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Discussion Starter #1 (Edited)
I have a 2001 Chevy Tracker 2.0 I4 Manual Trans 147k miles, that overheats but only at high speed.

Symptoms: Overheats when engine is warm and driven over 35 MPH. Under 35 MPH with heat on it runs OK. No check engine light when running. I'll have to check it when not running.

I've replaced the radiator, radiator cap, thermostat (twice), both belts, pulled the water pump and it spins freely, impeller appears to have no damage and is not overly worn.

After these things someone suggested that maybe I have a clogged cat, so I pulled the front o2 sensor and drove it around and it was better, I could drive at 55-60 MPH OK, but to truly test it I did high speed accellerating up hill and then it started to overheat again. I figured it was due to not having relieved enough of the back pressure with the small hole or it was running hot due to the bad code from the o2 sensor (I had unplugged it).

So then I pulled the rear cat off and ran it without the rear cat on (after pulling battery cable to reset codes) and it had the same symptoms. I could get to 55+ mph, but if I thrashed it, it would overheat.

I just tested again, this time sitting still and sitting still I can not get it to overheat, even if I run the throttle over 2.5k rpm for a few minutes. So it will only overheat under load (rear cat off).

So now I'm researching again, but I'm running out of rope. Either both cats are partially clogged, and there is some other issue, or there is some issue I haven't discovered yet.

I've searched this forum and only two issues seemed to possibly fit. One got a bad aftermarket t-stat, then one, maybe two others had a bad crankshaft pulley.

How do I test the crankshaft pulley? Where should I buy a t-stat I know will be good?

Let me know if you have any question I haven't answered.
 

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In stead of buying another t stat, check yours by putting it a pan of water and heat the water. The t stat should open at the temp its rated for ie 195°f. That will tell if your stat is bad or not.
 

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How are you judging "overheating"? :huh:

Boil over? Dash temp gauge? An independent temp monitoring (IR) device?

Any coolant loss?
 

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Discussion Starter #4 (Edited)
How are you judging "overheating"? :huh:

Boil over? Dash temp gauge? An independent temp monitoring (IR) device?

Any coolant loss?
Dash temp guage currently. I have an IR device, but have only used it while stationary and not overheating. Would it be helpful to drive it til the dash gauge says overheating and pull over and measure with IR? What would that tell me? How hot is overheating and where should I point the IR gauge?

Prior to removing the cat, it was literally boiling over.

no coolant loss.
 

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Discussion Starter #5
In stead of buying another t stat, check yours by putting it a pan of water and heat the water. The t stat should open at the temp its rated for ie 195°f. That will tell if your stat is bad or not.
Going to try this. Just tried it with the stock stat and the first aftermarket one I took off after deciding it was the wrong one.

They both opened at 90C which is over the 80-82C rating they are rated for. I am using a very reliable thermometer.
 

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1. It would be advantageous to know IR temps at key locations, with the system as hot as possible. Top and bottom of Rad, T-Stat housing at a minimum.

2. How much faith do you have in the dash gauge? :huh: An independent gauge might be in order. It is possible to have a sending unit fail in odd ways too.

3. Replacement radiator...was it NEW?

Edit:
I see now that you have literally boiled over in the past. That may negate the dash gauge being in error.

Ever test for combustion gases in the coolant (rad)? :huh:
 

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Just a thought. Is your fan shroud in place and intact? Air flow at speed is directed by the shroud. I have seen (rarely) these symptoms when shroud missing or broken. :(
 

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Discussion Starter #8
Just a thought. Is your fan shroud in place and intact? Air flow at speed is directed by the shroud. I have seen (rarely) these symptoms when shroud missing or broken. :(
Hmm...my fan shroud is intact, but not completely held on. It's just kind of sitting there.

Not trying to dismiss your advice, but it's been that way for a very long time. Probably 50,000 miles or more, long before this problem started.

Replacement rad was new. from RockAuto. It's thinner than the rad I took out, which was also an aftermarket part. The top plastic bit broke on the stock one.

This vehicle has always ran exceptionally cool, it has to be something substantial, IMO.

I have not tested for combustion gasses in the coolant. The coolant is not fouled, nor is the oil. I've always driven conservatively. If it's a head gasket, I'll be surprised, but not shocked I suppose. I've read it's a $45 test at the auto parts store. Is it worth that?
 

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On the Combustion Gases test...it may be worth a shot if all other troubleshooting attempts fail. A local Repair Shop may offer the service for less money than you purchasing the kit.

Ever have any signs of air collecting at the radiator upper most area or bubbling in the overflow tank? :huh:

I don't think it's a fan shroud issue, as by design it aids in pulling in FAN generated air at no and low speeds. Once the vehicle is underway, air movement is force-fed through the radiator.

Along those lines...is your A/C condenser in good shape? Free of debris and without bent fins that can impede air flow?
 

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They both opened at 90C which is over the 80-82C rating they are rated for. I am using a very reliable thermometer.
Two suggestions ...

