Can a MT overheat ..??

[shellslinger]

Originally Posted by humfrz

Oh, I figure I bore enough people by sneaking them back-in-the-day stories in other threads ....... without a dedicated thread ......


humfrz

[Ultramaroon]

Originally Posted by humfrz

You mentioned " So, in 15 minutes, we have put enough energy into the oil to heat it from room temperature (15C) to 1348.8 Degrees C." YIKES, I suspect your math/physics calculator overheated on that one ....... how could the transmission oil reach a temperature of 1348.8 degrees C ....... when that same oil would boil at roughly 300 degrees C ..... ?? Hell, at that temperature the oil would be lucky to be called tar and the transmission case would glow like an overheated pot belly stove ......


humfrz

He's saying the transmission would reach that temperature if it was perfectly insulated and wasn't able to shed that heat. It's just the input side of the calculation. Measure the actual temperature and you know the energy dissipated.

...ish. You'll forgive me if I don't actually do the math.

[Spartarus]

Originally Posted by humfrz

WOW! ....... what a dissertation ......impressive ......

A couple of comments.

You mentioned "It's not speed that does it, it's load". Well, I know this is an apple and orange thing but, I have sat on the top of transmissions (literally) for hours on end, with a big diesel tractor engine putting tons of torque through the transmission to pull heavy ground working equipment. The transmission just felt warm to the touch after pulling hard till I needed to re-fuel (or stop under an oak tree to take a nap).

You mentioned " So, in 15 minutes, we have put enough energy into the oil to heat it from room temperature (15C) to 1348.8 Degrees C." YIKES, I suspect your math/physics calculator overheated on that one ....... how could the transmission oil reach a temperature of 1348.8 degrees C ....... when that same oil would boil at roughly 300 degrees C ..... ?? Hell, at that temperature the oil would be lucky to be called tar and the transmission case would glow like an overheated pot belly stove ......


humfrz

Correct. To settle your comparison, it's load measured in power, not torque. Torque is just force, and doesn't make any heat at all. Power is a rate measurement. Force x distance / time.

A crude example: if you hold the brakes and mat the gas pedal in an A/T car, the brakes make enough torque to hold it still (assuming they're big enough) but do no work. That's a lot of torque, but they build no heat, because they make no power.. Stop that same car from 60, the discs will burn your hand, even though they made less torque.

The heat over time example... I'm sure an hour of highway traffic makes enough heat to make similarly absurd numbers in the brakes, yet they don't glow red. The heat does dissipate. I also didn't account for the rate of heat
transfer to the aluminum case, the capacity of the case to act as a heatsink, the capacity of the case to dissipate heat, etc.

You put enough energy through a header in track session at WOT to melt it to liquid hundreds of times over, yet it doesn't even reach sufficient temperature to glow... Because that heat is rapidly dissipated, and the absorption is limited.

Yes, the oil doesn't get anywhere near that hot. I refined the example to the potential increase in temperature per minute to illustrate the point.

Here's the relevant point from all the math, boiled down. The rate at which heat is added, through purely mechanical work, is very high. Much higher than people think. The rate of subtraction has to keep up, otherwise it will heat to failure very quickly. Other than that, it's not unreasonable to have very short oil change intervals in the transmission if you're applying a lot of sustained power to it. The more power you make, and the longer you do it, the more true that statement is.

Mainly, however, it explains that a street driver can get away with rarely or never changing the transmission oil, while a track driver can break down that same oil in a matter of hours, which answers the original question.

[humfrz]

Originally Posted by Ultramaroon

He's saying the transmission would reach that temperature if it was perfectly insulated and wasn't able to shed that heat. It's just the input side of the calculation. Measure the actual temperature and you know the energy dissipated.

...ish. You'll forgive me if I don't actually do the math.

NO! ....... you MUST do the math ........


humfrz

[Ultramaroon]

Originally Posted by humfrz

NO! ....... you MUST do the math ........

Embarrassing as it is, I'll admit being out of practice. It would take me hours.

You get Spartarus' point about force is just force until it moves something. work=energy power=work/time

[humfrz]

Originally Posted by Spartarus

Correct. To settle your comparison, it's load measured in power, not torque. Torque is just force, and doesn't make any heat at all. Power is a rate measurement. Force x distance / time.

A crude example: if you hold the brakes and mat the gas pedal in an A/T car, the brakes make enough torque to hold it still (assuming they're big enough) but do no work. That's a lot of torque, but they build no heat, because they make no power.. Stop that same car from 60, the discs will burn your hand, even though they made less torque.

The heat over time example... I'm sure an hour of highway traffic makes enough heat to make similarly absurd numbers in the brakes, yet they don't glow red. The heat does dissipate. I also didn't account for the rate of heat
transfer to the aluminum case, the capacity of the case to act as a heatsink, the capacity of the case to dissipate heat, etc.

You put enough energy through a header in track session at WOT to melt it to liquid hundreds of times over, yet it doesn't even reach sufficient temperature to glow... Because that heat is rapidly dissipated, and the absorption is limited.

Yes, the oil doesn't get anywhere near that hot. I refined the example to the potential increase in temperature per minute to illustrate the point. The rate at which heat is added is very high. The rate of subtraction has to keep up, otherwise it will heat to failure very quickly.

Well, OK, I was sitting on a tractors transmission that was transferring a lot of "power" ..... not torque ......

