"It is believed that the polar polyetheramine’s attach to the hydrocarbon deposit and via thermodynamic activation, softens the carbon. The flowstream across the valves and inside the combustion chamber then blow the hydrocarbon deposits to the exhaust stream.
Increases in hydrocarbon loads not only exit the exhaust stream, but can also enter the oil. It is always a good idea to change the oil after using a strong fuel system cleaner."
This is what I've always believed and is the reason I run a PEA FSC near the end of my OCI. I also believe it is better to run it during short trip driving (several stop and starts to allow the PEA to 'soak in' to the valves etc...) rather than on a long highway drive. It seems like a long highway drive is a good thing subsequent to the FSC treatment (to blow out the previously softened carbon).
I've also always felt that using FSC's in warmer weather was more effective but I'm probably being anal....