Thermostat bad?

[MichEnvoyGuy]

I replaced my t-stat in 2006 with an AC-Delco unit. Back then, I had a P0128 DTC that illuminated the SES light. Ive never replaced my ECT because Im one of the masterminds out there who can replace his t-stat without removing the alternator

Recently Ive been on GMTnation pissing and moaning about my once stellar (//sarcasm) mpg's gone to the crapper in my 2002 Envoy. I replaced the O2 sensor, inflated my tires to 36psi, checked everything under the sun. Im still getting 16.5 mpg city OR highway! I used to get 20.5avg on the highway easy. A recent thread on t-stat's here got me to thinkin'....

Today I drove to work with my Equus 3130 scan tool hooked up. Its no Tech II but it does read a slew of live info, including ECT, IAT, MAP, O2's etc.. It was 32f out and I encountered minimal traffic, only having to stop at 2 red lights for 3 minutes tops each. My work is 12 miles from my house taking about 15-20 minutes.

My observation is this: I remote started my truck and by the time I plugged the scanner in, the truck was 130f. It was running less than 5 minutes. By the time I hit the end of my street, the scan tool was registering 165f on the ECT. I started cruising 55mph for a 5-10 mile stretch. ECT read 190f then settled back at 185f and really 185f seemed to be the average temperature while cruising. When I stopped at a red light, the temps would creep up to 195f but after I accelerated, it would settle back down ~185f. For one stretch, I was driving 30mph and the ECT read 187f.

Heres my question: Bad t-stat again or just cold (32f) weather operation?

 

[MichEnvoyGuy]

Regardless, I went and bought a new t-stat and ECT on my lunch hour. Oh, and 2 gallons of Dex 50/50.

I replaced my t-stat in 2006 by loosening the alternator slightly and going through the drivers wheel-well. Took me 1 hour at the most.
But this time Im determined to replace the ECT which means, I think, having to remove the alternator?

Do I have to remove the alternator completely to get to the engine temp sensor?

 

[djthumper]

Well I read your post before I came into work and I wasn't sure what to post. It was 30 when I left the house and hooked up my laptop to monitor the temp, I got up to 203 when I was idling but it was running at 198 while driving. So I would say that the TStat needs replacing.

I do believe you need to remove the alternator to replace the sensor.

 

[MichEnvoyGuy]

Well I read your post before I came into work and I wasn't sure what to post. It was 30 when I left the house and hooked up my laptop to monitor the temp, I got up to 203 when I was idling but it was running at 198 while driving. So I would say that the TStat needs replacing.

I do believe you need to remove the alternator to replace the sensor.

Thanks DJ for posting that!!

Ok, my coolant sensor is original so Im going to try to replace that first and see if I yield any results.

When I drove earlier to pick up the new t-stat and ECT, I had my scan tool hooked up and the temp would vary from 178-198; 178 was when I was driving about 45mph, and 198 was when I was stopped at a traffic light. I read over on the OS an old post where a member had the same issue and replaced the sensor, fixing the problem.

Of course, if a new coolant sensor doesnt solve the temperature variations, Ive already got a new t-stat and if I did it in under an hour last time, Im aiming for 30 minutes this time

 

[djthumper]

No problem, it isn't very often I get to run at a similar temp like that to help check things.

 

[Chickenhawk]

That was probably my thread on the OS. I would put money on the fact it is your coolant temp sensor. Logically, thermostats tend to get sticky when they begin to fail, usually in the open position. They don't suddenly begin to open and close a lot more than normal. Thus, even a failed thermostat would not result in temperature swinging that much.

When you have any coolant temp swings like you do, I would say almost for certain it is the ECT sensor. They are an electrical component that sits in the coolant stream and it is just logical that they need to be replaced upon occasion.

In fact, if you are ambitious and want to take a chance, you can replace only the sensor and not the thermostat this time around. While they are side-by-side and should usually be replaced together, keep in mind you don't need to drain any coolant to get just the sensor out.

I think you will find that your new sensor now shows temps pretty rock solid at 205 or so on your scan tool.

One thing that helps is picking up a dedicated coolant sensor socket. They are not expensive and help getting the new one tightened down a bit.

You can get them at any good auto parts store, Canadian Tire here in Canada or any Nissan dealer.

