450SL temp guage shows 250 F
 

Since I bought this car the temp guage gets really high, I flushed the radiator, changed the water pump, temp sending unit and the fan switch and still gets as high as 250 degrees. Today I noticed that the electric fan doesn't kick in till the guage shows 250 degrees, So I checked the temp with an infrared digital instrument and it showed 221 degrees. Could the guage be wrong? Also, is it normal for these engines to go up to 220 degrees driving on highway speed in 70 degrees weather?. Any advise?. By the way, the car is 1978.