Hi all, I'm aware of the excellent sticky on swapping your OEM plastic water pump to an aftermarket metal impellor one & have planned to do this on my car for a while but just found this very interesting post from across the pond discussing the merits of OEM vs aftermarket vs 'performance' water pumps:
OEM Water pump - Bimmerforums - The Ultimate BMW Forum
First point to note from it is over there BMW used to use brittle plasitc impelled pumps, then switched to metal impelled, then around 1998 they switched to a moulded composite impelled pump. I've heard some people over here say that post 1998 BMW switched to metal impelled but its unconfirmed - I wonder if in the UK they actually followed the same pattern as the US?
Secondly, heavier metal implleors put more strain on the bearing & cause it to fail sooner than composite? It does make sense.
Thirdly there's a good youtube clip on the link comparing the design of an OE composite water pump to an aftermarket metal one & the composite OE one looks much better made, more sturdy & is 1-piece molded compared to the spot-welded metal pump with rough edges etc.
In addition to the above post, I recently rang All German Parts (I can highly recommend them for OE maintenance parts by the way - excellent prices & service & usually next day delivery. Jason is very knowledgable as well & a good bloke) for a quote on a metal impelled pump & he sounded surprised & asked why I wanted an aftermarket metal one & said the metal ones cause much more damage if bits snap off (which they're more likely to if they're more badly made & not 1-piece etc) & said VW TPS have an article on their website explaining why VW use plastic pumps from the factory.
This is on my agenda right now because my car is having an oil service, fuel filter & coolant change this week & I was planning on having the metal water pump & thermo done at the same time. PURELY because of the plastic bits snapping off issue not because I have any cooling problems.
My engine runs beautifully, doesn't use any oil etc & the fan kicks in exactly when it should my mechaninc tested it with software (was distracted when talking on the phone to him so didn't catch exactly what he did to test it) but he said in kicks in at exactly the temp when it should. Plus my car only has 70k on the clock.
I don't mind at all spending money on maintenance for my BM, like most of us enthusiasts I replace parts 'just because', but the last thing I want is to spend money making my cooling system WORSE & WEAKER, especially because my insurance & tax is due end of the month
Any thoughts on this?
Also forgot to say my car is 1999 so if BMW did the same over here as the US then mine will have a composite impellor which I'm staring to think is the best design & I would prefer to leave it alone if thats the case.