 

[MichEnvoyGuy]

That was probably my thread on the OS. I would put money on the fact it is your coolant temp sensor. Logically, thermostats tend to get sticky when they begin to fail, usually in the open position. They don't suddenly begin to open and close a lot more than normal. Thus, even a failed thermostat would not result in temperature swinging that much.

When you have any coolant temp swings like you do, I would say almost for certain it is the ECT sensor. They are an electrical component that sits in the coolant stream and it is just logical that they need to be replaced upon occasion.

In fact, if you are ambitious and want to take a chance, you can replace only the sensor and not the thermostat this time around. While they are side-by-side and should usually be replaced together, keep in mind you don't need to drain any coolant to get just the sensor out.

I think you will find that your new sensor now shows temps pretty rock solid at 205 or so on your scan tool.

One thing that helps is picking up a dedicated coolant sensor socket. They are not expensive and help getting the new one tightened down a bit.

You can get them at any good auto parts store, Canadian Tire here in Canada or any Nissan dealer.

Thanks CH!!

Ok so can you give me a few tips on getting to the ECT? I was planning on going through the wheelwell again, like I did with my t-stat years back. Do I have to completely remove the alternator?

 

[ScarabEpic22]

This is a hard one, you've already replaced the tstat but it could be the tstat again OR the CTS (coolant temp sender/sensor). I havent priced a CTS before, how much are they?

Good luck, Ive been really fortunate my 02 hasnt needed a tstat, CTS, or, get this, a fan clutch! Still running the OEM one that was installed when the truck was built in Nov/Dec 01!

Let us know what the result is, wish there was a way to test the CTS before buying a new one...

 

[Wooluf1952]

The CTS runs about $25.

 

[Chickenhawk]

Sadly - in spite of what one person tried to tell to a noob with a similar problem on the OS - there is only one ECT sensor. It feeds both the gauge and the PCM. If it goes bad, you get exactly the same symptoms and results as if the temp was running too low because the thermostat was sticking open. There is no easy way to tell if it's your thermostat and the engine is running too cool, or it's your ECT sensor and the engine only THINKS it is running too cool.

One rule of thumb is simple, especially if you are an aware driver and know the default position of your gauges. If your temp gauge is CONSISTENTLY one or two ticks to the left of center, it is almost 100% certain it is the thermostat, especially if it has been like this for a while.

(I still remember one member on the OS tried to argue with me and told me that ALL GMs run a tick or two to the left, but he is just ignoring the fact his thermostat is gone and needs replacing. Mind you, he shut up when we posted pictures to show the normal position is straight up or down, or a tick to the right. Plus, of course, I own two Trailblazers and they are exactly the same needle position - one tick to the right.)

If the temp seems to waver up or down a bit, especially on the highway, and you can confirm a variation in temps while driving with a scan tool, then it is almost certain to be the ECT sensor. Logically, temps CANNOT physically move up and down that much, especially with a failing thermostat. Failing thermostats become MORE sticky, not more active.

Mine went from 175 to 189 within a matter of a few seconds.

As for changing it, there is no way I would tackle it through the wheel well. I can barely even see close to it through the wheel well, let alone line up wrenches. But keep in mind that if you are changing only the ECT sensor, you may not need to drain any coolant. I didn't drain anything, and only a few drops escaped when i changed mine.

 

[MichEnvoyGuy]

This is a hard one, you've already replaced the tstat but it could be the tstat again OR the CTS (coolant temp sender/sensor). I havent priced a CTS before, how much are they?

Good luck, Ive been really fortunate my 02 hasnt needed a tstat, CTS, or, get this, a fan clutch! Still running the OEM one that was installed when the truck was built in Nov/Dec 01!

Let us know what the result is, wish there was a way to test the CTS before buying a new one...

We must've had a good batch of 2002's with 2001 build codes then b/c Im on my original fan clutch too And before today, original coolant sensor.

I gotta go, going to knock on some wood now....lol!!

 

[MichEnvoyGuy]

Sadly - in spite of what one person tried to tell to a noob with a similar problem on the OS - there is only one ECT sensor. It feeds both the gauge and the PCM. If it goes bad, you get exactly the same symptoms and results as if the temp was running too low because the thermostat was sticking open. There is no easy way to tell if it's your thermostat and the engine is running too cool, or it's your ECT sensor and the engine only THINKS it is running too cool.

