For those running dexcool, changing to a spring type design could make a great deal of difference.
The additional downward pressure of a spring, ensures additional sealing integrity over the oem weighted type cap. This additional protection can help keep out air which can bypass the recovery bottle and invade the system.
Once there is air in a dex system, the anti corrosion protection is inhibited. Air, for the "green" type, beyond the basic cooling issues of "hot spots", doesnt effect the anti corrosion inhibitors to the same degree as it uses silicates and "plates" all the surfaces. These "long life" types, need constant contact to maintain the protection. This is where the problem begins.
Essentially, there are two ways air enters the system.
1. the recovery bottle is ALLOWED to get low, and the system sucks air in through the vacume produced as the engine cools.
2. through the radiator cap. often in a dex system, one will find debris, which in itself may be harmless, or a sign of massive corrosion in the system migrating to the outside world. This debris will often form on the sealing surface of the cap..and through the magic of time, is breached and is no longer effective.
If you have a dex system, check the radiator cap sealing surface for corrosion. If it is present, you have some choices to make.
1. ignore it, and take your chances.
2. flush the system completely and thoroughly and either fill with another long life coolant (G-O5 comes to mind) or switch to Prestone "Green" which will put you back to 2-3 year flushes, but most likely you will be doing that with "long life" anyways.
And then...REPLACE that weighted oem type cap with a spring STANT to gain additional security.
Finally....MAiINTAIN the level in the bottle at ALL times. I've heard that the general is now suggesting that the level be maintained cold at the HOT level...for further security.
A good read on radiator caps and long life coolant.
this is a nice link, as you can see the corrosion on the radiator cap up close and personal. Nasty stuff.