About a month after changing the filter in our 2005 S Type R, I had a leak from the sleeve and had to redo things. BTW, I recommend the CTSC kit that comes with fluid, sleeve, about 5 larger bolts, and filter. Even after the short period, I found two bolts seized.

I used the opportunity to look into the directions about measuring correct ATF level. First, in my opinion the instructions are confusing and overly precise while being vague.

The directions I found said that the ATF must be between 30C and 34C before you start and that a small stream out the filler hole at 40C is correct. 50C is too high and you must let it cool down. But where do you measure temperature and is it a stream or a drip? Should you measure the temperature of the fluid itself or the external pan surface? After all, the pan material is insulating and would likely raise in temperature more slowly that the fluid. So, I asked CTSC and Klaus said that the outside would be about 3C cooler but that you should measure there.

The temperature of the ATF does rise very slowly, so it makes a difference to you if you are on your back under the car with the engine running. While waiting in that position, I began to wonder what difference the temperature in that range could possibly make.

I put three quarts ZF (measured) in a large pot and used low heat to measure the relationship between depth (volume) and temperature. (I hope someone else will replicate the process to confirm that temperature makes very little difference in the range.) The pot was about 12 inches in diameter. Given that the amount of ATF in the pan when the engine is running is about 2 liters (the amount added to an empty transmissionpan to reach the fill hole), my pot with 3 quarts (2.8L) should be a conservative test.

I began at 18C and went to 100C with several measurements in the 30C to 50C range. I then fit the measurements using a regression line to help control measurement error. Based on my testing, the difference in depth from 30C to 50C was 1MM (about 1/20th inch). The difference from 30C to 100C -- about normal operating temperature -- was about 3.5MM (about 1/8th inch). Given all the variables, including how level the car is, it is hard to imagine that the range from 30C to 40C or 50C could be critical. In fact, it is hard to imagine that even 100C would be a problem or even a very small leak would lead to a damaged transmission.

My guess is that this range is specified so that the ATF is warm but not hot and even at 50C (122F) is more cautionary and about the technician avoiding burning their hand. In this area of California, a 40C day is common in the summer and therefore an excellent time to do the job.

I hope someone will replicate this study, or do it mathematically using expansion tables or something, but my test suggests that anything in the warm range would be fine.

 

The whole trans will change volume as it heats.

I see no point in second-guessing the trans maker.

I think temp is supposed to be read using a (jag) diag tool (such as IDS/SDD) but people work on the basis that an IR gun or the like is good enough and I suspect it is..

Obviously each person can do as they like with their car.

 

Yes

 

+1 Expansion of the fluid is only part of the equation. The experiment is also invalid as it does not replicate the height vs. surface area of the fluid in the transmission. A tall thin column of fluid would show more variation in height with temperature than a broad shallow vessel, each having the same volume of fluid.

If the ambient conditions cause the transmission and fluid to be at 40C, so be it. It's easy enough to read the fluid temp via the fill point, so I'd use that.

 

My iCarsoft 930 gives trans fluid temp as well as valve body temp.. I also have an IR gun and will report outer IR temps as they relate to actual inner temps when I get to doing my ZF and see if these guys shooting the oil pan with IR are even close.. I plan to have mine full at 35c..seems then the max amount of fluid is in.

It just amazes me that there are two senders inside this transmission that send accurate temps one degree at a time.. I can drive and watch it go from 30c to 80c one degree at a time..

 

Reckon you get code(s) if they're wildly different and/or reduced performance?

 

Again, I hope that someone repeats the experiment. Here are my responses to substantive first replies.

The whole trans will change volume as it heats. -- That is true, but it is circulating and only the part that is in the pan can contribute to a change in height in the pan. That is about 2 liters.

I think temp is supposed to be read using a (jag) diag tool (such as IDS/SDD) but people work on the basis that an IR gun or the like is good enough and I suspect it is.. -- Don't know what that is. If it uses the transmission temperature as read through the OBDII port, then I think that is probably a good thing, but again, is there any appreciable difference from 30C to 50C? I intended to use that reading, and I believe that it is available through a scanner I bought, but I couldn't confirm that without running the car and I couldn't run the car without fluid in the trans. I will try to confirm the reading and level at another time.

+1 Expansion of the fluid is only part of the equation. The experiment is also invalid as it does not replicate the height vs. surface area of the fluid in the transmission. A tall thin column of fluid would show more variation in height with temperature than a broad shallow vessel, each having the same volume of fluid. -- I think that I mentioned that it was a pot with a 12 inch diameter. I think that would be similar in surface area of the filter or smaller. In other words, my test should have shown a greater change if anything. If someone has a filter handy, please send the dimensions or area.

 

That seems false to me. Imagine the whole inside swelled to double the volume it was when cold. You'd need twice the fluid. (Obviously it isn't going to swell so much.)

I'm not seeing what the point is of using anything but the recommended fill procedure. People have followed it OK and got good results. Why do anything else?

 

JagV8 is correct.

The fluid does not sit statically, it's being circulated continuously. How much the various cavities that it flows through expand/contract when heated to a given temp and what effect this has on the sump level is anyone's guess.

