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?