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Discussion Starter #1
I've noticed a few comments regarding temperature gauges reading too high/low. Mines always ran low and I've been watching it more lately. I found a strange glitch where it drops to 0 anytime I give it lots of gas. If I gun it, the temperature gauge drops off to nothing and then slowly climbs back up to the bottom third where it normally sits. Anyone else have disfunctional gauges?
 

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Hook up a scan tool and find out what the actual coolant temperature is moving between. It is a guessing game watching the analog gauge.
 

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Some say that the engine blows the thermostat open at high RPMs. The thermostat on this engine would have to be sucked open.
I find it difficult to believe that the small centrifugal water pump on this engine could draw pressure that low.
Centrifugal pumps are poor pumpers at low inlet pressures.

My bet would be a bad thermostat with a weak spring or partially stuck open valve pin.
 

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Discussion Starter #4
Ya, you're probably right. I thought it might be a faulty gauge, but I'm starting to think that the thermostat is actually opening. I wish I had a scan tool to test it but might just have to leave it in the hands of shop.
 

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twgiffin said:
Some say that the engine blows the thermostat open at high RPMs.
That would be I that said that. I just located the GM information to back it up. My 2004 did not do this but my 2008 does this.





Document ID# 1461920
2004 GMC Truck Canyon Pickup - 4WD
Engine Coolant Gauge Drop on Acceleration - kw 2.8 3.5 L52 LK5 GMT355 accelerate display drop indicator instrument temperature #PI01757 - (Feb 19, 2004)

Engine Coolant Gauge Drop on Acceleration

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When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

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Some customers may comment about the coolant temperature gauge dropping 20 degrees very rapidly on an acceleration. This is due to the thermostat opening like a relief valve when the pump draw overcomes the thermostat closed force. It is related to acceleration due to the fact that the pressure threshold is reached when the engine speed exceeds 3,000 RPM. This is a normal condition and no attempt for repairs should be made for this concern.

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.
Models:

(2004 Chevrolet Colorado 2WD/4WD) (3.5 L52 or the 2.8 LK5) and (2004 GMC Canyon 2WD/4WD) (3.5 L52 or the 2.8 LK5)
 

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Another one for ya.



Document ID# 1471209
2004 GMC Truck Canyon Pickup - 4WD
Temperature Coolant Gauge Low or Inoperative - GMT355 IP temperature #PI01865 - (Mar 11, 2004)
Temperature Coolant Gauge Low or Inoperative

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When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:

Customer may complain that the temperature gauge is inoperative or reads low.
Recommendation/Instructions:

The temperature gauge will not move until the engine temperature is over 160 degrees F. Warm engine to operating temperature. Monitor ECT sensor with the Tech 2. If the ECT reads 160 degrees or lower, the thermostat may be stuck open. Replace thermostat.

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.
Models:

(2004 GMT355 Colorado Canyon S1 T1 )
 

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My guess would be you have both of the conditions described above with Canyon08.

I have a scanguageII in my truck and merging on the highway I go from 184 degrees which is 1/2 for me, down to about 165 degrees which is showing at the 1/4 mark for my truck. This is staying under 4,000 rpm in cool weather, anything under 2,800 rpm is rock solid at 184 degrees. Depending on where your guage is at normally a change of 1/4 is right on with what I and a lot of other guys are experiencing
 

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Canyon08Z71 said:
Another one for ya.
Yep! And a weak spring could also allow the T-stat to be sucked open easier. Right????? Not everyone experiences it, I wonder why???

So, just what did your quote of an obvious result do to disprove what I said?
 

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Discussion Starter #9
The amount it costs at these freakin' dealerships in Calgary, I'd be better off just having the thermostat replaced rather than anything checked. It'd probably cost me under $100 to replace it and $150 to have a dealer check it.
 

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twgiffin said:
Canyon08Z71 said:
Another one for ya.
Yep! And a weak spring could also allow the T-stat to be sucked open easier. Right????? Not everyone experiences it, I wonder why???

So, just what did your quote of an obvious result do to disprove what I said?
I am just trying to help the fella out and share information. :? Anything is possible.. I am not attempting to disprove anything you said.

Another one for ya = for the thread starter.

I quoted you because you said "Some say that the engine blows the thermostat open at high RPMs".

I showed that GM states "the engine blows the thermostat open at high RPMs". :?
 

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I think this is kinda funny. I only notice this on my truck when it is cold outside. Let the truck get warm and then drive it down the road and punch it... and watch the temp guage flop! lol... and it actually is dropping the temp a good bit, enough to notice the change in temp in the cab while running the heat.
 

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Discussion Starter #12
That can't be good for the vehicle! Pilots use all sorts of techniques to avoid sudden cooling of the engine, called "shock cooling". If you don't, you end up with cracked heads! I don't see why a water cooled engine would be any different.
 

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Canyon.Off.Road said:
My guess would be you have both of the conditions described above with Canyon08.

