1996 C1500 with 5.7 Vortec Running Cold

[TStowell]

Hi I've got a 1996 c1500 with 5.7 Vortec and about a month ago the thermostat got stuck closed and it was overheating and then I replaced the thermostat with a stock 195° Thermostat and now my motor will warm up to the 195-200 then the thermostat will open then it stays at around 155° and no matter what I do I can not get the motor close to operating temp. the weird part is before the original thermostat got stuck I had no problem staying at operating temp. I have rebled the coolant multiple times replaced the thermostat twice and still nothing. it is colder where I am around 30-55F but it's odd even trying to rev the motor higher I still can't get it warm and tips or help is appreciated. Thank You

 

[movietvet]

So, is there a difference in the heater out put? Is it blowing cooler air inside the cab? Where are you getting your temp reading, from the dash gauge? May have damage the temp sender and the gauge is reading lower than what it actually is? Readings with IR temp gun? At the thermostat? What is the temp reading at the in hose and out hose of the heater core?

 

[Sean Buick 76]

I think you have a massive air pocket in the system.

Try this:

Remove the rad cap, start the engine and let it run till the coolant starts to bubble out of the top of the rad. Shut it off, top up the rad and replace the cap. This will burp out any air.

 

[Schurkey]

Compare dash gauge temperature to coolant temp sensor temperature via scan tool. Find out if the dash gauge is anywhere close to accurate.

Air pockets on these trucks are uncommon. Rad cap is higher than the rest of the cooling system, so air naturally rises to the top.

 

[GoToGuy]

Yep what he said ^ . Are you using the dash gauge as your temp indicator? Its more a guide than accurate. Did you take the thermostat and through it a pot of water , heat it up with a check thermometer watch to see when it opens ? Don't assume with parts you can physically check, save time and gas. As said does your heater blow hot? Recheck your installation , you wouldn't be the first.
Start it , run it with cap off, put the thermometer in the neck what temp are you getting. This isn't fuel , no vapor lock, no bubble lock . Even if you had some excess air, once it got hot enough expanded some coolant to coolant tank , it would burp, then when cooling would draw only coolant back into radiator. Top off expansion tank. Need to verify what the actual eng coolant temp is. Your dash gauge may be lagging.

 

[TStowell]

I Finnaly Figured it out i know its simple and i probably should have checked first but my motors temp is fine the temp gauge on the dash is wrong and it gets stuck and 150 on the gauge byr the motor stays at operating temp around 205-215.