"slow" oil pressure?

[tesavage]

I started my '82 300D for the first time in over a month yesterday. Temps were in the teens and it started right up with a crankcase full of 15w40 conventional oil. That's the good news.

The bad news is that after a 20 mile drive on the interstate I noticed the oil pressure was low. I freaked out and pulled over, and it registered a healthy 1.6 bar at idle just as it always has. Revving the engine slowly, it would peg at about 1200 rpm, but if I revved it quickly, it wouldn't hit 3 bar until 2000 rpm or slightly more.

I've heretofore always run synthetic in winter; is this just the nature of cold,heavy dino oil, or have I got something more serious at work here? I'm really anxious to start driving the car regularly again, but I'd appreciate some reassurance before I do so.

Thanks,
Tom