2014 GMC Sierra 1500 4.3L Trans temp question (6L80)

Willard Norris · April 9, 2023

2014 GMC Sierra 1500 4.3L Trans temp issue (6L80) 88k miles

Feb 2022: installed Range AFM deactivator to prevent going into 4 cylinders

Spring 2022: noticed transmission temperatures consistently going into the 200°+ range and increased shuddering while shifting. Highest temp was 237°

Sep 2022: installed “Superior Solutions” thermostat, but temps didn’t really change

Nov 2022: rebuilt transmission with new torque converter

Nov 2022: first long drive, trans temp got to 205° in stop & go traffic

Nov 2022: transmission shop re-checked everything, and trans was functioning properly, but cooling fans were not going into high mode except when he would force it into high mode with scanner

Nov 2022: replaced temp sensor on cooling unit

Mar 2023: first long drive since temp sensor replacement, and trans got to 217° after 2 hours of cruising with outside temps around 50°.

— stopped and removed Range AFM deactivator. Trans temp settled around 178° during next 2 hours of driving except going in stop & go traffic: 186° under those conditions.

Apr 2023: Returned to trans shop, and the specialist states cooling fan still doesn’t go into high mode. Thinks the computer is somehow preventing it from going into high mode

2 questions:

Is it possible that the Range AFM deactivator was somehow causing high trans temps?
Would resetting the computer possibly help the cooling fan to operate normally? If so, how do you do a reset? The fan will work on high mode only when forced by mechanic using a scanner, but not under normal operating conditions.

I live in Georgia without too many steep hills.

Any other recommendations?

Edited April 9, 2023 by Willard Norris

m3n00b · April 9, 2023

When did you do the 4.6 swap?

Willard Norris · April 9, 2023

4.6 swap with what? I don’t understand your question.

mikeyk101 · April 9, 2023

Although mine is a 5.3 and a 6l80 trans, I have been using a Range AFM delete for several years and not had any issues with increased trans temps. I did have some significantly higher transmission temps when towing on more challenging roads but that didn't have anything to do with the Range delete. I have since changed out my original trans thermostat to the updated 154⁰ GM one and that has helped my trans temps to drop as well. I also changed out my original coolant thermostat to a 194⁰ coolant thermostat that I feel has also helped.

But IIRC, and hopefully @Grumpy Bear will jump in on this, the 2014-15 models had the trans fluid routed through the radiator but was later changed to run though the condenser with 2016+. I am assuming that with the original cooling thermostat and therefore higher radiator temps, it adds to the lack of cooling with the transmission fluid. I would bet going with a lower temp cooling thermostat may help you. Changing out the transmission thermostat to the Superior Solutions should have also helped but might be struggling with radiator temps.

You also don't mention what part of the country you live or about ambient temperatures where you're at.

Willard Norris · April 9, 2023

Thx Mikey. I live in Georgia. We have hills, but they’re pretty mild.
The Range AFM module may have nothing to do with the temperature. I’m throwing darts at this point.

Where did you get the 194° cooling thermostat?

newdude · April 9, 2023

What engine do you ACTUALLY have? 4.3 V6? 5.3 V8? Because GM does not have a 4.6L.

Edited April 9, 2023 by newdude

newdude · April 9, 2023

57 minutes ago, mikeyk101 said:

Although mine is a 5.3 and a 6l80 trans, I have been using a Range AFM delete for several years and not had any issues with increased trans temps. I did have some significantly higher transmission temps when towing on more challenging roads but that didn't have anything to do with the Range delete. I have since changed out my original trans thermostat to the updated 154⁰ GM one and that has helped my trans temps to drop as well. I also changed out my original coolant thermostat to a 194⁰ coolant thermostat that I feel has also helped.

But IIRC, and hopefully @Grumpy Bear will jump in on this, the 2014-15 models had the trans fluid routed through the radiator but was later changed to run though the condenser with 2016+. I am assuming that with the original cooling thermostat and therefore higher radiator temps, it adds to the lack of cooling with the transmission fluid. I would bet going with a lower temp cooling thermostat may help you. Changing out the transmission thermostat to the Superior Solutions should have also helped but might be struggling with radiator temps.

You also don't mention what part of the country you live or about ambient temperatures where you're at.

You are correct on the year change and the transmission cooler path flow except if its a 4.3 V6. The 4.3 from 14-18 are just transmission to the radiator and do not have an aux cooler in the condenser. The V8s do have the aux so 14-early 16 they flow from transmission to radiator, radiator to the aux, then back to the transmission. 16-19 they just go transmission to the aux and then back to the transmission.

Willard Norris · April 9, 2023

10 minutes ago, newdude said:

What engine do you ACTUALLY have? 4.3 V6? 5.3 V8? Because GM does not have a 4.6L.

I totally mistyped. It’s the 4.3 V6. My brain combined the two. I corrected the title.

Grumpy Bear · April 9, 2023

1 hour ago, mikeyk101 said:

But IIRC, and hopefully @Grumpy Bear will jump in on this,

@newdude got it covered.

CamGTP · April 9, 2023

I would just do the pill flip to completely remove the thermostat from working. Enjoy the 30-40 degree cooler running transmission.

mikeyk101 · April 10, 2023

7 hours ago, Willard Norris said:

Where did you get the 194° cooling thermostat?

Oops, I knew I was reading something wrong when I saw 4.6 but went with it anyway, my bad. Anyway, here is the coolant thermostat I changed to:

Motorad 815-194 housing Thermostat https://a.co/d/aShalRM

I know it's the correct lower temp replacement for my 2016 5.3l but not sure if it is also correct for a 4.3l. You would have to verify that.

Willard Norris · April 10, 2023

4 minutes ago, mikeyk101 said:

I know it's the correct lower temp replacement for my 2016 5.3l but not sure if it is also correct for a 4.3l. You would have to verify that.

I’ll call and ask about it. Did you install yourself? If so, how much of a pain was it?

mikeyk101 · April 10, 2023

Yes, installed myself. Wasn't much of a job at all. Took all of 20 mins to do after watching a few YouTube videos. And if you watch a couple of the different YouTube videos, you will find tips on how to minimize the coolant loss. I did mine in my driveway during the winter because the motor was having a problem getting up to the proper temps. Once I swapped thermostats, no more issues.

mikeyk101 · April 10, 2023

And I just hopped over to the Rock Auto site and it showed the Motorad 815-194 is the correct one for the 4.3l if you were considering doing that. The OEM factory thermostat is a 207⁰ so this gives you a little buffer. Some have gone with even lower temp thermostats but then I think you may have to get into tunes to get it running right.

Grumpy Bear · April 10, 2023

1 hour ago, mikeyk101 said:

Oops, I knew I was reading something wrong when I saw 4.6 but went with it anyway, my bad. Anyway, here is the coolant thermostat I changed to:

Motorad 815-194 housing Thermostat https://a.co/d/aShalRM

I know it's the correct lower temp replacement for my 2016 5.3l but not sure if it is also correct for a 4.3l. You would have to verify that.

They all use the same thermostat.

2015 CHEVROLET SILVERADO 1500 Mishimoto MMTS-VET-180 Mishimoto Thermostats | Summit Racing

The revised gasket is like the stock one. This one is 180 F and requires no tune. Fits stock housing. I tried the JET brand early on with the 'other' gasket and they failed faster than they could send them to me.