Thermostat Swap

Tools you will need:
Channel Locks
  • Funnel
  • Catch Pan*
  • A rag or two
  • 10 mm socket
  • 3" extension
  • ratchet
  • Torque Wrench
  • 1 Gallon of Dex Cool Coolant**
  • 1 Gallon of water (preferably Distilled)
  • Expect approximately 20 minute – 60 minute change time 
    * You will need something that holds a gallon of fluid at the least
    **You can choose to reuse your fluid but it is best to put new coolant in the engine.  Dex Cool Coolant GM Part Number 12346290
    Date:  July 4, 2000
    Car:  1999 Z28 Camaro, 13,820 miles
    Installers:  Eric and Kelly Barger
    People who helped us from major tech talk to general advice:
    • eboggs_jkvl)
      Elmer Boggs (
    • Jack (Jack98SS)
    • Eddie (EddieSilver98)
    • mrgto
    • ED B98SS
    • Amarillo
    • Patman
    • badaSS#141
    • Tony (Nine Ball)
    • ZPilot
    • Special K '98 T/A
    • CUJO98TA
    • Blackhawk2000
    When purchasing, viewing, using, and/or any other method applied to this publication you agree to the following statements.  You, your next of kin, heirs or assigns release, all other persons associated in the making, production, participation, and sale of this publication.  Rephrased in plain English:  When you purchase this CD, book, or view this web page you, your next of kin, heirs or assigns agree not to sue any associated persons with the publication for any accident or damage in ANY form (mental or physical to your car and/or yourself) because of this publication or your failure to heed proper safety, maintenance and/or modification procedures.  You also agree that your next of kin, heirs or assigns cannot sue all persons associated in the making, production, participation, and sale of this publication.  
    Perform all these installs at your own risk.  Know how to use all of your shop equipment and take necessary safety precautions when performing ANY modifications and or maintenance items to your vehicle.  Seek the advice of a paid professional and do not substitute this publication for the advice of a paid professional.  This product is how we accomplished our installs and is not meant to be carved in stone.  We are not responsible for a mistake, misprint, or any other error found in this guide.  This guide is intended as a supplement and not to be your only source of information.
    Purpose:  Replacing the stock thermostat with a thermostat that has a lower opening temperature has several advantages.  The cooler your car runs the better for performance at the track; that is the theory at least.  The thermostat cannot completely control the operating temperature but steps in earlier than the stock thermostat to help control it.  
    Preface:  Do this install when the engine is cool.  Otherwise, you WILL burn yourself.  Be sure you are performing this thermostat swap on a cool car.  Before you start this install be sure you know how to use all of your shop equipment.  Take your time and be careful.
    1.  Read this whole step before proceeding any further.
    Locate and turn the radiator cap counterclockwise slowly (See Figure 1).  This should relieve any unwanted pressure from the radiator.  If you hear a hissing or spurting sound, STOP!  Wait until the pressure relieves itself before opening the cap all the way.  Once the pressure is relieved, place the cap back on (no need to tighten the cap) to make sure you keep any contaminants out of the radiator.
    Figure 1
    2.  We parked our car on level ground (did not use ramps or jack stands).  Locate the radiator drain plug (see Figure 2).  This view is underneath the front of the car looking toward the driver's side.
    Figure 2
    3.  Now is a good time to place the catch pain directly underneath the drain cock.  Turn the drain cock valve counterclockwise until coolant begins to pour out of the valve that is turned down toward the ground (see Figure 3).  Be careful not to unscrew the drain cock valve all the way.  You will get a BIG surprise when coolant flows out that end three times as fast.
    Figure 3
    4.  We drained all the coolant out of the radiator.  When the coolant stops flowing, tighten the radiator drain cock to 13 in-lb.  Look at Figure 4 to see how much coolant drained out of the radiator.
    Figure 4
    5.  Locate the thermostat  and thermostat hose clamp (see Figure 5). Push your catch pan underneath the thermostat.  Go ahead and push the plastic push screw back out of the thermostat housing.
    Figure 5
    6.  We then removed both 10 mm screws out of the thermostat.  We used a 3" extension on our ratchet and socket combo.  You can see the extension and screws in Figure 6.
    Figure 6
    7.  Use a pair of pliers (channel locks, etc.) and squeeze the hose clamp together (see Figure 7).  Then pull the hose off the thermostat by simply twisting the thermostat inside the hose.  We found this to be the easiest way to remove the thermostat from the hose.  When you get the thermostat off you will have a large amount of fluid drain immediately.  We found the amount to be approximately the same amount we drained out of the radiator.
    Figure 7
    8.  Take a rag and try to clean up around the opening in the block where you pulled the thermostat out.
    9.  You will notice that your o-ring will be free and not in the groove of your new thermostat.  You will need to make it stick in the groove to ensure that you seal the thermostat to the block properly.  The way we accomplished this was to place some high temperature silicone gasket maker in the groove where the rubber o-ring goes See Figure 8).  We placed the RTV silicone gasket maker in several spots around the groove.  Then place the rubber o-ring in the groove.  Wipe clean and you are ready to install the thermostat.