Now, about the transmission case dissipating all that heat ....... if that is so, I would think the heat from the transmission would heat up the transmission tunnel and roast our feet ...... ??

So, I wonder if anyone has actually measured the temperature of the transmission oil in a FR-S/BRZ, under or just after, an extended load (like a heavy track session) ...??

Anyone out there .. ??


humfrz

[humfrz]

Originally Posted by Ultramaroon

Embarrassing as it is, I'll admit being out of practice. It would take me hours.

You get Spartarus' point about force is just force until it moves something. work=energy power=work/time

Hey, don't go to all that trouble ...... why not? .... cause then I would have to spend even more hours checking your math .....

Ya-ya-ya, I got the F=MA thing. I didn't fall off the pumpkin wagon here in Puyallup ...... I'll have you know it was a turnip truck.....


humfrz

[Spartarus]

Originally Posted by humfrz

Well, OK, I was sitting on a tractors transmission that was transferring a lot of "power" ..... not torque ......

Now, about the transmission case dissipating all that heat ....... if that is so, I would think the heat from the transmission would heat up the transmission tunnel and roast our feet ...... ??

So, I wonder if anyone has actually measured the temperature of the transmission oil in a FR-S/BRZ, under or just after, an extended load (like a heavy track session) ...??

Anyone out there .. ??


humfrz

Air is an awesome insulator. There are a few inches of rapidly moving air between the case and the tunnel to spirit away all that heat.

The temp question. I'd ask Velox. They measure everything.

Element added a high capacity transmission oil cooler after they started burning up transmissions, but they are very protective of their information.

...I don't suppose those tractors had transmission oil coolers...?

That, and you said they did get warm on the outside... which takes quite a bit of energy with a thick-walled nodular iron case.

As for me, I haven't burned up a transmission... yet. If I do, I suppose I'll have to start measuring.

[humfrz]

Originally Posted by Spartarus

.................
Mainly, however, it explains that a street driver can get away with rarely or never changing the transmission oil, while a track driver can break down that same oil in a matter of hours, which answers the original question.

About "breaking down" the oil. Do you mean like "cracking" the oil as in breaking down the long chain hydrocarbons ..... ??

If so, at what temperature and pressure do you think it would take to perform that process .. ??

Now, how could a transmission do that .. ??

humfrz is fading fast ...... I had a hard day ..... the two older daycare-ees were in a pissy mood and the 3 month old one has a cold. However, I'm finally getting the hang of these new fangled diapers .....


humfrz

[humfrz]

Originally Posted by Spartarus

Air is an awesome insulator. There are a few inches of rapidly moving air between the case and the tunnel to spirit away all that heat.

The temp question. I'd ask Velox. They measure everything.

Element added a high capacity transmission oil cooler after they started burning up transmissions, but they are very protective of their information.

...I don't suppose those tractors had transmission oil coolers...?

That, and you said they did get warm on the outside... which takes quite a bit of energy with a thick-walled nodular iron case.

As for me, I haven't burned up a transmission... yet. If I do, I suppose I'll have to start measuring.

Nope, the tractors (at least the ones I drove) didn't have any kind of oil coolers.

Yep, they would get warm on the outside which was nice in the late fall to keep warm by draping an old trench coat over the transmission tunnel.

Who or what is Velox ... ??

Yep, my transmission hardly gets warm ...... to the school ..on to the grocery ...back home ..... let it cool off ..... before I make the afternoon run ....


humfrz

[Ultramaroon]

Originally Posted by humfrz

Who or what is Velox ... ??

http://www.velox-motorsports.com/

[Spartarus]

Originally Posted by humfrz

About "breaking down" the oil. Do you mean like "cracking" the oil as in breaking down the long chain hydrocarbons ..... ??

If so, at what temperature and pressure do you think it would take to perform that process .. ??

Now, how could a transmission do that .. ??

humfrz is fading fast ...... I had a hard day ..... the two older daycare-ees were in a pissy mood and the 3 month old one has a cold. However, I'm finally getting the hang of these new fangled diapers .....


humfrz

Heat plus air plus mechanical pressure, doesn't physically break moecules, but it accelerates degradation through oxidation. It doesn't need to be all that hot for that.

Oxidation is what I'm referring to when I say breaking down.

This happens in many ways, with heat and mechanical work, and especially with air entrainment.

This slowly turns your nice oil into a mixture of aldehydes, ketones, peroxides and carboxylic acids that don't do a great job lubricating things.

Oxidation in oils accelerates quadratically at temperatures above approximately 75 C. The rate doubles every 10 degrees. In theory, it will oxidize with ambient air, but not fast. Fast oxidation comes from rapid adiabatic heating of entrained air bubbles. Like when they get crushed between gear teeth.

[humfrz]

Originally Posted by Spartarus

Heat plus air plus mechanical pressure, doesn't physically break moecules, but it accelerates degradation through oxidation.........

Oh, that's heavy ....... I'll think on that tomorrow ...... as soon as I get my housekeeping done ...... hey, I set the vacuum out to remind me ..... that's a start ....

It' ma med time .... nite all ...... ZZZZZZZZZZ

[JDM4E]

This is a good question that I had also. My bet would be to add a MT oil cooler with a gauge, possibly with a thermostat. Couldn't hurt and common sense would tell, that operating more at a optimal temps would be beneficial for everything. The same goes with the diff.