Sorry to tell you this, but yes it does. Which is why you always check the fluid level with the vehicle at operating temperatures.

 

Yes you are out 50 bucks. I think you have confused compress with expand and contract. That's why there is a hot and cold level on many radiator tanks as well as engine and transmission dipsticks.

I'm not sure but I think everything expands and contracts with temp changes.

 

[ QUOTE ]
I had a bet with a friend of mine . He insists tranny fluid expands under heat . I thought the whole idea of hydrolics was fluids don't expand or contract .

Anyway , he just showed me in a chiltons book , and well yea it says it expands when warm .

Am I out 50$ or what??

[/ QUOTE ]
Based strictly on terminology, you are out $50.
All known materials expand or contract with differences in steady state (after a long time) heat. I.E. If you leave something in a hot enviroment for a long time, it will expand or contract based on the material. The same goes for cold.
BUT, the hydraulics are, for our purposes, incompressible. There is a big difference. Incompressible means you can't squish it(very much). This is a desirable trait for fluids transmiting power (ATF).
BTW, this whole incompressible fluid goes flying out the window when you talk about high pressures(>2500PSI or there abouts). Such is the case w/ the new Cummins & the Bosch HP common fuel rail.
As a tidbit, bet your friend $100 that water does not have a constant expansion rate. At the end of the day you should be $50 richer than when you got up. Remember the three basic states of matter? Solid, liquid, gas. They all have different expansion/contraction rates for the same matter(material, substance, stuff).

Daniel

 

[ QUOTE ]
... BTW, this whole incompressible fluid goes flying out the window when you talk about high pressures. (>2500PSI or thereabouts)
Daniel

[/ QUOTE ]

I think you meant to say 25,000 pounds/square inch, not 2,500 pounds/square inch.

2,500 pounds/square inch is a fairly typical pressure for hydraulic systems and has been for many years.
25,000 pounds/square inch is a typical for new common-rail Diesel fuel injection systems, and it's only recently that pressures have been cranked up that high.


Back to the original question: Yes, it's true that transmission fluid expands when it heats up, (and that's true for both automatic and manual transmission oils) but it's a small percentage which for all practical purposes can be ignored.

But you don't have to take our word (or Chilton's) for it; it's simple enough to put a sample in the fridge and in the oven and see for yourself what happens. (don't exceed about 250 degrees F)

 

"(don't exceed about 250 degrees F)"
/ubbthreads/images/graemlins/biggrin.gif

 

Automatic trans fluid can see much more the 250 degrees when in operation and being worked HARD. Of course it's not gonna like it.

 

It rises enough to see about an inch difference depending on what transmission and what dipstick. I would call that pretty significant expansion.

Birken

 

[ QUOTE ]
[ QUOTE ]
... BTW, this whole incompressible fluid goes flying out the window when you talk about high pressures. (>2500PSI or thereabouts)
Daniel

[/ QUOTE ]

I think you meant to say 25,000 pounds/square inch, not 2,500 pounds/square inch.

2,500 pounds/square inch is a fairly typical pressure for hydraulic systems and has been for many years.
25,000 pounds/square inch is a typical for new common-rail Diesel fuel injection systems, and it's only recently that pressures have been cranked up that high.


Back to the original question: Yes, it's true that transmission fluid expands when it heats up, (and that's true for both automatic and manual transmission oils) but it's a small percentage which for all practical purposes can be ignored.

But you don't have to take our word (or Chilton's) for it; it's simple enough to put a sample in the fridge and in the oven and see for yourself what happens. (don't exceed about 250 degrees F)

[/ QUOTE ]

No, I meant 2,500PSI. That is about where things *start* to get strange. It is really *gone* out the window by the time you reach 25,000PSI. Hence the reason it has only been done recently, among other reasons.
Assuming that a fluid (air, liquid, transmission fluid, etc..) is incompressible makes an ungodly set of equations somewhat managable with the use of other assumptions like Newtonian fluid, linear shear force, and about 5-10 others. /ubbthreads/images/graemlins/vomit.gif /ubbthreads/images/graemlins/vomit.gif /ubbthreads/images/graemlins/vomit.gif
Only the past few years has the metalurgy and manufacturing been able to *reliably* produce a system that works at 25000PSI. But a good computer is needed to work the equations that are needed to design the mechanicals of the system (pump, plumbing, fittings, etc).

Daniel

 

Cowboy Dan I just looked at your profile and I had guessed right.
What kind of engineering degree are you working on? The water bet should work great for igotrobbed IF his buddy does not read this forum.

The main thing with transmission fluid is to keep it from overheating as that can cause all sorts of problems. I like to use synthetic fluid as an extra level of protection as well as a add-on cooler.

 

[ QUOTE ]
Cowboy Dan I just looked at your profile and I had guessed right.
What kind of engineering degree are you working on? The water bet should work great for igotrobbed IF his buddy does not read this forum.

The main thing with transmission fluid is to keep it from overheating as that can cause all sorts of problems. I like to use synthetic fluid as an extra level of protection as well as a add-on cooler.

[/ QUOTE ]
Mechanical Engineering @ IUPUI.

 

Then why not use a non-newtonian fluid as a lock-up medium in the torque converter of a transmission?

Sorry to potentially hijack the thread, this idea just popped in my head. Guess I'll have to fire up SolidWorks and design the converter now /ubbthreads/images/graemlins/biggrin.gif

 

So fluids do compress also is what your saying Cowboy Dan ?

