Overheating issue...please chime in

[zephyr429]

Greeting. I've been a member for a few years now, and the info/advise here is invaluable. This is my first post and I could really use some help. I'm having an overheating issue that I cannot track down. Any help would be a tremendous help.

My daily drive is a 2003 TB (4.2, 4x4, 261k miles), and I commute 64 miles on the highway each way every day and never had an issue with it that I couldn't find the answer to here on the forum (thanks for all the info) until now.

A little over a month ago my air went out. The compressor had given out and I sent it to a local shop to have this fixed. Here in Georgia the summers can be brutal (96-102 degrees daily) so I didn't hesitate to have the AC repaired, worth every penny. The day after I got the TB out of the shop I headed to Atlanta for work. I made it half way before I got the "check gauges" light. I was starting to over heat. The needle was just past the the 3/4 mark. I pulled off and popped the hood to find that the water had migrated into the reservoir. Left the hood popped to cool as I waited for the tow truck. Once I got it home I took a look and found that the radiator cap had broken in two pieces. Replaced it and went on my way. Started to over heat again. The temp stays normal (to the left side of 210) as long as I'm driving around town, even with the air on, however once I hit the highway it will tick up to 2 marks above normal after about 10-20 minutes. Service engine soon is not on.

Two years ago I:

- replaced the fan clutch (Dorman...clicking piece of crap)
- replaced the radiator (broken upper hose connector)
- replaced the water pump
- replaced upper and lower radiator hoses

Trying to track the current problem down I have:

- changed the thermostat
- changed the fan clutch (OEM AC Delco)
- cleaned the radiator (small blockage in the center)
- flushed the engine and radiator
- had the fan clutch software updated (GM stealership...$109 to plug up a computer and hit buttons)
- cleaned throttle body
- replaced oil sending unit (lost oil pressure at idle, problem hasn't returned)
- checked the temp gauge against my scan tool and it's dead on.

I got it back from the radiator shop yesterday and test drove it down the highway today to check for progress. Still moves up 2 marks. But I did notice that it feels like it had no acceleration. The transmission would hit passing gear just to speed up, and my gas mileage is down from 19.9mpg on highway to 15.1 mpg. I have also ruled out the head gasket as I have no water in my oil or oil in my water.

My line of thought is starting to lead to towards maybe a clogged or clogging catalytic converter causing excessive heat in the engine. if this isn't the issue then I am at a loss and have no idea where to go next. It's starting to make me question all that I thought I know about engines.

I love my TB and have always planned to drive it until the wheels fall off, and I refuse to let a few exrta degrees be the death of her. Any help or advise would be greatly appreciated.

 

[Sparky]

I'm kind of leaning towards the cat, but that's just a guess on my part.

 

[Mounce]

Time for an exhaust backpressure test to see.

Could be two totally unrelated issues though.

 

[Blckshdw]

Interesting idea on the cat being the source of the heat. Buddy of mine has the same issue with his Voy, and we've replaced all those same parts as well. Would be interesting to see if the cat has anything to do with it

 

[MAY03LT]

I have also ruled out the head gasket as I have no water in my oil or oil in my water.

A blown head gasket can also allow combustion into the coolant. They make a combustion gas test tool just for this:

https://www.amazon.com/dp/B000NPDL76/?tag=gmtnation-20

I'm not suggesting that is the problem in your case, just throwing it out there. Overheating on the highway only usually points to a flow problem. Clogged passages in the radiator is the number 1 offender in this case.

 

[gmcman]

I agree, don't rule out a head gasket. If the combustion gets into the coolant, the aeration will disrupt coolant flow.

Definitely get an exhaust back pressure test as well as a coolant pressure test.

 

[Mooseman]

What brand thermostat did you use? It might be crapping out despite its age. Did you replace the temp sending unit? It could be giving false readings.

 

[Sparky]

I gathered from his post that he had just replaced this stuff recently.

 

[zephyr429]

The thermostat is a stant. It's been in maybe 2 weeks. As for my temperature sensor, I don't believe it's the problem because it reads dead on with what my scan tool tells me, as well as what my IR thermometer is reading.

Yes all of those parts that were listed as being replaced to find this issue were all replaced within the last 3 weeks.

Just a question about the head gasket. I've never actually blown a head gasket before so I only know what I've been told. Wouldn't there be cross contamination of my oil and water? Or water loss through the tail pipe? I don't lose a drop of water and there is no mixing of the two.

