Just an FYI about 8 spd transmissions

[GaryM]

For a year or more I've had to resort to a technique to get my 2025 RS into 8th gear. I've been told it's operating as designed. Since I live in a very cold climate in the winter months another shifting issue came up, no 7th and 8th gear. It usually shows up when outside temperatures are less than 20 deg F. Again I was told it was working as designed and the issue was created by the extreme cold. I get that, but the transmission system is designed to operate "normally" in cold weather. It has a heat exchanger which does double duty; warms the ATF in the winter using engine coolant and prevents overheating in summer months. The trans control module has programing specific to ATF temps and will restrict access to upper gears if the AFT is too cold. The 8 spd is actually a 6 spd with two additional overdrive gears to get 8 spds. Access to these gears has very specific rules in the TCM, which include very sensitive temperature guidelines, which if not met, will lock out 8th gear or 7th and 8th in cold climates. After some on highway testing we determined the ATF was not reaching appropriate minimum temperature. The TCV (thermal control valve) for the heat exchanger is stuck closed which doesn't allow coolant to warm the ATF to the minimum temp of 150 deg. Normal ATF temp is usually 20-30 deg lower than engine operating temp, which in the Equinox is 190 deg F. Our testing showed much lower ATF temps after a significant on highway test. The TCV is on back order and will be replaced when it comes in. We'll do a retest to document the ATF temp after the TCV is replaced. If you're experiencing similar behavior you might want to "encourage" your dealer to check ATF operating temps. I've seen other posts on here commenting on 8th gear issues. This could be the issue.

 

[2025 Red Equinox]

For a year or more I've had to resort to a technique to get my 2025 RS into 8th gear. I've been told it's operating as designed. Since I live in a very cold climate in the winter months another shifting issue came up, no 7th and 8th gear. It usually shows up when outside temperatures are less than 20 deg F. Again I was told it was working as designed and the issue was created by the extreme cold. I get that, but the transmission system is designed to operate "normally" in cold weather. It has a heat exchanger which does double duty; warms the ATF in the winter using engine coolant and prevents overheating in summer months. The trans control module has programing specific to ATF temps and will restrict access to upper gears if the AFT is too cold. The 8 spd is actually a 6 spd with two additional overdrive gears to get 8 spds. Access to these gears has very specific rules in the TCM, which include very sensitive temperature guidelines, which if not met, will lock out 8th gear or 7th and 8th in cold climates. After some on highway testing we determined the ATF was not reaching appropriate minimum temperature. The TCV (thermal control valve) for the heat exchanger is stuck closed which doesn't allow coolant to warm the ATF to the minimum temp of 150 deg. Normal ATF temp is usually 20-30 deg lower than engine operating temp, which in the Equinox is 190 deg F. Our testing showed much lower ATF temps after a significant on highway test. The TCV is on back order and will be replaced when it comes in. We'll do a retest to document the ATF temp after the TCV is replaced. If you're experiencing similar behavior you might want to "encourage" your dealer to check ATF operating temps. I've seen other posts on here commenting on 8th gear issues. This could be the issue.

How did you determine your vehicle was not shifting into 8th gear appropriately?

How did you determine your vehicle’s transmission was not reaching appropriate minimum temperature?

Is the testing being done by a Chevrolet dealer? Were any trouble codes stored?

Interesting that the TCV is on back order. Every part that has been ordered for my 2025 Equinox RS AWD (not the TCV) was on back order.

 

[GaryM]

How did you determine your vehicle was not shifting into 8th gear appropriately?

How did you determine your vehicle’s transmission was not reaching appropriate minimum temperature?

Is the testing being done by a Chevrolet dealer? Were any trouble codes stored?

Interesting that the TCV is on back order. Every part that has been ordered for my 2025 Equinox RS AWD (not the TCV) was on back order.

Engine RPM's at road speed were too high. I determined it was running in 7th gear. 8th gear brings 1800 rpm's at 70 while 7th gear brings 2200 rpms at the same speed. I used a OBD2 code reader that provides live data and includes transmission access. No fault codes are recorded when this happens in most cases. No check engine lights either. The dealer tested as well as myself. The dealer had never sold a TCV. The tech that road tested was not familiar with the ATF temperature requirements. I don't know how they came up with operating as designed as they had not road tested for operating temp until I pressed them hard about it. I'm a retired mechanic. I'm assuming because it was -7 deg they just assumed it was too cold. They also were not that knowledgeable about the TCV in the heat exchanger and how it works.

