By on November 18, 2015


cvt. shutterstock user Pixel B

Steve writes:


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 [email protected]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.

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38 Comments on “Piston Slap: Less Octane = More CVT?...”

  • avatar

    I don’t believe for a second that it would make a bit of difference. Unless your wife is in the habit of always driving 100% of the time with the throttle pinned to the floor. Otherwise, you are rarely anywhere near peak torque, and any reduction in max torque caused by the lower octane fuel will be made up by pushing the throttle a little more to get the desired acceleration.

    Forums wildly exaggerate the frequency of issues. Nobody ever posts to say “hey, absolutely nothing is wrong with my car today”. Chances are, the overwhelming majority of these transmissions last a really long time, given a bit of care.

    • 0 avatar

      Agreed. Most of these components are designed against fatigue failures rather than any discrete overload. Since the endurance limit of the parts governs their lifespan, operation below certain limits simply doesn’t accumulate fatigue.

      My wife has a 2007 MINI with the CVT and 60,000 miles. Despite the internet forum horror stories, it’s been extremely reliable. The only problems we’ve had were the CVT acting up when the battery lost a cell and an early failure in one of the speed sensors. I hate the driving experience with that transmission and I think some of the German engineering solutions are stupid, but it’s been a reliable car.

      It’s probably noteworthy that neither of us are particularly aggressive drivers. It’s my opinion that smooth driving inputs and thoughtful operation extend useful component lifetimes for reasons I’ve explained above.

    • 0 avatar

      +2. How often do you even get the accelerator even halfway open in city driving, or for that matter, any kind of driving, especially in an automatic equipped car?

      • 0 avatar

        “How often do you even get the accelerator even halfway open”

        I’ve had several CVT-equipped rentals (i.e. Altima) where I had to start out by flooring the go-pedal out of the airport rental lot, just to get the car rolling.

        Once you get rolling then you ease up on the gas.

  • avatar

    He’s in your neighborhood, Sajeev, time to admit the error of your ways and sell him that oddball Sierra.

  • avatar

    Luck – in the 80’s about 5% of K-cars were as reliable as a Corolla.

  • avatar

    Using a lower octane fuel than specified only causes a power reduction when the engine load and temp are at that specific set of conditions that would cause detonation/ping, in which case the ECU will retard ignition timing a little more running lower octane fuel than it would have done running the higher octane fuel. Same for fuel economy. This information has been readily available for many many years, I don’t understand why it seems to be understood by so few.

    I did a semi-controlled experiment a few years ago where I ran recommended octane fuel for a year and then switched to lowest grade standard fuel for a year and compared fuel consumption (I record gallons and miles at every refill). Based on standard statistical tests, there was no difference ZERO NOTHING NADA. Only a sample size of one, but I believe my methodology was good.

    I don’t understand where you are coming up with statements like “using lower octane fuel reducing HP by 10% (or 7-8%)”. Are you just making this stuff up? Are there data somewhere?

    • 0 avatar
      heavy handle

      Low-octane fuel may well reduce max torque by 10%, but it’s not 10% across the board, just at maximum load. That’s not something you would notice in the city. You probably never use full throttle for more than a few seconds.

      Turf3, your experiment is interesting, but the conclusion may be valid only for your car and driving style. I’ve anecdotally observed 10% better mileage using high octane fuel in my Saab. I tend to drive that car at low revs/high loads, just because the turbo is so sweet in that range. It feels like you could climb Mount Everest in 5th gear just under 2000 rpm. That’s prime detonation range, so every bit of “octane” helps.

      • 0 avatar

        There are many variables. Each car is tuned a bit differently. Some are better tuned than others at excepting lower octane fuel. (Talking about premium required cars) I had an uphill spot on my test drive route that would cause Mercedes running 87 to ping just for a second. Thanks the mock sensors would retard the timing and all would be good again.

        • 0 avatar

          And most new cars nowadays have that electronic circuitry incorporated to monitor knock and ping and then dial back spark timing to compensate for lower-octane gasoline.

