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  1. #1

    Question Truck Overheats & Heater doesn't heat up & AC doesn't get very cold

    First quickly, I'm not a mechanical idiot, I had a 2005 GTO that I did alot of engine mods and mostly by myself... And it's nice to have a truck now, but I'm having a few issues.

    Alright guys, so I'm basiclly having three problems...

    Firstly my truck doesn't totally overheat (to the point of steam/engine problems) but the thermostat in the truck gets up to around 250 degrees and a warning comes on the dash that engine temperature is high... It only does this for short periods of time, usually at slow speeds, then goes away... (I'm guessing radiator or thermostat)

    Secondly my heater heats up very slowly, and takes a while to get up to temperature (guessing thermo).

    Thirdly my AC doesn't get very cold, it works, but not well...

    So what do you guys think? It's a 2004 Silverado Z71 w/ 55000 miles. If I just get my thermo replaced should that fix the problem or am I looking at something bigger? Any recommendations on tests to do or how to go about figuring this problem out?

    Thanks y'all.


  2. #2


    I would check for air in the cooling system first. Also make sure the fan is working correctly as the fan makes the coolant and A/C both cooler by pulling air through the radiator and condenser.

    2004 SILVERADO 2500HD LS
    Pro Comp Leveling Kit
    285-75-16 Cooper ST All Terrains
    Pro Comp Programmer
    Bilstein Shocks
    Linux Bed Liner
    Tinted Windows

    Other rides:

    1967 Landcruiser <350 Chevy>
    1970 Camaro
    1990 Geo Metro Convertible
    2007 FJ Cruiser

  3. #3

  4. #4


    Its 5 yrs old might as well go and spend 8 bucks and get a 195 thermostat.

  5. #5

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    I would also do a power flush of the entire system, maybe something is plugged
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  6. #6

    dwill3015's Avatar
    Join Date
    Jan 2007
    Yacolt, Washington
    Blog Entries


    Plugged heater core perhaps? My son has the same probs on his Ranger and his core is plugged.
    Washington State
    2006 Silverado 2500HD LT3 4X4 CC SB Duramax LBZ
    Tuff Country 6" lift, 35" Toyo M/T's on 20" Ultra Peacemaker wheels, Quadzilla Stealth2 programmer, Diamond Eye 5" cat-back exhaust, factory Special order color Yellow.

  7. #7


    you might also see if your fan clutch is working properly if you turn the fan by hand when the motors off and theres no resistance then its needing replacement if its really bad then you can hold the fan still when the motors running dont try this if your not shure it will cut yours hands up pretty bad

  8. #8

    Join Date
    Aug 2008
    East of Branson, Missouri
    Blog Entries


    I'm going to go for clogged/plugged heater core as well.

    "The Sarge"
    1999 Chevy Suburban LT- K2500
    7.4 454 Vortec, 4WD
    305/70/16 on Eagle Alloy

  9. #9


    See the thing is that makes me a little lost is that when it overheats, it corrects itself rather quickly. I could be driving at 45 mph, the temp will go really high for about 30-60 seconds, then drop back down to where it should be or maybe a little high on the gauge. If you guys think a flush will help, I'll get it done. Don't have the equipment anywhere close to me to do it myself sadly... I'm also going to get my thermo replaced just in case.

  10. #10

    Join Date
    Aug 2008
    East of Branson, Missouri
    Blog Entries


    Clogged core doesn't take much - just a garden hose, really. Look for the two hoses on the fire wall and (with them NOT hot, of course!) take them off and almost gently shoot some water from the hose through them. If you get junk coming out then you're doing good. If water hardly passes then you might have to think about a new heater core - it might be too tightly packed with junk.

    I've a link somewhere I'll PM you if I find. It might be helpful for you.

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