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H3T Alpha won't run cool...at wits end!

Hubbs

Member
Messages
21
Location
Dallas, TX
I installed the factory OE auxiliary twin electric cooling fan set up on my Alpha after moving to Phoenix. Made a big difference and was well worth the $800 the parts cost me from my dealer. It’s not a kit . You have to piece it together. PCM of NC enabled my pcm to control the fans so they run and cycle as needed including when A/C is running. This was standard on the South African built Alpha units for the Middle East and Australia I was told. The wiring package and fan relay box is configured for RHD models so some modifications were needed.

This sounds like a nice upgrade! I think it could be done wirh an external fan controller just as easy though. Might save a few bucks that way.
 

Hubbs

Member
Messages
21
Location
Dallas, TX
Our H3 Alpha always ran hot in Texas in the summer. Not unusual for it to hit 230 in the summer with the AC on. That is just what it did. Dealer said that was normal and not to worry about it.

I agree, but mine was still climbing at 240-245. That's too hot.
 

Glenn

Member
Messages
16
Location
Tennessee
Worrying about 250+ degree coolant is not nothing. Sorry, wholeheartedly disagree.
When did it reach 250 degrees? Of it did you never mentioned it, or I missed it. Everything I have read so far is you describing pretty normal temp operation. It sounds like the issue is not that it is overheating, but your fear of it overheating. Face your fears and just drive the damn thing. you have no idea what, if even anything is wrong. If something is wrong it will show itself. I think your just freaking out over a non issue. This summer when it overheats and the block melts please come back and let us know what the issue was.

Sent from my SM-N960U using Tapatalk
 

Hubbs

Member
Messages
21
Location
Dallas, TX
Your first post says idles at 202 drops to 195 when driving. That is lower than the designed operating temps. Drive it.

Yes, but what I'm saying is, whats it going to do when its 110 degrees out? Thats my concern, not the 202. I'll drive it if you put up cash for a new engine should it overheat. Deal?
 

Hubbs

Member
Messages
21
Location
Dallas, TX
When did it reach 250 degrees? Of it did you never mentioned it, or I missed it. Everything I have read so far is you describing pretty normal temp operation. It sounds like the issue is not that it is overheating, but your fear of it overheating. Face your fears and just drive the damn thing. you have no idea what, if even anything is wrong. If something is wrong it will show itself. I think your just freaking out over a non issue. This summer when it overheats and the block melts please come back and let us know what the issue was.

Sent from my SM-N960U using Tapatalk

Last I checked it was wise to avoid burning up the engine. Your comments are not helpful.

BTW, yes I did mention above that it reached 245 and was still climbing.
 

JPaul

Well-Known Member
Messages
2,400
Location
Way up north, UT
Thanks for the detailed reply! I'll try to respond to all the details.

I fully understand how the thermostat works. Thats why I said it should be running a little hotter than the rating. It runs about 30 degrees hotter on a warm day and I'm afraid it will go out of control on a hot day. That's the whole point I was trying to make. I was expecting it to run about 185 on a cold day, but its higher.

I have no reason to think it has a head gasket issue per my prior comments. I also HIGHLY doubt there's a blockage since that would almost always result in a cylinder or 2 pinging due to excessive heat. All runs perfectly.

The parts I used were not ac delco, but I don't put a whole lot of trust in that anyway. I did go with good quality parts. I understand they could be bad, but the unchanged symptoms don't point to any of that. The sparkplugs all look perfect, so not likely a cylinder issue.

I measured the coolant with a thermocouple and multimeter and it was pretty consistent with the ECM readings. I haven't tried the thermo gun because I figured the readings would be less meaningful.

I haven't checked the O2 sensor temps. Thats a good thought, especially since I did get some O2 codes a few months back. I'll look into that!

As far as burping the system, I did it using a filling kit designed to do that properly and I took a long time to make sure it was fully at temperature and at different RPMs to force any air out. I then let it xool.overnight and did the process again. I'm confident that's not the issue.

