JPR also had a great post on coolant somewhere...
From what I know, it's OE or G-05, but just yesterday saw a BMW coolant bottle posted here that had a typo...said Volvo in one instruction and BMW in another...so some Volvo coolant would work too, I suppose.
It should be a $25 investment every few years. I have to do mine...will plan on it in the spring when I put in a new WP just to be safe(r).
Debut Radio Show Tuesdays from 1-2-ish p.m. EST on Hamiltonradio.net The Mechanical Animals
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A recent set--NSFW audio: https://youtu.be/_dcxcZfD6dg
Mangofy your E46!