Notice the same, sitting at the light if I am at 215F and accelerate from dead stop, temperature drops. Highway speeds cruising, not so much. I think my pipes are clean.

 

Not pipes>PASSAGES! Did you add a bottle of

AS205

AS205

? Btw, increasing rpms off idle to around 2k should drop coolant temp around -10° under a minute. Passages shown here:

 

Well you did say engine needs an "enema", figured pipes would be more appropriate vs. passages.

I haven't done the chemical flush yet. Just got the front baffles in today, gonna do some work up front first to see how much difference it makes . Then I'll do the flush. I don't like to change a bunch of things at once without testing, otherwise you'll never know what the fix was.

 

Add the cleaner and drive on. After a few hundred miles, drain. Someday, I may need to clean mine? I still NEVER exceeded 210° coolant temp, not necessary at this time.

 

Even with ambient temps over 100-105F??? Are you using a separate cooler for the transmission? How much warmer are these transmissions supposed to be relative to engine temp? Is there an operating temperature range?

I can say that adding all the seals and baffles definitely helped (about 10 degrees or so) but mostly on the street or while idling.. On the highway, no difference coolant temp 220F with transmission temp pinned at 235F. Once off the highway, engine temps drop 10 degrees but transmission temp remains at 235F. Replaced the radiator cap just in case and checked all the overflow lines and tank for any blockage. Also checked to see if I notice any hoses collapse at 2-2.5k RPM, all good. Will take it for another spin tomorrow and see. Next step will be the chemical flush.

front sides to help redirect airflow towards the radiator.

bottom grille

bottom bumper installed

you can see the plastic baffle redirects airflow down towards the bottom of the radiator where the transmission cooler tube is located. I am not exactly sure how far back stock diffuser supposed to go. Would love to see a photo if anyone still has both the front baffles.

 

While were on the subject, Hummerz have you done the thermostat move to the top?
And if so did it make a difference?

 

NOPE! I did replace the OEM T-STAT with housing many years ago due to low temp(stuck open). Still in the same position, on the drivers side of the block, and never a problem since!

 

@hummerz do you have an separate cooler/radiator for your transmission?

 

NOPE! Still connected to my Silla I installed over 11yrs ago.

 

That's right you mentioned that. Met a fella yesterday with a Hummer H3 2.7L, his doesn't run hot either. Had a short chat, after I told him all the stuff I did, he asked if it's tuned. I didn't even think of that, maybe previous owner messed with the timing. Might take it down to Chevy and ask them to flash that sucker back to stock.

Meanwhile, driving around letting that coolant flush stuff do its thing.