Hello everyone. I’ve got a 2015 Hyundai Sonata with 62,000 miles. After the car sits a while, the RPM shoots up real high and then goes back to normal while shifting from 2nd to 3rd gear. It only does it when it’s cold out, probably anything below 40F. The dealer recommended to change the transmission fluid. Could that make the issue worse? I don’t know I should do that because I don’t want to make it worse than it already is. Any recommendations? Thank you.
Changing the transmission fluid at 62K miles is not an outrageous thing to do, in fact it's normal maintenance.
Will it make things better or worse? Hard to say. If the fluid is maybe just a little bit dark-looking and not gritty it should be safe to change it. If black and gritty that friction is the only thing letting a worn trans operate at all and it should be left in. In any event best not to let them flush it, just drain and refill.
If you're very lucky there may be a TSB out with a fix though the dealer should have checked for that already. You might also ask in a Hyundai-specific forum where mechanics familiar with those cars may be hanging out. Here's one from 2017 found via an internet search to get you started:
https://www.hyundai-forums.com/threads/hyundai-dealer-technician-here.550425/
If the trans really is bad and you're the original owner it should be covered under Hyundai's infamous 10-year/100K-mile drivetrain warranty, though the dealer will probably do everything possible to weasel out of replacing it.
I'm frankly appalled at stories of early transmission failure which seem pretty common. A well-designed and built automatic transmission's life should be measured in decades and hundreds of thousands of miles.
Well it's worth to try but knowing those vehicles and transmissions probably starting to go out you're pretty junky transmissions as they age
