2001 chevy s10 2.2 will not reach normal operating temp. First noticed when defroster was blowing cold. Replaced thermostat with Stant superstat with no change whatsoever. Coolant level is normal. Out of ideas, please help.

  • 1
    What does the temp gauge show?
    – Moab
    Apr 7, 2018 at 21:06
  • Welcome to Motor Vehicle Maintenance & Repair! Apr 7, 2018 at 22:59

3 Answers 3


First Check the heater valve is working and opening to allow the hot coolant through.

Second check to see if the heater matrix (a small radiator) is blocked.

Either of these could be the cause or even a blocked pipe. It could also be a failing or failed water pump, but it should have shown signs of overheating...

I have assumed that the new thermostst is functioning correctly - perhaps testing it would be a good idea...

  • the temperature gauge indicates midway between 100 and 210, approximately 160F. I am considering having the radiator shop flush out the dexcool and replacing it with the green stuff. I did not test the new stat.
    – balatro
    Apr 8, 2018 at 0:47
  • What is the temperature specifications of the new thermostat? If too low, the whole cooling system may be held at a too-low temperature. Oct 11, 2019 at 14:38
  • @David “what are...”
    – Solar Mike
    Oct 11, 2019 at 15:52
  • @SolarMike Is my comment unclear? Thermostats (at least in the old days...) used to come in several temperatures. Here, the OP would want to determine that a) the thermo has the right specs, and b) that it's opening at the right temperature, and not at a lower temperature than expected. Oct 11, 2019 at 16:14
  • @David what are the temperature specifications or what is the temperature specification... usually a range though and they are not very precise in my experience. Best electric fan control I ever had was when i used a cylinder stat (from a hot water tank) on the bottom hose...
    – Solar Mike
    Oct 11, 2019 at 16:46

I noticed that you mentioned Dexcool in your comment to solar Mike's answer. There is a known issue with Dexcool turning to a kind of sludge or mud after many years of use in a cooling system. This could easily clogged up something like a radiator core. Just do a Google search for Dexcool sludge or Dexcool mud. You may want to check your cooling system to see if it needs to be flushed here is a good Guide to the subject :


  • Could you quote the relevant parts of that article, in case it goes down, so we have the resource here still too?
    – Cullub
    Jun 14, 2019 at 0:43

Is the fan constantly running? This is the main thought that would account for your issue based on it running fine otherwise. Your thermostat retains the coolant back until the radiator has removed enough heat to match the set temp of the thermostat. I early on thought the Thermostat was purely designed to open the cooling system to the radiator once the engine coolant temp reached 185/ 195/ 205 etc. But when in college my instructor explained the true working of the system. If an engine flowed freely without thermostats on a long drive the engine would run far too cold causing the engine to run less than efficiently. One point here on your car heating system. The heater uses a bypass system to push and circulate the coolant to the heater core inside the car via the aprx. 5/8-inch hoses connected forward of the thermostat and water pump regions. Lack of heat to the heater core may be lack of flow past the heater control valve (closed/ frozen) and no coolant is reaching the heater core inside your car. I have replaced many heater control valves over my career.

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