Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 16 of 16 Posts

·
Registered
2004 isuzu ascender
Joined
·
42 Posts
Discussion Starter #1
OK as the title states my engine only overheats when the AC is on. If I drive with it off the temp is at normal position. Things I have done is a new water pump, new fan clutch, replaced the coolant and a new serpentine belt. What on earth can be the problem? Do you think the radiator is so old it can't handle the extra load of the AC being on? And to note the AC still blows ice cold air.
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
1,029 Posts
OK as the title states my engine only overheats when the AC is on. If I drive with it off the temp is at normal position. Things I have done is a new water pump, new fan clutch, replaced the coolant and a new serpentine belt. What on earth can be the problem? Do you think the radiator is so old it can't handle the extra load of the AC being on? And to note the AC still blows ice cold air.
Did you flush the radiator and use a 50/50 mixture of Dexcool coolant and water?

You may also want to check this thread out:

http://forums.trailvoy.com/showthread.php?t=44109
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
Does it overheat only when you're driving slowly or in traffic? That may be a fan clutch that's not running as designed. Yes, you changed it, but did you check it for functionality, especially when overheating? The fuse, harness or speed control relay (or the new fan clutch itself) could be at fault. A high end scan tool that can read commanded fan RPM versus actual fan RPM might be necessary, if you don't have an oscilloscope to apply to the relay's PWM output that goes to the fan.
 

·
Registered
2004 isuzu ascender
Joined
·
42 Posts
Discussion Starter #4
Ralph, I will try and replace the thermostat as well as clean out the radiator.

Roadie, Sorry man I'm not that mechanically inclined so you lost me. NTB did all the work for me, so hopefully they did all of what you mentioned.

Thank you both for your response.
 

·
Registered
2004 isuzu ascender
Joined
·
42 Posts
Discussion Starter #5
On the engine temp gauge I know that the center position is 210 degrees. Can someone tell me what the 3rd hash mark temp is? I run just under the 210 mark almost all the time except when the AC is on. The AC then climbs to the 3rd hash mark and stays there. Is this extra heat damaging my oil prematurely?
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
Can someone tell me what the 3rd hash mark temp is?
Just do the math. Simple interpolation. The far right mark is labeled 260, right? Count the number of hash marks on the gauge between 210 and 260. Divide that number into 50. That's how much each hash mark is worth. Multiply it by three, and add to 210.
Is this extra heat damaging my oil prematurely?
Yes. And other engine parts and accessories and fuel economy is suffering.
 

·
Registered
2004 isuzu ascender
Joined
·
42 Posts
Discussion Starter #7
Just do the math. Simple interpolation. The far right mark is labeled 260, right? Count the number of hash marks on the gauge between 210 and 260. Divide that number into 50. That's how much each hash mark is worth. Multiply it by three, and add to 210.
Yes. And other engine parts and accessories and fuel economy is suffering.
I have an Ascender it only has 4 hash marks and no numbers. Thanks for telling me the last hash mark is 260. I might have to change my oil out at 3k then.
 

·
Registered
2004 chevy trailblazer_ls_ext
Joined
·
11 Posts
Hello all, I'm having similar problem 04 tb ext 4.2. In the last week I have changed water pump(first), and then fan clutch(yesterday). I ran the car with air on full and drove for 30 mins and it was fine until it finally creeped up to third hash mark so I just turned off air to prevent overheating and it went back down to 210. Just as a note, it was 106 here yesterday. Any thoughts? Thanks in advance.
 

·
Registered
2002 gmc envoy_slt
Joined
·
3,203 Posts
What are the temps if you drive steady state of 40 mph or higher? - Does it still get that hot?

If highway speed is fine, then its most likely an airflow issue, if not then there's more than likely another issue with the cooling system. Went through a similar issue a few weeks ago.

Things to check:

1) Shine a flash-light through the radiator/condensor and check for both light passage AND debri. If there's debri, hose it out from the engine compartment out....reverse of how it flowed in.

2) Like Roadie stated, check the wiring going to the clutch, as well as the fuses and relays for the clutch circuit. The a/c condensor gets any air first and warms it up for the radiator, so any air hitting the radiator is quite abit warmer than ambient with the a/c on, so more air is required to cool it. (It places approximately a 160 degree heater in front of the radiator). Its possible the fan clutch isn't speeding up when the a/c is on, you should be able to perceive the fan turning faster (blowing more air) with the a/c on, if not, there's a problem. - Also note that there was a PCM update issued for the new clutch to increase clutch engagement during a/c usage, it will make more noise, but also move more air.

