It was discovered that late model Volkswagens used a type of engine oil cooler that was easy to adapt and use as a heated filter element.

Two of these heated filter assemblies were obtained from the (not quite) local Pick N Pull.

    



A flat plate was machined to fit the gasket mating surface and two 3/8 inch hose barb fittings were installed. Originally the plan was to tap the quarter inch aluminum plate with 3/8 inch NPT pipe threads. But due to either my inexperience with NPT tapping or the fact that the aluminum was too soft to hold the threads, the fittings did not seal.

They were JB welded in place. :-)

After these were installed and plumbed into the coolant system, this is what the system looks like:

The primary filter element is a PZ-22 oil filter, which is the stock oil filter for a VW rabbit or Volvo diesel. It is a 20 micron filter. Autozone had an off brand PZ-22 compatible for around $2.80.

[Note: Experience and other sources have shown that the cheapest oil filter may not be the best. Personally, I have found that cheap Purolator filters work well and are long lasting. Some filters refused to clog up at all, thus trashing the $15 secondary filter element. -Jay]



The secondary filter is a 3398 from NAPA. Just in case that link disappears:

Item#: FIL3398 

Price: $15.39 

Attributes:
Gasket I.D. (Inches):2.25
Gasket O.D. (Inches):2.6
Gasket Thickness (Inches):0.175
Height (Inches):4.72
Inlet Thread Size (Inches):3/4-16
O.D. (Inches):3.72
Style:Spin-On Fuel

The 3398 is a FUEL filter, so it filters down to 5 micron, and importantly does NOT have a pressure bypass valve.

The Mercedes Benz 300 and some others have an auxiliary coolant pump located in the area underneath the air cleaner. This was rewired in stage6 to pump coolant through the system constantly instead of only when the heat is on which improved warm up times signifigantly.