hi mate,
I'm sure they are different, I thought mk3 were 5x114 and mk4 were 5x100 - maybe the ET (offset) is different anyway, hence the caps pop off. I have a mk3 8v GTi and im was led to believe the mk4 wheels dont fit.
Anyone else know better?
If they are mk4 wheels, and they do go on ok, you might get away wi a spacer to bring the wheel out slightly.
The centre cap on a wheel doesnt keep the grease in the wheel bearing anyway, thats the job of the wee cap on the end of the stub axle which stays there even wi the wheel off.