All modern cars both over cool and under cool by design , the older cars (30s 40s 50s) used to have massive radiators and huge sumps , this gave horrific drag coefficients , so modern cars went to tiny radiators and sumps .
They over cool at speed , (better head design, pumps and rad airflow , etc ) so the stat controls the flow - the goal is CONSTANT temps no matter what the load is .
When stationary the car is undercooled , even at no load /idle it would overheat , so fans were added again the goal is a constant temp .
Better quality cars use a viscous fan as it gives a more constant temp , but if no room is available , sideways fitted engines or as a cheaper design option then electric fans are used - these cause cyclic temp changes due the use of an electrical temp sensor ( fan on /off temp targets and delay times)
Aluminium cylinder heads are damaged by over temps and cyclic temp variations - expansion causes cracks in valve seat and spark plug areas and fatigue it also stresses gaskets causing sealing issues.
The oil system as a secondary heat control is fine BUT at high speeds , the temp rises even without adding power tuning , 120 degree oil is common on fast motorways with many cars , the oil temp is sump oil temp , so return oil after its done its job . Around the engine this temp can be 60-70 degrees higher , so up near 180 degrees at the piston rings !!
Same thing under the piston where the oil is cooling the piston with a spray , these higher temps thin the oil , so the oil film at the rings is thinner , this effects the temperature at the rings , the heat passes across the piston surface and through the rings to the block .
Detonation is now much much easier with a tuned ( read higher boost) engine .
This is why race engines use dry sump systems , it allows very close temp control and usually cool both the scavenge sump oil and the return to tank oil , using two oil coolers .