Folks - all those pages made fo interesting reading. On My Def 110 I'll fo the following:

1. get the P38 fans

2. Install them in FRONT of the rad.

3. They were installed in front of the rangie anyway, drawing air in to cool the AirCon radiator

4.They will go at the front lower half of the rad

5. One day I will find an intercooler of the right size that I can install in front of the upper half of the rad and I'll be done.

6. I'll have the viscous fan removed as I like to live dangerously

If my engine fries I'll let you know - also as I had a medical procedure done and I have to be quiet, if you know of any Def specialist that can do this in South England / Surrey let me know

Cheers!!

G

FWIW (given that I have only just come across this thread - guess what I'll be fitting to my 90PU when the 200 tdi goes in...) the reason that cowlings are fitted is to allow fans to draw air through the rad. Without the fans and cowlings in the way, something like a Defender cools itself pretty well unless it is going very slowly or very quickly.
Slow speed means not enough air is passing over/through the rad.
At high speed, air can't travel through the rad fast enough to stop air 'backing up' behind it. You use this effect when you generate a bow wave if you are wading. Air can be thought of as a very thin fluid, sort of lo-cal water! So at high speed you build up a blanket of insulating air in front of the rad and the heat can't be dumped efficiently from the hot water in the rad into fresh cool air (air is a very good insulator).

You should always get better cooling if fans are behind the rad, but sometimes they have to go in front for engine packaging reasons.

These days, cowlings are also used to control heat build up in engine bays from higher output motors. Not for the motors benefit, but because most saloon cars are expected to provide such high levels of passenger comfort.
Hmmmmm..... I wonder if there's a reason that I drive a Landy and ride bikes....?