Bad thermostat? See photo

Ed H

Original poster
Member
Oct 18, 2012
167
My gas mileage sucks, and I am somewhat paranoid about having a bad thermo after all the posts I read. The truck comes up to temp quickly indicating the thermo is not stuck open, but is THIS where it should read? Many posts indicate straight up, or slightly higher is normal. This is my normal everyday.

View attachment 25394

I assume it is good, but assuming anything is foolish. Thanks for the input. (Fingers crossed). :cool:
 

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gmcman

Member
Dec 12, 2011
4,656
Taking a pic directly in front of the needle may show a different perspective. Looks to be living slightly on the cool side though. Generally they are straight up or about a needle width to the left at 195 deg.

Perhaps use a scan tool to see what the ECM is reading as a temp when hot.
 

Voymom

Member
Feb 3, 2012
2,523
Ed H said:
My gas mileage sucks, and I am somewhat paranoid about having a bad thermo after all the posts I read. The truck comes up to temp quickly indicating the thermo is not stuck open, but is THIS where it should read? Many posts indicate straight up, or slightly higher is normal. This is my normal everyday.

View attachment 11149

I assume it is good, but assuming anything is foolish. Thanks for the input. (Fingers crossed). :cool:

Thats where mine sits...always has, even after a new t-stat was put in. Although now I have a sticky t-stat as it takes about 30 minutes for the truck to reach that temp lol
 

CaptainXL

Member
Dec 4, 2011
2,445
Your correct to not assume. You need a scan tool to see what the coolant temp sensor is reporting. You can't go by the gauge because it is buffered by the PCM.
 

CdnGMan

Member
Nov 22, 2011
1,393
Toronto
Mine was doing the exact thing and it finally threw out code P0128 and the CEL... the temp needle was about where yours is... now it's almost dead center...

The CEL went out after a day tho... I ended up bringing it to my mechanic and had it changed...
Talk about a PITA - that bottom bolt is simply horridly placed... good thing that my mechanic had a 3-ft extension for his 10mm socket which allowed him to go thru the wheelwell - I'm sure that saved him about 15-20min at least...
 

CaptainXL

Member
Dec 4, 2011
2,445
I've been with this site and the OS for over 5 years now. And ive learned by observation many members and newcomers seem to get bad tstats around the 5 or 6 year mark.

The coolant is due to be changed every 5 years. Likewise changing the coolant requires taking off the thermostat housing. So replacing the tstat as a preventative maintenance item seems logical at that point. Because it will save you the grief of draining the coolant again when the thermostat fails between now and the next time the coolant needs to be replaced. So lather rinse and repeat this procedure every 5 years.:twocents:
 

ScarabEpic22

Member
Nov 20, 2011
728
Lucky me then, my 02 has the original tstat (flushed the coolant about 4 years ago, guess its due again in the spring) and fan clutch.

That might be reading 1 tick low, get a scanner on it and see what the actual temp is. Bill (Blazernut aka Blade) had his 03 TB look about the same, when we touched his tune up I noticed he was only getting 185F. Changed the tstat, picked up 2mpg (at least).
 

blazinlow89

Member
Jan 25, 2012
2,088
That is about what mine sat at before the CEL came on. Torque said the temp was 165*, stayed like that for about 3 months. Changed it and now it sits a bit to the right torque reads between 195-202. I did not notice a change in gas mileage though. Still getting 275-300 miles before the gas light will kick on.

Not sure about the bottom bolt, I had no issues with that. The alternator was a bit of a pain but nothing bad. The damn nut on the fan clutch is what drove me insane, after battling that for over an hour and a half re installation went smooth.

My truck is an 04 and it went bad the end of 2011.
 

jaguarjoe

Member
Nov 22, 2012
73
CaptainXL said:
Your correct to not assume. You can't go by the gauge because it is buffered by the PCM.

I would put a lot more faith in that PCM than I would in any electromechanical gauge.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
jaguarjoe said:
I would put a lot more faith in that PCM than I would in any electromechanical gauge.
Even worse, the PCM fiddles with the data before sending a value to the gauge. It tries to present a steady 210 to the gauge while the truth is different on the data stream. In a similar way, the oil pressure value sent to the gauge on an I6 is a totally fake and invented out of thin air number, because the I6 oil pressure sensor is an on-off switch, not a true sensor. GM went to a lot of trouble to save a dime and keep Ma and Pa Kettle happy.
 

CaptainXL

Member
Dec 4, 2011
2,445
jaguarjoe said:
I would put a lot more faith in that PCM than I would in any electromechanical gauge.

Its not only the PCM your trusting. Its the input sensors.

Also exactly what Bill said.
 

Sparky

Member
Dec 4, 2011
12,927
Mine has always looked like that and my mpg and everything has been fine. I just got a BT OBDII adapter + Torque on my phone so I'm going to plug it in and see what it is actually running at out of curiosity.

CaptainXL said:
I've been with this site and the OS for over 5 years now. And ive learned by observation many members and newcomers seem to get bad tstats around the 5 or 6 year mark.

The coolant is due to be changed every 5 years. Likewise changing the coolant requires taking off the thermostat housing. So replacing the tstat as a preventative maintenance item seems logical at that point. Because it will save you the grief of draining the coolant again when the thermostat fails between now and the next time the coolant needs to be replaced. So lather rinse and repeat this procedure every 5 years.:twocents:

Why do you have to take out the thermostat to change the coolant? I know it could make it easier but that's only if the stat isn't a pain in the neck to get to. I haven't yanked the stat on any cars I've changed the coolant in.

