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post #1 of (permalink) Old 05-26-2017, 05:49 PM Thread Starter
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Possible Bad Thermostat?

My car's been exhibiting these symptoms for about a month or so and I think I've cleared up to some point what exactly is happening on a regular basis.

Once in a while (once a week, perhaps?) the coolant temp will keep climbing after I start the car in the morning. I will have to pull over and wait a few minutes, then I can resume my trip. I do not have this problem later in the day. But the temperature does seem to exceed normal operating temperature, usually no more than 215 degrees but occasionally more. I keep an eye on it but I've never had to pull over.

I've asked around and my theory is that the thermostat is not opening all the way/early enough (and/or sticking). What I think I need to do is flush the system completely and bleed it afterwards to remove any air pockets. I'm also considering a lower degree thermostat (180 instead of 195). I don't want to remove it completely or cut out the middle as I've heard that could be problematic.

FWIW, I probably neglected to properly bleed the system when I replaced the radiator cap a few months ago. Also, there seemed to be a little bit of gunk on the cap. So flushing and bleeding seems like a good idea.

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post #2 of (permalink) Old 05-26-2017, 06:33 PM
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Possibly an air embolism in the system from an improper filling procedure. Many newer thermostats do not have a bleed hole and if air gets trapped behind the closed thermostat it cannot see the actual water temperature since the air bubble temp acts as an insulator an at a lower temp. once the air reaches temp to open the thermostat the water is already over thermostat opening temp.....once opened the temp approaches normal.
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post #3 of (permalink) Old 05-26-2017, 06:42 PM Thread Starter
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Originally Posted by Thomcat View Post
Possibly an air embolism in the system from an improper filling procedure. Many newer thermostats do not have a bleed hole and if air gets trapped behind the closed thermostat it cannot see the actual water temperature since the air bubble temp acts as an insulator an at a lower temp. once the air reaches temp to open the thermostat the water is already over thermostat opening temp.....once opened the temp approaches normal.
So, was I wrong to fill the coolant through the radiator instead of using the overflow tank?

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post #4 of (permalink) Old 05-27-2017, 09:31 AM
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So, was I wrong to fill the coolant through the radiator instead of using the overflow tank?
No.

If you fill the radiator, excess coolant will expand and enter the coolant jug. After several drive cycles, you may need to add coolant to the jug because air bubble were purged from the block and radiator.
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post #5 of (permalink) Old 05-27-2017, 03:35 PM Thread Starter
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Originally Posted by 1999 White C5 Coupe View Post
No.

If you fill the radiator, excess coolant will expand and enter the coolant jug. After several drive cycles, you may need to add coolant to the jug because air bubble were purged from the block and radiator.
Okay, then it has bubbles (possibly) for another reason.

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Originally Posted by hg3300 View Post
Okay, then it has bubbles (possibly) for another reason.
Several suggestions:

I would not change the thermostat to 180 degrees from 195 degrees. Use what GM recommends. Once the thermostat opens, the coolant temperature will reach whatever it is possible. It doesn't matter if it opens at 180 or 190 degrees.

You now mention bubbles. Where are the bubbles? When do they occur? Bubbles the coolant jug can indicate a head gasket or intake manifold gasket leak - into the coolant. Or it can indicate a bad radiator cap and/or hose that connects the jug to the radiator. It is very common for the hoses to have pinhole leaks that allow air to be sucked into the coolant reservoir jug as it cools. It is also possible that the clamp at either end of the hose is not tightened correctly, allowing air in.

Flushing and bleeding the system is a good idea if it hasn't been done in years. Some people mix different formulations of coolant, which causes the coolant to wear out prematurely and gel.

Are you SURE the engine temperature is climbing to 215 degrees? Is this based upon the dash gauge? Are you driving during hot weather with the a/c in operation? You may be able to buy or borrow a thermal gauge gun, and next time the temperature goes high - pull over and quickly check the temperature at the thermostat outlet neck.
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post #7 of (permalink) Old 05-27-2017, 04:43 PM Thread Starter
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Originally Posted by 1999 White C5 Coupe View Post
Several suggestions:

I would not change the thermostat to 180 degrees from 195 degrees. Use what GM recommends. Once the thermostat opens, the coolant temperature will reach whatever it is possible. It doesn't matter if it opens at 180 or 190 degrees.

