and it's right side up. I'm not sure if it is a failsafe thermostat, but I get how that could be the problem if it does have one

 

did it start this before or after you started working on it? if it was after then what was it doing before?

 

Ever since I bought it I've had issues with getting heat in it. It started not getting to temp a little while after replacing the heater core