Sealed for life transmissions: an epic fail coming your way

The logical fallacy of ‘sealed for life’ transmissions' means you should change the oil anyway: that’s right, they’re bullshit…

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‘Sealed for life’ transmissions are bullshit; the name is anyway.

At best they are a self-fulfilling prophesy, and at worst an extremely cynical way for a carmaker to engineer-in some epic, deal-breaking major failures, which really need not occur that early.

Here’s a sample of what I’ve received lately from you on this issue and before you get carried away, no, I’m not isolating Subaru here, because they’re not the only ones.

I’m focussed on the entirely stupid prospect of sealing a transmission for life and calling it thus.

I have a 2012 Subaru with CVT, and whilst it has been flawless Subaru do not (sic) give a service interval for the transmission. 

They essentially say its (sic) "lifetime". This concerns me as they don't state what the lifetime should be. What are your thoughts on the lack of service interval with the Subaru's CVT?

-Alan Featherstone

Alan is speaking about the Subaru CVT specifically, but I don’t consider this to be a special case. I’m essentially calling bullshit on all ‘sealed for life’ transmissions - autos, CVTs, DCTs, whatever. Sealing a transmission for life is bullshit.

CVT oil, of course, does a vastly different job than oil in an auto transmission or a DCT. All oil in all transmissions is designed to stop the precision metal parts from touching, because the oil film is very tough when it’s very thin. It’s also sometimes a heat transfer medium.

But in a CVT the oil carries the additional onerous burden of directly transmitting the drive from the input shaft to the output shaft by carrying that drive as shear in the thin film that keeps the belt between the two shafts off the variable pulleys.

If you don’t know what a CVT is, brush up here before continuing >>

And if you do know what a CVT is, but can’t decide between it or a dual-clutch transmission, here’s some guidance >>

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Top cog

In all transmissions, this ‘sealed for life’ business is simply disingenuous carmaker bullshit. If you ask them what ‘life’ actually means, as in: ‘What is the life of the transmission?’ They’ll stare blankly at the floor for a while and retort: ‘As long as it lasts.’

Which is meaningless. Because if the oil wears out, becomes ineffective and kills the transmission earlier than it otherwise might have, then there’s your self-fulfilling prophesy. It was ‘sealed for life’ - but that’s hardly a win for the good guys, I think you’d agree.

For a carmaker it’s probably good enough for the transmission to last the length of the powertrain warranty in the big overseas markets. So, up to five years and 160,000 kilometres, broadly. But you’d probably want your transmission to go longer than that if possible. Especially given the cost of a rebuild or replacement, versus the value of the car at that point.

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Heat is work

So here’s the thing: ‘sealed’ really just means: no dipstick, and maybe no drain plug - and maybe a lot of complexity if you want to change the fluid in a modern car.

You might easily need a scan tool and you might need to follow a convoluted fluid replacement protocol. So it’s pretty safe to say it’s not a backyard job any more.

Gone are the days of pulling out the 13mm socket, driptray on standby and precariously trying to catch the drain plug before it drops in the oil, forced out by an impending torrent of murky old tranny lube - those were the days.

Shitsville tends to be rather a hot place, like, it’s gunna be 40 degrees here today, in the Fat Cave, and although synthetic fluids are durable, they are broken down by heat - and the hotter the transmission fluid gets, the more accelerated and the more severe the degradation of the fluid.

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Conclusion

So, if you buy a new car every three to five years, and you’re an average driver, transmission fluid changes are not going to be a factor in your vehicle servicing.

But if you buy used cars, or if you buy a new car with the plan being to own it for years and years, you will want to change the transmission fluid. Even if it’s so-called ‘sealed’.

Even if there’s no transmission service schedule with your car, officially, I really think 100,000 kilometres (60,000 miles - ‘Murica). That’s a rational interval, given the durability of modern synthetic fluids. But if you do a lot of heavy towing, you might want to do it every 60,000 kays.

Pretty important to get the particular grade of oil right, too, because we’re talking microns in the tolerance domain - metallurgy has to be separated by the absolute ‘Goldilocks’ lubricating film thickness, in a modern transmission.

For average drivers in Australia, 100,000 kays is about six or seven years, and yes, it is an additional servicing expense, but if it saves you a four- or five-figure replacement bill, it’s probably well worth it.

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