An Auxiliary Oil Cooler Option:
The Audi 5000 Cooler Mounting
by Ron Van Ness
November 29, 1998

     The 1600 in my '71 Westfalia sometimes reaches a peak oil temperature range of 230-250° F on a long, sweltering summer highway run (measured with a VDO dipstick sender and gauge). To maintain my sanity on those particular days, after a thorough assessment of my engine's proper state of tune and its cooling hardware, I decided it was time to add an additional oil cooler. This wouldn't bring my cylinder head temperature below its typical highway range of 300-350° F, but it would at least keep my oil from the threshold of breakdown. Since I installed a full flow filter at the time of my engine rebuild, adding a second cooler simply required routing lines and deciding where the cooler should reside. I had some criteria for that last decision that kept me stewing for awhile. My first thoughts were: I did not want long oil hoses, I wanted the cooler in an air flow area so that an electric fan would be unnecessary yet the cooler must be relatively protected from harm, little or no modification to the bodywork/chassis, the cooler had to be cheap and easy to replace if necessary, and it would have to bring my maximum temperature down by at least 20°. The most difficult criterion was to keep the second cooler close to the engine to reduce hose length while simultaneously providing a non-electrically assisted source of air flow--and without cutting bodywork to properly utilize and duct air from the existing engine scoops. Eventually I was able to satisfy all but the hose length criterion to my satisfaction.

     Among Veedubers, the oil cooler of choice appears to be the "Mesa", plate-style oil cooler, which works on the same principles used in aircraft oil cooling (passing the oil through plate-like cooling passages that expose the oil over more surface area directly cooled by the air). This is far better for cooling than the tubular style cooler with heat dissipating fins on the exterior of the tubing. Tubular coolers tend to cool only the oil running nearest the tubing, leaving the oil traveling at the center relatively hotter. Permacool makes a variation on the tubular design called the "Maxi-Cool Turbulator", which circulates the oil better along the outer area of the tube to overcome the weakness of the traditional tube cooler. I have yet to see data comparing a Mesa cooler with a Turbulator of comparable volume, but the Mesa's aircraft engine cooling heritage is persuasive in its favor.

     I was leaning toward the Mesa cooler when at a swap meet I found an Audi oil cooler mounting for $5 that provided a neat solution. 1985-1988 Audi 5000 non-turbos (and Audi 100 from 1989-1991) use as a stock component, the '71-up Volkswagen beetle "doghouse" style oil cooler (part # 113 117 021). On the 5000 it's mounted near the front passenger side fender (though not confirmed with the Audi parts microfiche, I have also heard from an Audi 5000 turbo owner that the 1980-1988 turbos also use the "doghouse" cooler). Two oil hoses (inlet and return) route to and from the cooler mounting via threaded ports. By making simple modifications to the mounting (Audi part # 035 117 185 C) and utilizing the fittings crimped to the ends of the hoses I was able to easily add a second doghouse style cooler to my oil plumbing. Without an electric fan and without optimizing air flow, maximum oil temperature dropped by 20° (so now under the worst conditions oil temperature tops at just barely 230° F. Next summer I plan to add a horn/duct before the cooler to force more air over the cooler's plates in an attempt to bring temperatures down even further. Another benefit to the Audi mounting is that one could also use the even larger Type IV oil cooler with the same mounting to cut temperatures even further. A nice economic plus is that a new doghouse cooler sells for less than $50 and is widely available--and you'll always have a spare handy in the unlikely event that your primary cooler in the doghouse fails. Also, it is a very compact size and tucks under the bus nicely, picking up air flow without ground clearance worries. Advertisers of after market oil coolers make the claim that with every drop in oil temperature of 20° F, the life of the oil and the lubricated parts is doubled. That seems a bit too much of a generalization, but does confirm that a drop of at least 20° is a significant reduction.

     I've seen two versions of the Audi cooler mounting. The one pictured (removed from an '87) was well anodized and had a rectangular metal band spot welded to the mounting directly before the cooling plates. This presumeably allows attachment of stock Audi air duct to better conduct flow over the plates. I've seen an earlier version of the mounting that was not well anodized and did not include this convenient duct attachment.

Audi mounting, front view

Audi mounting, side view

Audi mounting, cooler installed

     This plan is only economical if you can find a junkyard with Audi 5000 parts. Dad's Auto Dismantling, specializing in Audis, quoted $15 for the cooler mounting. The one I purchased at the swap meet for $5 (grungy cooler included) had been removed rather brutally by cutting the inlet/return hoses, so the proper fittings for the threaded ports were included. Apparently for Audi enthusiasts, these hoses are valuable (Dad's wants $60/pair!) so unless you find the mounting with hoses cheaply at a junkyard that doesn't specialize in Audis, you can buy the mounting from a place like Dad's and then buy threaded hose fittings at a hydraulic shop inexpensively. The design of the mounting is quite simple and with the correct tools one could be fabricated (you'd have to weld hose fittings to a steel plate that is milled to accept the doghouse seals). Unless you have tools to accomplish this, if you can't find the Audi part, buying a typical after market cooler is probably the more prudent alternative.

