Engine not reaching operating temperature

[Chiller449]

I have a problem with my 2004 Chevy Tahoe. Long story short I take frequent trips pulling my boat to go fishing. I noticed on the longer trips with lots of hills the engine temp would start to creep past the safe zone. I pulled the radiator and bought a big aluminum 3 core radiator. I also replaced the water pump, fan clutch, and thermostat. The truck ran great after that. Never had an over heating problem. The one day I noticed the heat gauge wouldn't get past 165 or so. I figured the new stat I put in must have failed. so I put a new one in and nothing. still wont warm up. i'm on my 4th stat now from 3 different places and it still refuses to warm up. I now get a trouble code stating my engine coolant is too cold. I was thinking maybe the big radiator and the cold weather is not letting the engine warm up? I'm not sure. If I drive the truck for a while and then pop the hood and look at my coolant reservoir I can see coolant rushing out of the return line from the engine. Almost like the thermostat is open. Is it somehow leaking past the thermostat or am I just so unlucky I keep getting bum stats over and over again.

 

[bottomline2000]

i have a question on how your hoses are routed. Can you take a pic of the hoses running from water pump to the surge tank? I never see fluid moving in my surge tank while the engine is running. The level will fluctuate from cold to hot, but i don't see any actual flow.

Also, does your lower radiator hose get warm as soon as you start the engine?

Last, have you plugged up a tech tool to confirm the temp gauge is reading correctly? Those stepper motors can go bad over time.

 

[iamdub]

Last, have you plugged up a tech tool to confirm the temp gauge is reading correctly? Those stepper motors can go bad over time.

But he's getting a trouble code for coolant temp too low. This is from the PCM, which gets it's readings from the coolant temp sensor.

I'd test the sensor and maybe stick a thermometer in the coolant to confirm if it actually is running too cool.

 

[Danny3737]

Was the the thermostat open or closed when you replaced it? It may sound too simple, but I’ve seen many that were installed upside down. What temp thermostat are you using

 

[swathdiver]

...am I just so unlucky I keep getting bum stats over and over again.

Might be, what brand do you keep buying?

 

[Chiller449]

i have a question on how your hoses are routed. Can you take a pic of the hoses running from water pump to the surge tank? I never see fluid moving in my surge tank while the engine is running. The level will fluctuate from cold to hot, but i don't see any actual flow.

Also, does your lower radiator hose get warm as soon as you start the engine?

Last, have you plugged up a tech tool to confirm the temp gauge is reading correctly? Those stepper motors can go bad over time.

Unfortunately my camera is busted on my phone but ill try to explain how my hoses are ran. From the top of the pump (outlet) runs to top drivers side of radiator. Top passenger side of the radiator goes to top of surge tank (not the overflow on surge tank) Bottom of surge tank goes to an inlet on the water pump behind the thermostat. Bottom passenger side of radiator goes to thermostat housing. What I believe is happening is the pump is pushing coolant into the radiator, the thermostat is closed so it runs into the surge tank and comes out the bottom hose which runs right back into the engine because that hose goes behind the thermostat. I plugged that top hose coming off the surge tank and now the truck heats up just fine. My temp gauge stays at one line before 210 and I have excellent heat now. My check engine light also went away. Obviously this is not the correct fix and just a band-aid. Any ideas?

 

[Chiller449]

But he's getting a trouble code for coolant temp too low. This is from the PCM, which gets it's readings from the coolant temp sensor.

I'd test the sensor and maybe stick a thermometer in the coolant to confirm if it actually is running too cool.

I know its running cold because my heat is very poor and i can hold all of my coolant hoses and they are luke warm.

 

[Doubeleive]

Was the the thermostat open or closed when you replaced it? It may sound too simple, but I’ve seen many that were installed upside down. What temp thermostat are you using

I don't think you can get the thermostat in upside down on these trucks but maybe

 

[Chiller449]

I guess my question is how is the engine supposed to heat up if it has coolant constantly running through it? My only guess is that if your using the stock radiator it will warm up like its supposed to even with coolant running through it because its a smaller hose and not a ton of coolant is running through it? I dont see how you could stop the flow other than plugging that top hose like I did. Maybe my big radiator is working too good and not letting the coolant warm up like it should. Im guessing this is some sort of overheating safety feature incase the thermostat gets stuck closed.

 

[Chiller449]

Sorry for so many posts but i keep remembering stuff, I read somewhere that if you put a new water pump on but use the old thermostat housing they wont match properly and wont hold the thermostat correctly. this lets coolant flow past as if the thermostat was stuck open. Could this be my problem? It still doesn't make sense why I get constant coolant flow through the surge tank though.