I recently had my radiator go bad on the way to work. By the time I got pulled off the road my temp gauge was at 260 and my engine light just came on when I was able to shut off the car. After changing the radiator while driving the car I noticed at 70 mph my rpm was 3800. I'm sure the transmission is in overdrive. The car runs and drives fine but it seems like the rpm's are running high. Before the cooling issue the car was at about 2000 rpm at 70 mph. Does anyone know what could of happened?

 

Sounds like the "tach" (trim package in dash with wavy pointer, loosely correlated at times with engine RPM, designed and intended to promote "sporty" image) broke.

Not related to the cooling system issue.

 

Is there a way to check the tach ?

 

Check it against a piece of actual test equipment. Some timing lights include a tach for example.