My BMW i3’s rear differential has been a gigantic pain in the butt in that — thanks to a Technical Cost Reduction by BMW after the first model-year — it no longer features a fill plug. How, then, am I supposed to change the oil? BMW doesn’t want me to, but I’m doing it anyway, and my first attempt went horribly wrong. Now, thanks to a brilliant suggestion by a reader, I came up with the perfect solution. All it required was for me to spend an exorbitant sum on a drain plug.
A few days ago I wrote about how I had purchased from a BMW i3 forum-member a custom drain plug that featured a fitting that allowed me to pump oil in. The issue was that the fitting was so tiny I had to use a gravity feed — a three-hour long process — to get the differential filled with 500 ml of 75W85.
But that never happened, because I found contaminants in my oil thanks to brass fitting that the forum-member had cut to to minimize the height of the inlet fitting so as to minimize wasted oil stuck in the IV-bottle. I should have brake-cleaned all the parts prior to using them, so that’s on me, but regardless: I had filled my differential with 200ml of contaminated fluid, and I had no way to fill my diff.
Then an Autopian reader, ironically named Cheap Bastard, recommended I buy this drain plug. At over $50 after tax, it was a bit steep for my tastes, which mirror the reader’s username, but I had wasted enough time, and so what if I spend a bit of coin on my i3; it’s my most expensive car by far, so it deserves the biggest repair budget.
So I bought that plug, and then I bought this humongous syringe:
In a few days, the Amazon packages arrived, and, after draining and flushing the contaminated oil from my rear diff, I installed the drain plug’s base, which is to remain permanently screwed into my differential, with a crush washer in between:
Then I threaded in the red “key” piece, which when tightened allows flow into or out of the differential:
Then I simply filled my giant syringe, hooked up the hose to both it and the drain plug’s “key,” and pumped in a little over 500 mL of gear oil. Then I just loosened the key, which shut off flow in either direction, and I installed the cap with a crush washer:
That was it. That was the whole operation. It was way, way better than my dumb IV drip, and now, when I have to change this diff oil, I’ll just take the cap off, spin the “key” on, and oil will flow out. At that point, I’ll pump fresh oil in, unscrew the red piece, and then reinstall the cap. So easy.
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Was it worth the $80 I had to drop on the syringe and drain plug? Actually, yes. Yes it was.
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How often will you change this fluid? Is this something that needs to be done multiple times in the lifespan of a car?
I’m not used to differential fluid being a regular wear item unless someone is fording through deep water. Maybe that’s your secret endgame for the i3. It’s your next Moab adventure vehicle!
It’s funny how the terminology evolves. Today’s “technical cost reduction” was yesterday’s “material cost management” (MCM). Back in 2002, during one of DaimlerChryser’s financial crises, we used to say the MCM stood for Missing – Can’t Mention.
What do you use to flush the contaminated oil? Did you just sacrifice an extra 500 ml of gear oil or did you use a lighter 20W engine oil or ATF?
He didn’t. He already messed it up bu filling it with dirty oil during an oil change so there is no hope left besides avoiding these BMWs on used car market to avoid getting his that he broke
Me, a week ago: “$90 is too much for this RV-specific thing, I can just get the bigger one from Lowe’s for $40 and cut it down.”
Me, removing it from the RV before camping because it’s still not done after a week of cutting, trimming, banging, drilling, and hunting for the right screws: [redacted]
What is different that you’re ok with just pumping in the oil this time?
I thought the whole point of IV drip was this fear of yours:
At some point you just have to throw caution to the wind. In this case, throw caution into the giant syringe and squirt it into the differential with much prejudice.
The irritating thing here is that David is making me thing I need to replace all the fluids in my 10 year old GTI. Dammit!
Are we supposed to be changing our differential oil? I have never ever done that.
Eh, probably. But I’ve seen vehicles go over 220k miles on the original fluid sooooooooo
I’ve also heard vehicles without any meaningful amount of oil in the engine.
So, must be ok, right?
My father did “Lifetime fluid” changes before there was such a thing. Ran his 1980 Ford van to 180k miles on the original fluid in the 4-speed manual. Was it the best decision? IDK. The transmission was howling like a wounded wolf, but really that could have been darn near any rotating part on that 33 year old rattle box. I kinda think that by that point the transmission self-evacuated most of the fluid based on the puddles.
