Skip to content

Cooling System Refresh

    Although I received some maintenance documentation when I purchased the car, there was no mention of any water pump or radiator replacement and the cooling system appeared to mostly be the original 15 year old items, so it was time for a refresh.

    Given the condition of the fins on the engine side of the radiator, the front of the engine had been worked on at some point. The crimped fins may have been the result of a water pump replacement, or perhaps an accessory drive belt swap.

    Engine Side of Radiator with Telltale Crimped Core Fins

    I keep a stock of large flat sheets of cardboard around, mostly recycled shipping boxes; a radiator-sized chunk of cardboard tucked in on the engine side of the radiator during the job would have prevented such damage.

    Lots of interesting debris captured between the A/C condenser and the front of the radiator:

    BMW replacement radiator, manufactured by Valeo:

    Some of the other cooling system and belt drive items that were replaced during this episode:

    The water pump had been replaced with a steel impeller BMW pump, which looked nearly new, and might explain the radiator fin tweakage. I already had a Stewart pump on hand for the job.

    Comparison of a Stewart pump with a standard BMW water pump:

    Stewart vs. OEM BMW Water Pumps

    Given the stories I have heard and read of BMW plastic fans shedding blades and perforating hoods and cooling systems, I’m going to try the mechanical fan delete option that other Z3 owners have used with success; however, I’m skeptical.   

    I treated the Stewart pump to a Fan Delete nut:

    I replaced the OE phenolic OEM thermostat housing with a surprisingly nice $15 aluminum casting made by Üro; I went with a Üro aluminum water pump pulley as well.  I know people have had issues with some aftermarket aluminum T-stat housings that either developed hairline cracks or had less than flat gasket surfaces; I carefully inspected the Üro casting and lapped the gasket surface on a surface plate to verify the flatness. I suppose there could be an internal casting flaw, but when it comes to cooling system hard parts I’m an old school kinda guy; in most cases aluminum trumps plastic. I was tempted to go with a racer-oriented all-aluminum radiator and expansion tank, but the OEM BMW radiators and expansion tanks seem to hold up pretty well; the phenolic T-stat housing just seemed wrong and had to go. Less than perfect logic I know:

    Ready for shroud and hose installation:

    Brass Air Bleed Screw and new OEM cap:

    The cooling system was refilled with distilled water and BMW blue antifreeze / coolant:

    Done!: