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2003 chevy trailblazer_ls
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[Note: If the pics don't show up IN this post, you can find them in the gallery: http://gallery.trailvoy.com/member.php?uid=19&protype=1; ]

Finally got the job done.
Time to do the job.... 4.5 hrs. Why so long?
I looked around and was trying to figure out how some on here claim they didnt have to remove the alternator. I tried to stick my hand in the areas around the wire looms and alternator- and theres no way I was going to get in there without messing with all the wires- and possibly damaging. So I chose to loosen the alternator. I soon realized that I was going to need more space to work comfortably. I have small hands- so if you have large hands- I recommend you remove the alternator. To do this I found it easier to remove the black bracket right above the alternator.
Also- I dropped 1 bolt 2 times- Each time I had a heck of a time locating the bolt. It was well hidden. This added to my repair time. (the bolt is one of the ones that holds the black metal bracket).
Also-had a major hiccup. Put in new thermo and o-ring. I put everything back toghether again. Including serpentine belt. I then opened the radiator cap- and soon after I started to hear dripping antifreeze.
Turns out that the o-ring had moved. and got pinched. I had to take it all apart again. I ended up reusing the old o-ring which was in good condition. But to make sure it didnt move around like the other one, I put 4 small dabs of gasket maker. just a small little spot to hold the ring while I maneuvered it around.
The problem was I started seeing the engine temp about 2 hash marks below the 210 mark (it would go a little lower on the highway)- when it used to be right at the halfway mark.

A few days later the SES light comes on.

The items youll need are a new thermostat- yes thats the whole piece. And a bottle of DexCool. I bought the premixed 50/50 bottle. Ready to pour.

Youll need to remove the serpentine belt. Here I used a rachet and a metal pipe I had laying around- to make it easy to move the tensioner.

Once I decided I would remove the alternator- I decided to loosen this clamp that holds that wire bundle in place- in case I need to move it out of the way. I did end up moving it slightly to get to a bolt.

Here is a side view. You can see the neg battery connection (I did end up disconnecting it once I knew for sure I was going to be moving the alternator around) You can see the socket extension I used to get to the bolts in the area.

here is another shot of the socket extension- and one of the easier to get to bolts for the alternator. Its visible in the pic, towards the bottom of the alternator I left a wrench so you can see where the 3rd bolt for the alternator is. THis bolt was the one that was the hardest to remove since theres a hose (AC I think) right next to it. Its also visible in the pics.

Here the black bracket has been removed- Its held in place by 3 bolts.
2 are at the front of the engine- very easy to remove. The 3rd one is right in the area where other alternator bolt is (previous pic where the socket extension is) Note that I also removed the screw to that metallic bracket for the black pipe/hose.

heres the alternator moved a bit forward. Now you can see the thermostat.
also note the alternator has 2 electrical connections. 1 is that clip on connector. easily removable by lifting a plastic tab. The onther is the thick + battery wire. I think its a 10mm socket I used to loosen the nut. Note the 2 shiny bolt holes- this is where the 2 bolts for the black bracket go.

In this image you can see the thermostat housing. 1 bolt is visible, the other is at the bottom. in the picture you can see the + battery wire I removed. Its right at the point where the hose clamp is on the thermostat housing. Also note on the upper right hand corner of the picture. 3 bolt holes. 2 are for the alternator and the highest one is the 3rd bolt for the black bracket.
At this point youll have to get some pliers and squeeze the clamp so that you can remove the hose. Youll have to maneuver the pliers to loosen this. (unless you have some special tool).
Once the dexcool spills into a pan (and the floor) I proceeded to reach the 2nd thermostat bolt from underneath. I crawled under and ws able to maneuver my hand to be able to loosen that bolt.

