No 4th Gear until engine warms up - What's the REAL story?

[Skibane]

What's the idea behind this "feature"?

Emissions?

Transmission wear?

Fuel economy?

Practical joke?

[FarFetched]

Faster warm up!Cheers!

[Jesda]

WITCHCRAFT

[Skibane]

Faster warm up!

Faster warm-up for what - the engine, or transmission?

How does high engine speed at low torque (3rd gear) result in quicker warm-up than low engine speed at high torque (4th gear)?

[Blamecanada999]

Huh? I've never heard of this feature before. What year range is it on? So if the temp sensor gets a low enough reading, you can't engage 4th gear? Jesus, between that and the launch control, it's no wonder the transmission is considered the weakest link of the early Q's.

[Q45tech]

The TC lockup clutch is the weakest link in any transmission.

Most brands of European and Japanese and Domestic trannies of that era had temperature monitored ATF viscosity to limit abuse. Until the ATF gets thin enough by being warm enough economy features are traded away to increase life and durability.

I've always thought that even more restrictive limits should have been placed on Q systems like BMW's V8 low rev limit that progresses with coolant temp.

US Operators will just crank and drive without warm up whereas a trained chauffeur knows better.

[maxnix]

What's the idea behind this "feature"?

Emissions?

Transmission wear?

Fuel economy?

Practical joke?

What does the phrase "operating temperature" mean, grashopper?

[hannibal]

Faster warm-up for what - the engine, or transmission?

How does high engine speed at low torque (3rd gear) result in quicker warm-up than low engine speed at high torque (4th gear)?

Both the motor and the transmission as both are spinning faster in 3rd than in 4th. (OK at least half the transmission is)...

torque really doesnt have much to do with it...

[Q45tech]

The FSM defines AT operating temperature as 122F - 176F.

Test procedure for AT themistors shows 2 values of voltage 68F and 176F.

Most ATF types are 5 times thicker at 96F than at 212F, so assumming linearity so 4.3% thinner per degree F assumming 96F is 1.000 relative.

So 122F ATF is 2.32 times thicker than 176F ATF pretty significant! Considering the volume flow vs pressure and how much you would have to change psi to equalize volume.

[Skibane]

Most brands of European and Japanese and Domestic trannies of that era had temperature monitored ATF viscosity to limit abuse. Until the ATF gets thin enough by being warm enough economy features are traded away to increase life and durability.

How does driving 65 MPH in 3rd gear result in less transmission wear (let alone engine wear) than driving 65 MPH in 4th with the TC locked up? This seems counter-intuitive - Generally, high RPMs are to be avoided until the vehicle warms up.

[Q451990]

How does driving 65 MPH in 3rd gear result in less transmission wear (let alone engine wear) than driving 65 MPH in 4th with the TC locked up? This seems counter-intuitive - Generally, high RPMs are to be avoided until the vehicle warms up.

I'm not sure if the concern is more lugging or over-reving. That's why I always let the car warm up at least until the needle is off of the stop and into the bottom of the normal range before driving away. The only exception was nearly redlining it on the way out of my neighborhood one day when I was meeting an abulance at my parent's house...

Heath

[Q45tech]

Just another reminder to let the systems warm up gradually in cold weather.

In Summer AT pronably reaches 122F in 2-3 minutes after a 70F ambient crankIn Winter your heated garage should still be 40-50F.

The thick viscosity of cold ATF causes so much friction [in TC and pump] that the ATF heats up fast......................viscosity self regulates the heat.

Those that park them outside still crank the engine and heat the interior for 10 minutes before driving away RIGHT?

Notice that the HVAC Heat doesn't start up until the coolant is also 122F.

As I remember my 1981 Impala [4AT] did the same thing no overdrive until warm. The LS400/430 follows the same CORRECT proceedure no overdrive until warmish.

[PopPop]

Just another reminder to let the systems warm up gradually in cold weather.

In Summer AT pronably reaches 122F in 2-3 minutes after a 70F ambient crankIn Winter your heated garage should still be 40-50F.

The thick viscosity of cold ATF causes so much friction [in TC and pump] that the ATF heats up fast......................viscosity self regulates the heat.

Those that park them outside still crank the engine and heat the interior for 10 minutes before driving away RIGHT?

Notice that the HVAC Heat doesn't start up until the coolant is also 122F.

As I remember my 1981 Impala [4AT] did the same thing no overdrive until warm. The LS400/430 follows the same CORRECT proceedure no overdrive until warmish.

Like D said the Torque Converter Lockup Clutch is the weak point to most Trans. When I was at the Trans. I watched as they cut the TC open on the lathe and then took it threw the parts cleaner and they showed me how the clutch liners on the lockup clutch were worn all the way down so thin that you could see the bonding glue that was used to attach the clutch liner. Over time this is another reason why we have so much shudder prior to warmup.

[Q45tech]

The clutch in the 4AT can only handle about 20 hp momentarily! Why the TC goes out of lockup even during mild acceleration.

Lockup clutches were first used in 1949 Packard Ultramatic AT.

The stick/slip characteristics of the ATF are very importantand and must match the friction material in the TC lock up clutch otherwise you get a noticable shutter going in and out of lockup....................a really bad mismatch in ATF will stop the TC from locking up or releasing PERIOD!

Why one has to be careful with stick.slip modifiers like LubeGuard BLACKhttp://www.autobarn.net/lubgarworfin.html

http://www.bdub.net/transmission/Two...df%22

Mercedes problems:http://www.altousa.com/np23.pd...df%22

[Jeff Williams]

Layla wouldn't go into 1st gear, until I shifted the lever into 3. This happend late in her transmission life, and she did this for nearly 40,000 miles, before I sold her. Once she had ddriven about 60 feet, she would shift into 4th just fine. I suspected it was the clutches in the TC, but never wanted to spend the money to rebuild it, especially when Lola was just sitting in the driveway, waiting to be put in service.

I wouldn't worry too much, until she won't go in drive anymore. Just take care of her for a while and don't thrash her.

A full transmission flush and syhnthetic fluids didn't help a bit.

[maxnix]

A full transmission flush and syhnthetic fluids didn't help a bit.

No evidence at all in the inner pan surface, the magnetic plug nor the filter upon inspection?

[Q45tech]

Consider an airplane how would you like to be a passenger if the pilot cranked the engine and immediately took off at maximum power............what so many drivers do in the morning.

BMW "Variable tachometer warning zone

This innovation reminds drivers that a cold engine - especially a high-performance one - should be treated with care. When the engine is first started, the tachometer's warning zone (indicated by orange LEDs) begins at 4000 rpm. As the engine warms, LEDs are extinguished to lift the limit in increments of 500 rpm until the warning field begins at its normal 6500 rpm. The actual rpm limit is 7000"

[elwesso]

I wonder if somehow robert could make this work on our ECUs!!

[qship96]

easy way to do is just manage the right pedal with your foot and keep below 2000 rpm until engine is at normal temp. no need for fancy computer interface for idiots!

[Jesda]

"The biggest danger to a cold engine is LOAD. Revs are not your enemy, it is far better to maintain low load at higher revs than use low-end torque. That is why BMW increase the shift points when the engine is cold."

http://www.bimmer.info/forum/s...ssion