Piston Slap: Less Octane = More CVT?

Sajeev Mehta
by Sajeev Mehta

Steve writes:

Sajeev,

My wife drives a first-generation R50 Mini base model with the dreaded CVT. This is a transmission widely reported (read: complained about on message boards) to not last well beyond 75,000 city miles. Hers is just now clearing 80,000 and it shows no signs of early struggles, even under the hellish torment of stop-and-go traffic in Houston temperatures.

Perhaps coincidentally, my wife has never put premium fuel in this car, despite it being a requirement. Premium fuel would supposedly generate 114 horsepower; without premium fuel, I would guess 7-9% lower, at, say, 105 horsepower. It is a slow car no matter what, but at least it makes up for it in urban maneuverability.

Nevermind what this is gradually doing to her engine (I’ve never tested out whether we’d get better fuel economy and save with premium fuel), is it possible that her derated engine is saving her transmission? Less power through the transmission means less heat, so we can get more miles out of the CVT, right?

Once that CVT goes, it’s crusher time, unless batteries and electric motors suddenly go on a huge sale.

Sajeev answers:

Crusher time? You and I know that Houston has so much wealth/prosperity there’s a market for your MINI. Put it on Craigslist for $1,000 with a hurt gearbox and it’ll be sold in less than a week.

That said, I reckon you’re right about low octane fuel being a (not the) reason why your CVT fares better than average. CVTs, like any moving part in a vehicle’s powertrain, like any fastener installed to a torque specification, is rated to a specific torque limit. If only we knew the MINI CVT torque limit!

Not that the MINI is a torque monster, but if your wife keeps the revs low (read the multiple comments from “simbasat” on this thread), if switching to regular fuel lowers torque from 110 lb·ft to about 10% less (let’s say it’s an even 100), then yes, she’s effectively given the CVT a longer life.

By how long is hard to know. Perhaps I can interest you in a Mercury Grand Marquis while we ponder?

[Image: Shutterstock user Pixel B]

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.

Sajeev Mehta
Sajeev Mehta

More by Sajeev Mehta

Comments
Join the conversation
2 of 38 comments
  • Dal20402 Dal20402 on Nov 18, 2015

    Houston city driving is not the harshest in the world on cars. Blocks are very long, even city trips use substantial amounts of freeway, and so there are fewer stop/start cycles than you would have in a coastal city. I think 75,000 miles in Houston probably is equal to 30,000 miles in New York, Boston, or Baltimore.

  • Indi500fan Indi500fan on Nov 18, 2015

    Don't know any specifics, but here's a site with a lot of info: http://www.minicoopercvttransmissionrebuild.com/ Rebuilt transmissions are 3500 bucks (plus $500 core) on eBay so they obviously are priced at German levels. Compare with a GM 4L60 or Ford AOD for about a grand.

  • CanadaCraig You can just imagine how quickly the tires are going to wear out on a 5,800 lbs AWD 2024 Dodge Charger.
  • Luke42 I tried FSD for a month in December 2022 on my Model Y and wasn’t impressed.The building-blocks were amazing but sum of the all of those amazing parts was about as useful as Honda Sensing in terms of reducing the driver’s workload.I have a list of fixes I need to see in Autopilot before I blow another $200 renting FSD. But I will try it for free for a month.I would love it if FSD v12 lived up to the hype and my mind were changed. But I have no reason to believe I might be wrong at this point, based on the reviews I’ve read so far. [shrug]. I’m sure I’ll have more to say about it once I get to test it.
  • FormerFF We bought three new and one used car last year, so we won't be visiting any showrooms this year unless a meteor hits one of them. Sorry to hear that Mini has terminated the manual transmission, a Mini could be a fun car to drive with a stick.It appears that 2025 is going to see a significant decrease in the number of models that can be had with a stick. The used car we bought is a Mk 7 GTI with a six speed manual, and my younger daughter and I are enjoying it quite a lot. We'll be hanging on to it for many years.
  • Oberkanone Where is the value here? Magna is assembling the vehicles. The IP is not novel. Just buy the IP at bankruptcy stage for next to nothing.
  • Jalop1991 what, no Turbo trim?
Next