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2003 chevy trailblazer_ls
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Like with everyone who read this thread, it was a great help. It took me most of the day. ( I'm a slow mover/thinker I guess) The hardest thing for me was that bottom bolt on the alternater. Using a box wrench It takes a long time!
While I had the alt and thermo out I replaced the lower hose. Was able to reuse the factory clamps. If I were needing to do it again, I might consider taking out the fan to get a bit better access to the lower alt bolt. Over at harbor freight I bought a ratchet wrench extension set with an 18"er for going through the wheel well for the upper thermo bolt. Made it easier. Last summer my local dealer said I needed a water pump replacement. Glad my wife talked me outa that one. This forum will help me get through that easy enough. The funniest thing that took me awhile to figure out was how to attach the wrench to the tensioner pulley.:duh: Thanks all.
 

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2004 chevy trailblazer_ls
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21 Posts
In the tenth picture is that the sensor that should be replaced? (right above the thermostat.)
 

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2006 chevy trailblazer_ls
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286 Posts
yes.... that's the coolant temp sensor....
 

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2005 gmc envoy_slt_xl
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My check engine light came on last nite on the way home from a short road trip. After taking it to Advanced Auto today, the guy told me the coolant sensor needed replaced after hooking up to his handheld. After reading here, I figured I might as well replace the thermostat while I am in there. However, my engine temp still reads 210 degrees on the highway. Does this mean that those parts don't need replaced and I should be looking elsewhere for the source of the check engine light?
 

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2004 gmc
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...the guy told me the coolant sensor needed replaced...
That advice was worth what you paid for it. :no: If it was code P0128, it's almost always the thermostat, not the sensor. A slow thermostat could set off a P0128 code, even if the final temperature ends up being the expected 210.

But you need to buy your own code reader, or go in with a group of buddies to own one. Then you could get the exact code and Google for it, instead of hoping for free and accurate diagnoses from parts store staff who would be working as mechanics if they were competent enough to be hired as such. :confused:

See if you can get the exact code.
 

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2005 gmc envoy_slt_xl
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That advice was worth what you paid for it. :no: If it was code P0128, it's almost always the thermostat, not the sensor. A slow thermostat could set off a P0128 code, even if the final temperature ends up being the expected 210.

But you need to buy your own code reader, or go in with a group of buddies to own one. Then you could get the exact code and Google for it, instead of hoping for free and accurate diagnoses from parts store staff who would be working as mechanics if they were competent enough to be hired as such. :confused:

See if you can get the exact code.
I asked what the exact code was and he wouldn't tell me. I am still going to replace it, but it won't be until next weekend when I have the time. I assume it should be ok until then? I did look at some code readers while I was there. Any particular models you guys prefer?
 

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2004 gmc
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If you go a year with a P0128 code, you could waste a few hundred $$ of fuel, and put your cat at risk for a clog, but a week or two is fine. Especially if it gets to 210 degrees eventually.

Cagy guy there, concealing the code. Many folks use the ScangaugeII to constantly watch items on the data bus, but that can be $150 or so.

Low end code readers can be had for $20 if you have an Android smartphone, or $20-30 on Ebay, or $40 for Harbor Freight cheapies. 4-5 guys in a group or neighborhood can EASILY chip in and get one to share.
 

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2005 gmc envoy_slt_xl
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8 Posts
On the way home from work I noticed the check engine light was no longed illuminated. I have not changed the thermostat and temp sensor yet. Is this normal?
 

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2002 gmc envoy_slt
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17 Posts
When I baught my Envoy (2 months ago) the temp gauge read 210 on the dot after it warmed up, then 2 weeks ago, it was reading 1 to 2 clicks to the left (cool). I never had a SES light come on, but I heard about this causing low MPG's and could clog the cat and also we're taking a 6 hour trip one way next weekend. So I ordered a thermostat from RockAuto.com (ACDELCO Part # 1511006) and replaced it the other day. It seemed as though I added less coolant than what was spilled to fill it up. After I got it filled and washed down the engine bay, I started it and let it warm up in the driveway. I do not recal what the gauge read :bonk: Then I shut it down. Before it cooled down all the way, the wife and I drove it 15 minutes to the store and it was 2 clicks to the left of 210 when we got there, and it was the same on the way home. Does this sound like a malfunctioning thermostat? Could I have air in the system that may cause the sensor to read slightly cooler? I do plan on taking a few more small trips before we leave to Michigan this weekend and I'll watch the gauge. Any advice would be great! Thanks in advance!

Another Question, Does the ecm get the temp reading from the same sensor that the guage does?
 

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2004 gmc
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On the way home from work I noticed the check engine light was no longed illuminated. I have not changed the thermostat and temp sensor yet. Is this normal?
A slow thermostat could pass the diagnostic some times and fail it other times. It's normal, but if you ever got the SES light and P0128 code, I'd swap it.

