I've recently purchased a used 06' Hummer H3 with 120k miles knowing that she needed a bit of TLC. Over all there were no red flags (I thought) and @ 12.5k I felt that I'd still be in the green after everything was done and said. After a few days of driving I noticed that the motor was running abit warm. While normal driving temps were just above the half way mark, at idle it seemed to climb alittle higher. But what really concerned me is that when I go to park and turn off the truck and then turn the key back over just so the cluster turns on.. the temperature gauge climbs just above the 3/4 mark. After about 6-8 minutes the temperature then will start to drop. So I'm thinking faulty thermostat? or maybe fan clutch? I replace both with GM parts, flushed radiator, added new coolant. Unfortunately unsuccessful. I take the H3 over to my local trusted mech to have a looksy. He points out that the head gasket is blown and that is whats causing my over heating issue...(exhaust mixing into the cooling system would cause that). So for $1,300 head gets sent out for resurfacing, new seals, new gasket, cylinder head temperature sensor, all new fluids..and basically a comlpete valve job... my mech is super cool and legit. I go to pick my H3 today and shes running very smooth!! Super excited at this point. I'm on my way home keeping an eye on the temperature gauge the whole fkn time. Driving temperature is now at the half way mark.. @ idle she's still just above the half way mark.. and when parked, turned off the temperature still climbs up to 3/4? Wtf?!? Is there somthing that I'm missing?? Do I need to look into an aux fan>? I've never owned a vehicle the got hot after parking.. kinda stumped! Any advice would be great at this point.

Many Thanks!!

 

i never checked my 2 different h3 the way you did after shutoff,but neither ever went quite up to half way even in hot summer stop/go traffic.
next time i drive ill chk after shutoff.

so far i never saw the gage up to 1/2

 

Apparently we need to learn you how a cooling system works.

First, 3/4 mark temps are not overheating to begin with. Overheating is when the needle is in the red.

1) When your motor is running your water pump is turning and circulating coolant through the radiator and motor, passed the temp sensor which is reading the temp of the coolant exiting the motor at the head. The radiator cools the fluid from the motor by air heat exchange cycles through the motor which heats it. This is a continuous cooling cycle.

2) When you shut off the motor, what happens? The water pump stops and so does coolant circulation. Hence, the sensor is now in coolant within the head that is not moving and experiencing a rapid climb in temp because it is direct contact with the motor/head and not being flushed with cooler fluid from the radiator. The cooling cycle has stopped. You turn the key on a few moments later and what do you see? Higher temp than when you shut it off because of "heat soak."

Start the motor and and that starts the cooling cycle, go back to #1. The temp decreases after a few minutes.

So what you have observed is completely normal for every water cooled automobile.

Get a scan gauge or borrow one. The dash temp gauges are not highly accurate so you have only an idea of what the actual temp is, and for most applications that is all the operator needs. It is almost like an idiot light with a moving needle. BTW your DIC will display "ENG HOT" when your H3 starts to overheat. If you had the AC on when it begins to overheat, the AC will shut off before the temp triggers the DIC display.

The actual temp at the 3/4 mark is about 212-218F depending on your particular truck's gauge accuracy, plenty of room before an overheat. When I turn my 3 off and the actual temp is say 190F (1/2 on the dash gauge), in about 10 seconds if I turn the key to on, it will read 204F. All of which doesn't matter because with the engine off, everything is beginning to slowly cool, no more heat is being made.

FYI: 50/50 water and Dex-Cool has an open boiling point of 228F (in an open pot, no pressure) and in a pressurized cooling system @ 15PSI, 265F.

 

My normal operating temp is bit above 1/2 and idle could go as high as right underneath 3/4 mark but never on or over 3/4...I have 06 H3 Adventure package...with 53k on clock..

 

Thank you Doc for the run down, much appreciated Sir!!

Before taking in my H3 I noticed that smell of burnt coolant, which I've seem a few people talk obout here in the forums... is that due to "heat soak"? I currently live in So Cal where temps are far from extreme. Would it be worth a shot try for straight coolant rather than the 50/50?? Sounds like my operating temps are inline with the norm.. just looken to run abit cooler if possible because I might be picking up a small box trailer for camping/fishing soon.

Overall I'm very happy with how she operates for an IL5. She's got the adventure package so I recently went with the BFG KM2's (285's).. Also looking to lvl her out and go with the Bilstein Hummer H3 Leveling Front & Rear Shocks.

Thanks again for the pointers everyone!

 

Higher coolant % is for freeze protection, water is the best cooler in the truest sense.

