I’m not sure what the ‘normal’ behaviour of the oil pressure should be, but I have had the same on my 12/68 280SL after the engine was completely refurbished: whether at idle or full regime, cold or hot, the oil pressure would never come off the maximum of 45psi on the gauge.
Until one very hot day last summer, when it dropped a bit at idle once the engine was really warm. I was so used to seeing the needle at the maximum pressure all the time that it actually scared me, and I nearly shut down the engine immediately. Instead, bravely (and probably foolishly) I gave a brief nudge to the accelerator, and immediately saw the oil pressure needle move up; more nudge, more pressure. Then I remembered that on my other vintage engines, that is in fact the ‘normal’ operation of these older engines.
Summer yielded to autumn, and the gauge returned faithfully to the maximum under any and all conditions, never moving down. It still behaves this way to this day.
