Thermostat Preventative/Proactive Replacement

[wormwood1978]

2008 4.2 TB, 118k.

Weather has been in the teens and 20s, local drive and the check engine light came on, P0128 and temp gauge not working, have good heat. Next day, light still on, good heat. Torque apps says has my engine temp 160-181. I reset the light, good heat, temp gauge in the middle, torque app saying temp is 180.

I understand how the thermostat works, stuck open, stuck closed and so on.

Tstat replaced in 2019 at 84k, 2015 at 54k. My maintenance notes say in 2015 before I had the tstat replace, the shop said my tstat was stuck open and torque app said I had a temp of 160-170.

I'm thinking I should do the tstat again rather than wait for the idiot light to come back. Any thoughts?

 

[mrrsm]

As long as long as you have a nice dry place to work and not during a driving Blizzard. These are your choices for the replacement of the Thermostat (Stant or ACDelco) if YOU are doing this R&R. The system comes as a Unit... not with a separate Thermostat "Drop-In" Item:



Oh... And One Last Suggestion... Take heed that unless you want to risk the often Knuckle-Busting, Blood-Letting Experience of trying to LOOSEN & CONTROL the STRONG GM OEM Factory Coolant Hose Spring Clamps with just a pair of Pliers ...or some Channel-locks... Getting and Using THIS Tool will put a Smile on your Face in the Dead of Winter Cold while under the Engine Hood and doing this Thankless Task... and Saving Your Hands and Fingers, To BOOT:

Amazon.com

Here is a a decent Step By Step Video for this otherwise complicated, Non-Trivial R&R:

 

[wormwood1978]

As long as long as you have a nice dry place to work and not during a driving Blizzard. These are your choices for the replacement of the Thermostat (Stant or ACDelco) if YOU are doing this R&R. The system comes as a Unit... not with a separate Thermostat "Drop-In" Item:

View attachment 111288View attachment 111289View attachment 111290View attachment 111291View attachment 111292View attachment 111293View attachment 111294View attachment 111295View attachment 111296View attachment 111297View attachment 111298View attachment 111299

Oh... And One Last Suggestion... Take heed that unless you want to risk the often Knuckle-Busting, Blood-Letting Experience of trying to LOOSEN & CONTROL the STRONG GM OEM Factory Coolant Hose Spring Clamps with just a pair of Pliers ...or some Channel-locks... Getting and Using THIS Tool will put a Smile on your Face in the Dead of Winter Cold while under the Engine Hood and doing this Thankless Task... and Saving Your Hands and Fingers, To BOOT:

View attachment 111300View attachment 111301

Amazon.com

Here is a a decent Step By Step Video:

thank you!

 

[wormwood1978]

Problem has not occurred again. I'm thinking I will replace the tstat this summer though.

 

[budwich]

Problem has not occurred again. I'm thinking I will replace the tstat this summer though.

I think you might be looking in the wrong place (ie. thermostat). If your temperature gage wasn't working then its more likely a problem than the thermostat. The system has no way of "talking" to the thermostat and even if it could, I am not sure what it would say... "yes I am open", or "yes, I am closed". Having said that, I am not sure from your first post that torque provided a reading while your gage did not... or that torque just provide you with a "digital update" and your gage was now "working". IF your gage was not working but torque was then it is a gage problem / IP problem. However, IF it is an "accuracy" problem (ie. poor sensor) then replacing your thermostat will likely not solve the issue.

 

[mrrsm]

The ECT in any Modern Automotive System is completely independent of the Thermodynamics governing whether or not the “Center Button” Opens or Closes inside of the Thermostat (1) mounted in the Engine Head, based upon the rise and fall of the Coolant Temperature. There are different types of Sensors that rely upon different principles of operation than the Mechanism inside of a Thermostat.

BOTH of these Devices become completely irrelevant if the Coolant Level either Fails to KEEP FLOWING or if the Coolant Fails to remain in direct contact with BOTH devices while they acting independent of each other… but for different reasons and using different methods of action for what makes them BOTH operate in relation to Changes in Temperature.

The ECT Sensor (2) is located on the Passenger Rear Side of the engine on a 06-09 Trailblazer with the 4.2L Engine. First, locate the Passenger Side Rear Valve Cover Bolt and look directly below it to find the position of the ECT Sensor. The 02-05 Trailblazer 4.2L Motors have the ECT Sensor situated on the Front, Driver’s Side of the Engine Head, just behind the Alternator and above the Thermostat/ Housing.

An Automotive Thermostat would have very little use of function if its operations were dependent upon the behavior of ANY Fluid Temperature Sensing Device in any way. But if the ECT Sensor ever goes sideways… it is of a trivial consequence, since its only purpose is to REPORT the changing Thermal Conditions of the Cooling System.

A better Warning System comes from a Coolant Level Senor (3) tripping a Dashboard Warning Light and the Message “Low Coolant” as a preemptive Fail Safe that there is a Dramatic Loss of Coolant that deserves an immediate investigation. And thus, the Coolant Temperature Gauge (4) of the Dashboard ends up as being "The Fourth Leg" in this group of inter-related components that might need to be Replaced if suspect or at the very least... Inspected and Tested using a Tech 2 to perform an Instrument Cluster Panel Dial Sweep.

