Tempature issue with 04 Sierra

04_Sierra_boy · January 17, 2012

Ok well I'm new to the forum so I want to first say, hi my name is Nick and I'm glad I found a good forum! I have 2 GMC turck's. Both 04's one HD2500 and one Sierra. The problem I'm having is with the Sierra, it has the 4.8 and is 4wd. I replaced the thermostat about 2 weeks ago and ever since my temp gauge goes crazy. I live in Maine and its cold..real cold. So normal day with the truck now is I go out start it and leave after about 2 mins of solid warm up time. After about 3 mins of driving the temp guage is 3/4 of the way to hot but I know the engine isn't warm enough yet to be that high. Right after the gauge creeps over the 3/4's mark the heat will be warm and it seems as though if I am giving the truck gas it will stay warm but as soon as I slow down the engine the heat goes cold. Also after the heat gets to the 3/4's mark and is warm if I shut the heat off the temp gauge goes to 210 which is normal or where it has been since day one. I didn't bleed the system of air when I changed the thermostat but from what I saw on this forum you dont have to? When changing the themorstat the housing broke so I had to go to the dealer and get a new housing which was deffrent then the original housing it also came with the thermostat and bolted up fine and doesnt leak. I don't think I got the wrong thermostat from the dealer. Maybe the thermostat is bad or there's air in the sytem or the water pump is shot. I don't know what to do..I dont feel like removing the thermostat again if i dont have too. Any advise would be helpful and much appreciated. Thanks! I'm uploading some pics now of the old girls.

jdnoble18 · January 17, 2012

Is your coolant level low? Any wet spots on the ground/snow u park on? Sounds like you either have low coolant which would be bad water pump diaphram or air in the system.

04_Sierra_boy · January 17, 2012

The antifreeze level seems to be fine. I really think it's air in the system. What my next question would be is where are the bleeders located if any? Also if I have to bleed it I just jack up the front of the truck and take the radiator cap off and let the truck idle until it opens the thermostat and the air should come out right? Thanks for the quick reply. I'm going out of my head trying to figure this out, it's my wifes truck and I just dont want her to break down or start warping blocks due to heat ect...but at the same time I refuse to take it to a dealer they have caused me enough issues. I'm pretty mechanically inclined, I have a 92 3000gt VR4 TT that I do all the services on ect...

jdnoble18 · January 17, 2012

Yeah your idea of bleeding it should work AFAIK. I haven't done this on my truck so I don't know forsure. You might be able to get away with just opening the coolant tank lid (don't have to jack it up) since I think it is pressurized, and higher than the radiator, on those models.

Once you think you have all of the air out, you should keep a close eye on the coolant level for a few days to make sure you arent losing more.