Another reason I'm leaning towards the CAT is that for a while I was getting a SES light for burning rich. I finally tracked it down to a bad fuel pressure regulator. This plus the lack of power on acceleration. I do agree that it may be unrelated and just a coincidence occurring at the same time. I will have my fingers crossed for sure.

Tomorrow I'm taking it to the muffler shop to have the CAT checked. I assume they will do a back pressure test. I'll update as soon as I get the results.

Please keep chiming in. I could use all the help I can get.

 

[Sparky]

It depends where the head gasket went bad. If it blows between an oil channel and coolant channel then yes you get cross contamination. But, if it just blows between the water channel and cylinder, then the cylinder shoves gasses into the coolant system but there is no oil/coolant cross contamination. This is what happened to my parents' old 96 Ford Windstar with the infamous Ford 3.8L. However, it would cause it to rapidly overheat and it would do it quite quickly when accelerating due to higher engine speeds pumping combustion gasses into the cooling system faster. I don't want to say for sure as there is always that chance, but I'm fairly confident this isn't your issue since it only happens when cruising.

 

[zephyr429]

I'll keep that in mind if it's not the CAT as kind of a worse case scenario. It's just strange, annoying, and expensive. I have never had a over heating issue like this. It all started after the AC repair. Well maybe before and I wasn't aware because I couldn't run the air. Lol.

 

[Mooseman]

Did you check the fan fuse and swap the relay with the one for the headlights? (they are the same) Even though the fan clutch is new, did you test it?
How to test the electro-viscous fan clutch

 

[MAY03LT]

Yes all of those parts that were listed as being replaced to find this issue were all replaced within the last 3 weeks.

So it did get a new rad not just the cap? Just making sure we're on the same page.

 

[Chickenhawk]

I am almost ready to say your cat needs replacing anyway, whether it's the source of the overheating or not. (The engine struggling against a blocked exhaust could very well run hot.)

Two reasons I say this. You report running rich, to the point that you got a trouble code. Even a few minutes of running too rich could plug up your cat. (They run on a VERY narrow range of air/fuel mixtures.)

Secondly, you reported that your "normal" temp as a tick to the left of center on your gauge. Normal is actually dead center or even a slight tick to the right.

Whether the gauge is entirely accurate or not (which it isn't) and whether it indicates a linear temp or not (which it doesn't) is irrelevant. If it has been running for any length of time indicating to the left by even a tick or two, you have started plugging up your cat.

 

[Sparky]

Well I have to disagree slightly about the "even 1 tick to the left" comment. My 2002 did, for a very long time. Never plugged the cat because it was still warm enough to be in closed loop so it never was running rich (checked temperature with a scan tool, 190-192 degrees, and mpg and power was always good). Now, it did move up to straight 210 (195-198 actual according to scan tool readout) when I replaced the thermostat after it started to not hold temperature, but that didn't happen until 80k+ miles after I got it.

Since mine was normally 1 tick left, and mpg and stuff was good, I was OK. Now, if your truck normally ran straight up, and then it at some point started falling 1 tick left, then that could likely indicate a tstat issue. And of course 2 ticks would be far enough that it would be not hitting closed loop, but your mpg would show that pretty darn quick.

My 2 cents of experience, for what it is worth.

 

[littleblazer]

Are you losing coolant? I'm sorry if I missed it.

 

[zephyr429]

@Mooseman : the thought had occurred to me about the fuse and/or relay but the fan engages with no problems. Moves plenty of air. However if I am incorrect in my logic we have 2 other trailblazers that I can pull one from. My mom loves my trailblazer and I found 2 dirt cheap, an 04 with a rusted out frame, but a great low mileage engine, and a 03 with great body and frame, but a locked up engine. Im gonna put the 04 engine in the 03 and call it a day. Haha.

@MAY03LT : the radiator was replaced 2 years ago, and the cap 2 weeks ago. There was a blockage in the center of the radiator that was cleared 3 days ago at a radiator shop.

@Chickenhawk : my "normal" isn't one mark below 210, it's just touching the left side of the 210 mark. I calibrated it using my scan tool when I pulled the cluster out to solder in new stepper motors and bulbs. But when I run on the highway it will move 2-3 marks above 210. It will slowly back down to normal if I turn the air off. But if I hit passing gear or any incline it climbs right back up.

@littleblazer : no I'm not losing any coolant, nor do I have any cross contamination of the water and oil.

