Auto Trans Fluid Change 90,000

I have a Pontiac with 90,000 miles and I do not know if the transmission fluid has been changed in the past.

I've heard that it may not be a good idea to change it now as changing may cause further damage. Is this a wives tale?

What should I do.

Transmission/car works fine. No sign of problems.

Much thanks in advance.

Depends on the year. Newer cars with Dextron/Mercon 4 fluid are considered "fill for life" and can be left alone, older dextron/mercon 2 or 3 fluids should be changed. The owners manual will tell you what fluid was used at the factory.

In general, cars that have never had a FLUSH (or history is unknown) should only be flushed if under 100,000 miles. Flushes are done on a professional machine that uses new clean fluid mixed with special detergents to wash away built up gunk. The detergent rich fluid is then pushed out and replaced with regular fluid. If this is done at 100,000 + miles, it tends to release big deposits of crap stuck in odd corners of the transmission, sometimes causing them to re-deposit in a bad spot in the valve body, leading to premature failure.

A simple pan drop 'n' drain with a replaement filter isn't as good as a flush but is always safe - even if service has been neglected in the past.

The ultimate cleaning involves doing a flush, then dropping the pan and replacing the filter. It's pretty expensive due to the huge amount of fluid that gets thrown away, but will extend transmission life.

I guess the best way to decide is to take out the dipstick and let a few drops of fluid fall on a white sheet of paper. If the fluid is:

Bright neon red: just leave it alone

Dark red: have it flushed by a shop, opting for a flush and filter is worth it

Brownish red: change it, replace the filter. DO NOT FLUSH

Brown and smells like something died in it: Don't waste your time. Get a rebuild, or start car shopping immediatly.

this is a common belief, that if you go beyond a certain time frame, that you're better off leaving it alone.

There is a small amount of truth to this, which is, if a tranny is DAMAGED, flushing it might bring a problem to the front that wasn't obvious before.

But really, the tranny is already in trouble at that point. Purposely NOT servicing it isn't really an effective way of solving the problem, unless you want to sell it anyway.

If you care about the car, get the system flushed. If you don't care about the car, sell it.