One rule of thumb is simple, especially if you are an aware driver and know the default position of your gauges. If your temp gauge is CONSISTENTLY one or two ticks to the left of center, it is almost 100% certain it is the thermostat, especially if it has been like this for a while.

(I still remember one member on the OS tried to argue with me and told me that ALL GMs run a tick or two to the left, but he is just ignoring the fact his thermostat is gone and needs replacing. Mind you, he shut up when we posted pictures to show the normal position is straight up or down, or a tick to the right. Plus, of course, I own two Trailblazers and they are exactly the same needle position - one tick to the right.)

If the temp seems to waver up or down a bit, especially on the highway, and you can confirm a variation in temps while driving with a scan tool, then it is almost certain to be the ECT sensor. Logically, temps CANNOT physically move up and down that much, especially with a failing thermostat. Failing thermostats become MORE sticky, not more active.

Mine went from 175 to 189 within a matter of a few seconds.

As for changing it, there is no way I would tackle it through the wheel well. I can barely even see close to it through the wheel well, let alone line up wrenches. But keep in mind that if you are changing only the ECT sensor, you may not need to drain any coolant. I didn't drain anything, and only a few drops escaped when i changed mine.

My gauge stays in the same spot but my scan tool is reporting fluctuations. When I drive, it goes down to (sometimes) 178f, but then works its way back up to 180f. When Im at a red light, it goes from 185f to 195f. Most of the time though it settles at 185f. I was alarmed when I was cruising at my scan tool said 178f!!! No wonder Im getting crappy mpg's on the highway!

 

[Chickenhawk]

Trust the scan tool over the gauge.

 

[MichEnvoyGuy]

Trust the scan tool over the gauge.

Well I replaced the coolant sensor, that wasnt too bad. Figured, I have the new t-stat I might as well replace it while Ive got everything apart. Put new thermostat in, the lower bolt broke off in the block!! I made another thread about it, so I wont double post...but my god...when can I catch a friggin break around here?!??!

 

[lynch55]

Man, what a bummer! Is it enough of the bolt sticking out to get a pair of vice grips on it? If not you may have a hell of a time trying to use an easy-out. Good luck to you friend!

 

[MichEnvoyGuy]

Man, what a bummer! Is it enough of the bolt sticking out to get a pair of vice grips on it? If not you may have a hell of a time trying to use an easy-out. Good luck to you friend!

Check my other thread I have going. I was able to get it out, a friend came over who has a lot of experiencing in an automotive machine shop. He heated it up with my propane torch, went to town with the vice-grips.

After replacing the original coolant sensor, and replacing the t-stat I put in 5 years ago, Im running 190-195f according to my scan tool - better than the 180-185f I was running before.

 

[The_Roadie]

My gauge stays in the same spot but my scan tool is reporting fluctuations.

That's because the gauge lies, and steadies the needle to not disturb Ma & Pa Kettle with fluctuations that make them nervous. They can't handle the truth.

View attachment 17608

 

[MichEnvoyGuy]

That's because the gauge lies, and steadies the needle to not disturb Ma & Pa Kettle with fluctuations that make them nervous. They can't handle the truth.

View attachment 2250

Well understandable about the gauge being 'dumb', dont like it but it is what it is I guess....

According to the scan tool - no more fluctuations!! It stayed right at 190f during driving. Before it would go from 180-185-178-189, etc... Now the only time the temperature fluctuates is when I stop. Then it inches its way up to 195f.

Of course Ive only driven it once since I replaced the t-stat and ECT tonight, tomorrow Ill be taking the alternator off to tighten the worm clamp and Ill be doing some driving tomorrow to continue monitoring the temperature via scan tool.

 

[Mark20]

I could not find a CTS socket (18 MM) so I used a Crowfoot wrench to tighten. My OEM one came with too much Teflon tape that balled up when tightened and leaked. So check it. 2.5 wraps of Teflon plumbing tape is more than enough.

Also the sensor is closer to the alternator and may even ne hidden by it.

Sent from my Android using Tapatalk.

 

[MichEnvoyGuy]

I could not find a CTS socket (18 MM) so I used a Crowfoot wrench to tighten. My OEM one came with too much Teflon tape that balled up when tightened and leaked. So check it. 2.5 wraps of Teflon plumbing tape is more than enough.