Here are the old and new side by side. Note the old one had NO gunky buildup on anything......NONE!!!! Note the O-rings. Also note the engine block opening, its super clean!!!! I can still see the design on the engine block from the styrofoam casting. No gunk whatsoever. And this is on a 110,500 mile + engine with Dexcool!!!!!

after I put it back toghether..... during the tigheneing process the o-ring moved. I put EVERYTHING back toghethe- as in I was ready to start engine and then found a leak when I removed the rediator cap. The removal of the cap- allowed fluid to flow and I started to hear fluid leaking into the pan I collected the used dexcool. Note how the new o-ring was piched in 2 locations.. Now worthless. I used the old one- It was still in good condition.
So I used a bit of gasket stuff to hold the o-ring in place. I mean very little. Just to make the o-ring stay in place.
I put everything back toghether. The clamp is a bit hard to put back in place. I recommend trying a few different arm positions to see what works best for you. Also- I placed a little oil on the outside of the hose so that the hose clamp slid over the hose. I did this after trying countless times to slide it. Make sure youre very careful putting the 3rd bolt for the black bracket. Thats the one that was dropped 2 times- It fell and was a pain in the butt to find. Im guessing it added about 30 min to the repair. Youll have to put back the + battery wire. then screw the alternator back in. Youll have to experiment/fumble around with the 3 bolts to get the bottom one in. It was the most troublesome to get in of the 3. Dont forget to reconnect the other clip on connector. Put Serpentine belt back on. Reconnect battery (I didnt want that + wire on the alternator to touch ground)
I then turned the engine on and let it run for a bit- while refilling with Dexcool.
I used up the entire bottle to refill the radiator and a bit of the overflow bottle. Im sure that as I drive it some- air pockets will be removed. Ill refill as necessary.

Heres the end result. After driving about 15 miles at 70 MPH- the needle now sits slightly above the 210 mark.
 

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2003 chevy trailblazer_ls
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Heres the result with the Code reader. It actually showed no Codes.
Few days ago- It showed 2 P0128 codes. I guess once the temps were normal- the codes were erased.
Just to be shure- I went ahead and selected erase.

If the o-ring would not have moved- THis would have been a 2 hr job I think.
For those that dd the repair without moving the alternator... man... I have to applaud you............
so total for the repair.
$28.57 thermostat + $9.71 Dexcool= $38.28 + a few hours of your time. An occasional extra hand was helpful.

I had called dealer out of curiosity- and they said estimate was $250 to replace (parts and labor). ( I think it would have been more-dont they also charge for scanning codes and..... tax.)
 

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2009 chevy
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Nice job :thumbsup:. I checked the Chilton manual, 2nd step = "remove the alternator".
 

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2003 chevy trailblazer_lt
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Good job ....That's the way I did mine. Always remove the alternator...saved 200+ dollars and now others can view this and save also. And if its not leaking now using the old O-ring. It probably won't. Your temp is running at 210-215 just slightly to the right of the 210 mark. Mine runs at 205-210 just slighty to the left. That might be a gage setup. What was to temp in S Calif yesterday? On a real hot day here in NC 95+ in summer my gage will be dead on 210. As a ad on to the removal of the bottom alternator bolt. I used a ratchet wrench. Slides on real easy and misses the A/C hose.... Anyway..... GOOD JOB...:thumbsup:
 

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2003 chevy trailblazer_ls
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Discussion Starter #8
it was about 70-75 degrees here yesterday.
Today I refilled the overflow bottle. Im guessing theres still a little bit of air pockets left in the engine
 

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2003 chevy trailblazer_lt
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That should take care of it. It feels good to know that just plane old Joe's like us can do these things that the dealer can also do. :woot:
 

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Western Canada Chapter
2003
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it was about 70-75 degrees here yesterday.
Today I refilled the overflow bottle. I'm guessing theres still a little bit of air pockets left in the engine
Great stuff! I fear mine is doing the same thing as mine sits well below the half way mark. I will be referencing your article when Fish gets it posted!:thumbsup:
 

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2003 chevy trailblazer_ls
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Discussion Starter #11
since the install. I did have to re-fill the see thru recovery tank as it was all sucked into the radiator.
After 6 days- the radiator and overflow tank are stable in level.
In order to try to get any more bubbles out of the system- I got on freeway and floored it- RPMS's hit something like 5,000 RPMs.
(my thought was to get the pump moving the fluid in there as fast of possible in order to get rid of pockets).
But while I hit the 5000 range. I noticed that my engine temp dropped from slightly past the halfway point, to below the halfway point.
Once I let off the temperature went back to its usual spot.
Im guessing the sudden rush of cool air thru the radiator and the fast flowing coolant brought engine temp down- until the thermostat could react.
but so far so good!!!
 

