Summary: I had an aluminum plug machined, modified the OEM LDU coolant manifold by cutting off the tube that runs into the hollow rotor shaft, milled a bypass channel, and pressed in a plug. I anticipate no more coolant leaks in my LDU.
Background:
The Tesla Large Drive Units ("LDU") of the original Model S (and derivatives such as the GEN2 RAV4 EV and the MB original Electric Drive (later: B250e)) went through many, many internal revisions from its inception in Jun2012. Many of the early issues were ironed out over the course of the first four years, culminating in a relatively reliable "Revision Q" in 2016.
However, there remains one issue with the LDU that hasn't been adequately addressed. The rotor is cooled via a water-based glycol mix coolant, via its hollow shaft. Johan ("DIY EV Guy" on YouTube), a RAV4 EV owner, has done us a service by making a set of vids that go into aspects of the LDU's "water" cooling system; if you're interested in the details I can recommend watching a couple of them, esp. this one.
The Tesla design for the rotor cooling involves a lip seal on one end of the hollow rotor's shaft. That seal has had at least three revisions, and none have proven reliable. In addition, Tesla provided no "weep hole", a standard engineering practice for water pump shaft seal designs, which Tesla design mirrors.
The result of this rotor seal leaking is that "water" leaks into a sealed chamber, works its way through the outer rotor bearing (eventually leading to its destruction . . . if run long enough), then to the stator cavity where it compromises the electrical isolation resistance of the stator. If the LDU is driven further (if the isolation resistance issue doesn't trigger a BMS fault which prevents the HV contactors from activating), more coolant makes its way through a "tunnel" at the bottom of the gearcase, where the three HV phase leads run, and makes its way to the inverter electronics. If you're lucky, it fouls some wiring harness connectors and the monitoring system prevents operation, triggering many -- often spurious -- Alert codes. If you're unlucky, it wipes out the inverter electronics and renders the LDU salvage (for parts only).
This rotor seal leak issue has been well known for many, many years. If you're an owner of an LDU, until recently your options were limited, among them:
But, you couldn't actually obtain a reliable sealing situation. LDUs remanufactured by Tesla subcontractors have had a very spotty record of longevity, ranging from hundreds of miles to ??? but they always leak eventually.
This has become a significant issue for Model S, MB B250e, and RAV4 EV owners, now that they have some time on them. The LDUs are time bombs. They can leak if you drive them a lot; they can leak if they stay in your garage.
Tesla has apparently given up on keeping these units sealed, as they had been shipping their own version of "coolant delete" on their remans. There is an cast aluminum manifold bolted to the very end of the rotor case cap, and this "coolant manifold" routes coolant three places:
Because Tesla is Tesla, and they sell no parts to the LDU, you & I cannot buy that newer coolant manifold
QC Charge sells a bespoke replacement coolant manifold for $770 (with tax).
Revolt is now selling their version of what QC Charge proposed last year; theirs also deletes the flyover tube to the gearcase heat exchanger (opinions vary as to the necessity of that heat exchanger), and theirs is supposedly around $550 (after tax).
So, there appears to -- finally -- be a more permanent solution to rotor seal leaks: don't cool the rotor with liquid!
Other ideas that had been floated:
Naturally, there are DIY approaches to modifying the old coolant manifold to bypass rotor cooling. There's 14-page thread over at teslamotorsclub.com with a lot of implementations (it's a long read). The approaches boil down to:
It should be mentioned that -- in the RAV4, but not in the Model S -- you can R&R the coolant manifold without removing the LDU from the car! If you have a dry/non-leaking/no-symptom RAV4, you could do a "coolant delete" upgrade yourself for less than $200!
I had purchased my 2014 with 49k miles on it, in Aug2017. At 59k mi. I had the LDU replaced with a Reman unit. It now has 119,300 mi., so I got almost 50k on my Tesla remanufactured LDU before I saw the Blue Drops of Death. I had just experienced a "Check EV System" dash alert, so I expected trouble.
I removed my LDU and was surprised and lucky to have found no traces of blue coolant in the "tunnel" or the inverter side; the coolant -- and attendent corrosion -- was confined to the stator cavity & rotor area.
The assumption is that, if Tesla is doing a rotor coolant bypass modification for reman LDUs, "anybody" can. It's unknown whether there are accompanying firmware modifications to Model S vehicles to accommodate this new Tesla "Coolant Delete" manifold. Opinions vary; my thought is that my RAV4 EV does not tow, and rarely sees full power for more than a few seconds, therefore for my uses, air cooling the rotor may be OK.
Leaving aside the partial disassembly of the LDU, cleaning, testing, reasembly and sealing, below shows how I implemented the "aluminum cup" rotor cooling bypass method on my RAV4 EV's LDU coolant manifold.
View with the left plastic side panel removed, and the large underbody plastic panel off:
(cont'd next msg)
Background:
The Tesla Large Drive Units ("LDU") of the original Model S (and derivatives such as the GEN2 RAV4 EV and the MB original Electric Drive (later: B250e)) went through many, many internal revisions from its inception in Jun2012. Many of the early issues were ironed out over the course of the first four years, culminating in a relatively reliable "Revision Q" in 2016.
However, there remains one issue with the LDU that hasn't been adequately addressed. The rotor is cooled via a water-based glycol mix coolant, via its hollow shaft. Johan ("DIY EV Guy" on YouTube), a RAV4 EV owner, has done us a service by making a set of vids that go into aspects of the LDU's "water" cooling system; if you're interested in the details I can recommend watching a couple of them, esp. this one.
