Replacing the ATF on my 2005 Sonata V6 for the first time

Hyundai says in the service manual to drain the automatic transmission fluid of the car with the engine running!

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ATF change

Since we're on a mission to change every fluid in the car, the Automatic Transmission Fluid (ATF) is a prime candidate. I was sure it'd never been changed in the lifetime of this car. I was really looking forward to seeing the AT oil filter changed, too. The dipstick showed a fluid level much higher than the recommended volume - this means that the fluid has been topped off or replaced at least once.

Draining the ATF isn't a tricky process but it sure is cumbersome, as you're going to change less than half the fluid in the system if you drain it the way you'd drain engine oil (i.e. by opening the drain plug at the bottom).

I read the section for ATF changes in the service manual of the car, and Hyundai recommends that you do it with the engine running! It was quite unorthodox for me, given that all the ATF changes I've seen on YouTube do it the drain plug way.

The process involves disconnecting the oil cooler hose for the trans and running the engine with the gearbox in [N]. Hyundai says the engine should be run for a max of 1 minute or until the oil stops flowing. I assisted my mechanic and timed it to run for 1 minute.

We drained a good amount of ATF this way. I'll know the exact figure tomorrow but it's over 4L for sure, so more than half the fluid in the system:

The oil itself was dark and cloudy but that's to be expected. Hyundai states that this is normal and shouldn't be cause for concern as long as it doesn't look or smell obviously burnt.

The drain plug was removed after this procedure to remove whatever remains. It contained some fine dirt (paste?) but all of that is very much normal. I was relieved to see a total absence of any metal shavings or particles! This old trans is A-OK.

You can't change the filter!

Videos of AT oil filter changes for the Sonata are impossible to come by - they just don't exist. I was wondering why because some videos mentioned dropping the oil pan from the bottom of the trans and just replacing the filter. Turns out there is no oil pan on the bottom of the car! It faces the front, located behind the radiator. But the filter itself is still on the bottom of the car! This 3-minute video explains.

I was reading through the service manual for instructions on how to change the AT oil filter and I came across this TSB (Technical Service Bulletin) that cleared the matter right up.

You cannot change the oil filter!

I've wasted ₹4-5k in actually buying two filters when I can't use even one. This is a very poor design decision from Hyundai (even my mechanic said he liked these old cars but this is an obvious gaffe).

Oh well. AT filters don't undergo the same loads that engine oil filters do, so this will mostly not be a problem, but I would have loved to get in there and replace the oil filter with a fresh new one.

Until next time...

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