Changing oil type question

[clickman]

I've been using Mobil1 0W-40 ever since I bought my 01 4 years ago. But after reading a number of threads regarding oil quality, I've decided to move to Castrol Syntec 5W-40.

Here's the question:

Is it a good idea to "flush" the engine the first time a new type of oil is used? I.e. drain the Mobil1, put in the Castrol, run it for a bit, then drain the Castrol and put in a new load?

Obviously I'd rather not do that, for the cost and PITA, but if it's important...