legacycentral bbs

I'm having a little debate at work. Maybe some of you out there can shed some light on the subjects.

I don't want anyone taking my side, so I'm going to keep it unbiased.

Tech A says: ALL gears inside of a manual gear box are turning while the engine is idling, manual gearbox is
in neutral.

Tech B says: The output shaft gear set and reverse gear are not turning while the engine is idling, manual
gearbox is in neutral; all other gear sets are turning.



Tech A says: A manual transmission will not reach normal operating temperature, during 25 deg. F ambient air
temps, simply by starting the engine and allowing the engine to warm by idling in neutral.
(Meaning, allowing the engine to warm up for like 20 to 30 minutes on a freezing cold morning)
This tech feels that the ambient air temp. surrounding the entire transmission is more than
sufficient to prevent the transmission from being warmed to operating temp.

Tech B says: A manual transmission will certainly reach normal operating temperature, while the ambient air
temp. is a mere 25 deg. F, simply by starting the engine and allowing the engine to warm by idling
in neutral. (Meaning, allowing the engine to warm up for like 20 to 30 minutes on a freezing cold
morning) This technician believes that the heat from allowing the engine to idle for 20 to 30
minutes, will be enough heat and ample time for the heat to transfer from the engine to the
transmission via the bell housing mating surface. He also maintains that the exhaust will be a
contributing factor to warm the transmission, even though the exhaust first needs to heat the 25
deg. F ambient air that surrounds the transmission.


........Thoughts ??

I don't know about the first part but I have experience on the 2nd part.

This past winter there have been quite a few times that I had gone out and started my car and let it warm up for 20 mins or so and the trans did feel sluggish still but not as long as if I had just warmed it enough for the idle to drop. It makes a difference on my 1-2 minute trip out of the subdivision. I'll have better shifting if I preheat the car.

Fundamentaly: I agree with you that as the transmission gets warmer, it will shift easier. Also, as you allow the car to idle in neutral, the countershaft is in the bottom of the transmission slinging oil all over 1st. gear set, 2nd. gear set, 3rd. gear set, 4th gear set, 5th gear set.

The debate is specific to the information as I outlined it.

I do appreciate your feedback.

At least on the Subaru transmissions, the main shaft or input shaft from the engine will be spinning with the engine idling, clutch out, and transmission in neutral. The output shaft will not be spinning since these have the driven gears on them and the car would need to move.

I agree with Tech B.

Thanks Josh.

I need a real gear head to chime in with some rhyme and reasoning on the second arguement theories. LOL

There are way too many variables to generalize a statement that the transmissions will or won't warm up from idling. However, in my opinion I think the transmission temperatures would warm up by idling the engine. I don't know if the trans will reach full operating condition, but as FundamentalyConfused mentioned in his post it will certainly help.

I'm no professional on tranny warming up and gears moving and certain gears not moving, but from my 3 years as a mechanical engineering student tech B sounds much more logical about his/her thinking heat/thermodynamics of heat flow from engine warming up transfering to tranny allowing normal operating temps. Just my 2cents

I feel that a transmission with load on the gears provides more force and friction on the gears, thus generating increased gear temps while the transmission is being operated under load. If the gears operate at higher temps under load, then the gears, themselves would raise the temperature of the fluid. If the gears never reach normal operating temps, because their is not a normal operating load on the gears to heat the gear oil. Then how can the gear oil reach normal operating temp ?

On a truck, the trans temp is cooled by heat exchange with the engine coolant. When the trans temp is low, the coolant will heat the trans oil. Even after warming my truck's engine to full temp, the needle on my trans temp gauge won't have moved even the slightest. It was 32F yesterday, and when I left the yard empty last night, it took nearly 30 miles to reach full operating temperature, even with about 3 miles of 6% grade leaving town.

Daveh: Thats what I'm trying to explain. The arguement is that one party feels that a manual gearbox will reach operating temp at idle, while the other party believes the manual gearbox needs normal operation to get to normal operating temp to thin out the gear oil.

A manual transmission will not reach full operating temp at idle in neutral.
It will warm up above ambient temperature given enough time, but there isn't enough friction and load occurring to warm the fluid up to the same temperature you would see by driving around. So I guess A is more correct on this issue.

As far as what parts of the transmission are rotating at idle, B is correct.

I agree with you Alphius, Thanks for the feedback.