Holding gear when hot outside
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2020 GLS450 (wife) / 2024 Ford Bronco (mine) / 2014 VW Tiquan (son)
Holding gear when hot outside
Interesting development with my car (or one that I never really noticed until recently). If I leave it in the driveway on a hot summer day, when I go to drive it, it wants to hold the gear it's in for much longer. Usually it wants to race to 7th as fast as possible, and it still does when it's been sitting in the garage and I go off from there. But when I hop in from the driveway after it's been sitting for several hours in the hot sunshine - it wants to hold 1st, 2nd, 3rd and 4th until around 3k rpm. I am assuming it's trying to circulate the coolant as fast as possible to cool itself down?
I've even noticed when driving along at 40-45mph that it wants to hold in 4th or 5th, when usually that's 7th gear for me and my driving style.
When it's cool from the start, it doesn't do this. But when it's hot from the start, it does this.
Anyone else have this happen to them too?
Car has 67k miles now. The trans fluid and filter were changed around the 42k mark a couple of years ago. I'm not a hard driver on the car, just easy going and gentle.
I've even noticed when driving along at 40-45mph that it wants to hold in 4th or 5th, when usually that's 7th gear for me and my driving style.
When it's cool from the start, it doesn't do this. But when it's hot from the start, it does this.
Anyone else have this happen to them too?
Car has 67k miles now. The trans fluid and filter were changed around the 42k mark a couple of years ago. I'm not a hard driver on the car, just easy going and gentle.
Last edited by nc211; Jul 20, 2022 at 01:15 PM.
Out Of Control!!
Joined: Apr 2019
Posts: 11,924
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
tranny temperature related
What you've discovered is entirely possible: Temperature affecting the rpm. 
Do you have a scanner to look at your live temperature data?
You'll be able to see how temps go while driving with rpm changes
Do you have a scanner to look at your live temperature data?
You'll be able to see how temps go while driving with rpm changes
MBWorld Fanatic!
Joined: May 2018
Posts: 6,602
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From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
My hypothesis is this :
Hot days and more so when humid are not good for engine power, it is given, there is nothing we can do.
When we accelerate using throttle pedal, our sensory input is not throttle angle, but speed of the acceleration.
If you are during a cold weather with good cold air, for the same acceleration you expect in cool temperature vs now hotter temperature your leg will be pushing deeper on the throttle pedal and
that produce a throttle opening bigger than during the cooler months.
Bigger throttle opening is another way engine computer and the tranny computer translate you want more power.
So now the tranny hold higher RPM before gear change.
This is assuming the road you take is the same one, as any 1 degree of extra inclination is an engine power sucker.
Unless in MANUAL mode, our tranny gear change behaviour in full automatic is dependent on throttle angle/opening.
In marine engines, if ambient temperature hit 45C inside the engine room aka breathing air for the engine, some brands will derate 10% of its engine power.
Hot days and more so when humid are not good for engine power, it is given, there is nothing we can do.
When we accelerate using throttle pedal, our sensory input is not throttle angle, but speed of the acceleration.
If you are during a cold weather with good cold air, for the same acceleration you expect in cool temperature vs now hotter temperature your leg will be pushing deeper on the throttle pedal and
that produce a throttle opening bigger than during the cooler months.
Bigger throttle opening is another way engine computer and the tranny computer translate you want more power.
So now the tranny hold higher RPM before gear change.
This is assuming the road you take is the same one, as any 1 degree of extra inclination is an engine power sucker.
Unless in MANUAL mode, our tranny gear change behaviour in full automatic is dependent on throttle angle/opening.
In marine engines, if ambient temperature hit 45C inside the engine room aka breathing air for the engine, some brands will derate 10% of its engine power.
