I know that in diesel trucks I work on at work, the oil temperature generally stays even with the coolant temp, as long as your not working the engine real hard. Most of them are using dino oil in them, and its not uncommon to see oil and coolant temps hit 215*F. Ofcourse, they have oil coolers, so you would expect the oil and coolant temps to be pretty close under light duty driving. I'm not sure though what its like on a passanger car without an oil cooler. I know my Jeep's coolant easily hits 215-220*F in the summertime and it has no oil cooler. Unfortunately, I don't have an oil temp. gauge for it, so I don't know if oil temp stays relatively close to coolant in that type of application.