 

[ QUOTE ]
Then why not use a non-newtonian fluid as a lock-up medium in the torque converter of a transmission?

Sorry to potentially hijack the thread, this idea just popped in my head. Guess I'll have to fire up SolidWorks and design the converter now /ubbthreads/images/graemlins/biggrin.gif

[/ QUOTE ]
You let me know how that goes! I want to be a beta tester. /ubbthreads/images/graemlins/wink.gif If I remember correctly, toothpaste is non-newtonian. That would be funny to see. /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/laugh.gif Imagine someone at a truckstop buying a case of toothpaste because they blew a cooler line. I can imagine the crowd now....

[ QUOTE ]

So fluids do compress also is what your saying Cowboy Dan ?

[/ QUOTE ]
Yes. Fluids do compress. Some compress more than others for a given pressure, but they all compress. At least, all that I know of. There was an instructor who had some experience with unobtainium, though. Very expensive stuff.
Now that I think about it, I don't know what the factor (similiar to Young's modulus for solids) would be for the amount of volume change at a given pressure difference. I'm sure it exists somewhere, and someone will chime in with it soon.

Daniel
/ubbthreads/images/graemlins/smokin.gif /ubbthreads/images/graemlins/smokin.gif /ubbthreads/images/graemlins/smokin.gif

 

"Fluid" is not really the correct term. A "fluid" is something that flows. Air is a fluid as is water. A "liquid" is what is incompressible as far as our limited observations tell us. When the pressures get extremely high is when these strange things happen.

Birken

 

[ QUOTE ]

As a tidbit, bet your friend $100 that water does not have a constant expansion rate. At the end of the day you should be $50 richer than when you got up. Remember the three basic states of matter? Solid, liquid, gas. They all have different expansion/contraction rates for the same matter(material, substance, stuff).

Daniel

[/ QUOTE ]

Please be more specific with water, it has TWO opposing co-efficients of expansion in the liquid phase (expands as temperature decreases between +4C and 0c). I know you know that, but, for the sake of technical correctness, one should state so. Using that information with the uninformed is good for a $100 bet.

 

[ QUOTE ]
Back to the original question: Yes, it's true that transmission fluid expands when it heats up, (and that's true for both automatic and manual transmission oils) but it's a small percentage which for all practical purposes can be ignored.


[/ QUOTE ]

I was gonna say.....

Power steering fluid reseviors have Hot and Cold full markers.

The same with coolant reseviors

Their is also a reason that you cannot (should not) take the radiator cap off when the vehicle is hot.

I also recall seeing a hot/cold full mark on the transmission fluid dipstick on our trucks and every car for that matter. On the new explorers without a "drip tube" you have to check the transmission fluid below 80 degrees or so to get the correct reading. If you check and correct the level while it's hot, the fluid will be too low and the car won't go into gear when it's cold.

What choo talk'n bout Willis?

 

[ QUOTE ]
Their is also a reason that you cannot (should not) take the radiator cap off when the vehicle is hot.

[/ QUOTE ]

That one is different from the others you listed. The boiling point of water is 212* F at sea level, but artificially creating a higher pressure (by, for instance, enclosing the water in a pressure-tight system) will raise the boiling point considerably. The water is nominally 180-190* at the temp sensor, but quite a bit hotter elsewhere in the cooling system, but it does not boil because it's under pressure.

If you remove the cap, you allow the pressure in the system to instantly become the same as atmospheric pressure, which lowers the boiling point to 212, which makes a lot of the water boil into vapor and come surging out of where you just took the cap off, generally burning you badly.

Duncan

 

[ QUOTE ]
If you remove the cap, you allow the pressure in the system to instantly become the same as atmospheric pressure, which lowers the boiling point to 212, which makes a lot of the water boil into vapor and come surging out of where you just took the cap off, generally burning you badly.



[/ QUOTE ]

This was somewhat sarcastic. Point boint being, in a degas bottle system like our trucks have, you can watch the fluid expand (level rise in the resevior) as the system warms up.

On a normal system, if you open the cap when the vehicle is hot, fluid will come out regardless of wether the block or any of the components are hot enough to boil the coolant.

 

[ QUOTE ]
On a normal system, if you open the cap when the vehicle is hot, fluid will come out regardless of wether the block or any of the components are hot enough to boil the coolant.

[/ QUOTE ]

Isn't that just the effect of the pressurization, which is more of a case of entrained air pushing fluid out ahead of its attempted escape from the new opening in the system? Kinda like a shaken-up two liter bottle. It's not the fluid expanding in that case either, but a whole bunch of it sure comes out when you unscrew the cap!

Duncan

 

[ QUOTE ]
Isn't that just the effect of the pressurization, which is more of a case of entrained air pushing fluid out ahead of its attempted escape from the new opening in the system? Kinda like a shaken-up two liter bottle. It's not the fluid expanding in that case either, but a whole bunch of it sure comes out when you unscrew the cap!

Duncan

[/ QUOTE ]

No, it's the fluid expanding as it changes in temperature. Just as your house creaks and pops when it warms up in the morning and cools off in the evening. Or just as a bridge expands/contracts as it heats and cools. The cuts filled with felt in your concrete drive are their for normal settling and to all allow the concrete to expand/contract as it heats/cools. Valve adjustments on engines are performed when cold because the metal that makes up the block expands/contracts when heated/cooled. Your exhaust makes a ticking/popping noise when you shut your car off as it contracts as it cools. /ubbthreads/images/graemlins/shrug.gif