Also the sensor is closer to the alternator and may even ne hidden by it.

Sent from my Android using Tapatalk.

Yes, very good point Mark - you MUST remove the alternator to get to the coolant temperature sensor. I did NOT use the special socket to remove the ECT - I cut the wires, used a regular old deep well 18mm socket. Reinstalling the sensor was a little tricky. I used an open ended 18mm wrench and had to do 1/4 turns then rotate the wrench, do another 1/4 turn, so on and so forth. The original OEM temperature sensor wasnt that tight either. Didnt take any muscle to break it loose.

I just fixed the hose clamp on the t-stat (was dripping) which necessitated removing the friggin alternator again, but I have it down pat and it took 1/2 hour to remove alternator, bracket, and r&r the hose clamp. No more drips!

So went for another test drive with my handheld hooked up, still holding VERY steady at 190f. No more fluctuations. When I stop, it floats up to 195f on the scantool and stays there.

My bet is my t-stat & coolant sensor got lazy and replacing them together, this time around, was a good idea on my part. My coolant sensor was reporting swings and my t-stat was opening too soon. 5 years on the t-stat and 10 years on the coolant sensor isnt so bad I suppose.

 

[lynch55]

Check my other thread I have going. I was able to get it out, a friend came over who has a lot of experiencing in an automotive machine shop. He heated it up with my propane torch, went to town with the vice-grips.

After replacing the original coolant sensor, and replacing the t-stat I put in 5 years ago, Im running 190-195f according to my scan tool - better than the 180-185f I was running before.

Hell yes!! So glad you kicked it's ass! Feels good, don't it?:wootwoot:

 

[MichEnvoyGuy]

Hell yes!! So glad you kicked it's ass! Feels good, don't it?:wootwoot:

:wootwoot:

Does that tell you anything about how I felt?

Im not going to lie, I did panic for a minute yday after that bolt broke - it could've gotten ugly, real ugly. Had that bolt broken off flush with the block, I have NOOO idea how I would've gotten a drill in there to drill it out. For sure, there would be damage to the threads. I dont know how I wouldve tapped it in the case either. There was no room to work. My hands and forearms look like I was in a fight with a pissed off housecat as it is! lol.

Last time I did the t-stat I went through the wheelwell. This time I did it by removing the alternator. Both methods have their pros/cons and I would do either method again. The alternator is no big deal to take off but if I didnt have to replace the coolant sensor, then I would've just went through the wheelwell again. Either way, there isnt anything - no job too big or no job to small - we cant conquer on these trucks!

 

[Guenther]

I have it down pat and it took 1/2 hour to remove alternator, bracket, and r&r the hose clamp

Do you want to give a play by play on how you do it so fast? I've seen a couple other posts on how to but I'd be interested in hearing yours.

 

[MichEnvoyGuy]

Do you want to give a play by play on how you do it so fast? I've seen a couple other posts on how to but I'd be interested in hearing yours.

Sure!

Tools needed:
7mm socket to remove battery cable
Small/medium size slot screwdriver
15mm socket
15mm deep well socket
15mm wrench (ratcheting wrench will make this job amazingly faster and easier to get into tight spots vs. a rachet)
10mm socket
3/8" or 1/2" breaker (cheater) bar & 1/2" to 3/8" adapter if you plan on using the 1/2" breaker bar for the tensioner
3/8" or 1/2" rachet
Di-electric grease (if you choose)
Wire brush (if needed)

Before starting this job, disconnect the positive terminal of the battery completely, and bend it out of the way. This is critical as you will a.) be working in the belt/fan area with your hands and do not want an accidental start, b.) will be disconnecting a power lead from the back of the alternator.

Step 1: Take your choice of breaker bar or rachet into belt tensioner and remove serpentine belt. Whichever you choose, remember that the opening in the tensioner is in fact 3/8". So if you use your 1/2" breaker bar, you'll need a 1/2" to 3/8" adapter.

Step 2: Using a 10mm socket, remove the little bolt on the black engine lift bracket in front of the alternator. It holds the A/C line onto the black bracket. We'll be removing the bracket and you'll need the A/C line to flex a little so its important to remove.

Step 3: Using a 15mm short well socket and breaker bar or rachet, remove the two bolts holding the black engine lift bracket to the front of the engine.

