Piston Slap: Sealed for an Infinite Life?

Sajeev,

Thank you and the rest of the TTAC staff for providing the community with an entertaining and genuinely informative automotive website. I’m a long-time reader, and hope you can answer some questions I had about my wife’s 2009 G37 S 7AT.

We purchased the car new in 2009 and love it. It’s paid off and we see no reason to replace it anytime in the foreseeable future. It’s a keeper.

We carpool and thus only have accumulated 29,xxx miles in the years we’ve owned it. I try to be diligent with my vehicle servicing, and prefer to do my own maintenance. When preparing for the upcoming 30,000 mile service, I noticed something peculiar in the maintenance schedule provided by Infiniti:

‘Replace automatic transmission fluid(except 7 speed automatic transmission).’

Even more curious, the 7 speed automatic is not recommended for servicing at any point in the published maintenance schedule (which terminates at 120,000 miles). I’ve always thought 30,000-40,000 mile transmission services were optimal. There is no dip-stick, which I know is becoming more typical of luxury cars, so I can’t visually assess the condition of the fluid. Visiting some Infiniti forums reveals the transmission is effectively sealed to shade tree mechanics, and requires a visit to the dealership if you’re inclined to have it serviced.

I’d love your insight. I know there is no such thing as transmission fluid that never needs changed. I know any dealership I call will disagree with the literature and recommend it needs changed as frequently as I can afford it(~$350 for a flush and fill at the local dealership). What I don’t know is: When does this fluid really need changed, and why is Infiniti keeping it a secret?

Sajeev answers:

The 7-speed Infiniti angle adds a new twist to one of the quandaries that’s been around since the early days of the Piston Slap series. My first recollection of these “sealed for life” automatic transmissions was the 1997 Chevy Malibu, and the universal truth hasn’t really changed: change the ATF at regular intervals (being vague for a reason) and make sure to use the correct fluid.

Why be vague? Because while most folks wouldn’t go past 100k-150k on transmission fluid if they knew the benefits–and if they kept a car that long–the actual life of transmission fluid varies by owner. If you carry/tow heavy loads in a minivan that idles in traffic to and from school/work in brutally hot weather, consider a more aggressive ATF replacement schedule. But if you are one person traveling mostly rural highways in cooler parts of the country, you may never need to change the fluid at all. (slight exaggeration)

So what’s the right move for you?

The path of least resistance is to visit the dealer and have them do the deed, perhaps every 75k or 100k. Which isn’t a bad idea, and considering your low mileage…when will you reach 100,000 miles? So don’t sweat it!

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.