Transmission Thermostat Delete Pros vs. Cons

11bravoZ71 · November 12, 2021

I did the sure cool STL010 on my 19 5.3 8 speed and my averages for the last 2 weeks in 80 degree socal weather has been 140f on highway drives and in constant city driving it reaches up to 197f but I do drive my truck all day for about 6 hours daily.

so out of curiosity I removed the sure cool and did the pill “flip” on the OG thermostat to see if the results are the same in city driving or lower.

my question to anybody that might know is to check the fluid level with the pill being “flipped” is it still the same procedure and temperature range? For the 8l90’s considering that now theirs a constant immediate flow

also it would be nice if GM released a new T stat at 158f for the 8 speed and called it a day. Their must be a reason why the 6 speed got it lowered.

Grumpy Bear · November 12, 2021

2 hours ago, 11bravoZ71 said:

I did the sure cool STL010 on my 19 5.3 8 speed and my averages for the last 2 weeks in 80 degree socal weather has been 140f on highway drives and in constant city driving it reaches up to 197f but I do drive my truck all day for about 6 hours daily.

so out of curiosity I removed the sure cool and did the pill “flip” on the OG thermostat to see if the results are the same in city driving or lower.

my question to anybody that might know is to check the fluid level with the pill being “flipped” is it still the same procedure and temperature range? For the 8l90’s considering that now theirs a constant immediate flow

also it would be nice if GM released a new T stat at 158f for the 8 speed and called it a day. Their must be a reason why the 6 speed got it lowered.

Your hot check should be at the highest temperature you 'normally' see. The remainder of the procedure is the same.

The 6L80/8L and 10L all use the same thermostat housing. If the housing of the new 158F doesn't have the correct tubing style one can just swap the pill out.

Reasons 1.) The 6 speeds brain is in the oil inside the transmission. Electronics and heat are a bad thing. 2.) Every 18 F over 180 F doubles oxidation rate. Fluid oxidizes faster.

So what were the results. Was the flip lower or the same as the STL010 kit?

11bravoZ71 · November 12, 2021

Thank you for the response.

and I did the pill flip last night. so later today I should have an idea of the results. Same weather and driving style today. I will post back

11bravoZ71 · November 13, 2021

Results are in

STL010

average open highwaytemp is 140

Heavy city use is up to 197f

stays at around 197 if I idle for an extended period

flipped stock thermostat

average open highway is 150f

Heavy city use is up to 176f

Temp goes down to 167 if I idle extended periods.

same constant average load of about 600 pounds of loaded pallets with batteries in my bed with same routes and stops … All day for about 8 hours of total engine hours. 50/50 city highway. Average California 90 degree weather.

both tests were done in literally the same circumstances very consistent

2019 Silverado CC Z71 8l90 with 51k miles

transmission has had 3 drain and fills of about 6 quarts each time since purchased new. With blue label Mobil 1 atf. Filter was changed out 1 time at around 20k miles

Front and rear diff are running Amsoil 75w90 since 50k miles.

engine has had Mobil 1 0w30 since new no issues. and recently I’m trying out 5w30 Penzoil ultra. Always changed oil at 5k miles since new. No DFM disabled lol running it stock.

Edited November 13, 2021 by 11bravoZ71

Grumpy Bear · November 13, 2021

33 minutes ago, 11bravoZ71 said:

flipped stock thermostat

average open highway is 150f

Heavy city use is up to 176f

Temp goes down to 167 if I idle extended periods.

Almost identical to mine for a 90 F day. Amazingly close.

CadillacLuke24 · November 22, 2021

Food for thought

Some members have observed that the pill flip may lead to unusually cool temperatures for us folk in the butt numbing belt of the country

I'm out of Casper, WY. Last week on my way to Cheyenne (YAY Lowe's and Craftsman), the outside temp was 17 degrees Fahrenheit. Posted transmission fluid temperature as I barreled down I-25 at 80?

90 degrees

The pill flip works! And HOW hahahaha

I like Grumpy's train of thought. I think I will get a new 6spd thermostat and swap the guts with my factory trans thermostat I have as a spare. When I did the pill flip I got a new thermostat. I'm not sure why.

I could do a little thermodynamic research and see if they changed the 8spd thermostat too. There's a new part number, though it's close to the old 6spd thermostat, so I doubt it.

Grumpy Bear · November 22, 2021

7 hours ago, CadillacLuke24 said:

I'm out of Casper, WY. Last week on my way to Cheyenne (YAY Lowe's and Craftsman), the outside temp was 17 degrees Fahrenheit. Posted transmission fluid temperature as I barreled down I-25 at 80?

90 degrees

The pill flip works! And HOW hahahaha

You can also blind the grill or upper part of the AC condenser (air to air trans cooler) as an alternative. It was 19 F this morning and mine was in the mid 120's to low 130's. I don't have the second cooler in the condenser like you do.

