I have a Rotax engine which, when the oil is cold, shows a mild pressure drop when the rpms increase.
Here's a video which shows it happening. The oil pressure is shown in the top right gauge, and the tach in the middle left: https://imgur.com/a/CM5F4vR
I don't have a healthy explanation for why a positive displacement pump would see a pressure drop at the output when it spins faster. So the question is: is there ever a situation where it is okay for oil pressure to drop with increased RPM?
Additional details in case case it matter:
- The oil is fed from the oil tank to the oil cooler and then to the pump via rubber hoses.
- The above event only happens when the engine is cold, perhaps indicating suction hoses collapsing under vacuum.
- There is an oil bypass downstream of the oil pump, it is designed to trigger at 5bar