Tesla Large Drive Units are known for their durable design, enabling them to operate at high loads for many years and cover hundreds of thousands of miles. However, there is one design flaw identified by engineers: the cooling system, specifically the main rotor seal. Over time, this seal can wear out and start leaking coolant into the motor.

The ceramic rotor bearings typically suffer first; the coolant washes out the lubricant, causing the bearings to produce a whistling sound that increases during acceleration. This sound is easily distinguishable from the normal motor noise, indicating that your drive unit requires service.

In later stages, coolant can ingress into the Stator, causing insulation issues, potentially resulting in a short circuit. In this case, you may see warning messages on your Tesla screen indicating reduced external insulation, decreased power, and that the vehicle may not restart. You will notice a reduction in both power and speed.

**Attention!** If this situation has already occurred, we strongly advise against continuing to drive the car, as it is critical. The vehicle may shut down while driving, posing a serious safety risk.

First, we conduct a thorough diagnosis by opening the motor. Our technicians inspect the insulation resistance of the stator, assess the inverter's control circuit, and evaluate the condition of the bearings. If coolant issues are identified early, cleaning the stator and replacing the bearings is typically sufficient. Notably, we replace bearings in 100% of cases, as most motors have already endured between 50,000 to 100,000 miles or more, leading to natural wear — even aside from any damage caused by coolant exposure. It's also important to note that many Tesla owners mistakenly believe their motors do not require regular maintenance, such as oil changes, which is not the case.

If the stator insulation resistance measures below 5 mΩ — an issue encountered in 90% of cases as customers typically seek service when their vehicle experiences power limitations or stops moving entirely — it indicates that the coolant has infiltrated the stator. In such situations, stator cleaning up is necessary, which can be a complex and time-consuming process. We immerse the stator in 99.9% ethanol for 5 to 10 days to clean it thoroughly, followed by a 2-3 day drying process. If the insulation resistance does not rise to the required minimum after this treatment, we repeat the procedure. In some cases, this method may not yield satisfactory results, resulting in the need for stator replacement.

In the later stages of coolant intrusion, it can also enter the inverter. Although the PCB boards are insulated and not directly affected, the connectors can still allow for leakage, necessitating thorough cleaning. In more severe cases, some connectors may be destroyed, requiring restoration of the inverter board through replacing or resoldering the connectors. If the components responsible for the operational logic on the PCB control boards are damaged, they typically need to be replaced entirely.

The last issue, which is relatively rare but can occur — especially in Performance car motors — is the wear of the gear teeth on the rotor. Interestingly, this problem can also arise from coolant leaks. The coolant can wash away the special lubricant that manufacturers apply at the connection point of the half shafts to minimize friction. As a result, even sturdy metal components can get damaged; the teeth wear down and may begin to spin without effectively transferring revolutions to the wheels. Unfortunately, this issue is irreparable, and both the gearbox and motor rotor must be replaced.

The final stage of the repair involves installing a special coolant manifold instead of the standard rotor seal. Many customers are aware of this part and believe that it can resolve any existing coolant leakage issues. Unfortunately, this is a misconception. While the manifold effectively prevents future coolant leaks, it cannot reverse the damage caused by previous leaks. It does not restore worn bearings or clean the stator and inverter. However, installing the manifold is still an essential part of the repair process, as it ensures that coolant cannot re-enter the motor once fitted.

Rebuilding an LDU is generally more reliable than purchasing a used one, which can cost between $2,500 and $4,000. The condition of a pre-owned drive unit is often uncertain. As mentioned earlier, all Large Drive Units installed in Tesla Model S and X cars from 2012 to 2020 have issues with coolant leaks. Therefore, if you buy a used motor, it will likely also have a coolant leak, earlier or later, and you cannot predict how long it will last before requiring similar repairs.

If you opt for LDU replacement at an official Tesla service center, the cost starts at around $5,000 for the base version. The advantage of this route is that you receive a manufacturer’s warranty, but there are two important considerations. First, Tesla uses refurbished units for replacements, which means they are also repaired, albeit in factory conditions. Second, based on our extensive experience, coolant leaks are the only systemic issue with LDUs. As long as the coolant delite manifold is installed, you likely won’t need the warranty — these motors are quite reliable. So, why pay more for a similar outcome?