For the last two years, I’ve ran 10W-30 on my 48 N. Typically I see an idle pressure of about 10 psi and “running” pressure of ~30psi (after warm up for both). This weekend I decided to change the oil and used 20w-50 VR1 racing oil (higher zinc content). However, now my pressure is at 25psi all the time, regardless of RPM. If I slowly increase the throttle you can see the pressure start to rise slightly above idle but then it drops back down to 25 and stays there.
I would have expected a pressure increase across the RPM range. What’s going on here?