My Argument for Measuring ATF when COLD - PeachParts Mercedes-Benz Forum

shertex · #1 08-06-2012, 08:45 AM

Countless forum members have expressed perplexity when attempting to measure ATF level (including me, at one point). They are told to measure it hot, at operating temperature....say after a good run on the highway for 30 minutes. But then they encounter all sorts of uncertainties, basically revolving around the question of whether it was really hot enough when measured. Can be very frustrating.

It seems to me that the reason the FSM provides the "hot" method is that most people, and most mechanics, will be measuring the level on a warm/hot engine: during a trip, a visit to the mechanic, etc... So it makes sense.

But for DYI'er, there's absolutely no need for this method. The FSM specifies ANOTHER method: measuring at 20-30C (in other words, ambient temp on most days). See p. 1 and 3 here: http://www.w124performance.com/service/w124CD1/Program/Maintenance/My81/2710.pdf

So as long as the engine is cold and it's 68-86F outside, I know I can get an accurate reading every time.

When it's colder (e.g. a cold winter day), I don't know if the measurement would be different since I don't know if there's significant thermal contraction at lower temperatures. Anyone know?

tbomachines · #2 08-06-2012, 08:48 AM

Quote:

Originally Posted by shertex

Countless forum members have expressed perplexity when attempting to measure ATF level (including me, at one point). They are told to measure it hot, at operating temperature....say after a good run on the highway for 30 minutes. But then they encounter all sorts of uncertainties, basically revolving around the question of whether it was really hot enough when measured. Can be very frustrating.

It seems to me that the reason the FSM provides the "hot" method is that most people, and most mechanics, will be measuring the level on a warm/hot engine: during a trip, a visit to the mechanic, etc... So it makes sense.

But for DYI'er, there's absolutely no need for this method. The FSM specifies ANOTHER method: measuring at 20-30C (in other words, ambient temp on most days). See p. 1 and 3 here: http://www.w124performance.com/service/w124CD1/Program/Maintenance/My81/2710.pdf

So as long as the engine is cold and it's 68-86F outside, I know I can get an accurate reading every time.

When it's colder, I don't know if the measurement would be different since I don't know if there's significant thermal contraction at lower temperatures. Anyone know?

ATF expands and contracts very dramatically due to thermal expansion. The reading at a cold temp is much different than at operating temperature.

shertex · #3 08-06-2012, 08:51 AM

Quote:

Originally Posted by tbomachines

ATF expands and contracts very dramatically due to thermal expansion. The reading at a cold temp is much different than at operating temperature.

I know...my question has to do with the person wanting to measure level on a cold winter morning vs. a nice summer day. Would the level at, say, 20F be appreciably different from level at 75F? The FSM doesn't provide that kind of data. It only tells us about 20-30C vs. 80C.

tbomachines · #4 08-06-2012, 08:53 AM

Quote:

Originally Posted by shertex

I know...my question has to do with the person wanting to measure level on a cold winter morning vs. a nice summer day. Would the level at, say, 20F be appreciably different from level at 75F. The FSM doesn't provide that kind of data. It only tells us about 20-30C vs. 80C.

Ah my bad - I see what you're getting at. Good question.

shertex · #5 08-06-2012, 08:59 AM

Someone with a heated garage could conduct an experiment for us this winter!

Brian Carlton · #6 08-06-2012, 09:25 AM

You would be "short" 200 ml if you filled the trans perfectly at 70°F. and measured it at 0°F.

cho · #7 08-06-2012, 09:28 AM

Quote:

Originally Posted by shertex

I don't know if the measurement would be different since I don't know if there's significant thermal contraction at lower temperatures. Anyone know?

yes it is significant, but to determine exact level or ratio we have to had
those kind of data provided by ATF manufacturer,which is upon my quick
search hardly obtainable

the ratio in question SHOULD be the same as measured "warm"
twice... once upon the start of engine,second time after 30 min (or so) of driving ... both with P selected... I guess on .303 tranny the difference
on the stick is somewhat 5-7 mm.

using that logic if 30-80C oil temp difference give us a 5-7 mm upwards
oil temp 30-0 C will give us 2-5 mm downwards...(what ever method U use..cold or warm...)

