Transmission Cooler for 2021 Silverado z71

malibu43 · December 19, 2022

I wanted to know if anyone can recommend a good aftermarket transmission cooler for my 2021 z71 RST, 5.3l gas. Specific part numbers or links would be appreciated.

We tow a 6400lb (max gross weight) travel trailer. Over the past year we took it out over 20 times (some long trips, some pretty short). Under normal towing conditions (including over the Grapevine on I-5 in July and August), the transmission temp stays right around 192F with some spikes into the 210's or maybe 220's. However, a couple of times it went up around 250F. Once was on the final leg of a long drive once we got up into the Sierras in July, last 20 miles or so of the climb was windy, 1 lane road, around 4K-5K feet altitude. The second time was in November and it was colder. But the campground was on a hill and we had to make a couple loops through the campground on very narrow, windy roads, and then topped it off with having to back up, up-hill, to get into our site. Temp topped out at 255F.

So hopefully there are some aftermarket coolers out there that work well in these sort of low-speed, low airflow situations where I've seen issues.

Does adding a transmission cooler affect warranty?

Thanks!

newdude · December 19, 2022

34 minutes ago, malibu43 said:

I wanted to know if anyone can recommend a good aftermarket transmission cooler for my 2021 z71 RST, 5.3l gas. Specific part numbers or links would be appreciated.

We tow a 6400lb (max gross weight) travel trailer. Over the past year we took it out over 20 times (some long trips, some pretty short). Under normal towing conditions (including over the Grapevine on I-5 in July and August), the transmission temp stays right around 192F with some spikes into the 210's or maybe 220's. However, a couple of times it went up around 250F. Once was on the final leg of a long drive once we got up into the Sierras in July, last 20 miles or so of the climb was windy, 1 lane road, around 4K-5K feet altitude. The second time was in November and it was colder. But the campground was on a hill and we had to make a couple loops through the campground on very narrow, windy roads, and then topped it off with having to back up, up-hill, to get into our site. Temp topped out at 255F.

So hopefully there are some aftermarket coolers out there that work well in these sort of low-speed, low airflow situations where I've seen issues.

Does adding a transmission cooler affect warranty?

Thanks!

There is a thermostat on these transmissions. Adding an extra cooler won't help.

If you have a 10 speed, there is nothing you can do. The bypass is internal to the transmission. Bypass temp open is 143F.

If you have an 8 speed, you can do the "pill flip" mod to the thermostat bypass valve. Normal TBV temp is 194F on the 8 speed. Flipping the pill makes the cooler loop open all the time.

You should also have the truck inspected for kinked cooler lines. Tell the dealer what's up, and bring up 22-NA-182 to them.

Edited December 19, 2022 by newdude

malibu43 · December 19, 2022

4 hours ago, newdude said:

There is a thermostat on these transmissions. Adding an extra cooler won't help.

If you have a 10 speed, there is nothing you can do. The bypass is internal to the transmission. Bypass temp open is 143F.

If you have an 8 speed, you can do the "pill flip" mod to the thermostat bypass valve. Normal TBV temp is 194F on the 8 speed. Flipping the pill makes the cooler loop open all the time.

You should also have the truck inspected for kinked cooler lines. Tell the dealer what's up, and bring up 22-NA-182 to them.

Thanks. I'm not super familiar with transmission cooling on these trucks. I have the 8 speed. I'm sure it would keep the tranny cooler for normal driving/towing, but I wonder if the pill flip would help in my two scenarios since I'm so far above the bypass open temp anyway.

Also, was that the correct technical bulletin number? That one's for radio issues. Interestingly enough, I did have some radio issues early on (bought in August 21) and I think they already did the software update when I took it in for that...

Edited December 19, 2022 by malibu43

newdude · December 20, 2022

15 hours ago, malibu43 said:

Thanks. I'm not super familiar with transmission cooling on these trucks. I have the 8 speed. I'm sure it would keep the tranny cooler for normal driving/towing, but I wonder if the pill flip would help in my two scenarios since I'm so far above the bypass open temp anyway.

Also, was that the correct technical bulletin number? That one's for radio issues. Interestingly enough, I did have some radio issues early on (bought in August 21) and I think they already did the software update when I took it in for that...

That # is correct. It used to be this: PIP5792 Chevrolet Technical Service Bulletin (tsbsearch.com) but has been superseded to 22-na-182.

Pill flip won't let it get to 194F then open to the cooler. With it flipped (or the SureCool delete) it would allow for constant flow to the cooler and lower the temps quite a bit.

These don't go through the radiator any more either, just to an external cooler so engine coolant temp won't affect it via going through the engine rad then aux cooler.

IMO, I'd have the lines checked per that bulletin for any kinks. Then the fluid changed and do the flip/sure cool and re-test. See how it handles the trailer on a 50 or 100mi drive loop. Give it some WOT, etc. Manual mode and set it to a high gear it would use to pull some roads at times.

If its still getting too warm after that, say over 220F, then I'd go for a larger cooler.

