BEV E-Motor transmission/differential Oil - change?

I was just clicking through the technical manual and saw that the i3 BEV comes with 1.5L of transmission oil. (a gear oil)

https://www.ecstuning.com/b-genuine-bmw-parts/hypoid-axle-oil-g1/83222295532/
https://www.realoem.com/bmw/enUS/showparts?id=1Z63-USA-07-2017-I01-BMW_i-i3_94Ah&diagId=27_0072

BMW specifies the Oil as Lifetime - yet as with all my Fossil Fuel cars - I know that's not true.
The lifespan for those oils is usually around 50-100k miles and 5-7 years.
So not something I would tackle during the 4 year warranty.

In general a gear oil gets worse in lubricating things when it ages. Thus increasing friction - decreasing range.

Anyone ever tried to change it? It seems like you have to pump it out like on other "lifetime" products of BMW.

I'd change the Reduction Gearbox / Differential fluid early, then never again. This is to get out break-in metal as the gear surfaces polish down a bit when new. About 1,000 miles or so, whenever you can. .... You don't really have to touch it, only if you plan on keeping an i3 past 100,000 miles or so, to cut down the wear rate by getting out tiny steel particles floating around in the oil the magnet didn't catch. Sometimes iron particles can be washed back off the magnetic drain plug from fluid mass flow. Also, those magnets always allow some iron to circulate, seen from oil analysis done on many gearboxes, trannys, and diffs over the years.

Unlike all other EV gear reduction & diff boxes out there now, BMW specs some thicker stuff. The part number the OP linked to is 75w-85, although it is GL-4 which does at least make it somewhat similar to the lighter visc ATF fluid all other EV makers use. Bolt, Leaf, Tesla, Ford EVs, Kia, Hyundai, all use thinner standard ATF red fluids which look about like a 0w-16 motor oil in viscosity anyway (additive package is diff of course). Quite thin, for better energy efficiency & less heat generated.
I'd stick with the BMW-recommended fluid for sure, a GL-4 75w-85 here.

I've changed this on a couple of EV's recently, other brands, and from the OP's link to the part (see that original post), it does say it has a magnetic drain plug. (Nissan Leafs have a huge magnetic drain plug, and the same for the Fill Plug too, both of which catch a lot of iron particles from normal break-in & running wear, even at 1,500 miles on a new-ish Leaf!)

One would need to simply identify where the Fill Plug is, and where the Drain Plug is. Usually an aluminum or copper crush washer of the right size is needed. Actually the Service Manual should be consulted to find out if there is anything Unusual or Special to do, as BMW is known for over-complicating the simple stuff.

If you do change it yourself, which should be easy (probably!), then don't tell BMW you did, since they do not require you to change it during the long warranty period anyway.

If you do NOT change this fluid, do look for any leaks once every couple of years, or even check the level at the Fill Plug. At least look for leaks. .......These things are almost always designed to get the level right by opening up the fill plug & adding some until it starts running out the Fill Plug, although some are picky about what temperature you do it at, so reading a Service Manual would reveal how easy or hard this really is !!

Apparently, BMW deleted the transaxle's oil filler plug on BEV models beginning in 05/2015 and on REx models beginning in 04/2015. For models without an oil filler plug, oil must be added through the output shaft hole after removing either output shaft. Not very convenient! To me, this suggests that BMW doesn't intend on the oil being replaced during the life of an i3.

alohart said:

Apparently, BMW deleted the transaxle's oil filler plug on BEV models manufactured on or after 05/2015 and on REx models manufactured on or after 04/2015.

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Wow, interesting. Service Manual would have that info. Best hope there's no leaking, got to check for that once in a while.

When I was looking at a Sandy Munro teardown document, it showed what appeared to be a fill level plug.
Must have been an early model, first model year & most of '15 ones only!


From a big $10 yes ten dollar multi-thousand page document about the i3. https://insideevs.com/news/434166/sandy-munro-selling-bmw-i3-teardown-10/

alohart said:

Apparently, BMW deleted the transaxle's oil filler plug on BEV models beginning in 05/2015 and on REx models beginning in 04/2015. For models without an oil filler plug, oil must be added through the output shaft hole after removing either output shaft. Not very convenient! To me, this suggests that BMW doesn't intend on the oil being replaced during the life of an i3.

