AT Trans cooler ?

[BINZ]

Looked through the threads and could not find a link.

Anyone here have an issue with the AT trans heating up and changing RPM shifting ?

Thanks

[hansoac]

What exactly do you mean?
it shifts different when warm compared to cold?

[wstar]

Originally Posted by BINZ

Looked through the threads and could not find a link.

Anyone here have an issue with the AT trans heating up and changing RPM shifting ?

Thanks

I don't think reasonable trans temps affect the D-mode shift points in normal operation, no. Those should be determined basically by engine speed, vehicle speed, current gear, throttle position, and engine torque. I believe higher engine coolant temps will pull some timing on the engine and reduce available torque, so you could see some change to shift points in that case, maybe.

The best heat test I've done so far is 4x ~80-90 second SCCA solo laps spaced a few minutes apart, in 101F heat outside. Those were done in M-mode staying in 2nd gear all the way through, mostly at 4K+ RPM the whole time and pretty much constantly either accelerating or engine braking. I didn't have a trans cooler at the time, and nothing unusual happened to indicate any kind of trans malfunction.

In any case though, D-mode always makes poor decisions. If you care about which RPM you change gears at, use M-mode.

The 7AT does have a failure mode if the trans temp goes above the preset safety limit. I've never seen it happen in practice, but this is the description from the service manual:



To summarize above, basically if your TCM exceeds 145C for 2 minutes straight, or 150C even momentarily, the TCM will tell the ECU to limit your throttle position pretty dramatically, and it will go back to normal once the fluid gets back down to 140C *and* the car comes down to a 3mph roll or slower.

Note - this is the temp of the TCM (electronics control module on the side of the transmission housing). It would be affected by fluid temp, but it's not exactly the same as the fluid temp.

[OldGuy]

This thread's way, way over my head! Good night.

[BINZ]

Originally Posted by wstar

I don't think reasonable trans temps affect the D-mode shift points in normal operation, no. Those should be determined basically by engine speed, vehicle speed, current gear, throttle position, and engine torque. I believe higher engine coolant temps will pull some timing on the engine and reduce available torque, so you could see some change to shift points in that case, maybe.

The best heat test I've done so far is 4x ~80-90 second SCCA solo laps spaced a few minutes apart, in 101F heat outside. Those were done in M-mode staying in 2nd gear all the way through, mostly at 4K+ RPM the whole time and pretty much constantly either accelerating or engine braking. I didn't have a trans cooler at the time, and nothing unusual happened to indicate any kind of trans malfunction.

In any case though, D-mode always makes poor decisions. If you care about which RPM you change gears at, use M-mode.

The 7AT does have a failure mode if the trans temp goes above the preset safety limit. I've never seen it happen in practice, but this is the description from the service manual:



To summarize above, basically if your TCM exceeds 145C for 2 minutes straight, or 150C even momentarily, the TCM will tell the ECU to limit your throttle position pretty dramatically, and it will go back to normal once the fluid gets back down to 140C *and* the car comes down to a 3mph roll or slower.

Note - this is the temp of the TCM (electronics control module on the side of the transmission housing). It would be affected by fluid temp, but it's not exactly the same as the fluid temp.

If I understand correctly, when the trans heats up on M mode, after doing some lapping,the TMC will cause the trans to shift itself at a lower RPM ?
Right ?

This is the issue I have. I have been told that the 370Z has that problem.
I was told to check on your threads here because I have a Genesis 3.8 GT Coupe and have the same problem when I do lapping.
At some point my 3rd gear will shift by itself to 4th gear at 3800 RPM
I was wondering if anyone had solved the problem by installing a trans cooler.

Thanks for the help.

P.S. I owned 2 Altima 3.5 SE and 3.5 SER and never had that problem on the tiptronic auto trans.

[wstar]

Originally Posted by BINZ

If I understand correctly, when the trans heats up on M mode, after doing some lapping,the TMC will cause the trans to shift itself at a lower RPM ?
Right ?

No. If the TCM overheats, your gas pedal's position (which is electronic, not a traditional hard throttle cable) will be elecronically limited so it's like you can only barely use the gas pedal at all. This still wouldn't affect gearing. However, at least in my experience, I've never overheated the TCM.

This is the issue I have. I have been told that the 370Z has that problem.
I was told to check on your threads here because I have a Genesis 3.8 GT Coupe and have the same problem when I do lapping.
At some point my 3rd gear will shift by itself to 4th gear at 3800 RPM
I was wondering if anyone had solved the problem by installing a trans cooler.

If you're looking for help with a Genesis problem, nothing we're talking about here will help you at all. They will act completely differently and have different problems. The transmissions aren't even built by the same company, much less the same model.

There are several fault conditions in which the 370Z's 7AT will disobey your shifting inputs and protect itself, but those are not overheat conditions as far as I can see, they're for when components have completely failed and you need to take it in for repairs (although I guess you could fry something permanently with heat, so heat could be the indirect cause).

Assuming you don't have broken parts, the 370Z 7AT in M-Mode in 3rd gear will never go up to 4th at any RPM unless you ask it to. Even if you sit there and bang into the rev limiter for several minutes, it won't upshift without you telling it to do so.

A trans cooler is still a good idea for the track though, it will save excess wear on the clutches, and very hot fluid could result in slower shift execution.