- first, get an OE thermostat (try Suzukicarparts.com), the thermostat on this engine is on the return side of the cooling circuit and not on the cylinder head outlet as most are.

- second - measure the temperature, the dash gauge is not a precision device (notice it has no numbers?) - you may not even have a problem.
 

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Replacement rad was new. from RockAuto. It's thinner than the rad I took out, which was also an aftermarket part. The top plastic bit broke on the stock one.
This is a potential problem area - the replacement radiator quite possibly has less cooling capacity than the original - it may be a single row radiator, I believe the OE is double row - if that is the case you have less surface area for the heat exchange to occur, and given the fact that your overheat occurs at higher speeds, when the engine is developing more heat energy, I would not be surprised is this turned out to be the cause.
 

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Discussion Starter #12
This is a potential problem area - the replacement radiator quite possibly has less cooling capacity than the original - it may be a single row radiator, I believe the OE is double row - if that is the case you have less surface area for the heat exchange to occur, and given the fact that your overheat occurs at higher speeds, when the engine is developing more heat energy, I would not be surprised is this turned out to be the cause.
Yes, the replacement is a single row and the one that I took out is a double row. I kind of figured that wasn't a big deal because the car always ran so cool.

I'm going to pull the thermostat, test it in water and put the double row rad back in, maybe this weekend. Those sound like viable options. I suppose it's entirely possible I screwed up the cooling system with substandard parts while trying to troubleshoot that side of things before I moved on to the exhaust restriction.
 

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Discussion Starter #13
On the Combustion Gases test...it may be worth a shot if all other troubleshooting attempts fail. A local Repair Shop may offer the service for less money than you purchasing the kit.

Ever have any signs of air collecting at the radiator upper most area or bubbling in the overflow tank? :huh:

I don't think it's a fan shroud issue, as by design it aids in pulling in FAN generated air at no and low speeds. Once the vehicle is underway, air movement is force-fed through the radiator.

Along those lines...is your A/C condenser in good shape? Free of debris and without bent fins that can impede air flow?
Only time I've gotten bubbling has been when it boils over. Otherwise no signs of anything like that.

A/C condenser is in good shape and clean as far as I can tell. I looked in there last night because I had the same thought.
 

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I had similar thoughts on the new radiator thinking MAYBE you got a 2.0L version in lieu of a larger capacity 2.5L design. But the 2.5 wasn't available that year and I also noticed you stating the 2.0 currently installed anyways.

It would be odd (single row or not) for a radiator designed / supplied to you being inadequate, but you never know. :rolleyes:

SUCH a pain to swap back out and test too. :(

Get those IR temps at the upper and lower radiator portions. Let's see if you are flowing!
 

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Discussion Starter #15
I had similar thoughts on the new radiator thinking MAYBE you got a 2.0L version in lieu of a larger capacity 2.5L design. But the 2.5 wasn't available that year and I also noticed you stating the 2.0 currently installed anyways.

It would be odd (single row or not) for a radiator designed / supplied to you being inadequate, but you never know. :rolleyes:

SUCH a pain to swap back out and test too. :(

Get those IR temps at the upper and lower radiator portions. Let's see if you are flowing!
Agreed it would be odd, that was my thoughts on the single row when it showed up.

What should the upper and lower temps be? Upper rad hose was 155F Thermostat housing showed 133F. That was warm in the driveway. I didn't shoot the lower portion of the rad.
 

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The top rad temp should be close to the engine coolant exit temp. I'd be curious to see what the lower rad portion is, to see if it is particularly cold (indicating little flow through the system). Or conversely, hot all over indicating heat not being dissipated due to rad inefficiency.
 

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Discussion Starter #17
It seemed like the stat wasn't open when I was testing it. Flow seemed low, but it wasn't overheating at that point either. I'll test drive it again at lunch and get it to where the dash gauge says overheating and then pull over and take temps.
 

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This may help...

Looking at my GV (w/a 2.5) radiator which is an import replacement BTW, I see no definitive single or double row indications. I assume it is a single row, and IT measures 1" in depth, fin to outside fin. I've never had a hint of overheating issues. The original was replaced due to top tank cracking / leakage.
 

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Discussion Starter #19
Looking at my GV (w/a 2.5) radiator which is an import replacement BTW, I see no definitive single or double row indications. I assume in is a single row, and IT measures 1" in depth, fin to outside fin. I've never had a hint of overheating issues. The original was replaced due to top tank cracking / leakage.
My OE rad was replaced for the same reason. The replacement is like you described, about 1" thick. The one that is in there now is maybe .5" thick, maybe thinner.

Sounds like the new rad needs to come out and the old rad needs to go back in. I had no indication that it was clogged, I just felt like I had no choice but to replace it as a troubleshooting step.

Thanks for all your help. I'll update once I do more testing and/or replacement.
 

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Your aftermarket radiator sounds like mine in terms of thickness but I've never once seen my temp go above the mid-point....Still, I hope replacing it will end up solving problem for you.
 
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