BlaineBug · December 8, 2021

On 11/22/2021 at 6:25 AM, CadillacLuke24 said:

Food for thought

Some members have observed that the pill flip may lead to unusually cool temperatures for us folk in the butt numbing belt of the country

I'm out of Casper, WY. Last week on my way to Cheyenne (YAY Lowe's and Craftsman), the outside temp was 17 degrees Fahrenheit. Posted transmission fluid temperature as I barreled down I-25 at 80?

90 degrees

The pill flip works! And HOW hahahaha

I like Grumpy's train of thought. I think I will get a new 6spd thermostat and swap the guts with my factory trans thermostat I have as a spare. When I did the pill flip I got a new thermostat. I'm not sure why.

I could do a little thermodynamic research and see if they changed the 8spd thermostat too. There's a new part number, though it's close to the old 6spd thermostat, so I doubt it.

A safe alternative for us who live in regions where we see extreme cold is to install GM's newly revised thermostat bypass assembly which now contains a lower temperature thermostat.

CadillacLuke24 · January 30, 2022

On 12/8/2021 at 9:58 AM, BlaineBug said:

A safe alternative for us who live in regions where we see extreme cold is to install GM's newly revised thermostat bypass assembly which now contains a lower temperature thermostat.

Funny you mention that, that is exactly what I did. Trans temp is consistently 130s-150s now. All the time.

Barbarrino · February 2, 2022

On 9/27/2020 at 5:03 PM, 14burrito said:

Little 5 quarts ATF rejuvenation followed with the new ATF thermostat being installed. Curious to see if driveability will change at all and interested to see how ATF temps are altered.

Hello Sir, do you have the part number you ordered? I am looking to do the same thing.

14burrito · February 2, 2022

33 minutes ago, Barbarrino said:

Hello Sir, do you have the part number you ordered? I am looking to do the same thing.

So you kind of have two options now.

1. Pull flip

2. Check your new t-stat housing, if its stamped with a "70" it has a new lower temp 135 stat installed vs the original 180.

21-NA-199 will provide more details. You might be able to get the dealer to cover the cost of a new tstat assembly if you provide them that TB.

Thermostat part number is 13511136 which shows to have maybe been replaced by 86774933.

mikeyk101 · February 2, 2022

8 minutes ago, 14burrito said:

So you kind of have two options now.

1. Pull flip

2. Check your new t-stat housing, if its stamped with a "70" it has a new lower temp 135 stat installed vs the original 180.

21-NA-199 will provide more details. You might be able to get the dealer to cover the cost of a new tstat assembly if you provide them that TB.

Thermostat part number is 13511136 which shows to have maybe been replaced by 86774933.

86774933 is the part number of the lower temp thermostat I installed. I believe 13511136 is the part number of the one that comes on the 6L80 transmissions. Don't order that one or you will get the same one you already have...

14burrito · February 2, 2022

17 minutes ago, mikeyk101 said:

86774933 is the part number of the lower temp thermostat I installed. I believe 13511136 is the part number of the one that comes on the 6L80 transmissions. Don't order that one or you will get the same one you already have...

13511136 was for my 6L80, 2019 Tahoe L83 motor. 86774933 shows to be the successor, did your t-stat housing have a "70" stamped on it by chance?

If you read the TB, they state that the part number did not change and it requires the tech (or end user) to verify there is a "70" stamped in the housing. Whether that has changed or not, I do not know, as the verbiage does not show to have changed within the TB.

Hence why I stated, if one was to order the old tstat housing- they would need to ensure its stamped with a 70. If it is, it has the 135. If it doesn't, it has the 180 and can be used for a pill flip option.

Edited February 2, 2022 by 14burrito

mikeyk101 · February 2, 2022

2 hours ago, 14burrito said:

13511136 was for my 6L80, 2019 Tahoe L83 motor. 86774933 shows to be the successor, did your t-stat housing have a "70" stamped on it by chance?

If you read the TB, they state that the part number did not change and it requires the tech (or end user) to verify there is a "70" stamped in the housing. Whether that has changed or not, I do not know, as the verbiage does not show to have changed within the TB.

Hence why I stated, if one was to order the old tstat housing- they would need to ensure its stamped with a 70. If it is, it has the 135. If it doesn't, it has the 180 and can be used for a pill flip option.

As far as I can tell in that TSB which is what I went by, the 86774933 just recently came out and is the redesigned product at a lower temperature and was able to be identified by the 70 being stamped into it. My OEM which was the 13511136 definitely didn't have the 70 stamped into it. The 21-NA-299 also confirms that only the 86774933 which is the new part has the 135⁰ thermostat. Only order that one if you want to make sure you get the lower temp thermostat...

mikeyk101 · February 2, 2022

Taken from information in the bulletin:

"The new TBV can be identified by the “70” stamped into the bottom of the valve"

Unless a new trans thermostat was installed within the last month or so by dealer, it won't be part #86774933 and won't be stamped with the 70. I imagine the reason for stamping the new housing with the identifiable 70 is for the tech to be able to identify it for reasons of trans fluid service. With the old thermostat, the trans temperature would have to be increased to 180⁰ or so to do the exchange. With this new redesigned thermostat, the transmission temperature would only have to be raised to 135⁰ or so.