ok today i notice at idle my oil pressure was a little below 50 psi ...driving around it shoots up to 75 psi....i am using 15-50 mobil 1 ....before at idle i was getting around 75 psi and 90 psi driving around....should i be scared or is this normal for the hot weather.....am also due for an oil change ....the truck is running fine and i have no oil loss....thanks...