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2004 chevy trailblazer_lt_ext
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I did do a search for this, and frankly came away more confused than I did with an explanation.

I changed out the t-stat in my wife's 04 EXT I6 4.2L. After several rounds of running, cooling, topping off, running, cooling, yada yada yada.... the lower tank and rad hose are still cold. Like just pulled off the shelf cold. The heater blow hot and seems just fine.

The one thing that kind of eases my mind is the fact the temp gauge has not gone over 210*, and on the scanner it idles around 200-203*, and at cruise is between 195-200*. This at an ambient temp of 77*.

With that, if the coolant was not circulating, there doesn't seem to be any way the coolant could be in a good temp range like it is. But that lower hose and tank remain cold. Seems to me with the t-stat in the lower hose, would the hot coolant flow from the bottom into the radiator, cool, and flow out the top back into the engine at a much lower temperature?

My concern here is mainly with the trans cooler lines. They are both real hot at the lower tank. The engine seems to be cooling fine, but I don't want to overheat the transmission.
 

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non_gmt360 trailblazer_lt_ext
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Our coolant system is backwards of a normal system... Hot coolant comes in from the top to the radiator, and then through the radiator to the t stat.. I guess I never felt my lower hose when warm to see if how it feels.

What kind of scanner are you running? A Bluetooth adapter and torque for android?
 

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non_gmt360 trailblazer_lt_ext
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Gotcha, I don't know anything about the stand alone scanners, I just have the torque app on my phone, the reason I asked is with torque there is the option to view the tranny temp.
My truck runs about 203-206 at idle, and about 198-204 running down the road. My tranny temp never gets above 180* or at least at the times I have checked it. But that's just running up and down the interstate, just the truck and not towing anything...
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter #6
I'm going to see if I can find one to borrow just to be sure on the trans temp.

The only part of the lower hose/tank that is even remotely warm to the touch it the hose close to the t-stat. At the tank, and the tank itself, nada. Feels like it would first thing before it had been started.
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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I did do a search for this, and frankly came away more confused than I did with an explanation.

I changed out the t-stat in my wife's 04 EXT I6 4.2L. After several rounds of running, cooling, topping off, running, cooling, yada yada yada.... the lower tank and rad hose are still cold. Like just pulled off the shelf cold. The heater blow hot and seems just fine.

The one thing that kind of eases my mind is the fact the temp gauge has not gone over 210*, and on the scanner it idles around 200-203*, and at cruise is between 195-200*. This at an ambient temp of 77*.

With that, if the coolant was not circulating, there doesn't seem to be any way the coolant could be in a good temp range like it is. But that lower hose and tank remain cold. Seems to me with the t-stat in the lower hose, would the hot coolant flow from the bottom into the radiator, cool, and flow out the top back into the engine at a much lower temperature?

My concern here is mainly with the trans cooler lines. They are both real hot at the lower tank. The engine seems to be cooling fine, but I don't want to overheat the transmission.
Same issue. Did you figure it out?
 

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OK... time for a couple of questions for you....

  1. Does your TB have front & rear heating? This helps me, whatever it has in diagnosing if you really have a problem here or not.
  2. Can you feel if the upper part of the hose near the thermostat is warm... or the lower side... this is kinda important.... but many people miss this concept!
  3. Do you realize just how efficient the cooling system is? I mean... there's a lot of liquid flowing through the heater core(s) and lines than most people realize....and it has a giant capability to use more hot coolant doing other things than just going through the radiator and wasting it to the atmosphere.
  4. Thermostats are not usually either OPEN or CLOSED.... but they can very well be at anynplace in between those extremes....
I have worked on cement trucks that rarely ever open the thermostat! Really!

They overcool.... in fact.... and many times they have to block off the radiator with cardboard or carpet just to get a few degrees of engine heat to defrost the windshield.
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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OK... time for a couple of questions for you....

  1. Does your TB have front & rear heating? This helps me, whatever it has in diagnosing if you really have a problem here or not.
  2. Can you feel if the upper part of the hose near the thermostat is warm... or the lower side... this is kinda important.... but many people miss this concept!
  3. Do you realize just how efficient the cooling system is? I mean... there's a lot of liquid flowing through the heater core(s) and lines than most people realize....and it has a giant capability to use more hot coolant doing other things than just going through the radiator and wasting it to the atmosphere.
  4. Thermostats are not usually either OPEN or CLOSED.... but they can very well be at anynplace in between those extremes....
I have worked on cement trucks that rarely ever open the thermostat! Really!

