I already got that exact wrench for this job so all good to go there.

Here’s what I was just told by CTSC:“The steel oil pan has to accommodate the external filter and as you mentioned is slightly thinner, not as deep.

The main concern is when the transmission fluid gets hot and expands. Less room means the oil level will rise higher than within a plastic pan.

The danger is when the oil level reaches moving parts above and the trans fluid will turn into milkshake, resulting in slipping and overheating.

The steel pan overflow plug is lower than the filler plug in the transmission housing resulting in a lower fluid content in the pan.”

what do you all think of this?

 

I’m still not buying it. The original pan holds more fluid, the steel pan holds less fluid. If filling to the same point (the transmission fill plug), then the pan with the larger volume (plastic) will expand more than the one with less volume. If anything, using the steel pan means the fluid will reach a lower level within the transmission once to running temperature because it holds slightly less fluid. Filling the steel pan using the new fill port is more likely to underfill the transmission than overfill it.

Think of it this way: if the plastic pan holds 9L and the steel pan holds 8L when leveled to the fill plug, and trans fluid expands by 10% at operating temp over cold —which pan will have a fluid at a higher level once heated? 9.9L vs 8.8L

The reason the steel pan has that fill port is because it was developed for BMWs with the ZF 6HP26. They had a similar issue with the plastic pan, needing to remove cross members and exhaust to change the filter, but they had another problem: the transmission fill port is blocked by the exhaust. The steel pan has a new fill port on the pan so BMW mechanics can fill the fluid without removing the exhaust.

I don’t think you’ll do any damage using either fill port, but I know it’s safe to use the upper one from factory. People that run their trucks HARD off road, towing, and in hot climates all use the factory fill port, so I don’t see it as a concern.

 

Yeah... that makes no sense. The metal pan has slightly less capacity, so slightly less expansion.... Whoever wrote that is an idiot. It is not like the fluid expands 20% or something. It was actually calculated to be less than 1%. So that is WELL within margin of variances in filling.

 

Yeah from everything I've read I understand it exactly the same way as you both. Hence the confusion of "what am I missing here..."

Decided I'll go with the original fill hole.

 

The transmission fluid needs to be at a specified temperature when filling so the level is correct as the fluid expands. There is a document on the web that explains how to fill the ZF6hp26 trans after a filter change. https://www.disco3.co.uk/gallery/alb...luid_level.pdf
I agree with Dakota... it doesn't make any difference how deep or shallow the pan is.
The fluid needs to be at the specified level and temperature at the fill plug on the transmission case.

 

I believe the issue The CTSC is referring to is heat. There is indeed less fluid in the steel pan, but the amount of heat that it absorbs is the same as the fluid in the plastic pan. To give a simple analogy, which will be hotter after one minute in the microwave, a cup of water or a gallon of water? Trans fluid most certainly has expansion coefficients that are temperature dependent, which we see described in the factory fill procedure. At equal fill levels, the expansion in the steel pan could be enough to create the milkshake conditions described. Reducing the fill level would prevent the trans fluid expansion from reaching the moving parts.

I am only presenting this as a possible explanation of what The CTSC is saying.

 

Ugh.... I repeat and beat a dead horse. The amount of fluid difference is not huge and the amount of expansion of the fluid is inconsequential. This was literally calculated once because some mental midgets were soooooo insistent it was a big deal. Let us put it this way. Hundreds have converted to a metal pan without issue. IF you think it will be an issue, dont do it??

 

do I leave the white plastic piece on the inside of the steel pan, or take that off?

 

Leave it. It won’t hurt anything.

 

I agree and if you take into account all the extra plastic around the filter there will be very little difference between the 2 pans, certainly not enough to think twice about.