The fan clutch sounds like it's working perfectly. Its pretty easy to tell when it locks and unlocks. Its working much better then the old one for sure.

I completely agree it's gotta be something simple. It's not really a complicated system. I'm going to do an experiment by installing a high flow 160 deg stat and see what it does. Not so much to leave it that way (unless it then runs about 190 consistently), but to use it to see how it reacts. I'd like to isolate the temp setting from the flow amount for better data, but oh well. The thing is it ran consistently cool with no thermostat, so I'm wondering if the flow rate improvement might be the key. I would think it should have taken longer to get there, bit it should have run well over 200 degrees if flow wasnt the issue. Unfortunately it looks like nobody makes a high flow 180 stat....weird.

If you place too much faith in brand new parts always working out of the box it will bite you one day, I say this because of my own experiences. QC only makes sure that x% of parts making it to the consumer are virtually guaranteed working, there is always a percentage, no matter how small, that slip through and become the bad reviews you see online.

Vacuum purging the coolant system is the best and recommended way of doing it. Using the extra tall funnel thing mostly works but you can still end up with air pockets in the system. They may work out eventually, but a vacuum system is a sure bet. Rent a pressure testing system from Autozone or Oreilly and get a hand operated vacuum pump from Harbor Freight and connect the vacuum pump to the testing cap and pull a vacuum on the system. Not a lot of volume in the system especially once you have coolant in there so it's easy to pull enough vacuum by hand to purge the system.

If your coolant is getting over 220 degrees and continues to climb higher than that then a cooler thermostat is unlikely to fix the problem of it overheating (unless the thermostat you put in previously is bad) since once it's open, it's open, The reason it continues to climb past that is you have hit the limit of your cooling system's ability to shed the excess heat faster than your engine can produce it. Even if you start out at a colder open temperature odds are you will put the 160 thermostat in and all it will do is cause it to take a little bit longer to overheat, unless the issue was still a bad thermostat. If you're taking the thermostat out to replace it I suggest testing the old one anyway to make sure it was in fact working. Also be aware that running a colder thermostat than the engine is designed and tuned for can cause issues. You really should get the engine computer reprogrammed to properly utilize the cooler thermostat, especially when going down to a 160 degree tstat. The computer is programmed based on an expected operating temperature for it's fuel maps and if it doesn't ever reach that temperature it might even throw a code. All depends on how the engineers decided to handle it.

Summit has a good article about running colder thermostats: https://help.summitracing.com/app/a...ur engine,will NOT solve overheating problems.
Basically unless you're putting it in a race car that has the ECU tuned to utilize the colder tstat you really shouldn't bother with them.

Thinking that you're not getting enough flow seems odd since it's not like you're the only one running a Hummer H3 Alpha in high temperature environments. We've got a handful of people over in the Middle East (read: hot, dry, HOT, DRY, sandstorm!) on the forum that haven't had the kind of issues you're having. There's also a fair number of H3's in Texas that run fine with stock H3's. This is especially true since it sounds like you're not even towing or anything severe duty like that when you overheat.

So something is clearly not working correctly on your truck and it's not because of how the stock system is designed. Either a part you replaced was replaced with a faulty part, or it is something you haven't replaced/tested yet. Have you tried blasting the heat to see if it brings the temperature down at all? I know it'd suck in the middle of summer but if your radiator isn't able to keep up you do have another mini radiator in the HVAC you can use to supplement cooling with, and the coolant is constantly flowing through the heater core regardless of what the thermostat is doing. I have had to do that on not only the H3 but other vehicles I have owned that were overheating in the dead of summer. It makes enough of a difference to be noticeable. If that works then you most likely have a problem with either your thermostat or it still could be your temperature sensor.


Honestly I still suggest verifying your coolant temperatures first with something other than the sensor on the head. Or at least test the sensor and compare it to a brand new one and then put the new sensor in. The sensor is cheap and fairly easy to replace. I would at least start there next. Right now you're making the assumption that the sensor is accurate without knowing for certain. Figure out the actual temperature compared to what the sensor is reading and then go from there.