 

[budwich]

there are resistance tests that then can be correlated to temp to determine IF the sensor is functioning "closely" to the "curve". Basically, get the engine up to temperature, somewhere after a good run cycle. Then measure. The other check is one of "physical squeeze" on the hoses from a "cold start" to see if there is pressure in both hoses which would likely indicate a stuck open thermostat. On a "cold start" there should be a significant difference due to a close thermostat (normal state).

 

[Mooseman]

In each of the times the tstat was replaced, was the sensor ever replaced? On 02-05, we suggest replacing it at the same time as the tstat because it is a fair failure rate and it's right next to it so easy to do at the same time. On 06-09, it's located on the head so on those it's recommended to replace only when failing. It's not expensive so I would recommend replacing it in any case just to eliminate that possibility. Original GM sensor seems to still be available.

FOr the tstat, I have found that the Mahle/Clevite is the same as ACDelco at half the price on RA. I had tried an aftermarket at one time and found that the temp was slightly lower than the ACDelco. I currently have the Mahle/Clevite and temp is always straight up on the IP gauge. With the aftermarket, it was slightly below.

 

[wormwood1978]

Sensor was not replaced when the tsta was replaced. I will definitely keep the Mahle tstat in mind when the time arises. thanks

 

[Chickenhawk]

If the 180-degrees is correct and the temp sensor is working, it is too low. If you look at the temp gauge, the thing to remember is that it is not a linear readout. One slight tick to the left of center is a big drop and the thermostat should be replaced. It should always read one tick to the right of center, and actual temps should be 190 or over. Any cooler and it dumps raw fuel into the cat converter and that can shorten its life dramatically.

The way I would tell which needs replacing is, if the temp drop is long term and it has been a slight bit to the left of center for a while, it is a thermostat. (Also, the most common cause.) If the temp gauge has been a bit to the right of center but the temp gauge rises and falls, especially on the highway, it is a temp sensor.

 

[mrrsm]

 

[Realism]

2008 4.2 TB, 118k.

Weather has been in the teens and 20s, local drive and the check engine light came on, P0128 and temp gauge not working, have good heat. Next day, light still on, good heat. Torque apps says has my engine temp 160-181. I reset the light, good heat, temp gauge in the middle, torque app saying temp is 180.

I understand how the thermostat works, stuck open, stuck closed and so on.

Tstat replaced in 2019 at 84k, 2015 at 54k. My maintenance notes say in 2015 before I had the tstat replace, the shop said my tstat was stuck open and torque app said I had a temp of 160-170.

I'm thinking I should do the tstat again rather than wait for the idiot light to come back. Any thoughts?

Timeline sounds about right. Usually only get about 30-40k on a tstat.
Dont forget you can come in through the wheel well for an easy replacement if you have enough extensions

 

[Mr. Peabody]

I think you might be looking in the wrong place (ie. thermostat). If your temperature gage wasn't working then its more likely a problem than the thermostat. The system has no way of "talking" to the thermostat and even if it could, I am not sure what it would say... "yes I am open", or "yes, I am closed". Having said that, I am not sure from your first post that torque provided a reading while your gage did not... or that torque just provide you with a "digital update" and your gage was now "working". IF your gage was not working but torque was then it is a gage problem / IP problem. However, IF it is an "accuracy" problem (ie. poor sensor) then replacing your thermostat will likely not solve the issue.

I have some experience with this on my 2008 Envoy that may help.

I experience a situation where I would start the car and everything worked perfectly, including the temp gage and the A/C. Then after driving for a short while both the A/C and the temp gage would stop working as if someone flipped a switch.

The next time I started the car everything would work fine and the same pattern would repeat.

I use my Envoy to tow a boat, and I noticed that this phenomenon never occurred while towing.

Long story short - It appears that for some crazy, unfathomable reason, the engineers at GM decided that if the engine temp doesn't rise to the full operating temperature of 200-212 degrees after a predetermined time, the system software is designed to disable the temp gage and A/C.

I'll give you a moment to sit back and say - Huh ???

It makes no sense to me, I would think a check engine light and code would be appropriate, but somebody had a "better" idea.

In my case, when not towing the engine temp would rise to about 180 and not get any higher. When the software detected that the engine wasn't going to get up to the target of 200-212 the temp gage and A/C was disabled.

However, when I was towing my boat the extra load allowed the engine temp to rise above the software threshold and the A/C and temp gage continued to work.

In fact, on some rare occasions the temp gage and A/C were disabled and then as I would climb a hill they would start working again.

When I replaced my thermostat all this nonsense stopped.

So, running at 180 is too low. Your temp gage should be at straight up at12:00 or a little past that after warming up in a "reasonable" amount of time.

I hope this helps you out.

 

[wormwood1978]

And as I write this today, the temp has been around 205-210 as where it should. Weird and things are back to normal.