 

[2025 Red Equinox]

Engine RPM's at road speed were too high. I determined it was running in 7th gear. 8th gear brings 1800 rpm's at 70 while 7th gear brings 2200 rpms at the same speed. I used a OBD2 code reader that provides live data and includes transmission access. No fault codes are recorded when this happens in most cases. No check engine lights either. The dealer tested as well as myself. The dealer had never sold a TCV. The tech that road tested was not familiar with the ATF temperature requirements. I don't know how they came up with operating as designed as they had not road tested for operating temp until I pressed them hard about it. I'm a retired mechanic. I'm assuming because it was -7 deg they just assumed it was too cold. They also were not that knowledgeable about the TCV in the heat exchanger and how it works.

Unknowledgeable auto dealers and mechanics are not unusual.

So you are assuming the vehicle is not operating as Chevrolet intended because it does not shift into 8th gear at 70 mph?

How did you determine what the correct transmission operating temperature should be?

 

[GaryM]

Unknowledgeable auto dealers and mechanics are not unusual.

So you are assuming the vehicle is not operating as Chevrolet intended because it does not shift into 8th gear at 70 mph?

How did you determine what the correct transmission operating temperature should be?

There's plenty of documentation regarding how the trans should perform in various scenarios. GM, as well as other manufacturers, use a heat exchanger system to warm ATF in cold weather. When it's working correctly all the gears are available. When I saw my tach at 2800 rpm at 65 mph I knew I wasn't getting into 7th gear. The ambient temp was 10 deg and I had warmed up the vehicle before heading out. By the time I got out on the highway engine temp was normal but the transmission refused 7th and 8th gears. It stayed that way until I reached our destination, which was 25 min away. That's not normal. Since transmission performance is controlled by the TCM there had to be something it didn't like to lock out 7th and 8th. ATF temp is the first and easiest thing to check. Mine never exceeded 130 deg. The threshold the TCM works with is a minimum of 150 deg. Bad things happen when ATF it too thick to flow correctly. Locking out 7th and 8th is a safety function in that scenario.

 

[ap19063]

All these comments remind me of back in the 70s, when cars were awful. Hard to believe 50 years of advancement brings us to that scenario again.

 

[GaryM]

All these comments remind me of back in the 70s, when cars were awful. Hard to believe 50 years of advancement brings us to that scenario again.

I guess I look at it a little differently. I like my RS Equinox. It's my third one and aside from some of the quirks we've uncovered, it's a nice vehicle and from a comfort point of view, much better than the cars we had back in the 70's. My last one was a 2018 Premier 2 liter. I would have preferred that engine versus the 1.5 but it's adequate. I got over 100K out of that one before I traded it for this one. This thing with 8th gear and now 7th and 8th seem to be related to ATF temp. I live in a cold climate so the heat exchanger function is something that should make everything work better. Given what I know now, it's possible all of it is driven by one component not functioning as it should and driving another component to malfunction. If I'm right, replacing the thermal control valve for the trans heat exchanger will solve all of it. Yes, it does have a lot of features and the more there are the more that could go wrong. Hopefully it lasts as long as the last two.

 

[ricklack]

I've heard folks with 6 speed trans have a similar issue where they will stay in 5th. I live in Canada and have not seen this, oddly enough. There are bulletins out there saying same thing you are, it is designed that way.

 

[GaryM]

I've heard folks with 6 speed trans have a similar issue where they will stay in 5th. I live in Canada and have not seen this, oddly enough. There are bulletins out there saying same thing you are, it is designed that way.

Thanks for the feedback. I had a 2018 and never experienced transmission performance like this one but we're comparing apples and oranges. It seems, with the exception of 8th gear access, all the shift issues are related to ATF temps being too cold. I have the tooling to test, which I did today since it was warmer, to see what kind of ATF temp I could generate at 40 deg F. 175 to 200 is considered normal. After 65 miles of on highway driving at 70 mph it finally reached 174 deg F. That's at the low end of "normal". That suggests the thermal control valve for the transmission heat exchanger may be leaking when closed, keeping the ATF colder longer. It's scheduled to be replaced.

