I found that to be the case with C34s.After fitting an FMIC and FFP, I somehow fitted a 26mm plastic rad instead of the 32mm. My fault it was early days with the Stags and never noticed it. I had overheating problems. The stock water temp gauge never went over halfway, but when coming up the mountain the oil temp gauge I fitted went up to 120/130.+.And it started to boil in the back of the plenum.
Once I fitted the 50mm alloy, no more boiling and oil temp always less than 100.
Had to do a bit of cutting but well worth it.