You can also check the temperature of the coolant coming out of the engine vs the temperature of it going back in. Top hose is the engine outlet and bottom hose is the engine inlet. If there is a large difference between the two yet your engine is overheating still then I would wager it's the sensor. Reason being if the top hose is good and hot but the bottom hose is much cooler then you're clearly getting flow, otherwise they will likely be about the same temperature as each other do to conductive heating in the coolant and no flow through the radiator to cause the lower hose to be filled with cooled coolant instead of heated coolant from the engine.
 
Last edited:

jakesz28

Well-Known Member
Messages
1,041
Location
Cabool MO
Yes, but what I'm saying is, whats it going to do when its 110 degrees out? Thats my concern, not the 202. I'll drive it if you put up cash for a new engine should it overheat. Deal?

At least 2 of us have told you 180 + 15 to 20 degrees is 195 to 200. The thermostat and cooling system is working you don't have a problem. GM wants the engine to run 220 to 230 degrees.
 

650Hawk

Well-Known Member
Messages
480
Location
SoCal
What I haven't seen mentioned in this thread is this: If the H3 gets too hot, it will protect itself by first disabling the A/C (A/C OFF message in the DIC), followed by going into limp mode (REDUCED PWR). The A/C does not have to be on for that message to come up, BTW; I have had it come up when the engine was cool and the A/C was turned off when my temp sensor malfunctioned. If you haven't gotten that message, then your truck is not getting too hot.
 

alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
When did it reach 250 degrees? Of it did you never mentioned it, or I missed it. Everything I have read so far is you describing pretty normal temp operation. It sounds like the issue is not that it is overheating, but your fear of it overheating. Face your fears and just drive the damn thing. you have no idea what, if even anything is wrong. If something is wrong it will show itself. I think your just freaking out over a non issue. This summer when it overheats and the block melts please come back and let us know what the issue was.

Sent from my SM-N960U using Tapatalk
Perhaps a bit of an exaggeration in the suggesting of running it until the block melts, but I understand your point in that for the most part the H3T is operating similarly to other H3Ts, both Alphas and I5s. I'm sure you didn't mean for him to intentionally harm his H3T.
----------------------

Separately, Hubbs, you're making a HUGE assumption, and I believe an incorrect one, that these vehicles are designed to run at 190ish. To say the cooling system isn't up to snuff is likely based on an incorrect assumption that the engineers wanted these vehicles to run that low. They want them to run at a minimum of 180 but 200+ is normal for every H3 and H3T that's been produced. Many vehicles don't even have their fans come on until much higher temperatures - my bike, for example, comes on at 215 even though the thermostat opens up way before that. If the bike were designed to run within 10 degrees of the thermostat, wouldn't the fan come on at that temp?

My earlier comment regarding that your new radiator might not be an improvement is based on years of participating here and listening to many owners replace their radiators with bigger, better radiators only to find no improvement and sometimes a loss in performance. Manufacturer claims do not necessarily translate into real world performance.

You obviously know your way around vehicles - that's apparent from your posts. The other forum members here are trying to provide H3 specific information to you that they have learned over the years. You may choose to disagree with their information, but that doesn't mean they are incorrect. If you really want to drive down temps - cut vent holes in the hood and install electric pusher fans. That's the next step.
 

SlcHummer

Well-Known Member
Messages
368
Location
Salt Lake City, UT
Yes, but what I'm saying is, whats it going to do when its 110 degrees out? Thats my concern, not the 202. I'll drive it if you put up cash for a new engine should it overheat. Deal?

Lol you bought the truck and sometimes it's a gamble. Here's a solution for you...don't drive it!
 

Hubbs

Member
Messages
21
Location
Dallas, TX
If you place too much faith in brand new parts always working out of the box it will bite you one day, I say this because of my own experiences. QC only makes sure that x% of parts making it to the consumer are virtually guaranteed working, there is always a percentage, no matter how small, that slip through and become the bad reviews you see online.

