0. So long as the coolant and/or ATF have not exceeded 230F, they're not overheated, they're just getting close.
I always advise replacing ATF & coolant whenever either has exceeded 230F because I'm a pessimist.
(ATF & coolant temp are measured where it was convenient for GM to put those sensors,
but there are spots where ATF / coolant can get even hotter under load, which explains my pessimism.)
1. Although you did not quantify road speeds, you differentiated 'inside the city', vs ... 'not', I guess?
Over about 48MpH, air's ability to remove heat by passing through a cooler exceeds a fan's ability,
so electrical fans are programmed to shut off to protect their motors.
2. It's sort of an AC-related issue, since AC cools the cabin by heating up the underhood area, however you're right,
it's not the crux of the issue.
3. Ever try using 'Tow/Haul mode' to see if the RpM change from the downshift would improve cooling?
It's POSSIBLE if the engine was at a higher RpM, the cooling system might remove more heat?
(A hidden reason why I recommend ecm & tcm tuning for EVERYONE: better powertrain protection.)
4. You replaced a T-pipe after a leaking. There's always a chance that you introduced air during the replacement,
or did not remove air introduced during the leak? Burp it again with the vehicle pointing slightly uphill, maybe it helps.
5. It's also possible that your ATF cooler upgrade's placement / location might be suboptimal for cooling the coolant.
Moving it to a different spot might help keep the coolant ... cooler.
1. I live in Lebanon, in a fairly small city with multiple steep hills. Inside the city I usually drive around 20 mph, and on some wider roads I can reach 40–45 mph. The steep hills are short but frequent. This is actually the first time I learned about the fans—I only started paying attention to them when this issue came up. I always tried to hear them, but couldn’t. I thought maybe they shut off after a while, or that I just couldn’t hear them over the engine and tire noise when going uphill. Thanks for pointing that out!
3. I also tried driving in manual mode while keeping the RPMs at a minimum of 2k, but it didn’t make a difference. I’m not sure if that’s the same as using tow/haul mode.
4. I parked on an uphill slope, waited until the next day, then opened the coolant tank. I turned on the engine with the HVAC set to maximum heat and low fan speed, then let it warm up to operating temperature and kept it running for another 15 minutes. I didn’t see any air bubbles coming out, and before the second cold start the coolant level hadn’t dropped. I’m not sure if that’s the right way to bleed the system. I’m still trying to find a shop with a vacuum machine to properly remove any trapped air—hopefully that’s the issue.
5. I installed the cooler at the beginning of summer, so I wasn’t sure if it was related to the rising coolant temps. At first I mounted it in front of the condenser, near the OEM external trans cooler. When I noticed higher coolant temps, I moved it to the bottom of the bumper, behind the small chrome piece. Normally that area is blocked at the back, but I opened the black plastic section a bit and mounted it horizontally with an air box. I had a modding shop do the work, and they told me this setup wouldn’t affect radiator airflow since the top and bottom parts of the bumper are separated by plastic and foam.
I'd start with cleaning out the radiator fins..... Don't use a pressure washer, just the standard hose end sprayer on a garden hose. Any collection of dust, dirt, pine needles, etc greatly reduces cooling ability. Usually on these vehicles it's not the radiator itself, rather the AC condenser in front of the radiator that has narrower fins. Compressed air works excellent also. I would do this first before proceeding on other options. You may have to use a flashlight and a mirror to get a good look that there or no obstructions.
Next on the list is your thermostat itself. I like to replace them roughly every two years.
You also have to assess if your electric fans are operating correctly. On a 90 to 100° day, with the front and rear AC running, both fans should be blowing full speed. While it could be an issue with a worn out electric fan motor, typically it's just a worn out relay.
Middle of the guage is the normal reading. When you shut the engine off it actually heats up a little bit before it cools, so it's normal if you restart it after a minute or two it will read a little bit higher and should come right back to the middle.
I run all aluminum radiators in both our Escalade and the Hummer H2, which is really overkill in the Pacific Northwest.... But if you live in a hotter climate such as Arizona, it's well worth the money for the more efficient cooling.
Deal, first I’ll try cleaning the radiator fins and properly burping the system. I do hear the fans, about a minute after turning on the AC. I even tested them through the OBD connector at all three speeds, and both were working. What I couldn’t verify is that they would keep running properly during a long drive, like 2 hours or so, or if they might shut off if there’s an issue.
I’m in Lebanon, and it does get pretty hot in summer. Isn’t the OEM radiator aluminum? If I decide to go with a custom radiator, would I also need to add an external engine oil cooler?
Might as well be thorough and buy the CO2 test kit, to ensure your head gaskets are good. I just went through this on one of my Jeeps, and it tested positive.
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If that's the case, shouldn't my coolant level / oil level drop? that's what's worrying me
Since it's highway speeds, maybe something with the airflow.
X2 on the trans cooler placement.. When did you install the cooler?
If it's large and covering your radiator? Thought I heard that being an issue for someone..
Radiator side flaps still present?
Yeah, the radiator side flaps are still in place with no cracks or wear. When I remove the bumper, I’ll take some pictures to show how the bottom trans cooler placement turned out.
Appreciate all your replies. I’ll report back once I find out. Thanks everyone for the help!