You now mention bubbles. Where are the bubbles? When do they occur? Bubbles the coolant jug can indicate a head gasket or intake manifold gasket leak - into the coolant. Or it can indicate a bad radiator cap and/or hose that connects the jug to the radiator. It is very common for the hoses to have pinhole leaks that allow air to be sucked into the coolant reservoir jug as it cools. It is also possible that the clamp at either end of the hose is not tightened correctly, allowing air in.

Flushing and bleeding the system is a good idea if it hasn't been done in years. Some people mix different formulations of coolant, which causes the coolant to wear out prematurely and gel.

Are you SURE the engine temperature is climbing to 215 degrees? Is this based upon the dash gauge? Are you driving during hot weather with the a/c in operation? You may be able to buy or borrow a thermal gauge gun, and next time the temperature goes high - pull over and quickly check the temperature at the thermostat outlet neck.
My reasoning on replacing the thermostat with a 180 is because my 'overheating' problem only occurs once, when I first start the car in the morning.

It was suggested that there is an air pocket causing my thermostat to delay opening. That's what I meant by "bubbles." There are no visible bubbles as far as I can tell.

The radiator cap was replaced a few months ago, doesn't appear to be leaking coolant.

I've been driving to work with and without the AC depending on how hot it is, I think it tends to reach 215 at various times while driving in either situation. It is based on the dash gauge and I'm not sure who I could borrow a temperature gun from.

One of my hoses appears to have a crack near the thermostat. Do you think that could be causing some problems?

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post #8 of (permalink) Old 05-27-2017, 05:32 PM
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If you are going to change the coolant, you may want to change the thermostat. I ALWAYS use genuine GM products (I do not work for GM) - instead of an aftermarket item. I would suggest using a GM thermostat - high quality. It is POSSIBLE that there is a piece of gunk stuck in the thermostat's opening, preventing full flow of the coolant when the thermostat opens.

One thing to check - when your engine is cool, turn it on and leave the a/c off, then have a helper turn on the a/c to see if the secondary radiator fan turns on (you could look at it with the hood open). There is a chance the fan is not turning on and providing enough air to cool the engine fully with the a/c in operation. The secondary fan (passenger side) should activate anytime the a/c is turned on. If you have only one fan - the fan should increase to a higher RPM.

Another possibility - you could have a slow coolant leak, which causes the coolant level to drop in the radiator. Periodically check the radiator level when the engine is cool (don't rely on the coolant reservoir level due to chances that coolant is not being drawn back into the radiator).

Another possibility - the front of the a/c condenser (in front of the radiator) could have debris build-up (bugs, leaves, etc) or junk such as a plastic bag. If the condenser looks rather dirty through the grille - use a hose and try to spray away the debris (don't use too hard of a water spray). You could also clean if from below or by removing the upper radiator close out panel (plastic - easy to remove).

I have owned and maintained GM cars for years (not professionally). I help take car of my brother's 2001 Monte Carlo (W-Body like Impala) but he has the 3.8 V-6 engine. I assume you have the 3.4 engine. I have owned four Impalas, including a current 2014 Impala 2LTZ.

Good luck.
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post #9 of (permalink) Old 05-30-2017, 05:01 PM Thread Starter
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Quote:
Originally Posted by 1999 White C5 Coupe View Post
If you are going to change the coolant, you may want to change the thermostat. I ALWAYS use genuine GM products (I do not work for GM) - instead of an aftermarket item. I would suggest using a GM thermostat - high quality. It is POSSIBLE that there is a piece of gunk stuck in the thermostat's opening, preventing full flow of the coolant when the thermostat opens.

One thing to check - when your engine is cool, turn it on and leave the a/c off, then have a helper turn on the a/c to see if the secondary radiator fan turns on (you could look at it with the hood open). There is a chance the fan is not turning on and providing enough air to cool the engine fully with the a/c in operation. The secondary fan (passenger side) should activate anytime the a/c is turned on. If you have only one fan - the fan should increase to a higher RPM.

Another possibility - you could have a slow coolant leak, which causes the coolant level to drop in the radiator. Periodically check the radiator level when the engine is cool (don't rely on the coolant reservoir level due to chances that coolant is not being drawn back into the radiator).

Another possibility - the front of the a/c condenser (in front of the radiator) could have debris build-up (bugs, leaves, etc) or junk such as a plastic bag. If the condenser looks rather dirty through the grille - use a hose and try to spray away the debris (don't use too hard of a water spray). You could also clean if from below or by removing the upper radiator close out panel (plastic - easy to remove).