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Thanks for the information!

so BMW did build a planned obsolescence into these cars

electrons said:

If you do change it yourself, which should be easy (probably!), then don't tell BMW you did, since they do not require you to change it during the long warranty period anyway.

If you do NOT change this fluid, do look for any leaks once every couple of years, or even check the level at the Fill Plug. At least look for leaks. .......These things are almost always designed to get the level right by opening up the fill plug & adding some until it starts running out the Fill Plug, although some are picky about what temperature you do it at, so reading a Service Manual would reveal how easy or hard this really is !!

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I'm not planning to change it myself during the warranty. So a few more years to go

Just in general wondering. In many cars those lifetime fluids - determine the lifetime of the vehicle. That's not only BMW, many others do the same.
Volvo has a rear differential and a gear vendor in the AWDs which is a similar pain.
Some people never change the fluid and are fine for 200k, yet for some people those gears disintegrate and have to be replaced entirely. Which is by that point often more expensive then trashing the vehicle.

In the Leaf discussion boards people reported of significant more range after changing this fluids.

We also have to think long term - the i3 is blessed with a battery which is somewhat easy to exchange and a none corroding frame - so those cars are potentially very long on the road. So far I don't see reason why the shell of an i3 shouldn't be able to go a million miles or more.

So 10 years from now - the transmission fluids are probably a lot better then today. I've put recently a new synthetic gear oil in my ancient Chevy van axle and it got two mpg more. (and the old fluid was not bad - just whatever the spec was 30 years ago)

A person could just leave it alone, yes. Don't change it. Checking for leaks once in a while is important though.

I've heard of these reduction gears in other EVs with high mileage getting worn down to the point where they rattle (after 100,000 miles or so), and others have reported nasty thick fluid coming out around 60k miles, cutting EV range via extra hydrodynamic drag, but the reduction gears will soldier on to somewhere north of 100k anyway.

I'm hoping BMW did what GM did with the Bolt: GM put a magnet inside the casing, in a "pocket" held in place & out of any swirling, fast oil flow, to attract & grab iron particles without having a strong flow knock them back off constantly to some extent. GM Bolt's fluid is their excellent Dexron HP (like Dexron VI) which is typically good for 150k miles in auto trannies in the ICE world, so their reduction gears can probably go 200k on Dexron HP.
----- The magnets should work to clean out the wear-producing grit circulating, making it closer to a lifetime fluid.

Nissan Leafs have two large identical magnets, one as the drain plug, the other as the fill plug, both oversized a bit to grab more grit. That works OK. (Leafs even have 2 plugs you could fill the gear case from, exactly the opposite approach BMW took by eliminating the only fill/level plug!!!)

As for other examples, I just changed the diff fluid in a VW Tiguan, early in its lifetime, & I put in drain & fill plugs with magnets to help out. The plugs were both very small compared to others. The Haldex AWD unit in the back is NOT lifetime, notably, and VW says it needs to be drained every 3 years, but they do say their transfer case (front bevel box) & rear diff is "lifetime".

This is all optional. Don't do anything if you plan on getting rid of the vehicle before 100k miles.

electrons said:

A person could just leave it alone, yes. Don't change it. Checking for leaks once in a while is important though.

This is all optional. Don't do anything if you plan on getting rid of the vehicle before 100k miles.

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Here the i3 had a huge advance - it already depreciated almost 70% when I bought it a 3 years old. ($14k for a $48k car)

In my past ICE life I usually don't bought vehicle if it not had at least 100k miles and I usually sell when they hit 200k.
I hate depreciation.

does anyone know what "operating temp" is?

For those people that drive a later model i3 with a single drain plug for the gearbox or e-transmission as they call it. You can drain and service your gearbox even though you don’t have a fill plug.

The exact gearbox fluid capacity is 500ml or .5 liters max. It takes very little oil and I have confirmed it with a local BMW dealer as well as other sources.

Upon removal of the aluminum access panel in the back, there is a breather vent on top of the gearbox. That breather vent has a black plastic vent cap on top. Please squeeze the vent cap where the knurls are on the cap with both your index and thumb fingers. With a little manipulation it comes off, absolutely no tools needed.

