I think your reported temps after the cooling work you have done are entirely reasonable in light of the outside temps you have been driving in. I wouldn't be ..... sweating it.

A tune should not make any difference in coolant temps unless it was done by some imbecile......... My 07 ran a tune for 10 years+, no issues. I would be in no hurry to have any GM dealership tune anything of mine.

I don't remember from back at the beginning of this long azzed thread ......, do you have an external Trans Cooler? If not, might look into that.

 

No external trans cooler. I flushed the system which doesn't seem to make a difference. It cools fine on the street or when parked, even when it's hot out. I'll get 205-208 while driving on the street, 210 max. On the freeway however I get 222-225... Why does it run hotter on the freeway but not on the street?

Also, would higher IAT cause truck to run warmer? My IAT seem pretty high. Where does this truck get air for intake? Looks like from the fender.

 

Great, you isolated the overheat only with HIGH RPM'S. Check hoses(weak collapse with high rpm's, restricting coolant flow) + check fuel trims, (constantly running rich increases engine temp)!

 

Checked the fuel trims, STFT fluctuates between -0.78% and -3% and LTFT is pinged at 4.69% at idle and drops to 2.34% when increasing rev to 2000rpm. AFR 14.7:1, IAT was 153F and timing advanced to 10 degrees during idle, and 38.5 degrees at 2000rpm. Why is the engine advancing so much timing? Or is that normal?

 

There is no "overheat", not even close. We all know about an H3's three layer overheat protection and he isn't even bumping the first one.

When was the last time your Trans Fluid and Filter were changed? How is the quality of your Trans fluid?

I would expect 36-40 degrees advance at 2000 rpm. You want all the advance built in by about 2200-2400 or so. I think your timing is about right where it should be.

 

Not overheating but rather running hot I'd say. 220F - 225F although not close to overheating is much hotter than any car I've ever owned. And I am having no luck finding anything suggesting it's within normal operating temperature range. In fact the only thing I found actually suggests that 225F as being the starting point to troubleshoot overheating.

Transmission fluid and filter was replaced 8k miles ago. Level, color, taste and smell fine. Not sure where to go from here. If timing seem within spec, fuel trims and AFR look fine, what else??

What about IAT? 140-150 IAT I can see causing hotter engine temps no?

 

Post a pic of your CAI.

 

Got new radiator hoses today, even though I didn't notice them collapsing when revving the engine to 2500rpm, figured I'd give it a shot. No difference. Still running fine on the street but once on the freeway 220F and transmission between 235-237F ​​​

Don't have a cold air intake, just a stock box. Actually got a new filter today also. It's still connected to the fender.

 

At this point, only thing missing is the actual thermostat. Come to think of it, maybe having some restriction via (thermostat) is needed for proper heat exchange at the radiator. Without one coolant flows just a bit too fast and doesn't have time to actually cool via heat exchange at the radiator, makes sense why at freeway speeds/higher RPM heat exchange is affected. It's like my central AC, fan speed across the evaporative coil makes a difference.. my buddy who's an HVAC Engineer actually pointed that out.

Gonna install the 180 degree t-stat at the upper radiator hose tomorrow and see what happens. Makes sense, when GM switched to a warmer t-stat it threw the whole heat exchange balance out of wack.. I bet that's not what the Engineers had in mind when they first released this vehicle. Cooling system was designed to run a 180 degree t-stat not 190. Warmer t-stat caused too much restriction, cooler t-stat would result in too much flow (like a stuck open t-stat or in my case gutted t-stat)

Running a warmer t-stat might make sense from emissions and fuel efficiency perspective, but that's assuming engine is brand new and there are no other problems (like wear and age). Throw a wrench into the equation (real life stuff) and you're running too hot.. everything is great on paper but as we see from many posts, and not just on Hummer forums, Colorado folks notice the same and all happened when GM changed the t-stat... Hmmm.. 🤔

 

Normal auto engine coolant temp since the 1990s has always been between 195 - 220F depending upon make, model, options ...... That is NORMAL. If it is extremely hot outside, that range will slide up.

Why is it hotter at freeway speed? LOAD. You are pushing a brick through the wind and the engine is WORKING to do it. I would be more concerned about your Trans temp than the engine if I was you.

This reminds me of those Threads on people wanting a "functional hood louver" to let heat out from under the hood to cool the engine. Searching for a problem to a solution.

Good luck.