What is really high? Don't let it go into the red. I wouldn't expect much heat at 90 but you should get heat when the needle goes into the normal operating range mark. At idle it's normal for the guage to go up to maybe 2/3rds until the electric fan kicks in. You won't notice that when the car is in motion or with the a/c on even at idle as the electric fans are in operation when the a/c is turned on