The picture on the left is a graphic demonstration of what happens when an oil cooler is incorrectly mounted on the engine case. This is usually caused by either installing the wrong seals, or applying excessive crush to the seals when tightening down the cooler.
The way to avoid this situation is by first understanding that the Volkswagen factory produced at least four different oil coolers over the life of the upright Type 1 and early Type 2 engines. These oil coolers are partially defined by the size of their oil passageways, among other things.
This variation in cooler galley sizing tends to reflect some of the oil galley internal diameters of the Volkswagen air-cooled engine cases. As the cases evolved over the decades, their oil galley sizes increased. During this same period, the Volkswagen factory also changed the design of the mounting points on some of the older oil coolers that were used on single port engines.
Despite these changes in overall galley sizing, the engine builder can generally use any of the four Type 1 oil coolers with any of the Type 1 or Type 2 engine cases. Note that this faq includes pre-'72 buses only. The video clips in this faq show the differences between all four oil coolers, but only as they are relevant to choosing and installing the correct seals.
When mixing and matching between coolers and cases, the engine builder may find that the stud in the case used for bolting up the cooler will have to be replaced with a step-stud. Some people even drill and tap the case for the bigger stud. Other concerns with mixing and matching coolers to cases include either drilling out or shimming the internal diameter of the two holes in the case, so that they match the oil cooler studs. You can see those two holes in the picture on this page.
There are several reasons for mixing and matching between coolers and cases with mis-matched oil galleys. One example would include the need to convert an older single port engine case to the far superior dual port intake manifold and fan shroud system. Along with the bigger late model "doghouse" oil cooler and wider fan, the engine builder should also see about using the newer 8mm head studs in place of the 10mm head studs. The oil cooler seals used for this conversion are called adapter seals. They are tapered end-to-end on the outside diameter, and they will have to be purchased seperately, since they are not included with the typical gasket kit used for engine building.
At the beginning of this faq, the picture shows that excessive crush on the seals will cause seal deformation, resulting in oil galley flow restrictions. The way to avoid this is to make absolutely sure that the cooler is mounted so that it is directly touching metal at all mounting points. The use of washers for *some* coolers, as demonstrated in the video clip, keeps the seal from spreading out due to excessive downward pressure.
In the third video segment of this faq, engine builder Mike Smith refers to the Type 3 oil cooler seals. These seals are the same reddish-brown color as the Type 1 oil cooler seals, but they are much thicker. Per his discussion in the video clip, make very sure that you don't use those thicker seals on your Type 1 engine.