To change or not to change old trans fluid

[GP4rsssfed]

I own a 2002 Grand Prix with the L36 engine and 4T65 trans. I am the only driver of the car which I have owned since new, the mileage is at 241,000. I have never replaced the transmission fluid. The car is mostly stock, and is in fair condition, and I plan to keep it running as long as it will go. The transmission shifts perfectly. I want to drain the trans fluid and put in new Dexron 3 fluid. But someone recently pointed out that on high mileage transmissions, one should not replace the fluid. I am not having a shop do this fluid change with a machine, I will replace the fluid on my own. So, I am being told that if I never changed the fluid in that many miles, doing so now could cause the transmission to start slipping. So, should I change the trans fluid or not?

[Tech II]

Good question.........

It's the old, damned if you do, or damned if you don't situation....

I have seen it go both ways, good and bad.....

at 241K, you are on borrowed time, as it is.......it's kind of amazing, that you haven't had problems thus far.....

[Stealthee]

I would personally not change it. I have been one of those people that changed the fluid on a high mileage car and had it fail within a few weeks. My problem was I was not the original owner and I didn't know the service history of the trans.

I decided to give it fresh fluid and a filter and one night a few weeks later it went bang as I was pulling away from a stop light.

The theory is unless you change the trans fluid on a regular interval that the clutch material build up in the fluid is essentially what is keeping the transmission working.

[GP4rsssfed]

Hence the reason I am asking is that I was told that if I changed the trans fluid, it was important to just drain out the old fluid and add new fluid. I was told to NOT take it to a repair shop that uses a flush system that forces out the old fluid and pumps in new fluid. According to some, it is the force of the transmission fluid from the flush "pump" that removes "clutch material", and the pressure of the new fluid forcing out the old fluid dislodges sensitive parts within the transmission. Some manufacturers, like Honda, now tell their car owners to not have a shop use a flush system.
Also, the reason I want to change out the trans fluid is that I have the car running in top shape, and unlike most high mileage cars in the rust belt, the underbody has very little rust, and where there is some rust, I am repairing with POR-15 to prevent further rust issues. The GP has been an everyday driver for the past few years (which makes it difficult to do some repairs that require parking it) and I have been driving as much as 25,000 miles per year or more. That's a lot of miles to put on a 14 year old car. I just want to be sure the transmission continues to perform as well as it has.

[Stealthee]

Yeah, when it happened to me I didn't flush either. And after thinking about it, it has actually happened to me twice. Change the fluid, and a few weeks later the trans goes bye bye.

[GP4rsssfed]

Thanks for the responses!
I currently own numerous Pontiac Grand Prix with the 3800 engine, and the 4T64E trans. In 2 previous GP's that I took to the salvage yard, I did have the transmission go out on them, but that was due to not having the proper modifications done to the transmission to handle increased engine horsepower. I did change out the tranny fluid on them, but that did not help in them failing.
Through the weekend, I have been gathering advice on what I should do. I plan on keeping this GP that I am using as a daily driver, as it has proven to be such a great car. It is also not rusted out like the majority of cars in the rust belt states. I can anticipate that I could go to 400-500,000 miles in this car, provided that I don't get into an accident with it.
One question I was asked by a neighbor who has been a GM mechanic for 30 years, is about the condition of the transmission fluid. It is brownish in color, not black. And it does not have a burnt smell to it. Also, the trans is not slipping. So, he advised to go ahead with a filter change and new fluid. He said it is likely the filter is clogged or nearly clogged, which of course is bad. He also advised to add a transmission fluid additive, like Lucas Stop Leak.
Other advice I received is to change out the fluid and the filter, and drive it a few thousand miles. Then drain everything and add new fluid and another new filter. This is to assure that the old fluid is gone.
Again, I would not even be concerned with doing any kind of transmission fluid change at this point, but I plan on keeping the car, and could possibly drive it a few hundred thousand miles.
So, I think I will change out the fluid and filter, and see what happens. If the new trans fluid causes the trans to start slipping, then I will be among many other owners who will warn that one should never replace the trans fluid in a high mileage car. Of course, I will drop the transmission if it does start slipping, and I will get it repaired.

[DrRadar]

I routinely add Lucas transmission additive when I change trans fluid, but I don't think it is called stop leak. I have a 99 gtp with 200k+ without transmission problems. Fluid and filter are changed somewhat routinely.

[GP4rsssfed]

Originally Posted by DrRadar

I routinely add Lucas transmission additive when I change trans fluid, but I don't think it is called stop leak. I have a 99 gtp with 200k+ without transmission problems. Fluid and filter are changed somewhat routinely.

You are correct. It is called Lucas Transmission Fix (stop slip) I was thinking of the Lucas "Stop Leak" for power steering systems.
As for my dilemma of getting the transmission fluid changed on my high mileage GP, I am not getting it flushed. I am removing the return line going into the transmission and getting most of the old fluid out that way. Then I am installing a new filter, then adding Dexron III transmission fluid, and then 1 or 2 bottles of Lucas transmission fix. I need to act as I am continuing to drive this old beast so many miles.
The old fluid does not smell burnt, and the transmission is not slipping. So, I have been told it is safe to change out the old fluid.
I will give updates as to how the transmission runs after I do this. Putting miles on it is no problem.
I had a 1997 GP that I changed the transmission fluid on it about every 60,000 miles or so (about every 2 years) And I ran 1 bottle of Lucas Transmission Fix in it. That transmission in that car lasted 170,000 miles with no problems whatsoever.

[Tech II]

I agree with Steelthee....leave it alone, based on the color of your fluid....

Hard to believe you have not had problems with this tranny not setting codes.

[richtazz]

Whatever you decide to do, do NOT do a full fluid exchange, unless you like rebuilding transmissions. Since your fluid is only brownish and doesn't smell burnt, you can probably get away with a filter change and only replacing the fluid that was drained from the pan. IMHO, it's a 50/50 deal. It may help stretch the longevity of trans, it could cause issues, your call. Good luck.