Tesla Model S lithium-ion battery pack in rolling chassis [photo: Martin Gillet via Flickr]
With almost 100,000 on the world's roads, the Tesla Model S electric car is a remarkable achievement.
It remains the longest-range electric car in volume production more than three years after it launched.
But reliability issues with electric traction motors in early cars--those from the 2012 and 2013 model years--have dogged the earliest owners.
Now, a new analysis of data provided to Plug-In America by 327 owners of early Tesla Model S cars suggests that as many as two-thirds of those early Model S drivetrains will need to be replaced within 60,000 miles.
[EDITOR'S NOTE: The title of this article originally said that two-thirds of the drivetrains would "fail" by 60,000 miles. As several readers pointed out, that's not quite accurate; Tesla's policy is to replace them when they begin to make noise, without waiting for them actually to fail mechanically. To make the title more accurate, we reworded it to say they will "need replacement," to match the sentence above more closely.]
This analysis has not been publicly disclosed before now. Before publishing this story, Green Car Reports asked several specific questions of Tesla Motors to help put the analysis in context.
Tesla declined to answer those questions. Instead, it issued general statements about its reliability. Both the questions and its statement are at the end of the article.
2013 Tesla Model S owned by David Noland, Catskill Mountains, NY, Oct 2015
Reliability: really a liability?
Since Consumer Reports dropped the Tesla Model S from its list of recommended buys due to a "worse-than-average overall problem rate", the barbs between the company's supporters and detractors have only sharpened.
At issue is the significance, if any, of Consumer Reports' findings. Given that Mercedes-Benz--another highly successful luxury brand--also gets a worse-than-average rating, does it really matter? And should one also consider TrueDelta's more pessimistic assessment?
Do a drive experience rated at "103 out of 100" points and 97-percent customer satisfaction mean Tesla has little to worry about? Or do lengthening waiting times at service centers foreshadow a fall in customer loyalty and brand prestige?
Without the proper context, it all reduces to an electric-vehicle version of the fable about the blind men and the elephant.
But there's a trove of statistics that can contribute to the conversation. And a Weibull analysis of that data suggests that two-thirds of early (2012 and 2013) Model S cars can expect a drivetrain failure within 60,000 miles.
Tesla Model S electric motor and drive unit [photo posted by user Tam to Tesla Motors forum]
Clearly, Tesla's eight-year warranty coverage on the drivetrain protects new and used buyers. And the company has said several times that it has made great leaps in quality as it gains experience in building the car.
Tesla's November update said the company has cut its failure rates by half, while CEO Elon Musk has expressed strong confidence in the improved drivetrains it has been shipping in recent months.
But the data set used to analyze drivetrain reliability includes about 10 times as many early (2012 and 2013) cars as recent ones from the 2014 and 2015 model years.
If enough recent buyers add their information, we may be able to improve the analysis and get statistical backup for the trend of improved reliability Tesla has mentioned.