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2004 chevy trailblazer_ls
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Discussion Starter · #1 ·
Ok, I have read just about every thread and post about this out there I think... Here is what's going on. I am driving 55-65 mph in open conditions, ambient temp about 85 deg, A/C is on. With no changes in driving the truck will begin to overheat and gauge will travel between 210 and 260 back and forth. I have replaced the following for various reasons:

Radiator (was leaking)
Water Pump
Thermostat
Radiator Cap

During the overheat you can see the Surge Tank boiling and totally filled? Coolant comes out behind rt ft tire (surge overflow?)

I can not see any visible leaks but when engine cools and I open radiator cap the system is low and upon adding coolant it seems like there is air bubbles coming up and dont seem to stop?

Thanks in advance!
 

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2003 gmc envoy_slt
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7,190 Posts
Are you getting any CEL's?

When the gauge goes to 260, does the fan get loud?

The least expensive fix would probably be a new fan clutch. If the fan is good, you may have a blown head gasket. :m2:

Good luck, I'm sure more members will jump in.
 

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2007 chevy trailblazer_ss_3ss
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767 Posts
did you purge all the air out of the system when you replaced the radiator/t-stat/waterpump?
 

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2004 gmc
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26,181 Posts
I6 engines don't have the same tendency to trap air and need to open a burp valve as the V8s. We don't even have a burp valve, so I don't think there's even a specific procedure to follow other than make sure the overflow tank is filled to the proper level.
 

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2005 chevy trailblazer_ls
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916 Posts
Check for restricted air flow through the radiator. I had an overheating problem that resulted from a front-end collision that pushed the tranny cooler & AC condenser up against the radiator. After replacing the head gasket twice and the head once, the problem was finally found. I haven't had a problem since the condenser was pulled away from the radiator. This happened about two years ago. I posted the incident if you care to look for the post.
 

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2004 chevy trailblazer_ls
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10 Posts
Discussion Starter · #6 ·
Ok next??

Ok. I have checked the following, please share your input:

Truck has been sitting for 4 hours and is totally cooled down.

Surge tank is totally full?

Radiator cap was very pressurized upon removing cap and no fluid is visible in radiator tank (just filled yesterday).

Clearance between condenser and rad is good but there are some bugs in the fins on the condenser.

What do ya'll suggest I look for from this point in diagnosis.

Thank you so much in advance. I am new here but have found a lot of valuable info and really appreciate the quality of info here.

btw - Roadie you really seem to know your stuff and I look forward to your response on this reply.
 

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2004 chevy trailblazer_ls
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Discussion Starter · #7 ·
Forgot to mention...

I also grabbed the fan while at idle, with a towel of course, the fan stops and starts making a lot of noise (raising hell is probably a better desc). When I release it didnt act as though it could return to idle speed. Dont have money for scanners or dealer right now either..

Thanks!
 

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Northwest Chapter
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11,824 Posts
Go to Advanced Auto/O'Reillys etc and use their scanner, its free and will let us know if there are codes we need to worry about.

Have you checked your oil? Is it normal looking, or is it milky? If its milky, your head gasket is blown.
 

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2004 chevy trailblazer_ls
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Discussion Starter · #10 ·
Go to Advanced Auto/O'Reillys etc and use their scanner, its free and will let us know if there are codes we need to worry about.

Have you checked your oil? Is it normal looking, or is it milky? If its milky, your head gasket is blown.
I have an OBD II scanner but that is all it does. there are no codes present. the oil looks good, mobil 1 and very clean.
 

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2003 gmc envoy_slt
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7,190 Posts
I don't think it will cause over heating, however if the over flow tank is full but the coolant is low in the radiator, the radiator cap isn't doing it's job. The rad cap should allow coolant to be sucked back into the radiator as it cools. :m2:
 

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2004 chevy trailblazer_ls
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Discussion Starter · #13 ·
I just replaced the rad cap 4 days ago and the problem didnt go away. is it possible that its a DOA rad cap from autozone?

I have noticed that when it does overheat and i turn on the heat full blast or the a/c it gets hotter faster???:undecided
 

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2002 chevy trailblazer_ltz
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3,250 Posts
I'm leaning toward what a couple of others posters mentioned....a possible blown head gasket. One symptom is air bubbles being blown back up through the radiator. Another is the disappearing coolant.
 

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2004 chevy trailblazer_ls
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Discussion Starter · #15 ·
Ok. I let the truck sit all afternoon with the radiator cap off and the surge tank cap off and all that coolant ran back in and filled the radiator?

So it seems that the real issue is that the coolant is filling the surge tank when the engine is running and once the surge tank gets totally full the engine begins to overheat due to a lack of coolant?

Does this theory fit in and make sense to anyone else??:crazy:
 

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2004 gmc
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26,181 Posts
I think coolant being pushed into the overflow tank by excess pressure in the radiator is an effect, not a cause. The cause is that the radiator has too much pressure build-up because it's too darn hot.

If you spot the temp gauge above 220, you need to just slow down, turn off the AC compressor, open the windows, and turn the HVAC system heat up full with the fan on high and use the heater as an aux radiator. Don't let the gauge get above 220, and it should not boil and shove coolant into the overflow tank. If doing those things doesn't help, it's time to quit driving it until you or a mechanic find the root cause.

Never let it go to 260, not even once. That warps things.
 

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2004 chevy trailblazer_ls
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Discussion Starter · #17 ·
Ok last post before it goes to dealer... I drove about 150 miles today and it never ran hot...

I could smell coolant through the vents while a/c is running??

Would this be a sign of a head gasket issue??

Checked coolant at end of day after engine cooled and the radiator is low on fluid.

All posts are appreciated. Thanks!
 

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2002 gmc envoy_slt
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549 Posts
coolant smell through vents is usually an indicator of a heater core leak. Have you checked under your front floor mats for coolant? Does the smell get stronger when you run the heat. Also, you'll experience your windows fogging up more than normal if your heater core is leaking. If not...then I'm leaning towards head gasget also. HTH c good
 

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2002 chevy trailblazer_lt
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211 Posts
+1 on getting the coolant checked for the presence of hydrocarbons (exhaust gases). Every time the piston goes up, it pressurizes the cooling system way beyond the 15 pounds its rated for, forcing coolant into overflow. On the downstroke, it is sucking coolant into cylinder and its burning off. Up-down up-down ect....
 
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