Can a MT overheat ..??
 

My question is, can a manual transmission in a FR-S/BRZ, overheat, if it's not defective, contains the proper oil and is not over or under filled ..??

Discussion??


humfrz

Yes.

I was just gonna leave it at that, but that's no fun.

Before I dive into explanation...

What circumstance makes you ask?

Absolutely can! Just tow something with it.

There is no such thing as a perfect gear mesh.

I'm not saying my transmission is overheating, but the other day after driving for 5 hours, I touched the base of my reverse lockout (it's the Raceseng aluminum), and it was slightly warm. Never noticed that before :iono:

Well, some folks (whom track their car) say they have been changing their car's transmission oil as often as every 5,000 miles or 2-3 track events.

I think that's excessive and maintain that the oil in a manual transmission of a FR-S/BRZ is not subject to such extreme heat nor contamination that would require that frequent of a change.

However, I have searched and cannot find any information to confirm nor refute my thinking, so, I thought I would ask you folks your opinions.


humfrz

Now, just how many people tow something behind their FR-S/BRZ ... ??

Yep, I agree, no such thing as a perfect gear mesh ...... but, it takes a whole bunch of mis-meshed gears to break a long chain hydrocarbon.


humfrz

Oh yes, it does get warm ...... but, does it get hot enough to break down the oil .. ??


humfrz

Haha... well, you asked. I'd send my used oil off to Blackstone and follow their advice. Heluva lot cheaper than blindly changing the fluid, for sure.

That shift linkage hangs off of a frame about eighteen inches behind the transmission. It's just picking up hot air in the tunnel.

I didn't keep my car long enough to test these things, but I ran Amsoil for 22000 miles in my transmission with about a total of ~20 track events/autocross/drift events, drove it weekly, and averaged well over 20k miles a year.

There was zero need for me to change it as often as others have suggested. I only changed it because I changed my differential and took the opportunity to swap fluids out to test.

http://www.ft86club.com/forums/showthread.php?t=88580

-alex

My reaction when saw humfrz as thread starter
http://i.imgur.com/NDPtAJ9.jpg

I though he started thread "back in my days..." stories.

I'll explain with physics. Here's the TL : DR. Remember the "drivetrain loss" people talk about when they talk about the difference between crank HP and wheel HP? The power doesn't just go away. It is lost as friction, which, in the real world, manifests as heat. That heat accumulates in the Tires, bearings, diff, and mostly, the transmission.

It's not necessarily mis-meshed gears that heat up. Doing work makes heat. Reduction gears do a lot of work, and that means a lot of heat. The work done by a reduction gear is equal to the work input. The output is equivalent to the input, minus friction losses. Losses translate purely to heat.

It's not speed that does it, it's load. High power track cars, or track cars running at maximum acceleration for long periods of time will create a lot of heat. The engine is well-suited to dissipate said heat, with dedicated cooling systems. The manual transmission has no suck system. It has to radiate all of its heat through the case.

So, back to drivetrain loss. Here's the scenario. Say it's about 20%, which is a realistic number. Lets run a 15 minute track session.

The car makes a peak power of 200 HP, which the gearbox turns into useful torque. We are racing, and we are on the throttle 50% of the time, staying in the powerband... Call it an average output of 175 HP, 50% of the time.

175 Horsepower is equivalent to 469790919.1 Joules Per hour. 20% of that is lost from the engine to the wheels. Let's say 40% of that is lost in the transmission. So, in 15 minutes, 58723864.887 Joules are sent through the transmission (175hp to J /4 *.5).

8% (40% of 20%) of that energy is lost in the transmission as heat. That's 4697909.191 Joules deposited in the transmission, as heat alone, in 15 minutes.

1670 Joules (1.67KJ) is the amount of energy required to raise the temperature of a kilogram of oil by 1 degree C.

There are 2.2 Liters of oil in the transmission. 1 Liter of 75W90 weighs .959 Kilograms. There are 2.109 kilograms of oil in the transmission.

So, in 15 minutes, we have put enough energy into the oil to heat it from room temperature (15C) to 1348.8 Degrees C. That's a bit warm. Now, it obviously doesn't get that hot. The aluminum and steel components in the transmission absorb a tremendous amount of heat and dissipate it into the air. But every minute, we are adding enough energy to heat the oil by 89 degrees C. Every minute. That has to dissipate really fast.

Now, I could start figuring the mass of the transmission case, the specific heat of aluminum, the outside surface area, and we could go all day. Really, this is monkey math based on imprecise assumptions. But it illustrates a conservative example of just how much heat goes into a transmission. Now, imagine that same car peaks at 400 WHP... This explains why Element Tuning literally burns up a transmission every 4 races. ... But a commuter can run stock fluid for 200,000 Miles.

This depends entirely on how much power you force the gearbox to transmit, and for how long. Above stock power, your ability to add heat exceeds the ability of the transmission to dissipate it. Significantly. This doesn't mean you will definitely burn it up... FRS Justin has managed a year at 710 WHP... For 9 seconds at a time, and Element Tuning can't go 100 miles at 400HP on track without roasting the thing to a crisp.

Another funny real-world example... The hottest oil in my turboprop engines is not in the turbine section, where the exhaust gas temperature is allowed to hold steady at more than 1400 degrees farenheit. Not even close. The oil from the gearbox is by far the hottest oil in the engine. The oil is all drawn from a common tank, and returned to a common tank, but by the time the oil delivered to the gearbox is scavenged from the gearbox, it is measurably hotter than any other oil in the engine. Enough so to heat the fuel in the fuel-oil heat exchanger.

Cheers. Another drunkmath night. :cheers:

:lol:

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


humfrz

WOW! ....... what a dissertation ......impressive ...... :thumbsup:

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 ......:eyebulge:


humfrz