@Sparky : the code I was getting was for burning rich on I believe bank 1. My gas mileage was in the toilet and would run fine except for an occasional elevated rpm when the light would trip and smell of gas outside and inside. RPMs would hold at 950 vs 650. I could get it to go back to a normal idle rpm by clearing the code with my scan code. This would last a few days or maybe a week. This problem was fixed months ago though, although it took me a while to diagnose the regulator with only 1 day a week off.

As for the burning rich, that issue was corrected with a new fuel pressure regulator. But the "service engine soon" light came on a several times before I could get it done. I do fear that I let it go to long before narrowing it down to the regulator and ruined my CAT. It's going to the muffler shop today to have it checked. If it is clogged it would explain the lack of acceleration and I'm hoping that if it is clogged the build up of heat and pressure if causing the overheating.

I would like to thank everyone. With all the posts and wealth of knowledge collectively from all the members, I have pretty much become an expert on trailblazers. I drive 128 miles round trip 5-6 days a week and if it wasn't for you guys there is no way my trailblazer would still be on the road.

 

[gmcman]

What coolant was used when it was replaced? Just asking because these motors use dexcool and is orange in color.

Also, keep in mind that 218 deg is still considered normal temp for this motor. 218 deg while on the warm side, may result in 1 or 2 ticks to the right of straight up. The graduations are closer together after the 210 deg mark.

What temp does your scan tool read when the temp needle is 2 or 3 ticks to the right?

 

[Sparky]

That rich is very likely to have caused a cat issue. Interested to see what the results are.

 

[zephyr429]

@gmcman : I only use dexcool. I noticed when I got my trailblazer several years ago that the graduation was closer together after 210. I could tow a fully loaded trailer in the dead of a Georgia summer and the needle would not budge. Two ticks the the right is abnormal for mine. If I let it go to the third mark past 210 I get the "check gauges" indicator.

@Sparky : I'm having the CAT checked today at 4. I'll update with the results.

 

[gmcman]

What does your scan tool read when it's two ticks to the right?

Reason I ask is the stepper motors are notorious for going bad.

That doesn't mean yours aren't accurate, since your light is turning on.

Just trying to fill in the blanks.

 

[zephyr429]

Well back to the drawing board. My CAT is clear and free flowing. About the only part I haven't replaced is the temperature sensor above the thermostat. It just raises one question, when I temperature sensor goes out is it all or nothing? Meaning could it be sending skewed reading, or would it show 0. Maybe it was damaged when I originally over heated a month ago. And this over heating could have been caused by the small clog in the radiator that I just had cleared. If it damaged the sensor then I've just chasing ghosts.

@gmcman : I replaced the stepper motors a while back. I think I'm going to take a reading with my IR thermometer at normal and when it's two marks towards hot to see if there is a difference. If they are the same I would think its the temperature sensor. It just hit me that if I'm gauging it with my scan tool, it's getting the temperature from the same sensor as my gauge. So it would match up even if it is defective.

 

[Sparky]

Bad sensors can do anything from just dead 0 to incorrect readings, to random readings.

 

[littleblazer]

I'm half wondering if you may have air in the system or something like that. You should not be overheating while moving even with a stuck t-stat. Maybe try turning the heat on all the way next time it happens and see if it comes back down. If it doesn't start dropping it could be a the sender. Even with my fan not working at all the hvac blower was enough to keep things under control.

 

[gmcman]

Get the front of the vehicle in the air, either facing up the driveway or on jack stands..just be sure the radiator is the highest part of the cooling aystem.

This should ensure you get the air bubbles out.

Also, the fact you had a clog in the radiator leaves the option open of having clogs elsewhere. Dexcool doesn't like to have air mixed with it, I think that's what makes it gel.....not 100% sure.

I wouldn't try the temp sensor unless you get a special slotted socket, or make one yourself...they can be a real pita.

 

[zephyr429]

The entire system was flushed a few days ago by a radiator shop. I thought of air also. I have two trailblazer engines in my garage right now. I'll prolly swap the sending unit out and run it down the highway.

 

[gmcman]

Not sure what radiator cap you have, but If you didn't get the new one at the dealer, I would go to the dealer and get one.

Just a base to cover.

Have you pressure tested the cooling system yet?

The only two things that were first in line with the overheating are.....someone changed your compressor, and your radiator cap was busted.

The cooling system must hold a pressure, don't know off hand what the 4.2 is but likely 15 psi.