3) Obviously the coolant flow through the radiator plays a big part, you can always pull the radiator and push water through it to test it. If the truck had the original coolant in it from '03-'04, a good flush may be in order to clean out the passages. (Mine's been drained and refilled a couple of times).

4) I know you replaced the thermostat, but what brand did you use? - Some of the after market units, Motorad (sold by the Autozone) for instance, has a significantly smaller valve openning.....which means, you guessed it, less coolant flow. (This was one apparently an issue on my Envoy).

5) Does the recovery tank bubble or does the level change substantially as the truck warms up? - A bad pressure cap can allow bubbles/steam to form, allowing the engine to run hot. (Might not be a bad idea to test it, although a new cap is like $9, might be cheaper just to replace it, unless you have a cap tester).

I was sure my LS1 fans had given up the ghost, replaced them with a 4600cfm set of flexalites (2.5x the flow), still ran hot. Replaced the thermostat (again) with an ACDelco unit and tossed on a new radiator cap, needle barely passes 210 no matter how hot it is or how I drive it with the a/c on.

To aid in coolant heat transfer, a bottle of either Red-Line Water Wetter or Purple Ice also improves efficiently and may help lower the temperatures as well.
 

·
Registered
2004 chevy trailblazer_ls_ext
Joined
·
11 Posts
The thermostat actually hasnt been changed in about 2yrs except by the dealership when I bought because it was running warm kinda like this. So what do I need to check wiring on clutch. And are the fuses the 20 and the 45 under hood? Also when I had the VVT replaced he flashed the PCM, but this was done before the water pump and fan clutch were done so would that have been included in the flash?
 

·
Registered
Joined
·
1 Posts
fan suddenly stops turning

I have a Chevy trailblazer 2005 when I put the a.c. on the fan will sometimes stop turning and car will over heat what should I check out first
 

·
Registered
2004 chevy trailblazer_ls
Joined
·
1 Posts
My engine overheats when ac is on, or when it's off and I'm at a stoplight and it's hot outside, the fluid in the Reservoir boils and smoke comes from under the hood. What should I start off replacing? The thermostat??
 

·
Registered
Joined
·
9 Posts
Just wondering I have a 02 trailblazer and it is overheating with a/c on .and I replace the thermostat waterpump radairor upper radiator hose heater hose not the fan clutch no check engine light it does go back to normal when a/c is off. It wont overheat with the a/c off. Does anyone have a thought on what can be? And the radiator cap and resavior also no smoke
under the hood or tailpipe no bubbles in the reservoir
 

·
Registered
2002 chevy trailblazer_lt
Joined
·
515 Posts
Can you detail what constitutes 'overheating' here? Do you get a warning from the dash? Steam out from the underhood? Or simply a gauge reading that seems higher than normal? We need actual numbers here.


Even without a code the fan clutch can be not functioning properly. Another possibility is an issue with the AC hi pressure sensor. As far as I know the PCM needs this sensor input to know when to command the fan clutch on for the AC condenser to operate properly.

I would check the operation of the fan clutch as well as the AC hi pressure sensor. If you are a do it yourself sort you should get a cheap bluetooth obd adapter and a smartphone app and you can monitor these things yourself. The inexpesive bluetooth readers require some hands on learning of how to work with them but they cost a fraction of what more user friendly scanners cost.
 

·
Registered
Joined
·
9 Posts
On my 02 trailblazer I had it check out by a mechanic and they hooked up a scan tool they did not find anything wrong with it except a camshaft sensor. They looked and no leakes or anything. they did a test and told me I blow a head gasket but I have no sign of it at all. Except for overheating ac on. The temperature reached the fourth line before 260 degrees is the red zone on it. I am wondering if it is the head gasket. Just wondering if the is just engine just ready to go out out completely. So I just wondering if it could be anything eles. I will take a look at the bluetooth scanner and thank you letting me know about the bluetooth scanner I will look into it. To see if there is something that the missed when they hooked there's up.
 

·
Registered
2002 chevy trailblazer_lt
Joined
·
515 Posts
Just to clarify here. When I spoke of reading things with the obd adapter I am NOT talking about codes. I am speaking of live realtime data. For the fan speed I mean reading the actual current fan speed and comparing that with the PCMs commanded fan speed.

If the test the mechanic did was maybe a comlression test, or testing for combustion gasses in the coolant system and that came back as a head gasket failure then that is likely correct. A faiked head gasket isn't always going to present itself in some catastrophic way.
 
1 - 16 of 16 Posts
Top