Diesel or gas doesn't matter. Normal for at a truly warm MB is between 1 and 2 atmospheres, so staying at 3 is not really normal assuming normal idle speed of around 650 on that car since it is not adjustable. If you are idling much higher, there is a problem in your air management system. Also what weight oil are you using?
P/S As a card carrying nudist, I can assure you that you can add to your fun by becoming a nudist. Check with AANR (American Association for Nude Recreation) on the internet for the location of a resort near you. You can spend a day as a guest and find out how nice and friendly everyone is. It may change your life.
Auto Zentral Ltd.