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2002 gmc envoy_slt
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Rbarrios - nice write up! :D

Ive argued on here forever, it seems, about loosening the alternator. How some members say that they didnt have to loosen or remove it is BEYOND ME. They must be related to Gumby or something and are able to contort their bodies in crazy positions...LOL.

I certainly had to loosen my alternator, actually had to remove 2 bolts and was able to move the alternator enough to mess w/the t-stat.:yes:
 

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2002 chevy trailblazer_ltz
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Nice writeup! :thx

I removed the alternator while doing mine @99k. The whole time I missed my smallblock chevy. :(
 

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2003 gmc envoy_sle
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Rbarrios Thermostat Replacement Article

Rbarrios - I just wanted to say thanks for your write up on the T-Stat replacement. It definitely helped me. The explanation of what to watch out for was right on and the photos were fantastic.
I have an '03 with 40k on it and this was my first dive under the hood with this particular vehicle.
Your write up convinced me to go ahead and do it myself.
It took me 5 hours, but I am happy to have done it.
I removed the alternator completely and even removed the battery and batttery tray. I know -a bit excessive - but I took my time to clean up the parts and engine compartment and just tried to enjoy the job.
No leaks and running great!
 

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since this seems to be a great thread on the replacement of the T-stat I thought I would ask this here.

To all of you that did this, did you remove coolant from the system before starting the replacement process? if so how much and where did you get it out from? If not, did any spill out when you did the swap out?

I am looking to do mine soon (I think that the vehicle is not warming as quickly as it should) and would like to have all my ducks in a row before I start this process... at least I have replaced the alternator already so I know what the process is for that part :)

thanks!
-John B
 

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Discussion Starter #16
szn8ky- youre welcome. I knew it would help someone.
I had been asking questions about it myself. I had not seen pics- only post about it. And since I had a new digital camera- I fugure Id document it.... Im very happy it helped. Makes it worth it.
k2jjb- I didnt remove any coolant. I figured that with the thermostat being at the lowest point in the system- it was going to spill no matter what.
I simply grabbed a flat container to try to catch as much as possible- when I loosened the hose to the thermostat- it came pouring out. Upon removing the thermostat- a bit more comes out- I captured much of it. but some still spills on to the ground. The stuff I captured I plan on taking to the hazardous waste roundnup we have around here.
Once the job is done- I refill with the bottle I bought. On subsequent days I did buy another bottle to top off.
Maybe someone else did drain from somewhere?
 

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Same here. There is no radiator drain plug. I took the bottom radiator hose loose. Then removed the thermostat from block to get the rest of the coolant out. If you have a lot of miles on car remove as much as possible. You will need 1 or 1 1/2 jugs of coolant 50/50 dex-cool. Last time I checked Walmart had Prestone Dex-cool $9.88. Once you have all things back together. Here is a neat thing to do. Take the top radiator hose loose and pour the coolant into the block first untill full, the thermostat has not opened yet this and will remove a almost all of air in the block. Then replace hose and pour rest of coolant into radiator. This should almost completely fill block and radiator. Crank engine and let thermostat open and look for coolant to circulate. Top off radiator replace cap. Any left over coolant pour in overflow tank. CHECK FOR LEAKS... You should be good to go..........:thumbsup:
 

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rbarrios,

GREAT WRITE UP!! I do not have to change my thermostat now but I have printed my own hard copy for future refrence.
Keeping the wrench in place when taking photos was a stroke of genius. It made everything so much easier to locate.

Thanks again for taking the extra time to help all of us.
 

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2003 gmc envoy_sle
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I just tried to capture as much as I could in a pan underneath the vehicle also. Most of the antifreeze came out of the hose and a little more when I removed the T-Stat. There is not really a good drainage path there and it tended to spread out by the time it cleared the vehicle. I'd say I caught about a gallon and about another pint or so ended up on the floor.
 

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Good job

:thumbsup:This is an awesome step by step procedure and the pics help plenty...this will certainly help me in my process, thanks for the post...
 
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