Drain the old fluid into a pan and remove all metal filings on the magnetic drain plug. Replace the aluminum crush washer and torque the plug to 20 to 25 foot pounds. Go to Home Depot and buy clear tubing 3/4 inch OD by 5/8 inch ID. It’s clear vinyl tubing made by Everbilt, Home Depot’s house brand.

The clear tubing fits very tight over the aluminum breather sticking out of the top of the gearbox. I usually put a small radiator clamp around it and not too tight and just enough to keep the tubing from popping off when you refill with fresh oil. Refill the oil slowly and with small quantities while pouring.

Cut the tubing around 3 feet long with a small funnel and fill with fresh synthetic gear oil. I use the oil that was recommended by Liquid Moly which is part number 22090 GL4/5 Synthetic Hypoid gear oil.

All though BMW says the gearbox oil is lifetime, I can’t believe that especially at 30K miles it was filthy. Such a simple job and easy to do that I will service my gearbox every 10-12K miles……it’s cheap insurance.

How do you know that the exact gearbox fluid capacity is 500ml or 0.5 liters max?

Did you measure the drained fluid?

You see.... There is a lot of informaiton out there about the capacity in this e-drive transmissions.

Some say 1.5 liters others 1.0 liters and you say 0.5 liters

Who is right?

Is it possible that the capacity changed from the 60Ah versions to the 120Ah versions or the REX versions?

I am planning to change the gearbox oil myself. Thanks you for the tip of filling the new oil trough the breather vent on top of the gearbox.

I have the Facelift 2018 BMW i3 with the 94Ah battery and no REX.

TurboPrius- Did you get a chance to change the transmission oil? Wondering how it went.

Just found this. A little narration wouldn't have gone amiss!

https://m.youtube.com/watch?v=4lDSFHXVGXM

With the drive shaft out, just wondering if there's any eccentric bolts for toe in or out adjustment?

I'm looking into seeing if the dealer will do this for me...and how much. My E-tran is a little on the louder side than I like...almost sounds like sand paper at low speeds. That doesn't mean it's gone bad as I feel no issues with it. But if they can change the oil, great. I have almost 48k miles on my car.

I did the differential fluid change myself earlier today (2018 i3s BEV). I drained exactly 500 ml. The entire procedure was super simple and straightforward. Took me about an hour. Later model years don’t have a fill plug, so you have to either follow the BMW shop manual and fill the diff by removing the drive shaft or like I did it through the breather valve. The procedure is very similar to changing the fluid in a manual transmission, so no need to measure the temp of the fluid etc…

deniska1 said:

I did the differential fluid change myself earlier today (2018 i3s BEV).

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How far had your i3 been driven? How did the drained transaxle fluid look? I guess with no magnetic drain plug, metal filings would not be collected anywhere. However, did you see any in the drained fluid?

Correction: A magnetic drain plug exists but there's no filler plug.

BMW doesn't seem to recommend a transaxle fluid change at any driving distance or after any time period. That along with the removal of the drain plug suggests that BMW doesn't expect the fluid to be changed ever. Do you feel that your transaxle fluid needed to be changed?

The mileage is 44K and the fluid looked bad to say the least… the plug does have a magnet though, so it did collect a lot of metal particles that would otherwise would circulate inside. You definitely wanna do the service unless you don’t plan on keeping the car for long. Even with the magnet collecting most of the shavings the fluid will eventually turn into acid with a bunch of metal particles circulating inside and it will destroy the internal components of the gearbox (bearings and gears)..

thanks for sharing your experience.

Something I'm probably going to do soon. Where did you buy the oil? Dealer?

deniska1 said:

I did the differential fluid change myself earlier today (2018 i3s BEV). I drained exactly 500 ml. The entire procedure was super simple and straightforward. Took me about an hour. Later model years don’t have a fill plug, so you have to either follow the BMW shop manual and fill the diff by removing the drive shaft or like I did it through the breather valve. The procedure is very similar to changing the fluid in a manual transmission, so no need to measure the temp of the fluid etc…

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Shame you didn't take photos or make a video of the process

I did the oil change too at 14k and its filthy. def not lifetime and no unicorns. took all but 15 min, don't even need to jack up the car. BEV here.