I have a 98 Silverado with 135000 miles It has 5.7 engine. I am the 2nd owner having owned it since 1999. The transmission has never been serviced and works with no problems. It is never used for towingg or any heavy hauling.Should I change fluid and filter now or leave well enough alone?

 

Absolutely you should drop the pan, clean up the magnetic square on the pan real good, and use a full synthetic grade transmission fluid. It will mix with non-synthetic fluid just fine. Two things that destroy automatic transmissions are overheating, and not changing the fluid.

It can get messy, but there is a plastic container made by Lisle that has an extended fluid catcher that makes it much less messy. Part number is 17922. it holds 7.5 gallons of fluid or oil.

 

I agree. I would definatly do a fluid change, and use the full synthetic. My father did his about 10 years and 100,000 miles ago on his truck. It was used as not only a daily driver, but also a work truck during the last 100k. I can safely say, without exagerating that the truck has towed a roughly 3000 - 4000 lb trailer about 25,000 city miles in just the time he has owned it. He put full synthetic and a new filter in it shortly after he got the truck, at about 100,000 miles. So yes, very good idea, because the truck still shifts more or less like new at a little over 200,000 miles.
I have done it to my own truck aswell, and one proablem I ran into is that their are TWO different filters, one is short and one is tall. So get the new pan gasket, and BOTH filters, then just return whichever one you didn't use. And as the previous poster said, it can get messy because their is no drain plug, you just drop the whole pan. You can buy aftermarket drain plugs you can install though, so concider that.

 

Thats great that the transmission has worked so well for so long, My 2015 Malibu ha the 6T40 transmission and you cant change the filter without busting the tranny open, so no filer changes can be done. There is no oil pan, just a drain screw on the bottom of the housing. Takes about 4.5 quarts per change and I've done two with Valvoline Dexon VI full-synthetic fluid. Figure if I cant change the filter I'll just change the fluid much sooner. Keep hearing Malibu's are awful, which is BS. At 55 mph this car is pushing 45-50 MPG and
at 70 anout 40-44 MPG. It's been a great car and I plan on keeping it for a long time. Transmission shift smooth as silk as does the motor.Only a few minor issues like the trunk opening up a block or two away, but I fixed that. No big deal. Lots of power without a turbo a 197 HP rated, and it moves out quick enough for me. No issues with valves or injectors, as it has direct fuel injectors, but I use top of the line gasoline in it, mostly Chevron with Techron, as I used to be in the fuel business, and Techron does work, Its not a hoax at all.

 

Good to hear @oilcanhenry . We have been surprised it has lasted like it has too, thats why I am such a proponant of the synthetic stuff. And since you mentioned it, was makes that fuel better?

 

You are crazy if you think that Malibu is getting that kind of mileage. We have a 2012 LT with the 2.5 and get 28 highway at best. We just replaced the Tranny and I did the same thing you did. Changed the fluid every time I changed the oil. Very easy to do. At 153K it let go. Had to get a new one from GM to the tune of $4,800. I will never have another Malibu again. Had a 2014 that was haunted by electrical problems that took over $2,000 to fix.

 

Pull the stick. If the fluid is cherry red you are OK. If not change it. Amazon runs specials all the time for Valvoline Dexron VI for around $4.50 synthetic. I stock up when they do this. Can only buy 6 at a time.