catback exhaust and higher oil temp

[wasti]

some days ago i got my catback exhaust installed.

great sound which fits the car very much but.....

i have oil temps which i never had before.
even during driving in the city with low speed its going up to 90 very fast.
driving on german highways (which dont have speed limits in some areas) with high speed is pushing temp up to almost 120 within some kilometers and i have to slow down.

i never had this before. with original exhaust and travelling with 240 km/h on german autobahn temp went never higher than 110 / 115 even after long distances.

asking the manufacturer of the exhaust system doesnt help. they have no glue and didnt have similar problems with other cars.

anybody here who could give me a advice what this can be?
how come a catback exhaust can change the oil temp in such a big way?

i am happy for any messages from you.

thomas