& don't kill me for this quick math,... just thinking out loud

)

cheers,

qwerty · #8 08-06-2012, 09:48 AM

Quote:

Originally Posted by cho

using that logic if 30-80C oil temp difference give us a 5-7 mm upwards
oil temp 30-0 C will give us 2-5 mm downwards...(what ever method U use..cold or warm...)

If you are going to use that logic, you need to use an absolute temperature scale, which Celsius is not. (40*C, for example, is not half as hot as 80*C.)

gatorblue92 · #9 08-06-2012, 09:52 AM

Why not put a quart of transmission fluid in the fridge and measure it then put it in a pot of hot water and measure that? This should be a good way to see how much it expands without any other variables.

qwerty · #10 08-06-2012, 10:01 AM

Quote:

Originally Posted by gatorblue92

Why not put a quart of transmission fluid in the fridge and measure it then put it in a pot of hot water and measure that? This should be a good way to see how much it expands without any other variables.

Will that tell you what the dipstick should read?

cho · #11 08-06-2012, 10:06 AM

Quote:

Originally Posted by qwerty

If you are going to use that logic, you need to use an absolute temperature scale, which Celsius is not. (40*C, for example, is not half as hot as 80*C.)

very true mate

we are missing basic ATF shrink/expand data,.. so me calculation
is a far cry of totally accurate...

.

rscurtis · #12 08-06-2012, 10:18 AM

There are other factors in play here besides temperature- mainly, how much fluid is in the converter and valve body at the time of measurement. Measuring the fluid with the engine hot and running assures that these items are full of fluid that could otherwise be sitting in the pan.

cho · #13 08-06-2012, 10:24 AM

Quote:

Originally Posted by rscurtis

There are other factors in play here besides temperature- mainly, how much fluid is in the converter and valve body at the time of measurement. Measuring the fluid with the engine hot and running assures that these items are full of fluid that could otherwise be sitting in the pan.

yeap... but worm or cold measuring approach (stated previously) assumes
engine runnin' and P tranny position.

.

cullennewsom · #14 08-06-2012, 11:07 AM

I found a reference for Dexron III which should be about the same as any other Dexron.
https://docs.google.com/open?id=1KXo09VmkZg_8tLfUkPIRz3M9RudFoZt3-5-UgFarRpxEleo26sIF9AqxzAQ6
Here's one for hydraulic oil
www.hyvair.com/pdf/hydraulicfluid.pdf

There is volumetric expansion which is proportional to temperature. That fact does not necessarily imply that you can't check it cold, but the marks on the dipstick are calibrated for "operating temperature". There is also a question about how to account for torque converter fill, fill of all the other various works of the transmission, and the oil cooler. These factors don't make it impossible, but might give you confusing results based on conditions other than temperature, if you aren't paying careful attention. Another thing you have to worry about is that the transmission is an irregular shaped volume. So if you want to determine where to put your cold calibration tick marks, you need to account for the shape of the transmission. Approximating it as a cube (simplest calculation) might yield bogus results.

Another thing to note is that filling a large reservoir cold might cause an overflow when it heats up, if you accidentally overfill. There are some anecdotal accounts of this happening, burping trans fluid onto a hot exhaust, and causing a fire. Probably in old motor homes with Chevy TH400 & 454.

Here's an explanation of how to calculate the expansion Thermal Expansion - Volumetric or Cubic

Here is a more thorough treatment of the subject. Hydraulic Fluid - Properties

The easiest way, is probably just to make empirical observations based on comparisons of hot vs cold readings, with all other variables fixed*.

* You can't easily fix the amount of entrained air in the fluid, but the difference is probably within the margin of error of measurement precision.

shertex · #15 08-06-2012, 11:09 AM

Quote:

Originally Posted by rscurtis

There are other factors in play here besides temperature- mainly, how much fluid is in the converter and valve body at the time of measurement. Measuring the fluid with the engine hot and running assures that these items are full of fluid that could otherwise be sitting in the pan.

But with the car running for, say, five minutes, aren't you confident that fluid is distributed to where it should be?