If you go with the coolant version, you have two options. My passat had the thinner version that you see on various other older vws. When it failed, I upgraded to the thicker version to provide more cooling circulation:
http://www.amazon.com/028-117-021-L-Volkswagen-1-8T-2-0-Cooler/dp/B005FN1DIK/ref=pd_sim_sbs_auto_3
These days there's a much cheaper aftermarket version:
http://www.amazon.com/Cooler-028117021E-VOLKSWAGEN-Passat-Allroad/dp/B002N4GPUA
Here's the thinner style, for reference:
http://www.amazon.com/Volkswagen-Co...Cabriolet/dp/B003OUALQQ/ref=pd_sim_sbs_auto_1
To use the thicker version, you just need the longer center threaded pipe to go with it. Just twist on/off to replace. We also combined that with a taller oil filter for more cooling volume/capacity. I think we got an extra .7L out of the swap.
http://www.amazon.com/028-117-021-L-Volkswagen-1-8T-2-0-Cooler/dp/B005FN1DIK/ref=pd_sim_sbs_auto_3

These days there's a much cheaper aftermarket version:
http://www.amazon.com/Cooler-028117021E-VOLKSWAGEN-Passat-Allroad/dp/B002N4GPUA

Here's the thinner style, for reference:
http://www.amazon.com/Volkswagen-Co...Cabriolet/dp/B003OUALQQ/ref=pd_sim_sbs_auto_1

To use the thicker version, you just need the longer center threaded pipe to go with it. Just twist on/off to replace. We also combined that with a taller oil filter for more cooling volume/capacity. I think we got an extra .7L out of the swap.