Does this sound like a malfunctioning thermostat?
Possibly. It's difficult to ever see 210 degrees at idle or in your driveway, and you might need a longer trip at higher speed.
Could I have air in the system that may cause the sensor to read slightly cooler?
The V8's need to be purged, but I don't recall the I6 having the same issues. Just turn on the heater to make sure it's circulating coolant through the cores. But a system with air in it typically overheats, not underheats.
Another Question, Does the ecm get the temp reading from the same sensor that the guage does?
Yes. But the PCM will report truthful data to a scan tool looking at the data stream, while the data sent to the gauge is heavily filtered and massaged before it's seen by the driver, so you don't see small changes in the vicinity of 185-220 degrees mostly, and the PCM commands the gauge to stay at 210 rock solidly, which is a lie perpetrated on us by the GM designers so as to not "alarm" the average non-enthusiast driver. :hissy: :hopeless
 

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chevy
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Yes. But the PCM will report truthful data to a scan tool looking at the data stream, while the data sent to the gauge is heavily filtered and massaged before it's seen by the driver, so you don't see small changes in the vicinity of 185-220 degrees mostly, and the PCM commands the gauge to stay at 210 rock solidly, which is a lie perpetrated on us by the GM designers so as to not "alarm" the average non-enthusiast driver. :hissy: :hopeless
Kind of off topic, but my gauge has always dutifully moved around the 210 mark, and seems to coincide roughly with the PCM coolant temp value. I wonder if the lying temp needle was introduced in later years...
 

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2003 chevy trailblazer_ls_ext
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58 Posts
I have a question related to the thermostat/temp.

Should a 30 minute drive w/ an average speed of 60+ mph be enough to get it the correct operating temp (a hair under 210)? The ambient temp this morning was about 80-85 degrees.

It never got close to 210 at all. Im wondering if I have a stuck t-stat as well.
 

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2005 chevy
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I have a question related to the thermostat/temp.

Should a 30 minute drive w/ an average speed of 60+ mph be enough to get it the correct operating temp (a hair under 210)? The ambient temp this morning was about 80-85 degrees.

It never got close to 210 at all. Im wondering if I have a stuck t-stat as well.
That's more than enough time, I'd say your t-stat is stuck. I usually hit 210 in under 10 minutes, going 45mph :m2:
 

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2003 chevy trailblazer_ls_ext
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That's more than enough time, I'd say your t-stat is stuck. I usually hit 210 in under 10 minutes, going 45mph :m2:
Could this be a cause of me only getting 14mpg with a 50/50 mix in driving?

Also, should the clutch fan sound like a turbine EVERY TIME you leave from a stop, even when cold?

Im starting to wonder if I have a 2-fold problem.
 

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2005 chevy
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Could this be a cause of me only getting 14mpg with a 50/50 mix in driving?
:undecided Hmm, quite possibly. I know I average about 14mpg per tank with mostly city driving.

Also, should the clutch fan sound like a turbine EVERY TIME you leave from a stop, even when cold?

Im starting to wonder if I have a 2-fold problem.
I know if I fire up the engine and then start driving right away, the fan will roar when I accelerate each time, until the engine gets up to about 2500rpm then it settles down. But if I stay in park for about 30-45 seconds before driving away, the fan won't roar. I forget what system is doing a startup check, too lazy to go look for it. :crazy:

Now if the fan is always engaged, then your clutch may be bad, and yes you'd have a 2 fold problem :yes:

I think what some people have tried to confirm it, is take a balled up towel and try to stop the fan while the truck is idling and cold. If it stops easily, then the clutch isn't stuck. Might wanna get confirmation on that before you try it in case I'm misremembering. :coffee
 

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2006 chevy trailblazer_lt
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censor

Hello first time here.I have a 2006 trailblazer recently i have had the thermostat replace and the censor but when i took it to get it inspected for the inspection sticker it did not pass said i had to drive it for 50 miles before it reset but it still have not reset any ideas:thx
 

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2005 buick rainier
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F this job.... Did it last night, took me a little over 4 hours! Replaced the sensor and stat. Zero room, removed the alternator which gave me sight of the parts but not much more room. Snapped the stat bolt in the block, but was able to back it our with a die set, havent noticed any leaks yet, but I have noticed a huge leap in mileage.

For the past few months I have been averaging 14-15mpg without the boat, around 10mpg with the boat. Today on my way to work, Temp Needle dead center, got 18mpg!!, hoping for around 12mpg this weekend with the boat.

As much of a PITA this was, I can now check it off my list of items never to volunteer to replace again, HA.

Thanks guys.
 

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2005 buick rainier
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Also, I did test both the old and the new thermostats...The old one apeared to work, but didnt open very far, but was closed initially (couldnt blow any air through the tube, not very scientific, i know). With the new one, I could hear a very small amount of air coming through, but the opening was like night and day. In boiling water took about 5 seconds for the new stat to fully open, the old one would open about 1/4 of the way in twice as much time. :eek:
 
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