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      04-02-2026, 02:37 PM   #18
evox
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Drives: BMW 325i, X3, X5
Join Date: Jan 2026
Location: Georgia

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Quote:
Originally Posted by smass View Post
This thread reminded me I need to come up with a preemptive plan for my original cooling system that has 125k miles on it. I checked FCP and ECS and the pricing seems to have jumped up 25% in the past few weeks. This was for my B58. Hopefully this is just temporary.
The B58 has a much different oil filter housing design than the B48; it doesn't suffer the same problem as the unit on the B48s. It's still made of the same thermoplastic manufactured by Mahle, but because of the way the coolant and oil passages are laid out it doesn't fail like on the B48s.

On the B48s 9 times out 10 it's the center squarish coolant passage that fails. It's a bad design.

I just did the one on my daughter's X3's B48. It failed at 70,074 miles. When I replaced her oil filter housing she also saw weeping from two other coolant lines. The turbo coolant return line, and the heater core return line. But there were a number of lines that the thermoplastic of the quick connects were showing evidence of browning degradation but weren't leaking, so I went ahead and replaced all her coolant lines. Which was a little overkill.

I fully expect to be replacing other components on her B48's coolant system before she has 125k miles on it.

For B48 owners I'd put this on the list of preventative maintenance BEFORE 70k miles or you to might experience the joys of paying for a flatbed tow.
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