See post #9...

https://xoutpost.com/929742-post9.html

That's it! I guess I was trying to fill through the pressure test port lol...(though my car is not diesel).
I've never heard of pressure tests on transmissions before. Definitely learned something new.

Well I think I have come up with a game plan for servicing my 3.0L GM A5S390R (GM 5L40-E) with 180,000 miles without a transmission service ever, at least for now unless I find some crystal ball that will predict the outcome of the transmission fluid and filter change.

I think what makes sense to me is to crack the fill plug when the system is cold and gather a few drops of the oil and determine the color (and health) of the oil. Basically see if it is red, dark red or black.

• red oil would indicate it is probably a safe move to changing the transmission fluid and filter
• dark red oil would be fair to drop 1/2 the oil through the drain plug and top off with fresh fluid leaving pan and filter intact and re-evaluate after 5,000 miles
• black oil would be a sign to tighten the plug back up and continue on borrowed time

Any other thoughts or suggestions from our specialists or speculists?

In these GM boxes original Texaco oil from factory is brown not red.

Why not change the whole oil content by flushing?

The main culprit on these boxes is torque converter lock up clutch wearing out. After the clutch material is worn out metal shavings will do the rest. For my E39 530d with the same GM box I renewed the torque converter as preventative maintenance after 300t km. Oil and filter changed by flushing every 120t km. Now 400t km on the clock with no problems.

Good input, thank you. So from my reading and researching, flushing is almost always a kiss of death if the abused oil is keeping the clutches from slipping. I have read several of your posts as being very knowledgeable so I value your opinion. I have not seen in any of my reading the color of Dexron III being brown so this is good information to consider. I guess I could duplicate the test with clear brown, dark brown or black.

*Edit was that the Texaco ETL 8072B

The main purpose of oil in auto gearbox is to work as hydraulic fluid. If a flush change (renewal of whole oil content) is done properly there is very little chance you could do any harm. Personally I've removed the the oil line on oil heat exchanger and guiding that fluid to container while filling the pan with fresh fluid (drill pump) with engine running. (Of course normal drain and filter change done first.) When the colour of oil coming out of exchanger changes you know the whole content is new and turn off engine. Reconnect hoses and do a normal fill up with engine running and oil temp 30-50 C.

I have the same transmission, did mine at 250000 miles. The oil was super dark or black.
Have been driving it for a couple of days with no problem. I dropped the pan, cleaned the magnet, changed filter and gasket and refilled.

BMW says the fluid lasts a lifetime, whatever that is. I have changed the trans fluid and filter every 50,000 miles since new. In spite of mods, other than 1 sensor, I never had a problem with trans in 118,000 miles. I look at color and smell it but only for an indication something else may be going on that I need to look into.

I only use OE fluid. IMO it is part of the design criteria even though some other fluids are compatible. I pull the pan and replace the filter. With pan back in place. I add fluid until it starts to drip out the fill hole. I replace the plug and run the engine until the transmission shows a reading with infrared temp tool of about 110 degrees F. Then pull the plug and add fluid until it starts to run out again. I replace the fluid and drive it 50-100 miles or so and drain and replace the fluid again since the torque convertor doesn't drain when the transmission is drained. Doing it twice increases the percentage of new fluid. Quite often if you are already having a trans problem changing the fluid will not help.

Thanks bcredliner,
No transmission issues, just want to give the trans some love. Just nervous about creating a problem that doesn't currently exist.