          All cars will run on 86-octane, even high-compression ones, some just better than others.

          In some places in the US you can’t get Premium 92 or Mid 89 gas, just 86-octane. There were times when we had to fill up our FFVs with the only gas available, 86-octane.

          It takes more pedal to make the car go — noticeable!

      • 0 avatar

        @Heavy Handle

        My experience exactly mirrors yours with Saabs and other cars. But as you say, it is the driving style that is exaggerating the effect. A turbo under heavy load at low rpm is the worst case scenario for knock. It is also a scenario that is almost impossible to achieve without a manual transmission, as an automatic will just downshift and shoot the revs up out of that range. With this driving style I tend to handily beat EPA estimates for my cars. It’s also why I largely feel that the EPA test advantage of current automatics is usually BS in the real world. Assuming reasonably similar overall gearing of course.

        I generally do what the manufacturer recommends as to octane, with one big exception. I run regular in my P38 Range Rover most of the time. Because I drive the old shed like Grandma Moses, so it is never under much of any load, and at 12-14mpg the cost savings is worth it. Premium does not result in a measurable increase in economy in that truck with my driving style. However, I DO fill it up with premium when I am towing with it.

    • 0 avatar

      What kind of card did you have at the time? I see a big improvement in fuel economy in my car with ethanol-free premium vs. regular (about 10-15%). I know the plural of “anecdote” ain’t “data”, but it’s proved to be true over the three years I’ve had this car so far. My guess is that turbocharged engines* like mine are a lot more sensitive to fuel quality than in normally aspirated engines.

      *Or, more likely, the knock sensors and engine management software in turbocharged engines…

      • 0 avatar

        2009 Volvo S60, low pressure turbo.

        If you are comparing ethanol-free premium against ethanol-containing regular, there is your fuel efficiency right there.

        It also makes me wonder whether a difference in ethanol content could be responsible for some of the premium vs. regular differences people believe they are seeing. Just because it says up to 10% ethanol doesn’t mean it contains exactly 10%.

        • 0 avatar

          I think you’re exactly right about the ethanol. I have a ’13 Escape with the 2.0 Ecoboost. I have not noticed any significant difference between E10 regular and premium fuels (even 93 octane) but a big difference with ethanol free 91 octane premium.

      • 0 avatar

        Ethanol is another matter than “low octane”; ethanol is a less energy-dense fuel (in addition to being an octane booster).

        Fuel quality isn’t even the issue there – it’s just “there’s more energy in a gallon of straight gas than in 10% ethanol”.

  • avatar

    I’d just like to say that the Mini I got as a rental to drive to Cincinnati last winter for work was hands down the worst new car I’ve driven in recent memory. I’d vastly prefer the base model Lancer or a Versa. My coworker and I felt like bears in the circus sitting side by side in that thing. Maybe in “S” trim with a manual transmission and on twisty roads I’d think very differently. But for everyday use it is horrible.

  • avatar

    I am also of the opinion that low octane fuel use under normal conditions, in most cars, probably has minimal, to no effect on torque OR horsepower. I will concede that my old Volvo seems to run better on 93 octane, and my late, lamented MB 420SEL ran like a different car on low octane fuel. On the subject of the MINI, I hate rubbing elbows with my passenger, and the damn things are just too narrow for me. As silly as I’d feel in a VW Beetle, at least the cabin is fairly wide.

  • avatar
    Pesky Varmint

    I have four side-by-side ATV’s (aka UTV’s) with CVT’s. Even worked on the clutch and belts in one. They do ok in those low powered, light vehicles.

    And if the CVT’s they put in cars )like the Dodge Caliber that we gave away because it was so hopeless) were put in these UTV’s they’d probably last forever.

    I will never buy another car/truck with a CVT. Only mechanical problem I could
    never solve by myself without spending gobs of money with little guarantee of success.

  • avatar

    I think the longevity and amount of issues has as much to do with driving habits than actual defects. Also, how often has the transmission fluid been changed? Once? Every 30k miles? Or are you holding out hope that it really is a “lifetime” fluid made of liquid duranium?

