Hi,Since i bought my denali 4 years ago my temp gauge showing about 212F the needle always at the mid of the gauge summer , winter cruising at high ways or even if the car a stop point but now a days i noticed that at high way the temp decreases but what got more worse that the temp needle will go to almost 0 while i am driving in dashboard i am getting Engine Hot / AC Off no engine code ,i stop the car open the hood and check the radiator hose i found not too hot it is warm i can keep my hand on it ,i noticed this porblem starts after i changed the lifters ,and intake valves i had done some searches on google and found some GM owners got similar problem they were talking about water pumps and t.state so what do you guys think what to start with ?

 

Could be the thermostat, or water pump assembly, hard to tell without seeing scan tool data, does the message come on right away when you start the truck up?

 

This happened to me when I experimented with drillling bypass holes in my thermostat, to try to get the truck to run cooler. First I bought a 160 dgree thermostat and that only dropped the eng temp down to like 200, so I said screw it and pulled it out and bored a couple of holes in the thermostat. The truck ran cooler then, like 180 degrees or so, but when I would drive for more than 15 mins or so, the ECU would shut the A/C off and the temp gauge would drop to 0 and it would display "Engine Hot/AC Off". I bought another 160 degree thermostat and the SOB is still running 200 degrees to 215 in traffic. Its like the ECU is programmed to think that there is something wrong (like a coolant leak) if the Eng temp doesn't run close to the range it is supposed to from the factory, and shuts off the AC and throws this code. I'll bet its the thermostat.

 

I noticed that engine is taking more time to warm than before ,i will buy a new thermostat and what happen .thanks guys for the info

 

Be sure to get all of the air pockets out when you replace that thermostat...since you mentioned that it happened right after you had the heads off, it almost makes me think that an air pocket could be the problem...unless a chunk of debris got knocked loose and is stuck in the t-stat...

 

How do you release this air is there any nipple to get this air out or i can release it from the coolent cap ?

 

I do it by "burping" the system. Fill through the reservoir while squeezing the upper hose and pulling it down toward the ground. While holding it down you should feel and hear air working it's way through the system and into the overflow. Keep repeating until you no longer feel and hear the the bubbles.

 

Problem solved ,when i open there was no thermostat i think the guy who change the lifters and intake valves forgot to install it .that why the engine took long time to warm .