Changing ATF Chevy 3500 Van Questions?

[HiccaBurp]

My '03 Chevy 3500 van is at 99k and has never had an ATF change. It has the heavy duty trans.. forgot the code but the parts guy said it's basically a TH400 with and overdrive??? Couple of questions..

1. What type of fluid? I am a fan of Mobil 1.. and they have DEX VI and also a full synthetic trans fluid?? Can you mix these new ones with the old factory stuff?

2. I was going to just drain a few quarts and top off now. In the meantime I wanted to order some inline transmission filter. Then in a few weeks, do a full fluid exchange. Is this a good idea?

3. Or should I do a few drain and fills over the next couple of months to get the trans acclimated to the new clean fluid slowly?

 

[SteveSRT8]

You have a 4l80E, definitely NOT a TH400 w/od!

Dex VI is perfect for this vehicle. We run a fleet of them and we love it.

I recommend dropping the pan, new filter and fluid, then a complete fluid exchange after. Easy DIY with directions on this site somewhere.

 

[eljefino]

Wiki says it is a descendant of the TH400.

http://en.wikipedia.org/wiki/GM_4L80-E_transmission

Regardless there is no "getting used" to new fluid. IDK how you plan to drain a few quarts, if you take the pan off (a great idea) you'll drain what you drain. Get the pan filter, get your line pressure up.

If you like M1 that's great; I like it too but don't like paying for it.

Dex VI is another great choice.

As fun as an inline filter sounds I'd worry about it slowing down your cooling... and frankly you should be dropping the pan and getting the stock filter more often.

 

[sciphi]

The inline filter has less resistance than a hose, I've heard. The one on the Buick hasn't degraded shifting any. Quite the contrary, it improved shift quality noticeably after the ATF got filtered by a finer filter than GM equipped the Buick's 4T65 with.

 

[bmwtechguy]

I recently service a friends truck with the same unit and 160k miles on the original fluid. The only reason he thought it might be a good idea to change the fluid is because after sitting a few days in the cold, it took some time to start moving. I told him his torque converter may have drained down for some reason, but that fluid was really dirty, but not burned due to the large secondary cooler, I am sure.

I dropped the pan and cleaned it and the magnet, changed the pan filter, then refilled/flushed by taking the cooler return line from the rear loose and putting a hose on it into a see-through container. We used some very inexpensive DexIII for $2/qt on this change/flush, about 16 qts. The plan is to run this fluid for a few thousand miles to clean up the internals, then change/flush the fluid again using Maxlife ATF, which is about the best performing ATF for the money that I have found. I got this last bunch from Advance Auto using a coupon code for 40% off. It works out to just over $3/qt for a full syn ATF. At that time we will also install an inline filter that costs about $15.

BTW, I saw that Maxlife ATF is recommended by Valvoline for DexVI, although not licensed for that spec. Yours only calls for DexIII anyway. M1 ATF can be bought for less than $6/qt the same way at AAP.

 

[SteveSRT8]

sorry, eljefino, but Wiki is wrong again! There's more than one error in the page you posted. That's why I'm not a fan.

And around 30k miles is a great service interval for this slushbox in heavy duty usage.

Dropping the pan uses about 5 quarts I believe. And you must be careful to get the seal right on the filter.

 

[AzFireGuy79]

No, in this case wiki is correct. The 4L80E is very similar to the TH-400. Many of the internals are the same. Obviously the overdrive changes things, and it is electronically controlled. I should know as I have one and spoke with Carl Rossler about it asking why they were so similar. He confirmed my suspicion.

 

[unDummy]

#1. Use ANY ATF that meets DexronIII, MerconV, or DexronVI, and they all can be mixed. But, if you plan on forgetting about it for another 100k, pick just one and stick with it. I'd recommend a full synthetic.
#2. Sounds like a great idea. If you don't like the way the fluid feels, you can use another one for the complete exchange.
#3. No acclimation is needed. No chemical flushing/washing of your AT is needed. Just exchange the ATF, either partial or all, and keep driving.

Find someone that can do a TAPs reset once all the new ATF is exchanged.

 

[HiccaBurp]

Thanks all for the info. I ended up only draining about 4 quarts and refilling with Mobile 1 Full Synthetic ATF. I didn't have time at my friends shop to do everything. My main priority was the leaking right rear axle seal and new Diff fluid as it was all original as well. Also an oil change.

I'm hoping to borrow one of his lifts in the next couple of weeks to do a pan drop and filter change. Then do a complete exchange via cooler line as well as installing a filter.

What is a "TAPs"?

BTW, the fluid coming out was not burnt.. but the color was a murky reddish/brownish color.