I would guess you still have air in the system.

 

Our '07 always ran at the 3/4 mark here in FL and let me tell you that after every car I've ever owned that ran at mid-range, when we bought her I thought the engine was going to melt on the 2 hour ride home! Even with the A/C on full blast in the summer or riding around in the "winter" it stayed at the 3/4 mark. We recently had to change out the radiator (due to a crack) and switched from the GM Dexacool to the regular green coolant...she never gets above mid-mark now....regardless of the A/C on or external heat temps. I'd say do a radiator flush and change the coolant if you want her to run at a cooler temp.

 

If it had been running at the 3/4 mark before the t-stat and coolant change I would say that may be normal for his truck. It was not, so something has changed. I am going to do a coolant flush on my Alpha very soon and some of the information here has been helpful. My mechanic also suggested elevating the front end and filling slowly. He says they have a vacuum system that they rarely use but he is going to use it on mine when we do the change. If you change form Dexcool to green, make sure you have completly gotten rid of all the Dexcool in the system. Mixing the two can have very bad consequences.

 

I had the same problem and here is how I solved it:


I drained out the coolant from the radiator. I then took off the top hose of the radiator and filled the engine with coolant pouring it into the top hose (The engine must be filled with coolant first). I then filled the rest of the radiator and the reservoir to correct level. My 2006 H3 went from running at 3/4 to 1/2. Must have been trapped air. The reason for this has something to do with the thermostat being at the bottom of the engine.


This procedure was given to me by a service tech and it worked! Hope it solves your problem!

 

Yes 3/4 is normal for Hummer even in my H3 before it use to reach 3/4 and even i went to the General Motors they told me in Hummer is normal the water pressure plug will open in hummer at 120 or something like that while in other cars it open at 85 to 90, but most of my friends they added a hummer h3 extra double fan in-front or there is another trick you can do its cheaper but just need to right word to say it not so into the mechanic words hahah but i will come back, to let you know and its 100% it will rich '..........(')...........' half

 

Whats normal for one vehicle will not be normal for another vehicle.
Only way to tell is hook up a scan gauge and monitor the system during its ranges. The OP is within spec even with his cluster gauge reading 3/4.

 

3/4 is NOT normal, maybe common, however NOT normal!

The temp gauge is there for a reason: running cool (below half on the gauge) affects performance, or running hot (above half on the gauge) causes damage.
Bottom line, Normal is 1/2 on the gauge:




CONSEQUENCES OF OVERHEATING
If the engine overheats, the first thing that will happen is a gasoline engine will start to detonate. The engine will ping and start to lose power under load as the combination of heat and pressure exceed the octane rating of the fuel. If the detonation problem persists, the hammer-like blows may damage the rings, pistons or rod bearings.

Overheating can also cause pre-ignition. Hot spots develop inside the combustion chamber that become a source of ignition for the fuel. Hot spots can also be very damaging and burn holes right through the top of pistons.

Another consequence of overheating may be a blown head gasket. Heat makes aluminum swell almost three times faster than cast iron. The resulting stress can distort the head and make it swell in areas that are hottest like those between exhaust valves in adjoining cylinders, and areas that have restricted coolant flow like the narrow area that separates the cylinders. The typical aluminum head swells most in the middle, which can crush the head gasket if the head gets hot enough. This will cause a loss of torque in the gasket allowing coolant and combustion leaks to occur when the head cools.

Overheating is also a common cause of OHC cam seizure and breakage.

If the coolant gets hot enough to boil, it may cause old hoses or an age-weakened radiator to burst under the increased pressure. Pistons may swell up and scuff or seize in their bores, causing serious Engine Damage. Exhaust valve stems may stick or scuff in their guides. This, in turn, may cause valves to hang open which can damage pistons, valves and other valve train components. And if coolant gets into the crankcase, you can kiss the bearings and bottom end of the engine goodbye.

 

Going "green" is not a good thing (with coolant)! :



DEX-COOL® Life 5/150 antifreeze coolant
is the latest long life automotive engine coolant
development from Valvoline. The patented*
carboxylate formulation has a service life of up to
five years or 150,000 miles. It incorporates state-ofthe-
art organic acid technology in an ethylene glycol
base for protection of all cooling system metals
including aluminum. ZerexÒDEX-COOL® 5/150
antifreeze coolant is approved by General Motors to
the GM 6277M specification.
ZerexÒ DEX-COOL® 5/150 antifreeze coolant
contains no phosphates, silicates, borates, nitrates,
amines and nitrites. It’s global formulation meets
the phosphate-free requirements of European
automobile manufacturers and the silicate free
requirement of Asian automobile manufacturers like
Toyota, Scion, Acura, Hyundai, Kia, Honda, Isuzu
and others. It can be mixed with any DEX-COOL®
and is approved by Opel, Dae Woo and Saab. It is
dyed orange to distinguish it’s unique chemistry
from traditional green and yellow silicate coolants.
When diluted 50% with water, ZerexÒ DEX-COOL®
5/150 protects modern engine components from
winter freezing and summer boiling. The chart at
the top right provides detailed mixing information.
ZerexÒ DEX-COOL® 5/150 antifreeze coolant is
storage stable for up to five years as both a
concentrate or diluted with water. It contains a high
quality defoamer and will not harm gaskets, hoses,
plastics or original vehicle paint.
ZerexÒ DEX-COOL® 5/150 antifreeze coolant meets
or exceeds the following coolant specifications:

http://www.valvoline.com/pdf/zerex_dex_cool.pdf

 

i am talking as the the dealer General Motors Hummer inform me that its normal 3/4 unless you want to add a fan, i installed something like that http://www.pcmofnc.com/index.php?option=com_aceshop&route=product/product&path=271_282&product_id=107&Itemid=106 but some of my friends install double fan Derale Electric Cooling Fans, Derale Dual High Output Radiator Fan and its working pretty fine, but for me i installed a fan and i change the Car Radiator Water Pump Thermostat http://www.sourcingmap.com/car-radiator-water-pump-thermostat-assembly-9091603129-p-319089.html instead of buying a hummer Water Pump Thermostat i buy a Chevy Blazer pump change it because the Blazer car pump open as i said early on 85 and hummer pump open at 120 that's why i change it and its working fine dont go higher than half .

 

Wtf???