I have owned and maintained GM cars for years (not professionally). I help take car of my brother's 2001 Monte Carlo (W-Body like Impala) but he has the 3.8 V-6 engine. I assume you have the 3.4 engine. I have owned four Impalas, including a current 2014 Impala 2LTZ.

Good luck.
I suspect gunk as well. I never drained the coolant last time we fiddled with the system (had some trouble finding/removing the drain plug)

Never thought to check the front of the condenser but that's a good idea. The fans I do want to check though it's rather difficult to see whether or not they're running (yes I have two)

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post #10 of (permalink) Old 05-31-2017, 10:48 AM
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If it were me and it were mine, would drain the radiator, run some clean water through, then run a prestone flush through. Drain and rinse cycle a couple times. Also would clean the radiator as best as possible with a low pressure sprayer on a water hose, amazing how dirty they can get especially if driving in dusty conditions and it will effect the ability for them to cool if the radiator is plugged up with dirt.

A bad thermostsat was my first guess in your other thread, but you said you had recently changed it. No more than they are, might not hurt to change it again on the chance you got the oddball bad part from the factory.

Oh and might want to change the oil too. Recall you used oil that was not the right viscosity(too thin), might be contributing to the overheating.
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post #11 of (permalink) Old 05-31-2017, 01:55 PM Thread Starter
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Originally Posted by 1999 White C5 Coupe View Post
Are you SURE the engine temperature is climbing to 215 degrees? Is this based upon the dash gauge? Are you driving during hot weather with the a/c in operation? You may be able to buy or borrow a thermal gauge gun, and next time the temperature goes high - pull over and quickly check the temperature at the thermostat outlet neck.
Thermal gun gave me a reading of 211, the gauge probably read about 220 at the time. Not sure if this is to be expected or whether or not I may have scanned improperly but I scanned the area where my thermostat would be at or near. The hose itself measures considerably less but I assume that's because it's made of rubber, which is an insulator.

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post #12 of (permalink) Old 05-31-2017, 04:04 PM
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Originally Posted by hg3300 View Post
Thermal gun gave me a reading of 211, the gauge probably read about 220 at the time. Not sure if this is to be expected or whether or not I may have scanned improperly but I scanned the area where my thermostat would be at or near. The hose itself measures considerably less but I assume that's because it's made of rubber, which is an insulator.


Page 3-35 of the 2003 Impala owner's manual states that during the majority of the time, the temperature gauge will read 210 degrees Fahrenheit for normal driving. It also states that during a load on the engine or going uphill, the temperature can approach 250 degrees Fahrenheit.

If your scan gun gave a reading of 211 degrees Fahrenheit - it would be almost exactly what the owner's manual states is normal (210). As such, I don't think the engine is running too hot.
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Originally Posted by 1999 White C5 Coupe View Post
Page 3-35 of the 2003 Impala owner's manual states that during the majority of the time, the temperature gauge will read 210 degrees Fahrenheit for normal driving. It also states that during a load on the engine or going uphill, the temperature can approach 250 degrees Fahrenheit.

If your scan gun gave a reading of 211 degrees Fahrenheit - it would be almost exactly what the owner's manual states is normal (210). As such, I don't think the engine is running too hot.
The engine temp used to remain steady at just under 200, somewhere around 190. I am seeing what it says in the manual but last week my car reached 245/250 just driving down the highway.

Of course because of this I plan on flushing it. Just thought it was odd that the 'average' temp is "210 or less." My brother's 2004 Impala (also 3.4) runs at or around the second hash mark below 200.

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The engine temp used to remain steady at just under 200, somewhere around 190. I am seeing what it says in the manual but last week my car reached 245/250 just driving down the highway.

Of course because of this I plan on flushing it. Just thought it was odd that the 'average' temp is "210 or less." My brother's 2004 Impala (also 3.4) runs at or around the second hash mark below 200.


I suspect if you flush the coolant, change the thermostat and clean the a/c condenser area - the car will return to the prior cooler operating temperature.

Good luck - let us know how things turn out.
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Originally Posted by 1999 White C5 Coupe View Post
I suspect if you flush the coolant, change the thermostat and clean the a/c condenser area - the car will return to the prior cooler operating temperature.

Good luck - let us know how things turn out.
Hopefully this will be done tomorrow, if not in the near future. I will keep you posted on the results.

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