I have a scanguageII in my truck and merging on the highway I go from 184 degrees which is 1/2 for me, down to about 165 degrees which is showing at the 1/4 mark for my truck. This is staying under 4,000 rpm in cool weather, anything under 2,800 rpm is rock solid at 184 degrees. Depending on where your guage is at normally a change of 1/4 is right on with what I and a lot of other guys are experiencing
It is refreshing to see the proper scan tool being used to monitor this condition. I would be interested to hear if anyone has had GM work on this specific condition. So far, I have just read of people talking about it but never heard of a solution or fix for it. Have you had GM look at this for you?

My 2008 does this particular "cool down", just not to the same extent as you are reporting or justplanecrazy. I will have to go back to my scanner data logs to see exactly what temperature mine is dropping to for a comparison.
 

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I noticed higher than normal temp guage readings after the cylinder head replacement work was done. My circumstances appear to be somewhat different than those described at the head of this thread though.

During summer driving, when I come off the highway to a stop, the temperature guage goes to just below 3/4. The reading on the guage returns to the half way mark upon subsequent excelleration and will go back up to just below 3/4 every time the motor returns to idle.

I called dealer service and described the above and was told that it was normal, that I needn't bring it in and that I shouldn't be concerned.
 

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Canyon08Z71

This morning I tried it on my 06 2.8L.

It is NORMAL FOR THE TEMP TO DROP suddenly during sudden accelerations !

I continued to accelerate and it started to rise again.

I am not going to replace my thermostat as I would have to say that it is an inherent undocumented feature in the Colorado.

In my opinion, the condition is caused by a slow thermal response rate of the thermal sensing pellet to relieve the stem pressure and the spring is
unable to close the thermostats valve. The higher flow of cooler water drops the temp until the thermal sensing pellet can contract and allow the
spring to close the valve increasing the ECT. Possibly a stronger spring would increase the rate at which the pellet retracts.

Unless there is something I'm completely missing, I just cannot see how the pump can overcome the pellet's force holding the valve open.

I apologize to the poeple on this thread for any confusion or offenses I may caused. I just don't like pat answers that may not be supported by the science.
 

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twgiffin said:
Canyon08Z71

This morning I tried it on my 06 2.8L.

It is NORMAL FOR THE TEMP TO DROP suddenly during sudden accelerations !
I continued to accelerate and it started to rise again.
I am not going to replace my thermostat as I would have to say that it is an inherent undocumented feature in the Colorado.
I never said to replace your stat. You were the one crabbing like a constipated old lady to me about a weak thermostat spring.... I said it was a DOCUMENTED event, DOCUMENTED by GM, not my own opinion.

Not every truck drops the temperature gauge by 1/4 click or more. My 2008 does it but my 2004 did not.

The wind is changing directions, don't piss into it.

BTW- I am here to learn with everyone, not dictate what you should do. If you do not want free thinking or the sharing of ideas/information then a forum is not the place to play.
 

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Canyon08Z71 said:
Have you had GM look at this for you?

My 2008 does this particular "cool down", just not to the same extent as you are reporting or justplanecrazy. I will have to go back to my scanner data logs to see exactly what temperature mine is dropping to for a comparison.
I was not too worried with a 20 degree drop - I think our guages are a LOT more sensative than most vehicles. If 1/2 is 184 degrees on mine and 1/4 is 165 degrees, then I think guage movement is to be expected. I just tell people it is to prevent detonation by cooling the engine during acceleration and helps provides momentary increased power by not heating the intake air quite as much :lol:

Seriously though, I think something important to remember is that we are talking about coolant temp here - the engine is still probably within a few degrees of normal during these short bursts. So if the thermostat does not respond quickly enough for the increased flow and pressure, the effects are short term and the engine has still maintained its true temp in the head, block, and rotating parts.
 

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Canyon.Off.Road said:
Canyon08Z71 said:
Have you had GM look at this for you?

My 2008 does this particular "cool down", just not to the same extent as you are reporting or justplanecrazy. I will have to go back to my scanner data logs to see exactly what temperature mine is dropping to for a comparison.
I was not too worried with a 20 degree drop - I think our guages are a LOT more sensative than most vehicles. If 1/2 is 184 degrees on mine and 1/4 is 165 degrees, then I think guage movement is to be expected. I just tell people it is to prevent detonation by cooling the engine during acceleration and helps provides momentary increased power by not heating the intake air quite as much :lol:

Seriously though, I think something important to remember is that we are talking about coolant temp here - the engine is still probably within a few degrees of normal during these short bursts. So if the thermostat does not respond quickly enough for the increased flow and pressure, the effects are short term and the engine has still maintained its true temp in the head, block, and rotating parts.
You are correct on preventing detonation, though. I am really reaping the benefits of a "lower temp thermostat" (hehehe) on the 2008 and high octane tuning!! Much nicer tuning this truck than my 2004 which kept a consistent 200 deg f coolant temp during WOT.