** not so fast cowboy! Theres a hidden bolt before you yank that bracket off the engine! **

Step 4: Using the short well 15mm socket, or if you have one, a deep well 15mm socket and a small extension (3"), look behind the bracket; you will see a 'hidden bolt' fastening the back of the black engine lift bracket to the motor. Gently fish the socket and extension through the wiring looms going to the PCM and remove that bolt.

Now the bracket comes off. You will have a better view of the alternator and the bolts that fasten it to the engine block. Note that there is a wiring loom attached to the bracket with a pine-comb plastic fastener. Gently pry it apart from the bracket.

Step 5: Using a 15mm wrench (I have racheting Craftsman wrenches that come in VERY handy for this job), remove the top two bolts of the alternator. There is a bottom bolt, feel around for it and gently attach a wrench to it (I could not get a socket due to the other A/C line being in the way). Be careful not to knick the fan or hurt yourself. Completely loosen the lower alternator bolt but do NOT remove (you likely wont be able to remove it totally anyway).

Step 6: When the top two alternator bolts are out, and the bottom bolt completely loosened (but not removed), jimmy the alternator out of its place gently. There is a wiring harness that unclips best with a small screwdriver and another wire that is attached to the back of the alternator with a 10mm bolt.

Tips:
* Removal of the lower alternator bolt from the alternator itself is NOT necessary; simply loosen it so its no longer threaded into the block at all and pull the alternator out with the lower bolt in it. Fighting with removing the bolt takes up valuable time and if you leave the loose bolt in the alternator, when you twist the alternator out of the way, it will come out with the alternator. But otherwise you will find the A/C line is hard against the bolt and you will be beating your head against your intake trying to figure out how to remove that bolt.

* Ratcheting wrenches are a lifesaver. I extensively use my 15mm wrenches on this truck.

* Be very careful when re-tightening the 10mm bolt on the back of the alternator- it needs to be snug but not gorilla tight. Clean it up real good (mine was lightly corroded) with some emery cloth or a wire brush and apply some di-electric grease if you have some handy. There is a rubber boot that needs to go back on to cover the post. Mine was ripped so I fixed it up with some HD electrical tape.

* To replace t-stat and/or coolant sensor, I did not remove the alternator completely; I just disconnected it completely, twisted it out of the cavity, and rested it in between the engine and fan. It gives your more than enough room to get the job done.


***** When re-installing the alternator, KEEP THE LOWER BOLT IN THE ALTERNATOR AS YOU TWIST IT BACK INTO PLACE!!! ***** Otherwise, with the other A/C line in the way, you'll never get the bolt back in by hand.

And with this method, is how I can remove the alternator in less than 15 minutes now

Last night I removed the alternator, fixed my hose clamp at the t-stat, and reinstalled everything, started the truck & took a sip of my hot chocolate/baileys in 30 minutes. I got back inside to watch the new episode of Gold Rush

To anybody else experienced with this: please feel free to add anything I missed to make this more useful!

 

[Guenther]

 

[MichEnvoyGuy]

I just updated it alittle to disconnect the battery (very important!!)

Maybe if Im feeling fine tomorrow (getting ready to go to a big NYE bash), then I can update my post with pictures!

 

[BeenBlazin]

does anyone know the torq specs for the t-stat housing bolts?

 

[The_Roadie]

89 INCH-pounds.

 

[gmcman]

I think you touched on the lower alternator bolt, I just want to add.....

DO NOT BACK OUT THE LOWER BOLT TO THE A/C TUBE WITH YOUR RATCHETING WRENCH!

I feel better now.

This way you don't need to remove your A/C compressor to remove the wrench.

 

[Mark20]

15mm stubby flex head ratcheting wrench to be exact for the lower alternator bolt, makes that a whole lot easier.

I had to take the alternator out twice for due to the leak and the second time was much faster thanks to experience. Its really not that bad a job and if you want to replace the serpentine, its a good opportunity.

 

[Iahawkeye]

I could not find a CTS socket (18 MM) so I used a Crowfoot wrench to tighten. My OEM one came with too much Teflon tape that balled up when tightened and leaked. So check it. 2.5 wraps of Teflon plumbing tape is more than enough.

Also the sensor is closer to the alternator and may even ne hidden by it.

