Saturday, June 16, 2007

Full-flow Oil Filtration

There’s still lots of people who simply Don’t Get It when it comes to full-flow oil filtration. They like to point to older aircraft engines such as the A-65 - - or even the O-200 - - and insist that changing the oil every 25 hours is all you need do to obtain maximum service.

Unfortunately, they are comparing apples to oranges. The O-200 was designed as an aircraft engine with more than adequate fin-area to deal with the three-horsepower’s-worth of waste heat that is generated for every horsepower’s worth of torque that appears in the crankshaft.

Nominal output of the Volkswagen engine is about 25bhp - - and only about half of that makes it to the rear wheels. (Start with the miles-per-gallon, work backwards.) Short bursts of acceleration, as when passing or merging with traffic, are dealt with by using the OIL as a heat-sink. That is why the VW’s oil pump is about twice as large as the pump from an O-200. Not only is it larger, it typically operates at nearly twice the speed of the O-200's pump. Bottom line is that the VW’s pump moves more than three gallons of oil per minute even though it only needs about six ounces for lubrication. The excess flow is for cooling.

The VW sump holds 2.5 liters of oil. 85 fluid ounces. Barely two and a half quarts. In 25 engine-hours it will re-circulate the sump’s oil nearly seven thousand times. Dirty oil, getting dirtier on each pass.

An aircraft engine will typically hold six to eight quarts of oil, more than twice as much as a VW. And pumps it at less than half the rate. Wanna figure out how many times the sump’s oil gets recirculated in 25 hours? (Go ahead, I’ll be over there copping a smoke.)

Apples to oranges.

The VW engine needs a full-flow oil filter. Installing one will literally double the life of your engine.

Volkswagen adopted full-flow oil filtration with the introduction of the Type IV engine. To retro-fit that feature to earlier VW engines you simply block the output of the pump and re-direct it through a modified pump cover-plate, ideally one having a pressure relief valve such as the Berg unit shown in the photos. After passing through the filter - - and the oil cooler, should you care to plumb one in - - the oil is returned to the engine’s main oil gallery.

This retro-fit became a standard feature of high-output VW’s in the early 1960's and has been depicted numerous times in manuals, magazine articles and even here on the internet. (Bill Fisher devoted a couple of pages to it in his famous ‘How to Hotrod Volkswagen Engines,’ published in 1970.) Indeed, it is such old news - - and such a necessary mod - - that there’s simply no justification for it to not be included on every flying Volkswagen.


(Ed.Note: Within minutes of posting an eagle-eyed reader asked: Is that another pump-cover being used as a vent?

Yes. It is an $8 bubble-packed item from a local VW after-market retailer. Vapor separation is accomplished by stuffing the chamber below the plate with a stainless steel pot-scrubber. The vent-line is plumbed to the carb-heat box. Since this engine will not use a fuel pump, that opening will used as the oil-filler.)