Back Fan Shroud Tech

Inside a late model "Dog House " fan shroud

There is currently a lot of miss information about the VW cooling system, in particular the fan shroud. Now I am by no means and expert and I am not going to try and baffle people with complicated words or formulae. Everything here is my opinion and understanding and I will happily discuss it with anyone who disagrees.

Firstly there are 3 main types or VW fan shroud

36hpshroud.jpg (19317 bytes) The 36HP fan shroud was found on the early type 1 engines which where known as 36HP engines. With a displacement of around 1192 cc. They have no horns for heaters and used to have the oil cooler inside. They are a very clean looking shroud with nice lines.
standardshroud.jpg (18494 bytes) Standard Shroud was found on most type 1 engines. It has horns to send air to the heater boxes and maintained the oil cooler in the shroud on the same side as no 3 & 4 cylinders. many people cut the horns off or plugged them with a welsh plug.
doghouseshroudbottom.jpg (11956 bytes) The dog house shroud, is shown from below, you can clearly see the area to the top of the photo which was designed to house the oil cooler. The theory here was to allow no 3 & 4 to get cool air as it no longer needed to come over the oil cooler. When using this shroud you need a bigger fan and different oil cooler. There are aftermarket versions of this dog house shroud that look very similar to the 36HP shroud from the front but have the dog house at the rear. These were found on late model 1300TP and 1600TP engines.
fancomparrison.jpg (12628 bytes) If using a dog house fan shroud you need a larger late model fan. You can see one here next to an early. The later is 5mm wider than the early. This extra 5mm was used to send air to the cooler part or dog house.

All the shrouds were very similar in the way the worked. The VW fan threw the air out and the shrouds controlled and directed the flow down over the cylinders. If you were running a standard shroud and decided to aid an external oil cooler in place of the standard one then you are changing the internal ducting and will decrease the amount of efficient air flow to your cylinders. If you are going to add and external cooler, do it in addition to the standard one not is place of it.

The internals on a fan shroud are very clever indeed. They take the air that is thrust outwards by the fan and redirect it to the cylinders.

cutshroud.jpg (16991 bytes) This late model dog house fan shroud has been cut open to show the directional fins inside. The standard shroud is similar but has less fins as it relies on the cooler to redirect much of the air flow. You can see how there is nice gentle curved fins that take the air and point in down
cutshroudfan.jpg (17753 bytes) He we see the type of output we get from a VW fan. The air is thrown at right angles from the fan. As it turns around. This is not like a standard fan which pushes air. You can see that if there was no fins then a lot of air would go into the side of the shroud were it would cause problems with the air flow.
cutshroudfan1.jpg (21653 bytes) After it hits the fins they direct it downward towards the cylinder heads, as shown by the black lines. You can see how important the fins are. They get all the air working together and heading in the right direction with a minimal amount of resistance. Imagine if you pulled a few of these fins out, the air would run into each other and create a sort of turbulence. This is why it is important to leave it alone .

The above photos show how important the internal fins are. The VW fan is a very different creature to most fans. This is why a center mount fan setup that uses a standard VW will not cool the engine properly. I would never run one on an engine I own. This is using the standard VW fan, not using a Porsche fan which is entirely different story.

If you have any question or comments please e-mail me and I will try to help. I will be updating this page as I continue on  building my type 4 upright kit with integral fan shroud and fins.