Change Trans Fluid or Not?

[Trenton]

Hey y'all, I have a 1998 Chevrolet K3500 Silverado CCLB with the 5.7L Vortec and 4L80e trans.

My transmission has no issues and shifts perfectly, but it also has 268k on it and I don't know the maintenance history of it. The fluid is dark red, but doesn't smell burnt. In the almost 4 years and ~28,000 miles I've owned it, I've never changed the fluid.

I've heard horror stories of changing trans fluid and the trans going out at this high of mileage. I just want it to last as long as it can.

I don't tow really heavy right now, maybe 6000 pounds at most. I do go off-roading in the rockies and drive up a lot of mountain grades since I live at 8000 ft elevation. I use Amsoil in the engine, transfer case, both differentials, and I even run their brake fluid, so I'd like to put it in my transmission if it's not a gamble.

So should I change the trans fluid or not?

 

[Supercharged111]

I tow heavy and flushed my 4L80 in my dually around 150k miles. It smelled original, was also somewhat dark red, not burned, but smelled like crayons. I've flushed numerous other perfectly functioning high mileage vehicles with ZERO ill effects. Do it now before the old broken down oxidized fluid creates a problem. Also, I used Amsoil fluid when I did the 4L80 swap in my 1500. Good stuff, but overkill for sure. At the end of the day, new fluid is better than old fluid.

 

[jjester6000]

Hey y'all, I have a 1998 Chevrolet K3500 Silverado CCLB with the 5.7L Vortec and 4L80e trans.

My transmission has no issues and shifts perfectly, but it also has 268k on it and I don't know the maintenance history of it. The fluid is dark red, but doesn't smell burnt. In the almost 4 years and ~28,000 miles I've owned it, I've never changed the fluid.

I've heard horror stories of changing trans fluid and the trans going out at this high of mileage. I just want it to last as long as it can.

I don't tow really heavy right now, maybe 6000 pounds at most. I do go off-roading in the rockies and drive up a lot of mountain grades since I live at 8000 ft elevation. I use Amsoil in the engine, transfer case, both differentials, and I even run their brake fluid, so I'd like to put it in my transmission if it's not a gamble.

So should I change the trans fluid or not?

Here's what I did for the original trans on my '95 suburban c1500 (340k).

The fluid looked like crap, so I replaced 2 quarts every 1000 miles (by pumping it out of the dipstick tube) until the fluid looked good on the dipstick. At about 335k I changed it, and it shifted very well until the rear seal blew at 340k (Killed the trans driving it home on low fluid).

Anyways, if I had replaced the severely worn slip yoke bushing and seal when I changed the fluid, it would probably still be going to this day.

 

[Trenton]

Also, I used Amsoil fluid when I did the 4L80 swap in my 1500. Good stuff, but overkill for sure. At the end of the day, new fluid is better than old fluid.

Appreciate the tip. Also, it is next to impossible to overkill when it comes to Amsoil

 

[df2x4]

Change it. I wouldn't do any kind of a "flush" personally but a drain and fill with a fresh filter isn't going to hurt anything.

 

[stutaeng]

Change it and move on...

I'd be more worried if your pan had a drain plug or not.

 

[Supercharged111]

Change it. I wouldn't do any kind of a "flush" personally but a drain and fill with a fresh filter isn't going to hurt anything.

Flush with a machine? No. Purge using the transmission's pump at idle? Absolutely.

 

[Trenton]

Change it and move on...

I'd be more worried if your pan had a drain plug or not.

Yes, sir, it has a torx bit drain plug on the bottom of pan. It's going to be so easy.

 

[PlayingWithTBI]

it has a torx bit drain plug on the bottom of pan. It's going to be so easy.

That makes it easier and less of a mess but, I'd change the filter too.

 

[Supercharged111]

I forgot to point out to you Trenton that I live over 6000' where my trucks do their work and do head up higher to go camping. But I cheat cuz my trucks have blowers. In fact the dually has had it's blower for the majority of its life, I snagged it just outside of Grand Junction back in 2016. These trannies are tough.