IMHO make sure you have fresh 50/50% Dex-Cool (if your mechanic has not replaced it), and consider a flush before the fresh coolant.

Then look into a trans cooler to spread some of the cooling load for the trans which should also help when trailering in warm weather climates.

Search here for trans cooler too.


WELCOME to the forums!

 

2006 H3. Got it at 41K in 08, currently has 174K. March 2013 Trans blew on the highway. The case literally cracked after the Torque Converter cam loose and slammed into it. That was at 149K. Rebuild installed for $1800. At 164K in the early Spring 2014, the temp gauge was running up to 3/4. Figured it needed an cooling system inspection and at a minimum a flush. My mech, who works in the building adjacent to my workplace, agreed and flushed the system and still it ran at 3/4. Mech suggested change the thermostat. I said do it. Picked it up at the end of the day and it was at 3/4 before I reached the highway. Returned to Mech. Mech suggested faulty thermostat and recommended changing that again and the waterpump too since it wasn't getting any younger. I agreed. Picked up 3 days later. Made it onto the highway and it was a warm day so I turned on the A/C. BOOM 3/4 within minutes. Turned off A/C car cooled to just above midway for the last 70 miles I drove home. On the way back to work, another 75 miles on the highway, temp stayed normal until I got off the highway and entered city traffic and again temp climbed to 3/4, this time the A/C was off. Out of curiosity and with the idea that I might be helping, I cranked the heat to bleed it off some. Surprise, it worked. Temp was back to normal within a few minutes. Arrived at the mech and told him to please figure it out. Next we changed the radiator, the fan clutch, the tensioner and belt (since they were both squeaking anyway) and let it sit overnight to ensure everything was good to go. Next day I get a call from the mech with the news that the system was still running up to 3/4.
He suggested it may be a head gasket problem with a repair cost of abot $1600. I said no to that since none of his other ideas worked and I was already our close to $800 on what had already been done. He also pointed out that my front CAT was split along the seam and suggested it may be a contributing factor of engine heat. Ordered a CAT and had that installed elsewhere for $600. Car still hits the 3/4 mark, mainly in city traffic and anywhere if the A/C is running. Temp still drops rapidly if I turn the heat on.
I asked another mech - friend of a friend - and he checked out my H3 and said that if turning the heat up allowed the engine temp to drop that fast it doesn't support it being a head gasket problem. There was no loss of coolant and no leaks of coolant into the oil or vice versa he pointed out. So he suggested it might be an air pocket. So he flushed the system again and refilled it but the temp still rises to 3/4!

So I'm at a loss...might this really be a head gasket or is something else going on?

Boom Torque converter locked up 8k over 10k warranty and the trans fluid lines were leaking from cracks associated with the clips that hold the lines in place.

Replaced torque converter and lines from GM Dealer. $500. more. Temp still goes up to 3/4. Mech now suggests adding a trans cooler. I don't tow anything I said, he said, it would help the trans stay cool and suggested the Torque converter may have overheated as a result of the engines original problems.

Anyone have any ideas that don't involve this being a blown head gasket. How can a head gasket be blown at 156k and yet since then I still put on 18k more miles, up and down the highway, 150 miles round trip twice a week.

 

Does your mechanic have/know how to use a block tester?

GM has determined there are calibration concerns with this gauge and no repairs should be considered at this time. The problem is worse with high temperatures when driving up hills or in stop and go traffic.

Try a new CTS?







OEM/Block Tester (27145) | Block Tester | AutoZone.com

 

You dug up a 2.5+ year old thread to complain about temp at the 3/4 mark of the dash gauge?????

Simple short answer, 3/4 temp is considered NORMAL. There are many threads here and elsewhere on this topic, you can stop pissing away $$ fixing what ain't broke. Please avoid necro-bumping from here out. Thank you.


https://www.hummerforums.com/forum/n...bumping-23220/

 

I googled the problem I was having and that post came up 1st. I never heard the term necro-bumping before. Thanks that was enlightening.

At any rate...it's my first time posting here...maybe should should be a little more welcoming you old so and so.

Thanks though for your advice. I'll mention the block test to the mech. In fact, I'll do the test myself and go from there and show him the results. My H3 never ran at 3/4 temp until after the trans was rebuilt. It was always dead center. To me that was normal. If 3/4's isn't abnormal then that's fine, I just don't get why the change. If it passes the block test I'll order a CTS just in case that is the issue but if that does nothing I will follow Doc Old's advice and stop wasting my money trying to fix what isn't broken.

My thanks for all the advice and the videos they were great.

Sorry for necro-bumping :P