Recently purchased a 86 420. I know it's summer and all and that I'm doing city driving, but it seems that the engine gets very hot. Cars runs smoothly, except for a slightly rough idle, but it seems that there is this wave of heat coming off the car. However, the temperature guage on the dash indicates that everything is fine, somewhere between 80-90. First of all, is this normal? Second, how can I check to see if the guage is actually working?