I just checked my scanner data logs from my last scan. 34 Outside air temp, ~185 coolant temp during 2k cruising... I hit WOT, ~3 seconds later, ~165 coolant temp. Once WOT is released, 5-10 seconds later, the coolant temps are back in the 180 range... I do not have any summer weather stats to provide, I got this truck in Nov 07... I will see what the temps do when the ambient temp is higher.

I agree and do not feel there is any possibility of damage to the engine at all but it is just my opinion. I have a robust 5yr 100k b to b warranty to cover me just in case this opinion is incorrect. :D
 

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twgiffin said:
Canyon08Z71

This morning I tried it on my 06 2.8L.

It is NORMAL FOR THE TEMP TO DROP suddenly during sudden accelerations !

I continued to accelerate and it started to rise again.

I am not going to replace my thermostat as I would have to say that it is an inherent undocumented feature in the Colorado.

In my opinion, the condition is caused by a slow thermal response rate of the thermal sensing pellet to relieve the stem pressure and the spring is
unable to close the thermostats valve. The higher flow of cooler water drops the temp until the thermal sensing pellet can contract and allow the
spring to close the valve increasing the ECT. Possibly a stronger spring would increase the rate at which the pellet retracts.

Unless there is something I'm completely missing, I just cannot see how the pump can overcome the pellet's force holding the valve open.

I apologize to the poeple on this thread for any confusion or offenses I may caused. I just don't like pat answers that may not be supported by the science.
twgiffin,

Sorry bro I took you the wrong way. I apologize for that and appearing that I was taunting you (or whatnot) because I was not.. Much respect to you bro.

I have not pressure tested the thermostat spring specifically nor do I have the output specifications of the water pump impeller.... I am fairly confident in GM's diagnosis of the "issue", it makes sense to me in a theoretical sense but I do not have any first hand testing or evidence of it. All I have available is the sensor outputs and inputs.

In my particular example, my thermostat should be fully closed and seated at 180-185°F (194°-225° thermostat)... So, when I floor it, it should be closed and not have to respond at all until the temperature raises. It should never have the chance to open because the coolant temperature plummets with in seconds of WOT. So, it should have been seated the entire time.

So in my opinion we are dealing with the spring close off strength and not the temperature aspect of its operation. After 3k RPMs, the pump is producing a lot more head pressure then at cruising RPMs (2k).. I wish I knew exactly how the pressure was changing......

I am also not in the mind set that I am not any more intelligent than the GM engineering department. I know they do some things funky but I would need some serious evidence to go against one of their technical bulletins.
 

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Canyon08Z71 said:
twgiffin said:
Canyon08Z71

This morning I tried it on my 06 2.8L.

It is NORMAL FOR THE TEMP TO DROP suddenly during sudden accelerations !

I continued to accelerate and it started to rise again.

I am not going to replace my thermostat as I would have to say that it is an inherent undocumented feature in the Colorado.

In my opinion, the condition is caused by a slow thermal response rate of the thermal sensing pellet to relieve the stem pressure and the spring is
unable to close the thermostats valve. The higher flow of cooler water drops the temp until the thermal sensing pellet can contract and allow the
spring to close the valve increasing the ECT. Possibly a stronger spring would increase the rate at which the pellet retracts.

Unless there is something I'm completely missing, I just cannot see how the pump can overcome the pellet's force holding the valve open.

I apologize to the poeple on this thread for any confusion or offenses I may caused. I just don't like pat answers that may not be supported by the science.
twgiffin,

Sorry bro I took you the wrong way. I apologize for that and appearing that I was taunting you (or whatnot) because I was not.. Much respect to you bro.

I have not pressure tested the thermostat spring specifically nor do I have the output specifications of the water pump impeller.... I am fairly confident in GM's diagnosis of the "issue", it makes sense to me in a theoretical sense but I do not have any first hand testing or evidence of it. All I have available is the sensor outputs and inputs.

In my particular example, my thermostat should be fully closed and seated at 180-185°F (194°-225° thermostat)... So, when I floor it, it should be closed and not have to respond at all until the temperature raises. It should never have the chance to open because the coolant temperature plummets with in seconds of WOT. So, it should have been seated the entire time.

So in my opinion we are dealing with the spring close off strength and not the temperature aspect of its operation. After 3k RPMs, the pump is producing a lot more head pressure then at cruising RPMs (2k).. I wish I knew exactly how the pressure was changing......

I am also not in the mind set that I am not any more intelligent than the GM engineering department. I know they do some things funky but I would need some serious evidence to go against one of their technical bulletins.
My 06 does this too. I tend to agree with the temp aspect vs. the spring pressure. A good test might be to try to give her some gas before the temp gauge rises fully to operating temp. If it gauge still drops when we KNOW the thermostat isn't open, it has to be the pump overcoming the thermostat spring pressure, or maybe there is a bypass under high coolant flow we don't know about.
 
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