And add me to the lucky few with still original good 2002 stats :biggrin:
 

CaptainXL

Member
Dec 4, 2011
2,445
Sparky said:
Why do you have to take out the thermostat to change the coolant? :


Because that's the only way to properly drain the coolant from the block. The thermostat is closed when the coolant is cold and it sits at the bottom of the block preventing the coolant from coming out.
 

97blazer

Member
Nov 23, 2012
39
My gauge was like that. Until I went in for smog and there was a code. After t-stat replacement it was straight up. I'm disappointed to hear about the gauge situation, being fake an all. Irritating to say the least. However, the ONLY gauges I've ever -truly- trusted were the old mechanicals. Bulb type temp positioned as close as practical to the t-stat ie old fashioned hot water out t-stat. And mechanical oil pressure, ie no sender, hose from motor to ga. Comes with being old I guess...:smile: PS mileage never changed. 16+, 'bout where it's always been with local driving. FWY maybe 19-20.
 

Menthol

Member
Dec 8, 2011
177
Sparky said:
Mine has always looked like that and my mpg and everything has been fine. I just got a BT OBDII adapter + Torque on my phone so I'm going to plug it in and see what it is actually running at out of curiosity.



Why do you have to take out the thermostat to change the coolant? I know it could make it easier but that's only if the stat isn't a pain in the neck to get to. I haven't yanked the stat on any cars I've changed the coolant in.

And add me to the lucky few with still original good 2002 stats :biggrin:

Did you get time to check the reading?
 

Ed H

Original poster
Member
Oct 18, 2012
167
I also installed Torque, and my BT OBD2 adapter arrived yesterday. :wootwoot:

I went out today for a maiden voyage with Torque and to get a reading. It was 16 degrees outside (not that it matters). With the needle in the position shown in my original post, it read 188.6 degrees almost steady as a rock. It hit 190.4 once, and dropped down to 186-ish a couple times. :no:

Since this truck is new to me, and I not sure what thermostat is in there...
 

ScarabEpic22

Member
Nov 20, 2011
728
Ed H said:
I also installed Torque, and my BT OBD2 adapter arrived yesterday. :wootwoot:

I went out today for a maiden voyage with Torque and to get a reading. It was 16 degrees outside (not that it matters). With the needle in the position shown in my original post, it read 188.6 degrees almost steady as a rock. It hit 190.4 once, and dropped down to 186-ish a couple times. :no:

Since this truck is new to me, and I not sure what thermostat is in there...

Unless someone installed a 180* tstat (I wouldnt recommend it for an I6), that tstat and/or temp sender has failed. Should read 199-207F fully warmed up all the time.
 

CaptainXL

Member
Dec 4, 2011
2,445
Ed H said:
I also installed Torque, and my BT OBD2 adapter arrived yesterday. :wootwoot:

I went out today for a maiden voyage with Torque and to get a reading. It was 16 degrees outside (not that it matters). With the needle in the position shown in my original post, it read 188.6 degrees almost steady as a rock. It hit 190.4 once, and dropped down to 186-ish a couple times. :no:

Since this truck is new to me, and I not sure what thermostat is in there...

16 degrees does matter. Especially if you are like me and have the recirculate actuator broken and your sucking in cold air all the time with the fan on. What you want to do is turn the fan off and let the truck idle for a bit. It should come up to 200ish. If you never see 195-200 with the fan off at any time then it needs to be replaced imho.
 

Ed H

Original poster
Member
Oct 18, 2012
167
that tstat and/or temp sender has failed.

Yes, that is what I suspected. :frown: It comes up to temp very quickly and remains stable, so I know it is not 'stuck open', which I have experienced in other vehicles.


What you want to do is turn the fan off and let the truck idle for a bit.

I will check it out tomorrow.


if you are like me and have the recirculate actuator broken

That actuator works. But the one that controls flow to the dash vs floor vents does not work. :hissyfit:
 

pejeeper

Member
Jan 27, 2012
81
Ed H said:
My gas mileage sucks, and I am somewhat paranoid about having a bad thermo after all the posts I read. The truck comes up to temp quickly indicating the thermo is not stuck open, but is THIS where it should read? Many posts indicate straight up, or slightly higher is normal. This is my normal everyday.

View attachment 11149

I assume it is good, but assuming anything is foolish. Thanks for the input. (Fingers crossed). :cool:

My temp sits a needle width ABOVE the 210* mark, every day, every trip, no matter what season and has been that way for the past 4 years. Weird.
 

Ed H

Original poster
Member
Oct 18, 2012
167
I changed the thermostat today (AC Delco from Rock Auto). It took about 3 hours start to finish including clean-up. Not as bad as I thought. My lesson learned was the power output bolt / cable on the alternator. It took a while to figure out why the alternator would not fully seat against the motor. Duh.. :redface:

I took a quick drive to check for leaks and to see what temp she runs now. No leaks, and I hit a max temp of 199.4 degrees. It held 198.6 almost rock solid. The needle is still just a sliver shy (left) of being straight-up, but I gained almost 11 degrees.

I am not expecting massive improvements in mpg from 10-11 degrees, but we'll see. Thank you for all your input.

On a side note, does Dexcool turn almost an orange color if it hasn't been changed in a long time?
 

CaptainXL

Member
Dec 4, 2011
2,445
Ed H said:
On a side note, does Dexcool turn almost an orange color if it hasn't been changed in a long time?

It is a pinkish/orangeish color when new.


View attachment 26255

The factory thermostat is gonna more than likely fail at the 5 or 6 year mark anyway which is the timeframe the coolant needs to be changed. This will drain all the old coolant from the block and radiator. So between replacing individual cooling system components and topping off I really wouldn't worry about "if it's been a long time" or not.
 

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