 

[dequardo]

Not buying this. If I’m at 72mph I’m at around 2200 rpms in D. If I then switch to L it ALWAYS will start at L6 and of course the rpms jump. When I flick the toggle + twice to got to L8 it then goes back to 2200 rpm. Every single time. So it is going into 8th gear all the time in D. All that said, I still hate the mpgs in this gen.

 

[Bold One]

I put a lot of emphasis on understanding my vehicles gas efficiency. My 2026 RS was floating around 28mpg in first 1000 miles. Currently less than 4000 miles still around 30mpg when i'm driving nice. So I started to dig...
First complaint, my previous equinox's (2013 and 2019 still have) had ECO buttons, that we ALWAYS leave ON for gas efficiency. I was disappointed to not be able to find it on my new state of the art fully loaded RS, ALSO there's an expensive "MODE" dial that "SHOULD" most certainly have the ECO mode. instead it has TWO options OFFROAD/SNOW.ICE that are essentially the same thing (AWD) what a waste. My sisters Chevy has 8 options on her "mode" dial.

FF. I recently discovered the same phenomenon about my NOX ALWAYS being in 6th gear, and NO I don't hear the engine raise RPMS when flipping into paddle shifting. Even when rolling down a grade on the highway, I see 6th gear regardless of speed above 50MPH.

Finally by manually forcing into 8th gear and using "neutral" on a downhill grade, I have my BEST MPG for 25mi at 49.7 AND 50mi at 44.5! Even with their attempts to feign a sporty persona, they left it BOTH sluggish AND with poor MPGs straightaway. This vehicle is capable of greatness but I think the engineers left it looking average at best.

 

[Bold One]

Not buying this. If I’m at 72mph I’m at around 2200 rpms in D. If I then switch to L it ALWAYS will start at L6 and of course the rpms jump. When I flick the toggle + twice to got to L8 it then goes back to 2200 rpm. Every single time. So it is going into 8th gear all the time in D. All that said, I still hate the mpgs in this gen.

Read everything above again , your vehicle should be @ 1800 in 8th gear (70-72mph), my RS is 1600RPM in 8th gear at 60mph. seems to be the sweet spot for best MPG.

 

[dequardo]

Mine in the same rpms at 70 mph regardless of whether I’m in 8th gear manually or in D. Not sure what else to tell you.

 

[Bold One]

For a year or more I've had to resort to a technique to get my 2025 RS into 8th gear. I've been told it's operating as designed. Since I live in a very cold climate in the winter months another shifting issue came up, no 7th and 8th gear. It usually shows up when outside temperatures are less than 20 deg F. Again I was told it was working as designed and the issue was created by the extreme cold. I get that, but the transmission system is designed to operate "normally" in cold weather. It has a heat exchanger which does double duty; warms the ATF in the winter using engine coolant and prevents overheating in summer months. The trans control module has programing specific to ATF temps and will restrict access to upper gears if the AFT is too cold. The 8 spd is actually a 6 spd with two additional overdrive gears to get 8 spds. Access to these gears has very specific rules in the TCM, which include very sensitive temperature guidelines, which if not met, will lock out 8th gear or 7th and 8th in cold climates. After some on highway testing we determined the ATF was not reaching appropriate minimum temperature. The TCV (thermal control valve) for the heat exchanger is stuck closed which doesn't allow coolant to warm the ATF to the minimum temp of 150 deg. Normal ATF temp is usually 20-30 deg lower than engine operating temp, which in the Equinox is 190 deg F. Our testing showed much lower ATF temps after a significant on highway test. The TCV is on back order and will be replaced when it comes in. We'll do a retest to document the ATF temp after the TCV is replaced. If you're experiencing similar behavior you might want to "encourage" your dealer to check ATF operating temps. I've seen other posts on here commenting on 8th gear issues. This could be the issue.

Please let us know how the TCV replacement goes!