     If you're on a terribly tight budget and wish to risk re-using an old cooler, the Audi mounting will be your only cost. In that case, you can also use the Audi mounting as a fixture to attach the cooler and feed chemicals through for cleaning--but I do not recommend resurrecting coolers (especially one off an engine whose history is unknown). It's far safer to start with a new cooler to avoid the risk of ruining your bearings from contaminants lodged in old, used coolers. To see how a professional, FAA approved shop cleans expensive aircraft oil coolers, visit Pacific Oil Cooler Service. As you can see, it's far cheaper to buy a new VW cooler than pay for this thorough treatment.

Modifications to the Audi cooler mounting:

     How you modify the mounting depends on where you plan to install the cooler. I'll describe the modifications I made and my chosen mounting location. The two arms on the cooler mounting that are grommeted for the stock Audi application might be utilized for a creative bus mounting. I cut these off and drilled two holes in the center of the mounting for bolts, spaced to accommodate the holes on the clamping section of a generic muffler pipe clamp. I bought two muffler clamps, set aside the U-bolts and used only the curved clamping sections that bite against the pipe. One of these went around the top and the other around the bottom of the rearmost end of my main heat tube under the bus. I had replaced my heat tube earlier in the summer with a 2-1/4" piece of steel fence pipe. Unlike many buses, on my bus this tube is extremely secure and therefore able to carry the weight of the cooler (which attaches to the tube just at the strong junction of the rear crossmember). Do not consider mounting a cooler in this area until you are confident that metal there is like new and sturdy (or disaster could result--if the cooler drops, so will your engine!). Mounting the cooler here allows it to just dip below the bus slightly to catch air flow, but not low enough to worry about hitting road debris (the lowest point on the mounted cooler is only an inch below the level of the transmission mount, so you'd have to drive over a sizeable road kill to impact it).

     Two bolts pass through the holes I drilled on the mounting, with the heads on the bottom. I ground the heads just a bit so they would not rub against the cooler. The bolts pass through the muffler clamp pieces and are secured on top with washers and nuts. The cooler itself is mounted last (using stock doghouse oil cooler seals). The seal end of the cooler is held to the mounting by three long bolts that pass through the cooler. For the other end I fabricated a bracket using perforated angle iron to provide support. The iron has an "L" profile, with the lower part of the "L" cradling the cooler with a piece of thin rubber between to serve as a cushion. The top part of the "L" is bolted to the stock Audi mount (grommet removed). Hoses run from the cooler, along the driver's side frame via an oil thermostat, up over the rear axle still against the frame, and to the cooler and engine.

cooler mounted under bus

In Practice:

     Thus far I've used this cooler setup for 8,000 miles. I contemplated removing the cooler for the colder months, but experimental curiosity compels me to keep it mounted a bit longer. I'm using a Permacool oil thermostat before the second cooler that diverts oil back to the engine until the temperature reaches 185° F. I have noticed that it takes a few engine cranks for oil pressure to begin registering on the gauge on colder days--this is the result of the added restriction and longer hoses. At this stage I doubt this will cause appreciable bearing wear--I have not noticed a significantly diminished oil pressure when the engine reaches operating temperatures. I will continue to be watchful of any affects.

The Permacool Thermostat

     I bought the Permacool thermostat (~$35) from a local speed shop that carried Permacool coolers. Call your local auto parts stores to see if they sell any Permacool products and special order one--or you can get one through a non-VW aftermarket parts business as found in "Hot Rod" magazine. Certain VW aftermarket businesses also list them in their catalogs (Larry's Off Road and CB Performance come to mind). These thermostats are generic items, and not particular to air cooled or water cooled oil cooler applications, so any convenient vendor will do. There are a couple different versions, the only difference being the threaded port size (you'll have to specify either 1/2" or 5/8"--I'm using 1/2"). The thermostat opens at 185°, but in its "closed" position it's not fully closed as you might expect. On startup, the thick oil takes the path of least resistance through the larger opening in the thermostat cavity to the engine and not through the auxiliary cooler. When the 185° temperature is reached, the thermostat opens, bypassing the quick route to the engine, sending the oil through the auxiliary cooler first.

     I received an old version of the thermostat that had been sitting in inventory for many dust layered years. This type did not have a mounting point on the thermostat body (it's expected that you'll buy the "mounting kit" which consists of nylon ties to wrap around it--the kit also includes four barbed, brass fittings). I bought the barbed fittings cheaply from a hydraulic hose shop and mounted the thermostat against the frame with a stainless steel strap and some stainless wire. I've seen a picture of the latest version of the Permacool thermostat in either the Jegs or Summit Racing speed catalogs that has a mounting point attached to it. It's more likely you'll get this version which would give you more options for convenient mounting (unless you're unlucky enough to buy from a supplier with an ancient inventory!).

     On a note of curiosity, I recently discovered a picture of an EMPI dual oil cooler setup on a drag car from the early '70s. The engine wasn't using a fan shroud, but had a mounting that accomodated two doghouse coolers oriented in a "T" formation, the coolers forming the top part and the mounting being the leg of the "T". So it appears I'm not the first to use dual doghouse coolers. Until I can build an engine for my bus that will run under 230° F under the worst circumstances without additional assistance, I'll use this convenient solution to dropping the oil temperature provided by VW's cousin, Audi.

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