We often get asked how far the temperature needle should go up on a hot day. Loads of factors obviously come into play, your definition of hot for a start. Here are a few basic pointers that may help. 
 
For some reason, in 1978 Porsche decided to switch from a numbered oil temperature gauge to one that only has white and red range markings, making it a lot harder to read accurately. To add to the confusion, three different styles of gauges are possible. So, the first thing to do is to identify what style is fitted to your car. 
 
Now, interestingly enough, the numbered scale is still there on these gauges. If you peer to the left side of the bezel you will see small temperature markings from 30-170°C. These, however, are not exactly easy to read on the go! 
 


Corresponding graduations to your style of gauge.
 
Looking at Style A of the gauge picture the temperature runs from 60°C (140°F) to 150°C (302°F) between the boxes. 
 
A running temp between 85°C (185°F) and 100°C (212°F) is recommended. Hitting 110°C (230°F) is not an issue, but anything above for a long period of time could lead to expensive problems.
 

As pointed out by Barry and Richard, our technical advisors, these small markings are likely there only so that the gauge manufacturer could quality check accuracy / calibration of sample gauges before shipping to Porsche while some of the early cars had prototype gauges fitted which only had a halfway indicator - so don’t break your neck trying to read the calibration if you have one of these.
 
The other critical factor to monitor, with regards to oil, is obviously your pressure. Fortunately, Porsche kept a graduated scale for this one (maybe a sign that Stuttgart engineers were more concerned about pressure than temperature).
As a rule of thumb, the bar pressure should be about the same as 1000 rpm on a warm engine. A quick check I was told by a Porsche Race Engineer a while back: fourth gear at 4000 rpm = four bar. 
 

Owner’s manual states oil pressure at 90°C should be approx. 4.0 bar at 5000 rpm. 
 
Do not worry if your oil pressure light comes on or blinks when your oil is very warm and your car is at idle speed (stopping at a junction after a spirited drive on a hot day, for example). 
 
A small blip of the throttle and the pressure needle will shoot straight back up, indicating all is well. However, should the light come on while driving and the oil pressure suddenly drops, do turn off your engine ASAP and get the car checked. (It could just be your sender playing up or a more sinister issue).