Vacuum purging the coolant system is the best and recommended way of doing it. Using the extra tall funnel thing mostly works but you can still end up with air pockets in the system. They may work out eventually, but a vacuum system is a sure bet. Rent a pressure testing system from Autozone or Oreilly and get a hand operated vacuum pump from Harbor Freight and connect the vacuum pump to the testing cap and pull a vacuum on the system. Not a lot of volume in the system especially once you have coolant in there so it's easy to pull enough vacuum by hand to purge the system.

If your coolant is getting over 220 degrees and continues to climb higher than that then a cooler thermostat is unlikely to fix the problem of it overheating (unless the thermostat you put in previously is bad) since once it's open, it's open, The reason it continues to climb past that is you have hit the limit of your cooling system's ability to shed the excess heat faster than your engine can produce it. Even if you start out at a colder open temperature odds are you will put the 160 thermostat in and all it will do is cause it to take a little bit longer to overheat, unless the issue was still a bad thermostat. If you're taking the thermostat out to replace it I suggest testing the old one anyway to make sure it was in fact working. Also be aware that running a colder thermostat than the engine is designed and tuned for can cause issues. You really should get the engine computer reprogrammed to properly utilize the cooler thermostat, especially when going down to a 160 degree tstat. The computer is programmed based on an expected operating temperature for it's fuel maps and if it doesn't ever reach that temperature it might even throw a code. All depends on how the engineers decided to handle it.

Summit has a good article about running colder thermostats: https://help.summitracing.com/app/a...ur engine,will NOT solve overheating problems.
Basically unless you're putting it in a race car that has the ECU tuned to utilize the colder tstat you really shouldn't bother with them.

Thinking that you're not getting enough flow seems odd since it's not like you're the only one running a Hummer H3 Alpha in high temperature environments. We've got a handful of people over in the Middle East (read: hot, dry, HOT, DRY, sandstorm!) on the forum that haven't had the kind of issues you're having. There's also a fair number of H3's in Texas that run fine with stock H3's. This is especially true since it sounds like you're not even towing or anything severe duty like that when you overheat.

So something is clearly not working correctly on your truck and it's not because of how the stock system is designed. Either a part you replaced was replaced with a faulty part, or it is something you haven't replaced/tested yet. Have you tried blasting the heat to see if it brings the temperature down at all? I know it'd suck in the middle of summer but if your radiator isn't able to keep up you do have another mini radiator in the HVAC you can use to supplement cooling with, and the coolant is constantly flowing through the heater core regardless of what the thermostat is doing. I have had to do that on not only the H3 but other vehicles I have owned that were overheating in the dead of summer. It makes enough of a difference to be noticeable. If that works then you most likely have a problem with either your thermostat or it still could be your temperature sensor.


Honestly I still suggest verifying your coolant temperatures first with something other than the sensor on the head. Or at least test the sensor and compare it to a brand new one and then put the new sensor in. The sensor is cheap and fairly easy to replace. I would at least start there next. Right now you're making the assumption that the sensor is accurate without knowing for certain. Figure out the actual temperature compared to what the sensor is reading and then go from there.

You can also check the temperature of the coolant coming out of the engine vs the temperature of it going back in. Top hose is the engine outlet and bottom hose is the engine inlet. If there is a large difference between the two yet your engine is overheating still then I would wager it's the sensor. Reason being if the top hose is good and hot but the bottom hose is much cooler then you're clearly getting flow, otherwise they will likely be about the same temperature as each other do to conductive heating in the coolant and no flow through the radiator to cause the lower hose to be filled with cooled coolant instead of heated coolant from the engine.

JPaul, thank you for the very detailed, thoughtful response! We're very much on the same page.

The idea to try a cooler thermostat is just an experiment. If it warms up to 185+ quickly enough I may just leave it in there simply because it would give me a few more minutes of idling time before it gets too hot. I realize it's not a problem for it to run 220 degrees. My issue is that it doesn't stop there, but keeps climbing (in the summer) without end. Its fine for now. This is all about getting it ready to cope with 100+ temps. I'm just trying to fix issues now rather than waiting for them to be a headache later.

