I have used castrol gtx maganetec engine oil and have overfilled by 5mm above the F mark on the dip stick, what likely damage will this cause if any.

 

can cause all sorts of issues............suggest you either drain some out to correct level or start again, don't leave it too long!!
alyn - asperformance.com

 

Totally agree with Stockcar. I did this once with my STiV3, had smoke on start-up and oil in the solenoid. Drain some out and run it at 1/2 level when cold. Messey, but not to hard when the oil is COLD!
My old 911 is exactly the same! Run between max and min, never fuller.
Graham.

 

The problem with the overfill is the vapours out of the cam covers and crankcase ventilation get into the intake pipe, coating that whole intake pathway, inside of the intercooler etc.
I made a separate breather filter and vapour oil catch can for the camcovers/crankcase, and cleaned out the intercooler which had a heck of a oil layer in it, that was a fast improve in the very low end criuse response.

 

Good point Joth, irritating as I've just put mine back on after a clutch change. I noticed a very small ammount of oil resting in the bottom of the link tube to the inlet manifold. I think a good sloshing out with petrol or thinners will do the job (and a very good dryout!)before refit.
Graham.