: transmission oil looks dark :S

10-03-07, 05:27 AM
its been 30k since last service, but I noticed that the fluid looks dark, dirty, I am ready to replace it, but I was wondering, should I use the DexronIII since the dipstick says I have to use that one? or should, or Can I use dexronIV or VI?
2000 Cadillac Deville 104,000 miles N*

10-03-07, 04:31 PM
The latest GM TSB's specifically state that DEXRON VI shall replace all earlier versions. I just did my '02 at 45,000 and the transmission is smoother and shifts quicker. (Or, to look at another way, when your car was built, engine oil was SJ designated. It is now SL or SM. Do you look for SJ?)

10-04-07, 09:23 PM
I would then guess that the fluids are compatable. You can not get all out so they will mix? Mike

10-05-07, 08:59 AM
The TSB states that the fluids are compatible. No need to obsess over flushing.......

10-05-07, 06:50 PM
The TSB states that the fluids are compatible. No need to obsess over flushing.......

Thanks now I just need to remember to call the person I bought it from to see if they had it serviced recently. My DIC says 99% at this point. Mike

10-05-07, 07:07 PM
99%? I bought mine with 50K miles, and did a fluid change, now at 105k it still says 100%, I wonder if it really works ...... :(

10-05-07, 07:31 PM
Yes, it works. Transmission fluid is not subjected to the combustion byproduct contamination of motor oils, and it is also a highly specialized hydraulic oil. The transmission high temperature cooling sequence does not begin until 302 degrees. When I did my change to DEXRON VI, at 44,500 miles, the life monitor said 98%, and 2/3 of the miles are Interstate. 99% of automatic transmission vehicles NEVER get a fluid change and live forever. Sort of like RWD axles.......(different principle, different oil.....)

10-05-07, 08:17 PM
live forever? you mean like 100K? almost every car that Ive known of has had transmission trouble right around 100K
I hope caddys are not like those :P

10-05-07, 09:07 PM
The 4T80E trans is pretty tough from what the Guru had told us.

10-05-07, 09:41 PM
:sneaky: Ibarria.......sorry for the flip answer. Most auto transmissions go about their business for far longer than recommended service intervals. There is no mechanical/lubricant reason why one should not function to 100K or beyond.

100k ?

Think of what the mechanism has endured with the same lubricant for that time/mileage. Go the same mileage, without oil/filter change, with the engine that's bolted to that transmission. Mechanical mayhem. As a SWAG (Scientific Wild Ass Guess), a 100k+ transmission is living on borrowed time. No matter whether it's GM or Rolls Royce.

Just as a BTW, consider that a RWD differential ring and pinion operates in 80/90 or 90/140 hypoid lubricant. The same ring and pinion analogy in a FWD transaxle operates in 10W fluid. No matter how you cut it, you still have to transfer power to the wheels. Pressure and shear are death on lubricants. Which is better at transferring power to the pavement? FWD or RWD? Your call.......