The flow idea was derived from the fact that it wouldn't warm up with no thermostat, but got hotter than I expected with a med-low temp one. I was probably expecting too little of an increase over the 180 mark.

I may try the vacuum bleeding thing. Never done that before. It can only help!

I tried the heater trick, but unfortunately no noticeable impact. I'm going to check out the sensor as you suggested. I'd like to know for sure how it's working. Also, my dash gauge only goes to half way. It hits mid point at 190 degrees, but doesn't increase, even when it hit 245. I hear thats a common "feature" of these trucks. I'd like to get it to work properly, but I'm pretty sure it's a gauge issue, not the sender and I don't believe you can replace a single gauge from what I've heard.

Thanks again for the great post!
 

Hubbs

Member
Messages
21
Location
Dallas, TX
At least 2 of us have told you 180 + 15 to 20 degrees is 195 to 200. The thermostat and cooling system is working you don't have a problem. GM wants the engine to run 220 to 230

degrees.

Yep understand. My point isn't that 220 is too hot, its that it won't stay there in warmer weather. The truck should be able to idle indefinitely without climbing to 250+ degrees as it used to want to. I'm just wanting to be confident it won't do that again this summer.
 

JPaul

Well-Known Member
Messages
2,400
Location
Way up north, UT
I tried the heater trick, but unfortunately no noticeable impact. I'm going to check out the sensor as you suggested. I'd like to know for sure how it's working. Also, my dash gauge only goes to half way. It hits mid point at 190 degrees, but doesn't increase, even when it hit 245. I hear thats a common "feature" of these trucks. I'd like to get it to work properly, but I'm pretty sure it's a gauge issue, not the sender and I don't believe you can replace a single gauge from what I've heard.

Thanks again for the great post!

I have never heard of that happening. If anything I have heard the inverse where the gauge reads higher than it should compared to what the actual temp is. Lots of people have come on here thinking their truck is overheating based solely on the dash gauge needle rather than checking it with a scan tool. When they do they find that it is in normal operating temperatures.

The cluster gets the temp reading from the BCM which gets the value over the serial line it has with the ECU. The needle may not be calibrated correctly but usually its reading high more often than not. Reading low seems highly unusual. Not impossible, but unusual.

Do you ever get the ECU going into limp mode or AC off messages when it overheats? If not then it has never actually overheated. I did a few times due to my bad fan clutch (finally replaced it yesterday while fooling around with this transmission issue I am having right now).

If the gauge is in fact failing to move past the halfway mark no matter what and a scanner shows the coolant temp high then you'll have to replace the whole cluster, you can't easily replace just the one gauge on it, even with a lot of electronics knowledge. The cluster is cross compatible with the Colorado/Canyon and so you can get a new one pretty inexpensively. Some people have swapped for the Colorado purely for looks. Probably can pick up a H3 cluster cheaply from someone like that. There is a caveat to replacing the cluster if I recall correctly. If the new cluster has less miles stored than your truck it will auto update with the vehicle miles. If it's the opposite the miles won't change on the cluster until the vehicle catches up. Not a big deal but something to be aware of. There might be a relearn procedure you can do, or take it to a shop/dealer with a Tech2 that can sync the miles. Or I am totally off and the cluster just goes with whatever the vehicles miles are. Not sure tbh.
 

alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
Yep understand. My point isn't that 220 is too hot, its that it won't stay there in warmer weather. The truck should be able to idle indefinitely without climbing to 250+ degrees as it used to want to. I'm just wanting to be confident it won't do that again this summer.
Being in the Arizona desert I'm also used to dealing with the heat. On the hottest days if I want to sit in the truck with the a/c on and idling, I'll need to periodically press on the gas to speed up the engine - which speeds up the mechanical fan and the water pump, bringing the temperatures back down.
 

650Hawk

Well-Known Member
Messages
480
Location
SoCal
Do you ever get the ECU going into limp mode or AC off messages when it overheats? If not then it has never actually overheated.

