Best Transmission and Diff Oil to use in 2001 C5 Automatic
 

Doing some fluid changes and could not find any definate answers so thought I would ask. I have an 01 (86,000 mi) with a 3.15 Diff and was wondering ...

1. What would be the best oil to use for the diff oil change? (* I was leaning towards Redline 75W90)

2. Best oil and filter for transmission (Auto A4)?

Thanks!

the redline 75-90 is excellent in the rear, the additive pack works great on our LSDs

no help on the auto but redline does make some ester based auto trans fluids that can hold up to some very high heat

AMSOIL has a very good A4 trans oil. INSURE that you read and follow the C5 A4 drain and fill procedure to the T or you will damage the transmission! MUST be filled warm and engine running!!

Any good GL5 75-90 differential gear oil will work fine. If you get clutch chatter in tight tuns you will need to add a little limited slip additive until it stops. I have not had to add any additional limited slip additive. Red Line is a fine oil.

Any good synthetic engine oil will serve the purpose. Use the GM Filter and some Mobile 1 and the engine will be happy.

Ok so do I have to drain the entire transmission to put the Amsoil stuff in or can I just drain whats in the pan, change filter and then put in the Amsoil oil?

Well,,, Seeing that it may not have been serviced in the past, I strongly recommend removing the pan and replacing the filter and then refilling.

You will never be able to completely change ALL the fluid as most of it is still inside the torque converter. However, this is what needs to be done to see if the fluid and the fluid level is the root cause.

Bill

I own a trans shop that specializes in performance 4L60Es. We ONLY suggest that our customers use regular Dexron III / Mercon (DexIII). Synthetic are a huge waste of money in a 4L60E, and provide absolutely no benefit.

Frank

Frank

Can you elaborate on how the synthetics don't provide any benefit?

I would have thought that they would be more heat stable and break down less over time.

Bill

how ? an ester oil like redline will not break down at 300deg

dex3 is done for at that temp

Just curious what your opinion is on Dexron VI. This is what GM services most previous specifications of Dexron with.

Also, all licenses for the Dexron III product have since expired, so that's why you get these names like "Dex/Merc" which is essentially unsupported by GM for anyone who didn't know.

Frank, I spent the past few days reading on Synthetic in a 4L60E and seems like there are alot of horror stories. I also read that DEXIII is not available from GM anymore??? ... Where do you suggest I get this DEXIII and how many qts will I need with a filter change as well? Thanks.

My experience with these transmissions have shown there's no benefit to synthetics. Trans temp should never get above 180-200 degrees. If it does, you have other issues. Normal trans fluid will last up to 30,000 miles without needing to be changed unless there is another issue causing a problem.
Most companies have relabeled Dex III as "multi-vehicle fluid". It's still the same stuff though.

Frank

If your trans gets to 300 degrees, you have bigger issues than what fluid is in it...LOL

Frank

you shouldn't

300deg temps are common on track days with some stock cars that have upped the power

in fact a turbo 300zx i use to have repeatedly got to 260-280 in an auto trans under power and that was just street racing

larger cooler would have obviously helped, but, there was no room to mount one on that car without a real plumbing project

i put over 20k miles on that car, lot of it drag racing, always used redline, trans never was rebuilt

I just remembered that when I had my 02 Escalade, the guys over at the caddy forum recommended Castrol Dexron VI... I did use it and had no issues with it in that vehicle... Wondering if I should use the Castrol brand in here hmmm....

Also thought I would share some findings after I searched for a while - this is interesting stuff! Makes me wonder know if I should just use Dex IV...

Not trying to hijack this thread but, since we have the information on trans temps right in front of us, what are the typical temps other A4 drivers see?

Mine will run up to 220 in heavy traffic and drop slowly to 200 to 210 on the freeway.

I have a good b&m cooler on mine. The radiator cooler is bypassed. I've never seen over 175.

Ron

I checked mine today while cruising around with a few hard take offs (hehe), it was around 190 to 205F and tonight it stayed at a constant 190F...

Ok so I went with Redline 75W90 for the diff and D4 for the auto trans, plus oem filter and gasket. I'll let you guys know how it all works out. Oh does anyone know if I will need the additive for the diff together with the 75w90 in there?

I change my trans fluid every year and I'd be lucky to get 2k miles a year on it. I use reg dex/merc and I set the dash temp gauge to show at all times. I'm always starring at it. lol. Trans temp runs between 180* -190* in traffic on 85* days. Moves up a few degrees when I lay into it hard, but never breaks the 200* mark. Car put down 565rwhp so it moves pretty good on the street. It also has a good b&m cooler in addition to going thru the radiator.

unless there are big NS letters on that 75-90 you don't

the redline 75-90 has borderline too much additive stock out of the bottle. healthy for the life of an lsd but a touch more lockup wouldn't be bad IMO

great oil though, group 5 esters {which redline is} are more or less ideal for older seals, they have a mild softening and swelling effect on them