You dont as David demonstrated by filling it with dirty oil again
Change it? Don’t you just keep adding more as it leaks out?
I have every reason to believe the diff oil in my 67 Camaro was original at 50 or so years old. I did change it when I did the restoration. Everything inside the diff looked fine.
isn’t it lovely when someone has carefully made the exact part you need ?
I pay happily for that..
Example, old Abu Ambassadeur fishing reels, Swedish-made, have a thriving aftermarket supply for parts from Japan. These let the reel with its beautiful Swedish engineering be rebuilt with modern lightweight spool, better drag system etc etc. Of course you spend more than the original price of the reel on pretty new parts, but it’s worth it, totally.
my Sport Trac had the opposite problem, a diff with a fill plug but no drain plug. This baffled me a bit, thought about a new diff cover, eventually went Cheap Bastard route using a suction pump to extract old fluid via the fill opening.
I think the original idea was, you would refill the diff oil after removing the cover to rebuild the diff, rebuilt because you hadn’t been able to change the diff oil. ? profit !
When it comes to stuff like this, you’re buying the idea and lack of economy of scale. It’s a similar deal with the Desert Does It Seat Slammers I bought for my Gladiator. In terms of material and labor, the cost of them is very likely 3x or 4x the price of their cost. But, they’re the only game in town with that solution and if you want it, you better pay to play.
First, the plug is now integral to the differential; that was fast.
Second, this will accelerate the process of changing the fluid.
Third, see how David admitted the first attempt flopped without being a jerk?
Meanwhile I’m over here bringing somewhat derivative content. 🙂
(Apologies to engineering types for any flashbacks)
Young David: Hello readers! I’ve taken a break from wrenching on my rusted-out Jeep to travel to the future to check in on my future self. Hi! Future David! What’s going on?
Future David: I just put the baby down for a nap while I implement this ingenious system to flush the oil from the differential on my BMW. Now I need to get back to running my industry-leading publication from our office in L.A. Have fun with the Jeep.
Young David: (mouth drops open, rusty wrench hits the floor)
Hey now! His tools were not rusty! It’s the rusty alternator that hits the floor.
Floor? Young David has a floor?
Future David would be sure to mention the drain plug for his BMW cost $50 to fully short circuit the mind of Young David.
Young David has a stroke over the idea of a $50 drain plug resulting in Future David as we know him no longer existing, causing a reality-ending paradox in the space-time continuum…
Cheap Bastard, look what you’ve done!
Young David: $50!! I would replace the entire rear diff/axle for less than $50! See this Holy Grail perfect condition differential I just got at the junk yard? (Points to a mis-shapen unrecognizable lump of rust in his yard.)
Future David: Oh yeah, that thing. Turns out it was garbage the whole time.
Curious. You probably gravity drain it, but is it possible to attach the empty syringe to the coupling and siphon out the old oil? I doubt 500mL takes that long to gravity feed, so you would not save much time and you’d get the syringe dirty with old oil so you would probably add time to the process by cleaning the syringe … never mind.
And, in X miles, you’ll do it again, but this time for free (diff. oil notwithstanding).
Q: What is X?
Asking for a friend.
I’ve found brass fittings to be the absolute worst when it comes to being clean/ready to use. Stainless steel or plastic are usually perfectly clean, but brass fittings definitely need a good scrubbing out.
Totally. There’s just so much fine brass “dust.”
Great upgrade! Now you can say your i3 has “differential injection”, a rare feature!
Filled
withby differential pressure!Not convinced that novelty syringe isn’t an AI photo.
According to my German wife, there’s an old saying that translates loosely to: “If you don’t have it in your head, you’d better have it in your back” (or knees, depending on the version). In other words, if you can’t solve the problem mentally, you’re going to have to solve it physically through hard work. Anyway, I’ll add a corollary that I have discovered as I’ve gotten older: If you don’t have it in your calendar, you’d better have it in your wallet. Time is money and sometimes the best solution is just to spend the money.
As I have progressed in my career (and gotten older), the bar for when I pay somebody instead of doing it myself has gotten lower and lower.
Same here. Kids are a similar factor.
I need to do a couple of things on my Hyundai. I bought the parts in spring, and they remain in my garage. I want to do them (end links, new belts) but am not excited about it.
TL;DR, David spent $80 on a Giant Douche kit for the i3.
But now it’s as fresh as a summer’s eve.