When is it too late to change automatic transmission fluid?

I've heard that once you reach a certain mileage, it is better to keep
the original transmission fluid instead of changing it.. Is this true?
If so, when is it "too late" to change the auto transmission fluid?
(in relation to what's best for the engine, not warranty)

I ask because I recently changed the fluid for the first time on my
78,000 mile Sonata (2000, V6). Before the change, the car was getting
stuck in gear, not shifting well, and the crank sensor code came up
during a scan. Now, it doesn't even start. I've ordered a new crank
sensor and really hope that changing the tranny fluid didn't screw up
the engine beyond the damage that was already there...

...Thanks you.

 

Changing the transmission fluid cannot affect the engine. The problems
are most likely unrelated, unless they're electrical. The engine and
trainsmission are both computer controlled and could malfunction due to
voltage irregularities and/or bad connections.

 

Changing the transmission fluid cannot affect the engine. The problems

Right. What I meant was: How does changing the transmission fluid at a
late stage (in my case at nearly 80,000 mi) affect the transmission
itself?

.... I've heard that doing this dislodges dirt and can be worse than
keeping the original fluid, but would like to hear from people who have
experience with engines and Hyundai's in particular.

Sorry for the misstatement though- I understand what you're saying but
it's a bit different than what I was thinking of in my post.


Best,
Dmitry

 

You never really know it was too late until you find out the hard way.
Realistically speaking, though, you've only provided an acceleration to a
trans failure which was going to happen anyway.

 

Wow.

...... so you're telling me the mechanic at my dealership had me
"accelerate" a trans failure by advising a fluid change?

I really, really hope that the reason my car isn't starting is the
busted crank sensor.

Hyundaitech- your post scares the crap out of me, and if you're right
then I will go absolutely crazy on the guy who told my to do this, esp
if a new trans is not covered by warranty.

best,
dmitry

 

Well, I think you're looking at it incorrectly. By your own admission, the
transmission was already not operating properly. If your fluid was in poor
condition, changing it could have very well have had the opposite effect of
helping the situation. The real acceleration of trans failure came when
the car was driven 78k without changing the fluid.

 

Interesting (to me). My 1990 (bought new then) Excel GL with 110 thousand
miles, still with the original transmission fluid (check levels but never
added or replaced) operates perfectly. I wonder if it's because I let the
dirt stay in there and don't disturb it. :O)

-- Throttle Vamp

 

Old wives tale. Keeping bad fluid in there is never a good thing.

The tranny fluid certainly didn't hurt the engine. Something else is
wrong, probably that sensor.

John