They overcool.... in fact.... and many times they have to block off the radiator with cardboard or carpet just to get a few degrees of engine heat to defrost the windshield.
1) yes it has both front and rear
2) I have felt the lower portion of the whose but I wouldn't imaging the difference is huge between the upper and lower parts of the hose given that its a bout a foot long.
3) I think its eficient but my engine ran little hot (217F using scan tool) so I changed the thermostat. Now it runs even hotter (223F). I think the typical for this truck is 190-210F
 

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1) yes it has both front and rear
2) I have felt the lower portion of the whose but I wouldn't imaging the difference is huge between the upper and lower parts of the hose given that its a bout a foot long.
3) I think its eficient but my engine ran little hot (217F using scan tool) so I changed the thermostat. Now it runs even hotter (223F). I think the typical for this truck is 190-210F
Let's play a game here --- about your hose and the things you need to observe if you want to be able to make a definitive, decisive decision about your (possibly) defective thermostat....

Wrapping your hand around the hose that returns TO the engine - on the 4.2, that's the one over the alternator......
.... just put it there and 'feel' if you can detect any zones of cooler or hotter coolant flowing through it.

You might be able to detect that either the top half is hotter or cooler than the lower half. Divided temperature zones have interpretations in and of themselves - later 4 that.

Laminated coolant flow indicates that the thermostat is partially open. In that - I mean that one half will be noted as hotter or cooler than the other half. Sorry for being redundant here - but this is kinda hard for some people to envision and/or feel.

A totally cold or cool hose indicates that the thermostat is completely CLOSED or that there's no coolant in the hose - and in this engine's situation, and since the coolant flows backwards as compared to most other engines.....the block is mostly empty too. Not good - but if you KNOW that the coolant's up to the top of the radiator neck - then keep letting it idle to complete the test.

1. This vehicle, with front and rear heating, gobbles up a LOT of calories! It takes forever to get heat in the whole system. AND ---> the heaters get the heating-up coolant FIRST to accommodate the persons inside the vehicle.

2. The heaters steal a lot of heat from the engine and in many situations, this will keep the thermostat at least partially closed to keep the heaters going as well as then can. This is why I asked about your vehicle having just one or two heaters. Thanks for the info.

3. About that SCAN temperature you're seeing.... it may be false.

Yup - the scanner takes it's readings from the values that the ECM believes is true since it has no other reference point in which to make the correct evaluation.

IOW ---> it may be reading and reporting from a bogus temperature sensor. ... OR the temperature's really that hot - but not dangerously so.

There are usually two sensors --- but I'm not up on the TBs yet and they may only have one that reports directly to the ECM and the ECM then sends out the values it does. I dunnow yet - watch this space for better educated information later this week - maybe (I've gotta get some fishing in before the next snow blizzard).


HERE'S a valid rule for you --->
  • OVERHEATING involves a loss of coolant.
  • Running HOT won't cause any coolant to hit the ground.
  • IF you sense a hot condition - turn ON the AC. Yup! because it turns on the radiator cooling fan!
....more later..... I gotta get a shower....... but I will try to give you some of my experience-based diagnostic techniques....
 

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2002 chevy trailblazer_lt_ext
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There are usually two sensors --- but I'm not up on the TBs yet and they may only have one that reports directly to the ECM
If you're not up on TB's, how can you be giving advice on them? There is only ONE sensor. And he has a BRAVADA and they NEVER had a rear HVAC as it was only ever made as a SWB. What he likely described as rear heat was the fan in the center console that just takes some of the air from the front system and blows it to the rear passengers, so it still has a single heater core.

@zaid3ssaf , what you describe seems to be normal operation. If it gets hotter outside and you use the A/C and the temp gets even higher as well as poor A/C performance, check the cooling fan clutch operation:
How to test the electro-viscous fan clutch
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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If you're not up on TB's, how can you be giving advice on them? There is only ONE sensor. And he has a BRAVADA and they NEVER had a rear HVAC as it was only ever made as a SWB. What he likely described as rear heat was the fan in the center console that just takes some of the air from the front system and blows it to the rear passengers, so it still has a single heater core.
I never knew it takes the heat from the front core. Sorry about that. I thought they were 2 seperate ones.