Edited December 20, 2022 by newdude

Grumpy Bear · December 20, 2022

This is like any other cooling system regulated by a thermostat. The thermostat sets a ceiling but only if there is enough cooling capacity to handle it. My 6L80E use to run up to 250 F on a hot day without ever pulling a load. I flipped the pill and it never got over 170 after that. That told me that the thermostat, which tested good by the way, was the restriction. Now having said that, it will still go over 200 F in stalled traffic on a hot day so I know pulling a load it would as well. It needs more cooler if and when I wish to tow or haul heavy or even run fast on a day over 90 F. And it needs one with a fan for heavy traffic. Just saying that this isn't a single source issue.

malibu43 · December 20, 2022

5 hours ago, newdude said:

That # is correct. It used to be this: PIP5792 Chevrolet Technical Service Bulletin (tsbsearch.com) but has been superseded to 22-na-182.

Pill flip won't let it get to 194F then open to the cooler. With it flipped (or the SureCool delete) it would allow for constant flow to the cooler and lower the temps quite a bit.

These don't go through the radiator any more either, just to an external cooler so engine coolant temp won't affect it via going through the engine rad then aux cooler.

IMO, I'd have the lines checked per that bulletin for any kinks. Then the fluid changed and do the flip/sure cool and re-test. See how it handles the trailer on a 50 or 100mi drive loop. Give it some WOT, etc. Manual mode and set it to a high gear it would use to pull some roads at times.

If its still getting too warm after that, say over 220F, then I'd go for a larger cooler.

Thanks. I looked into the Pill Flip. Doesn't look too difficult.

If I did decide to go for a larger cooler, is there one you'd recommend? Are those typically pretty simple installs?

malibu43 · December 21, 2022

Hey guys. I was researching the pill flip, and started reading through another thread on these forums on the topic. I eventually came across this post:

I pulled up that TSB and it appears it applies to my 2021 5.3l 1500. If that's correct, per GM the lower temp TBV should be installed on my truck, right?

I was all set on doing the pill-flip, but if I can take it into the dealer and they install the lower temp thermostat for free, I'll probably start with that.

newdude · December 22, 2022

19 hours ago, malibu43 said:

Hey guys. I was researching the pill flip, and started reading through another thread on these forums on the topic. I eventually came across this post:

I pulled up that TSB and it appears it applies to my 2021 5.3l 1500. If that's correct, per GM the lower temp TBV should be installed on my truck, right?

I was all set on doing the pill-flip, but if I can take it into the dealer and they install the lower temp thermostat for free, I'll probably start with that.

No. That was a 6 speed transmission thing, the lower temp updated thermostat. 21-NA-199 is for 6 speeds only.

8 speed TBV is 194F for 2019+up trucks. GM does not sell a lower temperature thermostat for the 8 speed applications.

From 22-NA-182:

The TBV will open at the following temperatures for the models listed in this TSB. 6 Speed (6L80, 6L90) - 158F (70C) - TBV is external to the transmission

8 Speed (8L90) - 194F (90C) – TBV is external to the transmission

10 Speed (10L80, 10L90, 10L1000) – 143F (61C) – TBV is within the valve body on all listed applications expect those equipped with 3.0 (LM2) Diesel. On the LM2 Diesel the TBV is external to the transmission.

Edited December 22, 2022 by newdude

newdude · December 22, 2022

On 12/20/2022 at 2:07 PM, malibu43 said:

Thanks. I looked into the Pill Flip. Doesn't look too difficult.

If I did decide to go for a larger cooler, is there one you'd recommend? Are those typically pretty simple installs?

I've never ran any aftermarket transmission coolers before. Mishimoto is a popular name that gets thrown around, but not sure if they offer one.

malibu43 · December 22, 2022

3 hours ago, newdude said:

No. That was a 6 speed transmission thing, the lower temp updated thermostat. 21-NA-199 is for 6 speeds only.

8 speed TBV is 194F for 2019+up trucks. GM does not sell a lower temperature thermostat for the 8 speed applications.

From 22-NA-182:

The TBV will open at the following temperatures for the models listed in this TSB. 6 Speed (6L80, 6L90) - 158F (70C) - TBV is external to the transmission

8 Speed (8L90) - 194F (90C) – TBV is external to the transmission

10 Speed (10L80, 10L90, 10L1000) – 143F (61C) – TBV is within the valve body on all listed applications expect those equipped with 3.0 (LM2) Diesel. On the LM2 Diesel the TBV is external to the transmission.

I see. I wasn't sure what MYC and MYD meant, but I see now those refer to 6 speed transmissions only. Bummer. I'll still plan on doing the pill-flip at some point.

malibu43 · December 22, 2022

3 hours ago, newdude said:

I've never ran any aftermarket transmission coolers before. Mishimoto is a popular name that gets thrown around, but not sure if they offer one.

I can't really find much info and am not sure how to know if what I'm looking at is an upgrade over what's already in the truck. Hopefully the pill-flip will be enough to keep the overall temp low so that when it does spike for short time, it's not spiking as high...

Grumpy Bear · December 23, 2022

FYI. The 70 C pill will fit the 8 speed

Ronjon · December 24, 2022

PPE has both a deep pan and upgraded cooler if that's what you need. Hopefully the dealer will have a quick fix though.

malibu43 · December 24, 2022

On 12/22/2022 at 9:21 PM, Grumpy Bear said:

FYI. The 70 C pill will fit the 8 speed

I figured that, but it won't be free if it's not part of the TSB. I'll have to decide between free pill flip or paying for the 70C thermostat. I guess just swapping the thermostat is a tiny bit less work...