I asked the same thing, but Hubbs never answered. If his gauge is not moving above half, as he now says, and he's never had the limp mode or AC off message, I'm not sure that his truck is actually getting hot, particularly since he claims that running the heater made no difference. Perhaps it is his scan-gauge(?) that is not working correctly. Anyone here know for sure at what temp the AC off message/limp mode kicks in?
 
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Happy Hummer

Well-Known Member
Messages
1,300
Location
Wisconsin
Perhaps a full test as follows:

Leave H3 turned off. Open hood remove sparkplug #1. With proper wrench rotate crank shaft to TDC.
Place appropriate air fitting on to air compressor hose. Regulate the flow to approximately #5 or less. Allow air to flow and listen at intake/TB.... Exhaust pipe. Oil cap. This test is to be done at all 8 cylinders. That is a pretty good way to tell if your engine is having intake or exhaust valve issues. Like wise a good way to diagnose coolant issues. They sell thread adapters that fit your spark plug hole. Also, make sure only one spark plug at a time.

If you find large amounts of air leakage at exhaust or TB you have valve issues. If you find air bubbles in coolant you have gasket issues. Good luck. This is a really handy way and quick to put a mind at rest.
 

Guerrero

Well-Known Member
Messages
124
Location
Spain
JPaul, thank you for the very detailed, thoughtful response! We're very much on the same page.

The idea to try a cooler thermostat is just an experiment. If it warms up to 185+ quickly enough I may just leave it in there simply because it would give me a few more minutes of idling time before it gets too hot. I realize it's not a problem for it to run 220 degrees. My issue is that it doesn't stop there, but keeps climbing (in the summer) without end. Its fine for now. This is all about getting it ready to cope with 100+ temps. I'm just trying to fix issues now rather than waiting for them to be a headache later.

The flow idea was derived from the fact that it wouldn't warm up with no thermostat, but got hotter than I expected with a med-low temp one. I was probably expecting too little of an increase over the 180 mark.

I may try the vacuum bleeding thing. Never done that before. It can only help!

I tried the heater trick, but unfortunately no noticeable impact. I'm going to check out the sensor as you suggested. I'd like to know for sure how it's working. Also, my dash gauge only goes to half way. It hits mid point at 190 degrees, but doesn't increase, even when it hit 245. I hear thats a common "feature" of these trucks. I'd like to get it to work properly, but I'm pretty sure it's a gauge issue, not the sender and I don't believe you can replace a single gauge from what I've heard.

Thanks again for the great post!


Hello Hubbs, Guerrero here (Óscar) from Spain:

I am totally with you about all your concerns, and is super easy to understand, is a fact: Hummer H3 i5 or v8 running out of the assembly line runs at 1/2 of temp gauge (more or less, 190 degrees), so.....something happens with the years!

In the case of the i5 is super easy to guess, is just the factory thermostat being replace with a hotter one and the ugly Dexcool....but in the case of the Alpha is more difficult, because if I am correct, GM did not sustitute the current thermostat to a hotter one (please correct me if I am wrong), so in my case, I would check temperature using a Scan Tool to verify correct needle operation, and after that replace coolant sensor just to remove that from the list. After that, investigate if the problem of the overheating (more temp than was is normal from assembly line) is maybe due to not having a OEM radiator (could be your cause) or the fact that the thermostats that is being sold out there, is not enough about flow.....

Please check my post about ALL the investigation about H3's cooling system...is very interesting and I resolve my cooling issues just with an aftermaket inline thermostat housing:

https://www.hummer4x4offroad.com/forum/showthread.php/14490-Guerrero-s-take-on-H3-cooling

Here in Spain I replace my 2006 Hummer H3 3.5 for a 2008 Hummer H3 Alpha and I am right now modifying it so I will be focus on this thread, because for my setup I will use the dual e-fan setup, that I used previously in the post above, and run another powerful pusher in front of the radiator....my plan was just to install new water pump with 180ºF thermostat....but keep looking your issue and investigation!

Hope this helps you out
Guerrero
 
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