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.
Was it worth the $80 I had to drop on the syringe and drain plug? Actually, yes. Yes it was.
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