    Figure 8
    10.  Carefully place the new thermostat back onto the block and get your two 10 mm screws started in their holes.  Once again, check to make sure your o-ring is still sealed properly in the groove.  Use a torque wrench to tighten both 10 mm screws to 89 in-lb (7.42 ft-lb) (See Figure 9).  
    Figure 9
    11.  Use a pair of pliers (channel locks, etc.) and squeeze the hose clamp together.  Place the rubber hose back on the thermostat.  Replace the plastic push screw back in the thermostat housing (see Figure 10).
    Figure 10 
    12.  Remove the wire harnesses from the intake air temperature sensor on the air box lid, the mass-air-flow sensor and the two throttle body sensors (see Figure 11).  Moving these wires out of the way makes it a lot easier to perform the next step.
    Figure 11
    13.  Locate the rubber hose that exits the throttle on the driver's side.  Squeeze the hose clamp on the rubber hose and remove the hose from the metal line (see Figure 12).  Removing the hose can be quite difficult.  We used a flat-head screwdriver and gently pried the hose back.  Once the hose moved a little the hose came off with ease.
    Removing this hose will allow us to remove the air from the cooling system quickly and easily.  This is MUCH better than the conventional way everyone removes air from the coolant system.  This works on the foundation that the rubber hose is the highest point in the cooling system.  When you add coolant you will force the air up and out of the engine block that would otherwise be left.  Removing all the air from the cooling system is CRUCIAL for aluminum blocks. 
    We want to thank Elmer Boggs (eboggs_jkvl) for telling us about this excellent method!
    Figure 12
    14.  You need to make a 50/50 mixture of Dex Cool coolant and distilled water (we used water out of the sink).  We picked up a plastic pitcher from the Dollar Store and poured two (2) quarts in the pitcher.  Then we filled the pitcher up to the four (4) quart mark using Dex Cool coolant.  That is your 50/50 mixture, two quarts of Dex Cool coolant to two quarts of water (See Figure 13).
    Figure 13
    15.  Read this whole step before proceeding any further.
    Remove your radiator cap and place a funnel in the radiator.  Begin to pour your radiator fluid down the funnel slowly (see Figure 14)While you pour the 50/50 mixture down into the radiator keep an eye on the rubber hose you disconnected that exits the throttle body.  You will actually be able to hear air escaping out of the hose.  When you see coolant exit out of the hose you know you have removed most of the air out of the coolant system (see Figure 15).  You must pour slowly or coolant will come out of the rubber hose prematurely and you will reconnect the hose too early.  
    It took is about 4 quarts for fluid to come out of the rubber hose when a drop of coolant was added to the radiator.  When this scenario happens reconnect the rubber hose (see Figure 16)Then continue to pour the fluid into the radiator filling it up to the top where it was when you first started this install.
    Figure 14
    Figure 15
    Figure 16
    16.  Reconnect your wire harnesses to the appropriate sensors (see Figure 17).
    Figure 17
    17.  Read this whole step before proceeding any further.
    Start your car with the radiator cap off and let it reach 190 °F or greater.  Watch the coolant level in the radiator.  It will rise and fall with the opening of the thermostat.  It is perfectly fine to add coolant at this time.  When you shut the car off you want the level to be at the top where it was when you started.  Do not forget to replace the radiator cap when you are finished.
    18.  In order to take full advantage of the thermostat you will need to reprogram your PCM so the cooling fans come on at a cooler temperature.  We set our cooling fans to activate at 160 °F using our Hypertech Power Programmer Three.  
    19.  That does it; you are done!  
    You might notice a high pitch squeal when you turn your air conditioner on.  Don't worry about this.  That is caused by spilling coolant on your air conditioner belt.  Our sound went away after about 2 hours of drying.  No big deal.
    You might want to take it easy on the car for a few miles (three full warm-up and cool down cycles) before you go laying rubber around town or at the nearest track.  This is a safety precaution in the unlikely event that all the air was not removed from the cooling system.  Keep an eye on the temperature and also check the thermostat to make sure there is no coolant leaking around the edges.
    We took the remaining 50/50 mixture and poured it back into the Dex Cool container to save it for a later date.
    Comments:  We have noticed that our car runs a hair cooler according to our crappy temperature gauge.  Yes, your temperature gauge in your dash should not be relied on for an accurate measurement of your engine's temperature.  We have documented using the Auto Tap scan tool that 185 °F through 225 °F reads approximately 210 °F on the dash.  Wow, such accuracy (great sarcasm).  1998 F-Body's seem to have a better sending unit that makes them more accurate than the 1999 or later models.  However, you should still use a scan tool to get the "correct" temperature of the engine coolant.  
    Using Auto Tap, we have documented that our car runs right at 183 °F cruising down the interstate with the air conditioner on.  The car averages around 194 °F in stop-and-go city traffic.  These Auto Tap logs were taken on a sunny 90 °F day.
    This is a definite improvement over the factory thermostat.  Our car would reach 230 °F in stop-and-go traffic and never see the underside of 200 °F on the interstate.