  • avatar

    Having driven a Mini of that era/spec, I distinctly recall low speed creeping being the biggest challenge for that powertrain. I doubt max power has anything to do with longevity here as everyone mentioned you don’t use it. Normal load and parking lot/traffic creeping with the bigger challenge.

    If you know its about to go…. sell it while it’s good.

  • avatar

    I don’t think I could look at such an awful mess of plastic interior every day while commuting in something CVT and with ~100hp. Have to give me some crazy pills.

  • avatar

    Sometimes I also wonder how many cars are specified premium fuel from the manufacturer when they don’t really need it. Some engines just aren’t that “picky,” methinks. The GM 4.9 wouldn’t seem that picky, for example. Even after I cleaned the intake manifold of all the carbon, spraying some MAF cleaner in there in the process.

    My dad says, “You’re gonna have a hard time starting it, might take a minute to get it going.” And I recall having that issue after performing the same cleaning on my Audi.

    It started right up as normal with no hesitation.

  • avatar

    Using regular gas she has a better chance of burning an exhaust valve (I speak from experience) than prolonging the life of her CVT. These CVT’s do OK when the fluid is changed regularly- if you’ve ever cracked the manual you’ll notice that the recommended change interval is 25k. If you haven’t had it changed go do it not and make sure they use approved CVT fluid- Redline CVT fluid is supposedly an improvement on the Esso fluid it came with. If it does crap out, I’ll take it off of your hands as a father son project- please don’t send it to the crusher!

  • avatar

    I’m going to agree with Sajeev on this matter; by not stressing the components, they simply will last longer. It becomes a matter of individual choice.

    As far as the argument about octane, here I will argue from personal experience with not one, but THREE different vehicles where a change of just two octane points makes a very visible difference long-term. But again, it’s a matter of personal preference because with the wide difference between Regular and Premium in price, any improved fuel mileage is eaten by the higher cost of the fuel. On the other hand, vehicle performance becomes very noticeably better as you use a higher-octane fuel. Of course, with better performance you also stress the components more and you can reach a point of negative returns in terms of reliability. Again, it’s a matter of balance.

    I also agree with Sajeev about the “crusher”. By no means should you junk the car when the CVT fails if the rest of the car is in good condition. That’s just waste. Personally I’m no fan of the Mini itself due to its high retail price–especially when you can get similar performance and fun factor out of a car sold at half the price from Fiat. Certainly the Fiat 500’s reliability is no worse than the Mini–perhaps better–and I have to admit I don’t know how much repairs will cost as I’ve not spent a penny on repairs on my Fiat 500–not even in fuel to take in in for warranty; I’ve not needed any repairs since I bought it (and moreover, it’s a former rental car so according to SOME who have written for TTAC it should be in sorry shape.) Mini is a car in demand however; so if it’s in any kind of decent condition, you could probably get quite a bit over his suggested $1K for it.

    • 0 avatar

      “I will argue from personal experience with not one, but THREE different vehicles where a change of just two octane points makes a very visible difference”

      I agree. And especially so if a person lives and drives in mountainous terrain.

      Running 86-octane in even my most-modest 2.5L 1989 Camry V6 results in severe loss of power, but it will run, with a lot more pedal required just to make it roll.

  • avatar

    Assuming that you haven’t abused it, the transmission will endure or fail based largely upon luck and its ability to operate in the conditions in which it needs to operate. My guess is that your wife has less of a lead foot than the average bulletin board enthusiast and therefore **may** be more likely to have better luck.

    In any case, the message boards should not be taken literally. You would need to have a pool of reliability data in order to estimate useful life with any accuracy, and even then you will have your own unique result that could fall at either end of the bell curve. You can probably combine those boards with surveys such as Ccnsumer Reports to know what the problem areas are, but not to predict exactly how many miles to expect from yours.

  • avatar

    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.

  • avatar

    Don’t know any specifics, but here’s a site with a lot of info:

    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.

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