Why not to replace ATF with high mileage

[Roger]

Forgive me if this has been posted before. But this is the first time I've actually read of a plausible explanation for why people experience problems when they change the ATF for the very first time in a car with very high mileage.

trustmymechanic.com article

Author claims the accumulated grit in the fluid actually compensates for the worn out fluid by supplying the friction needs of the tranny. I've never heard that one before, but strikes me as somewhat logical.

 

[Quest]

Another urban myth on the internet (EOS, or End of Story)

 

[Roger]

Okay, so why then do people continue to relate personal testimonials about tranny breakdowns after replacing ATF for the 1st time in HM vehicles?

 

[Kestas]

Because they only tell part of the story.

Typically, the owner notices a hiccup with his neglected transmission. His local car-guy-friend tells him to replace the fluid with hopes that this would cure the problem. Shortly after changing fluid the transmission takes a dump. (Sometimes this is because the new fluid cleans the "false seal" produced by deposits in the transmission.) So now this moron who neglected his transmission broadcasts to everyone that the fluid change killed his transmission, and that nobody should change fluid on a migh mileage transmission, ignoring the fact that his transmission was on its way out anyhow.

Stop listening to these myths and change the fluid. Old fluid cannot be good.

 

[Quest]

It's just urban myth my friend. While I wouldn't doubt that some 30 yrs or so back then this trick "may work" somewhat with the older AT design (still no proper merits to back up),try that on some new cars designed/released during the past 10 years or less and you'll be up for a serious repair for not only the aged ATFs deterioriates due thermal cycles, additive depletions, etc. but also lots of friction materials in-suspension that will clog those critical valvings common to modern electronically controlled AT designs causing overall drivability and shifting problems. Flushing the trannie to rid of all the crud and replace it with fresh new fluid makes a whole world of difference in ensuring proper transmission performance and longevity, and this should be treated as part of a maintenance schedule.

While I do not stop people from preaching this very same old tricks to the grand public, truth of the matter is, modern electronically-controlled AT gearboxes are quite expensive to fix than those some 30+ yrs ago and can be quite tempremental when the fluid starting to show it's age esp. with a relatively smaller sump.

Same with old hat tricks such as running ATF in engine to "flush", etc., they do not lend any merits in resolving the situation.

What else can I think of, oh yes! Those domestic vehicles up until the 80s, they have their brake booster reservoir sealed with a rubber diaphram and most mechs claimed that there is never a need for brake fluid replacement/purge/flush for as long as you own the vehicle.Truth is, moisture still seeps in from the other end of the brake cylinder/caliper piston seals to deterioriate the brake fluid. I would absolutely refused to drive those vehicles unless the brake has been regularly flushed with fresh fluid and purged properly.

 

[Colt45ws]

When I had the fluid changed at the dealer on my car, the fluid was scary, lol. It was clear with lots of black and metal particles. That was 10k mi ago. I think if it was going to die from a fluid change, it would have done so a long time ago. On the other hand, Im sure it would be dead by now if I left it alone.

 

[T-Keith]

That's the same tale I've heard before. The only credible defense I've seen is that the dirt loosened up will clog small passages. However, the fluid must first go through the filter first. BUT, anything in the cooler lines gets a direct trip to the tranny because it's after the filter. The solution is simple, drain and flush the cooler as well as dropping the pan. If it's really bad, I do both in short succession.

I have never had a problem after changing ATF in any high mileage vehicle and I do it to every one I've owned.

My 88 had 210,000 miles, black fluid that was below the dipstick. The first thing I did was to change the fluid as described above. After some AutoRX I changed it twice and haven't had a problem since. I have put 50,000+ miles on since then.

 

[benjamming]

I would add to Kestas' post that if the a/t has a serviceable filter, it might not get replaced when the factory fluid is replaced for the first time in a long time leading to more problems and blame falling on the fluid.

 

[ekrampitzjr]

Depending on how the fluid was changed, it could dislodge particles from the filter to create havoc, especially with the newer shortcut methods of changing fluid that do not include actually dropping the pan and changing the filter. The Amsoil website has a highly informative warning on this.