Sent from my Android using Tapatalk.

Man, I wish I would have read this thread before I did this job. I too used a crowfoot after wondering how I was going to get the new sensor back on. I now find myself with what appears to be a leak around the sensor. Mine new sensor had tape on it from AC delco, so I assumed I did not need to add any more. Is this my problem or did I not tighten down the new sensor enough? I know it is an old thread, but some advice would be appreciated. Thanks.

 

[Mark20]

Good chance the Teflon tape balled up as it screwed in. Common problem with Teflon tape, more is not better.

 

[BayWolf]

Would this kind of ECT behavior indicate a faulty coolant temperature sensor? That's a 20-deg increase in a 0.6-sec span at around the 13-sec mark. These data were recorded while cruising at 70 on the highway after the truck had been running for 15-20 mins.

View attachment 21493

Shortly after the recording stopped, the scan tool read successive temps of 197, 194, 185, 186, and 206 in a 5-sec span, as well.

 

[Chickenhawk]

Would this kind of ECT behavior indicate a faulty coolant temperature sensor?

Yes! Textbook symptoms.

 

[gmcman]

Anotherpossible culprit would be low coolant level.

 

[revamp]

I just had my mechanic look at replacing my thermostat and sensor. In the process realized the serpentine belt tensioner seized ad the only way to get the belt off may (or may not) ruin the belt.

The cost to do the work is still a fair price. I tried myself and realized I didn't have the ability, plus being 100 degrees outside didn't help. On top of this, I would not have gotten past the belt tensioner issue.

This task is so critical as I have found out. I changed my converter almost 2 months ago, and my new one is fried already because my engine has been running rich due to the fact that I didn't realize being a tick or two below 210 was bad. Now I know.

The shop didn't have time to do the full job today so I am bringing it back in next Saturday. Then I will negotiate to have the converter swapped, and finally get my inspection done.

Whew!

 

[6716]

I just had my mechanic look at replacing my thermostat and sensor. In the process realized the serpentine belt tensioner seized ad the only way to get the belt off may (or may not) ruin the belt.

I thought the tensioner worked on a spring, so I don't know what to make of the "siezed" bit. Even so, I believe you could get the tensioner out by removing the bolt in the center.

Even so, replacing the T-stat, while challenging to those of us who have much less wrenching time than many on the site, is not all that hard.

I did it in about 4 hours, mostly because I kept dropping sockets and having to look for them.

Getting the belt on and off was a trick solo, but do-able. The biggest thing I would say is get one of them there hinged bits for the socket set, since that helps a guy wrench around the corner. I only suffered a crisis of confidence once, when the t-stat was out and I wasn't sure I was going to be able to get it all back together.

 

[revamp]

I was told antifreeze would come pouring out when the hose was disconnected from the thermostat. How did you deal with that?

 

[6716]

I was told antifreeze would come pouring out when the hose was disconnected from the thermostat. How did you deal with that?

First, I bought a wildly insufficient drip pan for $2.00 at the parts store. Then, when the antifreeze pissed all freakin' over -- pretty much going everywhere but in my too-small pan -- I took the wife's car back to the parts store and bought a big bag of EconoSorb, ripped it open over the puddle, soaked it all up, and put it in the garbage.

Oh, and when you add the anti-freeze back in at the end, don't pour it into the overflow tank, like I did. Pour it into the radiator, like you're supposed to. Otherwise you'll watch your temp gauge go through the roof on your test drive.

 

[Menthol]

I just had my mechanic look at replacing my thermostat and sensor. In the process realized the serpentine belt tensioner seized ad the only way to get the belt off may (or may not) ruin the belt.

The cost to do the work is still a fair price. I tried myself and realized I didn't have the ability, plus being 100 degrees outside didn't help. On top of this, I would not have gotten past the belt tensioner issue.

This task is so critical as I have found out. I changed my converter almost 2 months ago, and my new one is fried already because my engine has been running rich due to the fact that I didn't realize being a tick or two below 210 was bad. Now I know.

The shop didn't have time to do the full job today so I am bringing it back in next Saturday. Then I will negotiate to have the converter swapped, and finally get my inspection done.

Whew!

What was his fair price? Not sure about that tensioner seizing up, sounds like a scam. How do you know the converter is bad?