@zaid3ssaf , what you describe seems to be normal operation. If it gets hotter outside and you use the A/C and the temp gets even higher as well as poor A/C performance, check the cooling fan clutch operation:
How to test the electro-viscous fan clutch
I guess my main concern is the high temp. I've seen somewhere that the normal temp should be between 190 and 215 F (or 220 F). I changed the thermostat cause I was at 217 F, but now it's even hotter at 223 F. I havent driven it more than 10-15 minutes from home so I'm not sure if it'll get hotter. I'll let you know tomorrow. I'll use your second method to diagnose the fan clutch since my AC need some work (a job for the summer lol)

One thing though, when I changed the thermostat, I drained and flushed all the coolant then filled up the radiator couple of times with water and ran the vehicle up to temp and then drain. When I did the final fill (with dexcool), I filled up the radiator to the top and ran the engine. Messaging the upper hose and "burping" the system as it goes. BUT, I ran the system for too long that the it started bubbling through the cap so I shut it off. Did I do something wrong? Do I need to jack up the front to bleed it better? Does a possible air pocket explain the high temp? Thanks man!
 

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2002 chevy trailblazer_lt_ext
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Please come over to GMTNation. Apart from myself, there a lot of people over there that can actually help. I'm not normally over here in this wasteland.
 

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If you're not up on TB's, how can you be giving advice on them? There is only ONE sensor. And he has a BRAVADA and they NEVER had a rear HVAC as it was only ever made as a SWB. What he likely described as rear heat was the fan in the center console that just takes some of the air from the front system and blows it to the rear passengers, so it still has a single heater core.

@zaid3ssaf , what you describe seems to be normal operation. If it gets hotter outside and you use the A/C and the temp gets even higher as well as poor A/C performance, check the cooling fan clutch operation:
How to test the electro-viscous fan clutch
Look, Mooseman --- I've spent 55 years in the business - and although I am not up to speed on the TBs, they still adhere to the rules of mechanical things ... and if a person says he has two heaters - I tend to believe him until I find out better. Your attitude is the kind that makes me sorry for people like you.

If you hate me for what I said... just say so --- but don't you EVER chew my @SS on the internet again.....
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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So I just put the ACDelco thermostat in, and son of a gun, it not overheating anymore. It stays at little below 210F on the gauge and on the scan tool it stays between 197F and 203F. Right on the money!!

For anyone reading this (TLDR) I had an overheating problem which I ruled out as a bad thermostat. SoI replaced it with another a coincidently defunct Dorman thermostat which made the problem even worse and possibly made me think that other parts of the cooling system are going bad. But no it was the thermostat. Always buy OEM for 10 bucks extra you get what you pay for.
 

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Good to see you got it solved. The vote for OE vs OER still rages all over the world, and frankly it seems to be hit-n-miss a lot more than just your example.

I've had genuine manufacturer's parts fail about as much as aftermarket and third party parts.

Vehicle manufacturers don't actually build those mundane things like switches or thermostats - they just specify what they want and the bean-counters send the job to the cheapest jobshop.

Ask any astronaut how they feel sitting atop millions of gallons of liquid oxygen and the whole thing was built by the lowest bidder!
 

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2008 gmc envoy_sle
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glad it worked out. take some advice, if possible stay away from dorman. oem when possible.

for the record, i like this 'wasteland' much better than the other site,
 

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I have always had issues with my AC/Heat to the car. Would something like that confirm that it is a thermostat issue? The A/C only blows through the front defrost when it is above 70 degrees F outside and during the Winter it takes maybe 10-15 minutes for the heat to kick in. I really hoping it isn't a head gasket because I can't afford to replace something like that. The thermostat is a pretty big pain in the ass to change on this car but I would gladly do that over a head gasket repair.
Sarkari Result Pnr Status 192.168.1.1
 

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GM HVAC Systems "condition" the air, not merely chilling or heating it. Air taken into the vehicle is first chilled by the evaporator, then it is reheated to whatever comfort setting you desire.

This chilling the air causes the dew point to drop and the moisture in the outside air is removed in the form of condensate that you can see under cars that are shut off in parking lots... actual water dumping on the ground.

DEFROST will invoke the AC compressor to pre dry the air so that the windshield doesn't have MORE moisture blown onto it, making things worse.
  1. This part is important....the DEFROST action is the DEFAULT, should the HVAC system somehow fail...
  2. Loss of vacuum to move diverter doors
  3. Loss of electrical servos/actuators
  4. Electrical command failure from the PARK POSITION or default position of the servos/actuators..... etc, etc.
Sooooo..... air only coming out of the defrost ducts allows you to AT LEAST have a somewhat clear view through the windshield... even ifvno heat can be added for any one of many reasons.

This boils down to having not only an electrical control problem.... but also something mechanical has failed (the usual culprit is an actuator with their very brittle gears).

Try this...
Disconnect your NEGATIVE battery cable for at least 1/2 hour.
Then reconnect the cable and wait.
WAIT for the actuators to find "HOME" or a default position.
Start engine,
Attempt to use various heater settings.

Report back.

Don't worry about head gasket failures... not yet anyway.......and where did you get that idea?
 
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