Except ZF, it seems they know

 

It's YOUR gearbox. Fill it any way and to whatever level and use whatever fluid you want!!!!!!

bob gauff

 

When you install a new filter, the first step is to add ATF until it comes out the fill hole. That is about 2 liters. Therefore, whenever the fluid is circulating, there can never be more than 2 liters in the pan or it would come out the hole. I started with 3 quarts on the stove so the level in the pot should have raised as much or more than in the transmission pan.

What I am suggesting is that any temperature from 30C to 50C is most likely fine and they probably picked 40C as the midpoint -- it just can't make much difference. There is very little expansion between 30C and 50C.

Your ability to accurately measure 40C (inside, outside, or by internal sensor), even with a perfectly accurate thermometer, and to be certain that the car is "level", etc. just are not going to matter. So, try to follow the directions but don't sweat it too much. In fact, you might want to cut it off at 35, especially if measured externally.

This little project was undertaken to try and determine how precise I needed to be given that there would be differences due to location and method of temperature measurement, etc.

 

That's still not true.

For a start there's quite a bit in the TC and it also expands.

I'm with Bob - fill it how you like. But - and it's a big But - I'd hate anyone else to think it's going to come out well and to do the same. It doesn't save any real work as far as I can see, yet it involves an unknown risk.

 

My two cents:

Just follow ZF's recommended fill procedure. Rick (joycesjag) and I have done it once on my wife's 2006 XK8 (using Lifeguard 6) in July 2013 and twice on my 2005 S-Type (using Mercon SP) in November 2014 and October 2015. The results all three times were smoother shifts with zero issues. Why waste time and effort doing it any other way?

 

Here's the video posted by ZFServicesNA demonstrating the correct drain/fill procedure for the 6HP26 trans...

ZF says, "It is of the utmost importance that the vehicle is level" but they also say "For your safety, it is important that the vehicle is level." So it seems that having the vehicle level is a safety matter more than a drain/refill necessity.

They say the transmission sump temp should be between 30-40C (86-104F) and, in the video, they point a Raytek Raynger ST2L non-contact infrared thermometer directly at the pan to read the temp.

The video goes on to say that fluid should drip from the fill hole in a "thin stream" while the engine is idling between 650-950rpm. If no fluid comes out, add fluid to fill hole until fluid "streams out thinly".

IMHO as a mechanical Luddite, the video is pretty clear and simple to follow. Why deviate from what the trans manufacturer says is the correct procedure for servicing your tranny? A transmission is just too damned expensive to mess with/experiment on.

 

Forums are indeed interesting places. I don't believe that I ever recommend that you follow a different procedure. The post was an attempt to better understand why to follow the instructions and whether or not the stated precision was critical and if critical, how best to measure it. These are remarkably expensive transmissions after all. My stove top experiment suggests that a broader temperature range was perfectly fine and is supported by the video stating that 30C to 40C as measured on the outside surface is fine.

I like to try to understand what is behind instructions, and I know for a fact that they can be wrong or at least include irrelevant directions. (Usually to take off items that don't have to be removed.) For example, I don't believe that the video says to turn the AC on even though the written instructions that I have do. Given that the temperature rises slowly, I see no reason to do this. The video recommends starting with a trans at normal operating temperature -- hot. The written instructions don't and I can't see why you would want to or should. The written instructions say to start the checking process when the fluid is at 30C to 34C and then take the reading at 40C, the video doesn't mention that and it makes no sense. If you want to use 40C, just go to 40C. The video says 30C-40C is fine and the written instructions specify 40C. I think that the video also says that it is important to follow the manufacturer's change interval and to use only ZF or the manufacturer's fluid. Etc. I have also found ZF instructions for this transmission in other manufacturer's cars that say 30C to 50C.

To summarize, in my opinion, ZF did the perfectly sensible thing of locating the fill hole so that fluid level could be checked at a sensible temperature range that would not burn the technician. They also used a temperature that would allow the process to be done in nearly every environment. After all, you can warm the trans but you can't cool it in a very hot environment like that of the Central Valley of CA on many summer afternoons (40C = 104F).

 

I have to disagree, "the sensible thing" would have incorporated a dipstick. But maybe that is overthinking.

 

Or the ability to read it via the OBD port!

 

While I still enjoy my 2005 S-Type very much, by far my biggest pet peeve remains the fact that there is no dipstick / fill tube on the ZF 6HP26. Same goes for my wife's 2006 XK8....

We picked up a 2013 Subaru Outback 3.6R Limited nearly a month ago. Not only does it have a dipstick / fill tube on the transmission, it also has a dipstick / fill tube on the differential! Now that's proper long-term service engineering indeed....

 

Given the sensitivity of the transmission to proper fluid levels and the very infrequent service interval, the removal of a dipstick might have been a bit of idiot proofing on ZF's part.

Having worked for an engine OEM for over 30 years, primarily in engineering and field support, I was always amazed at what creative things owners would to their very expensive machines.

 

More likely the removal of the dipstick / fill tube was calculated to drive more ATF service business to the various dealerships in which these ZF units were sold....

The problem is that most Jaguar dealership service departments know far less about these ZF units than we do....