Monday, November 20, 2006

VW - Oil Cooler & Tin Mods

I was never able to duplicate Gene’s claimed results regarding engine temperatures and external oil coolers. Indeed, Gene never clearly defined what he was measuring. I believe I’ve already mentioned this situation in an article on external oil coolers.

My original interest was in learning how the Volkswagen engine was cooled so I could insure adequate cooling when the engine was installed in an airplane . . . converted VW engines in airplanes being notorious for swallowing the rear-most exhaust valves.

I dismantled the blower-housing from a 40-hp engine (this was in the late sixties) and replaced it with a sheet of plexiglas. Running on the test stand, I could introduce smoke-streams and figure out what VW was trying to do. Later, I rigged the big squirrel-cage blower I used on my flow-bench to suck air down thru an engine with the blower housing removed, using Temp-L-sticks, thermistors and the like to gain some understanding of the temperature change in the heads based on air-flow and engine speed.

I discovered the major emphasis in the original design was in providing the corners of the engine with air, with a very intricate series of air vanes and dams devoted to this purpose. Because of the obstruction of the oil cooler, the left head didn’t flow very well and because of the offset of the cylinders, #3 got the least air of all.

Removing the upright oil cooler brought an immediate improvement in air-flow although you had to do something about the ‘hole’. I first tried various forms of air dam before realizing I was going at the problem backwards.

Adequate flow can only come when there is adequate pressure and Volkswagens’ method of sustaining adequate pressure using a pair of deflector plates and the tin-ware skirts across the ends of #2 & #4 cylinder didn’t work very well. To maintain sufficient air pressure to ensure adequate flow to the ‘corners,’ you must improve the cowling of the underside of the cylinders, a step Volkswagen got around to a few years later.

For aircraft use, a tight upper plenum combined with tight lower cylinder cowling did the trick. This was not a popular fix because many lightplane designs do not include pressure cowlings.

There is also considerable improvement you can make in the heads, getting rid of any casting flash and insuring maximum air-flow down thru the fins around the exhaust stacks.

Getting back to external oil coolers, the dog-house cooler . . . and that of the Type IV . . . is an external-type, in that air used to cool the oil is exhausted to the atmosphere and not used for engine cooling.

In one of my articles I described the auxiliary oil cooler I designed for my ‘65 bus. I didn’t give a lot of detail about the design process but it involved making a manometer from plastic tubing, plywood and colored water to measure the air pressure inside the engine compartment. Addition of air scoops caused a significant increase in engine compartment air-pressure. While many still argue the merits of air-scoops on early buses one need only examine the cooling-air inlets of later model buses to see they too incorporate a scoop-type design.

Once I understood the problem I was able to come up with the design of an auxiliary oil cooler that worked, and very well too, as demonstrated on a run to Kansas City when I had to tow a Westy over South Pass (outside of Needles, California) in temperatures of over 100 degrees.

A couple of closing points.

I don’t want to get into a pissing contest with a dead man but I was never able to substantiate many of Gene Berg’s claims. Indeed, in many cases I couldn’t even get him to explain what he was measuring, where he was measuring it and how it was measured. I said as much years before his untimely death. Nothing has happened to change that.

The information I developed on auxiliary oil cooling applies mostly to my ‘65 bus. The general principles may apply to later-model buses but the wiser course would be to run some tests before cutting metal.

I don’t see any benefit in your idea of removing the oil cooler in your Type IV. However, should you need an auxiliary oil cooler there are convenient means of installing such without removing the stock oil cooler.

All of the Type IV’s I’ve seen that were experiencing problems with overheating, the fault was due to poor maintenance, usually the result of missing air-seals or tin-ware.

-Bob Hoover

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