Or can I just use the small catch can style? Its my vanagon aaz conversion.
Not sure I understand. Are you asking if the tank needs to have more fluid put into it when it gets low? - yes, this tank's main purpose is to collect any air in your system as it should be the highest thing in the system... with the steep rake of most VW hoods and the height of the head, its not possible to have the top radiator tank be the highest as many other cars do.
good deal it will save me a lot of space using the the catch can style tank. Most that I see enter the bottom. But I will be sure to double check it.
You need the flow-through of the oem tank or you'll get some crazy air pockets. I'd highly recommend keeping that and the overflow tank...
The systems with one hose fitting also have a small bypass hose that goes to the high point in the radiator to allow all the air to collect in the pressure tank.
Chris