Transmission flush, or drain and refill?

drain all the fluid from the transmission.

Chrysler products, I am hoping to avoid problems with my Sonata by keeping the fluid fresh.

I'd do what the manual tells you to do and at that mileage too.

I've only ever had a problem with one auto tranny in 50 years of driving. It is also the only tranny I ever changed fluid in.

The engineers at Hyundai tell you what to do to maintain the warranty and keep your vehicle running well. The dealer is looking at making the best profit.

Which is preferred?

The dealer can do a "flush" with the correct SP-III fluid for $159.

The other option is to just do a drain and refill. This of course, does not drain all the fluid from the transmission.

After going through the well-known transmission problems with my 1990's Chrysler products, I am hoping to avoid problems with my Sonata by keeping the fluid fresh.

Thanks,

KM Honda recommends a drain and fluid replacement -- not a flush. I suspect Hyundai is the same.

Thanks for the responses. The recommend fluid change is at 105,000 miles for "normal" use, and 30,000 for "severe" use.

I know that with a regular drain, some fluid remains in the transmission. Maybe this is not an issue with modern synthetic fluids.

KM

"normal" use, and 30,000 for "severe" use.

this is not an issue with modern synthetic fluids.

Even though some oil remains, the dilution with new oil makes it insignificant. Severe use includes trailer towing and very high temperatures that most of us never see.

Other than additional cost is there any disadvantage to flushing the transmission?

On this car, no. Some cars have a filter, and this service would have the disadvantage that it does not replace the filter.