 

[zephyr429]

Its an oem cap. I use oem when ever possible. I haven't pressure tested it though.

 

[gmcman]

Also, I do know the radiator cap is stubborn to tighten, it feels like it's tight at first, but it likely can be turned more.

Its an oem cap. I use own when ever possible. I haven't pressure tested it though.

OEM aftermarket or OEM from the dealer?

 

[MAY03LT]

The clogged radiator is still bugging me. Mostly because I don't know what goes on with the shops process for determining a clogged/unclogged rad, and partially because the passages are so small that once they are gunked up, that's all she wrote.

Can you duplicate it sitting in park? Like if you held the rpms up for a couple of minutes will the temp go two ticks right?

 

[Mooseman]

If you're going through the trouble of replacing the sensor, while you're there, take out the thermostat and test it in boiling water to see if it opens at the rated temp. It can happen to have a bad new stat. Maybe it doesn't open enough. I just don't trust Stant.

 

[gmcman]

To clarify my statement about the cap, I was referring to a genuine ac delco cap.

 

[zephyr429]

Ok. Time for an update. Sorry for the delay I have been out of town for a few weeks house sitting for a friend.

Today I had the time to remove the alternator to get to the coolant temperature sensor and changed the sensor. Put everything back together and test drove it down in interstate 20 miles. Everything was perfect for 20 minutes until I turn around to come back home. The temp went up two notches again and maintained until I got back off the highway. The needle wouldn't go back down until I turned the heat all the way up to 90. Within a minute the temp was back to normal and stayed there until I returned home. However I did notice that it took about 30-45 seconds for is to start blowing warm. The radiator has been in for two years but I did notice a little water had leaked out from under the radiator cap. If it's leaking out it may not be pressurizing.

Can lack of pressure cause an overheating issue?

Tuesday I'm having a local shop swap out the radiator on a warranty to claim. I'm not thinking that it's still partially clogged. I'm gonna have the upper and lower hoses changed as well just to be safe. I hate to have someone else do the work but I just don't have time.

Attached are pics of the temp gauge to show what I'm talking about when I say two ticks up. The lower temp reading is what is normal for my trailblazer and the higher is the problematic reading.

High Reading



Normal Reading



@gmcman :the radiator cap is oem AC Delco ordered from Rockauto. Brand new.

@Mooseman :the thermostat tested fine.

@MAY03LT :I'm thinking the same now. New radiator is going in this week.

 

[Mooseman]

It is entirely possible that the radiator crapped out. My son put in a brand new one in his Silverado and it was cracked, leaked everywhere.

 

[zephyr429]

@Mooseman @gmcman @MAY03LT : Was out tinkering again before I sent it to the shop. Found that at normal temp it's between 207 and 210. Once it start going up its at 220-212. And then my oil pressure drops to zero. It's not actually dropping. The truck just thinks it is. Any ideas on that?

 

[Blckshdw]

And then my oil pressure drops to zero. It's not actually dropping. The truck just thinks it is. Any areas on that?

Flaky oil pressure switch. It's right above the oil filter.

 

[MAY03LT]

Does the 'check gauges' light come on when the oil pressure drops to 0?

 

[zephyr429]

Yes it does. I'm guessing that it rules out the problem being the step motor for the gauge. It only happens when I'm overheating and only at full stop. Once I start rolling the needle goes back up and the "check gauges" light goes out.

All of the trouble started when I had the AC compressor and all other required parts replaced to fix my AC.

 

[Sparky]

Possible they dinged up some stuff. Before you change that switch check the wiring to it. By the way, what oil filter you using?

If you're getting coolant seeping under the cap then yeah it isn't holding pressure properly and that can cause it to run warmer (you can get steam pockets/bubbles in the system too). Good thing is you're not really overheating yet, even though it is running warm.

 

[zephyr429]

So time for an update. I believe that I've corrected the over heating issue. After changing all the parts and chasing my tail it was staring me right in the face. I replace the radiator on a warranty claim, telling the it was leaking, and the over heating issue seems to have went away. Driving with a scan tool to watch the temp it never rises above 210 now. I didn't put to much thought into the radiator because it was only 2 years old, and had it rodded out 2 weeks ago. Evidently it didn't clean it well enough to maintain cooling.

Now I only have to track down the cause of the false no oil pressure indication. I'm gonna crawl under it and look at the wiring for it.

Anyways thanks for everyone help! It was Invaluable.