To change? Or not to change? 4l80E fluid

[Vortec 350]

Hey I just bought a 1998 c2500 350 Vortec with 204,000 miles. I'm going through it and doing a bunch of maintenance and I was wondering about the trans fluid. I've heard horror stories that the fluid was changed and the trans started to slip because the clutches got used to the way that fluid was. I don't really know much about auto trannies so I thought I would ask. Also the trans was apparently "rebuilt" 100,000 miles ago according to the previous owner, but he couldn't prove it. Any thoughts? Thanks!

 

[df2x4]

I would absolutely drop the pan and change the fluid and filter. Probably wouldn't flush it, but that's just me. I'm of the opinion that if a drain and fill hurts anything, you were on borrowed time anyway. I've never had any negative side effects from a fluid and filter change.

 

[94burbk1500]

I'm not a fan of flushing transmissions that are high mileage, but that may be superstition. You won't hurt anything doing a filter change and top off and I recommend it. It also gives you a chance to inspect the fluid and check the magnet on the pan for anything serious. I did it to my 1994 with a bone stock and unloved 4l60e at 124k miles and then drove it 3000 miles in a week and a half. Currently sitting at 129k miles and no issues with the transmission, I think it is working better.

 

[jsfrmsj]

I had mine flushed at 160k. A little more than 180k right now with no transmission problems, although with my luck it will blow tomorrow.

Don't forget about your rear diff, power steering, and brake fluid.

 

[Vortec 350]

Ok thanks for the replies. How many quarts does it take? It has the factory trans cooler (I think they all do?), And what trans fluid is the best for a high milage trans?

 

[df2x4]

Ok thanks for the replies. How many quarts does it take? It has the factory trans cooler (I think they all do?), And what trans fluid is the best for a high milage trans?

Not all of them got the factory AUX cooler, but all should have the one that's built into the radiator. Should be around 7 or 8 quarts. Stick to ACDelco Dexron 6 for fluid.

 

[RDF1]

It's really hit or miss. All I would do is filter and top off with fluid.
I use the cheap super tech ATF Dex/Merc from Walmart

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[Supercharged111]

I'd do a full flush. There is nothing good about old burned broken down 200k fluid. Drop the pan and do the filter. Remove the return line from the transmission. Refill with 2 gallons and start the engine. Pump a gallon out, kill the motor, add another gallon, repeat. Once the 3rd gallon starts pumping it'll finally start to run clean. Those first 2 will be nasty.