Tesla Large Drive Unit

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What Fails?

This drive unit is the primary motor in the Model S and X, RWD and Performance, made before 2020. It suffers from two design flaws, one of which affects all units, the other of which only affects early units. The motor is cooled by the same liquid which cools the battery and other vehicle systems. The coolant flows through the rotating part of the motor, which is sealed by a single mechanical seal. This seal, found on all units, will fail, leading to coolant leaking into the motor causing destruction of bearings, damage to the electronics, and damage to the motor's electrical insulation. The only motors to which this failure will not occur, are recent Revision U motors (~2023 and newer replacements from Tesla), and those that have been retrofitted by a 3rd party.

The other design flaw, affecting only early motors, is the all metal rotor bearings. The energy generated by the motor can cause these bearings to arc and pit, which can lead to failure of the motor. This issue is not as common as the coolant seal failure, but it is still a concern for early units. This failure also causes the motor to produce a sound often described as “howling” or “grinding”. These motors can be retrofitted with ceramic bearings, standard on all motors from 2016 onward, which permanently solves this issue.

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What To Do About It?

If you are still within the 8 year battery and powertrain warranty, you will be covered if this failure occurs. The motor that Tesla replaces it with will be a Revision U motor, which has a different design and is not prone to the same failure. If you are out of warranty, or if you have a motor that has been replaced, with a non Revision U motor, you will need to take action to prevent the failure from occuring.

The first step is to check your service history, if available, to see if you can determine if your motor has been replaced, or serviced by a 3rd party. While there are very few of the original motors still on the road, the majority of replacement units are not Revision U, and are still susceptible to the coolant seal failure. Motors manufactured before mid 2016 are also likely to have the all metal bearings, which are prone to failure and should be replaced with ceramic bearings.

For most owners, the best course of action is to perform the coolant delete which completely removes the rotor cooling channel, while leaving all other cooling systems intact. This is functionally identical to the Revision U motors supplied by Tesla and is a permanent fix to the coolant seal failure. If your primary use for the car for racing or towing there are high performance seals available, however these require machine work to install and may still require replacement in the future. A coolant delete is usually the best option for normal driving in North America.

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Who Can Do The Work?

Tesla does not offer a fix for the coolant seal failure and will only replace the motor if paid out of pocket, or after the motor has catastrophically failed within warranty. There are several qualified 3rd party shops that can do the work located around the country. Even with the cost of shipping a complete car, it is almost always more affordable than Tesla's replacement cost. While it is possible to DIY this repair, it is very difficult to access the drive unit without heavy lifting equipment. There is both mechanical and eletronics complexity to the repair and it is not recommended for the average owner to attempt. If you have experience in both vehicle repair and electronics and are interested in doing the work yourself, the following guide will be helpful.

Tesla Large Drive Unit Rebuilding Website

A qualified shop who performs this service properly will remove the motor from the vehicle, perform the coolant delete, and replace any another other components that are prone to failure or have been damaged by the coolant leak. Most motors on the road have some degree of coolant ingress and will require some level of repair beyond just the coolant delete. This is why a "No Drop" coolant delete is not recommended, as it does not address the other issues that are likely to be present among other issues. There are multiple methods that are effective and proven such as the cap method, and aftermarket machined manifolds.

List of Qualified Repair Shops

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What Happens If You Don't Have It Fixed?

If you have one of these motors that has not been repaired or recently replaced, it is only a matter of time before problems caused by the coolant seal failure cause the motor to fail. An un-retrofitted motor will typically ends its life in one of three ways:

Each of these failures will render the car un-driveable. In most cases the failure will cause the main high voltage battery to remain disconnected from the rest of the car because of the electrical conditions in the motor. This will kill the 12V battery and prevent the car from starting or from running many of the accessories. The vehicle will have to be towed to a shop for motor repair or replacement. Tesla does not perform repairs on the motors, only replacements, which typically cost $8,000 or more. Independent shops can sometimes repair the motors after they have been flooded, but this is not always possible and will cost significantly more than a coolant delete. If you have a large drive unit, it is highly recommended to have the coolant delete performed as soon as possible.

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