The Tesla design for the rotor cooling involves a lip seal on one end of the hollow rotor's shaft. That seal has had at least three revisions, and none have proven reliable. In addition, Tesla provided no "weep hole", a standard engineering practice for water pump shaft seal designs, which Tesla design mirrors.
The result of this rotor seal leaking is that "water" leaks into a sealed chamber, works its way through the outer rotor bearing (eventually leading to its destruction . . . if run long enough), then to the stator cavity where it compromises the electrical isolation resistance of the stator. If the LDU is driven further (if the isolation resistance issue doesn't trigger a BMS fault which prevents the HV contactors from activating), more coolant makes its way through a "tunnel" at the bottom of the gearcase, where the three HV phase leads run, and makes its way to the inverter electronics. If you're lucky, it fouls some wiring harness connectors and the monitoring system prevents operation, triggering many -- often spurious -- Alert codes. If you're unlucky, it wipes out the inverter electronics and renders the LDU salvage (for parts only).
This rotor seal leak issue has been well known for many, many years. If you're an owner of an LDU, until recently your options were limited, among them:
- You could check for blue coolant leaking into the speed sensor chamber on a regular basis, perhaps once or twice a year.
- You could add a weep hole so when coolant leaks it would exit the LDU via the hole to the outside, rather than forcing its way through the rotor bearing.
- You could install a water monitor instead/in addition to the weep hole, to light a lamp when coolant was detected.
But, you couldn't actually obtain a reliable sealing situation. LDUs remanufactured by Tesla subcontractors have had a very spotty record of longevity, ranging from hundreds of miles to ??? but they always leak eventually.
This has become a significant issue for Model S, MB B250e, and RAV4 EV owners, now that they have some time on them. The LDUs are time bombs. They can leak if you drive them a lot; they can leak if they stay in your garage.
Tesla has apparently given up on keeping these units sealed, as they had been shipping their own version of "coolant delete" on their remans. There is an cast aluminum manifold bolted to the very end of the rotor case cap, and this "coolant manifold" routes coolant three places:
- Down to the stator case (further: cools the inverter electronics)
- Through the hollow rotor (and back)
- To a "flyover tube" external to the LDU, which routes to a gearcase heat exchanger
Because Tesla is Tesla, and they sell no parts to the LDU, you & I cannot buy that newer coolant manifold
QC Charge sells a bespoke replacement coolant manifold for $770 (with tax).
Revolt is now selling their version of what QC Charge proposed last year; theirs also deletes the flyover tube to the gearcase heat exchanger (opinions vary as to the necessity of that heat exchanger), and theirs is supposedly around $550 (after tax).
So, there appears to -- finally -- be a more permanent solution to rotor seal leaks: don't cool the rotor with liquid!
Other ideas that had been floated:
- Swap out the water-based glycol coolant for a non-water-based one (ie "waterless coolant" or a light oil)
- Pull a slight vacuum -- and maintain it on the coolant system, to prevent coolant from leaking, via pressure differential
Naturally, there are DIY approaches to modifying the old coolant manifold to bypass rotor cooling. There's 14-page thread over at teslamotorsclub.com with a lot of implementations (it's a long read). The approaches boil down to:
- Drill a hole from the flyover tube down to below the reluctor chamber and run a metal tube from top to bottom.
- Weld up the internal passage to the rotor, either retaining or abandoning the flyover tube flow
- Same as above, using epoxy
- Replace the rotor seal with a "cup" that presses in place of the seal, preventing flow to/from rotor but maintaining flyover tube flow
- Aluminum cup
- Formed SS cup
- [20240509: after I was done doing the following steps I outline, some came up with this new idea] Cut the manifold "bottom" off that feeds the stator, replace the lower section with a hose barb and adapter plate, cap the upper half where you cut it (no flyover tube feed to gearbox).
- Both solutions require cutting and milling (or merely grinding) the OEM coolant manifold to remove the rotor tube and to provide as coolant bypass path, and this is destructive and cannot be reversed . . . and Tesla sells no parts of the LDU. So you kinda have to commit.
It should be mentioned that -- in the RAV4, but not in the Model S -- you can R&R the coolant manifold without removing the LDU from the car! If you have a dry/non-leaking/no-symptom RAV4, you could do a "coolant delete" upgrade yourself for less than $200!
I had purchased my 2014 with 49k miles on it, in Aug2017. At 59k mi. I had the LDU replaced with a Reman unit. It now has 119,300 mi., so I got almost 50k on my Tesla remanufactured LDU before I saw the Blue Drops of Death. I had just experienced a "Check EV System" dash alert, so I expected trouble.
I removed my LDU and was surprised and lucky to have found no traces of blue coolant in the "tunnel" or the inverter side; the coolant -- and attendent corrosion -- was confined to the stator cavity & rotor area.
The assumption is that, if Tesla is doing a rotor coolant bypass modification for reman LDUs, "anybody" can. It's unknown whether there are accompanying firmware modifications to Model S vehicles to accommodate this new Tesla "Coolant Delete" manifold. Opinions vary; my thought is that my RAV4 EV does not tow, and rarely sees full power for more than a few seconds, therefore for my uses, air cooling the rotor may be OK.
Leaving aside the partial disassembly of the LDU, cleaning, testing, reasembly and sealing, below shows how I implemented the "aluminum cup" rotor cooling bypass method on my RAV4 EV's LDU coolant manifold.
View with the left plastic side panel removed, and the large underbody plastic panel off:
(cont'd next msg)
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