most likely cause is either the mail reservoir cap is not tight, or there is a leak in the pressure hose from the engine to the reservoir tank (one hose takes crankcase pressure to pressurize the remote tank, the other hose lets the oil (under pressure) flow up to the tank on the motor. A small leak or slightly loose cap can reduce the pressure enough to not work while idling, whereas at WOT settings the pressure can overcome the leak and still push the oil up to the motor.Thats my guess…You can always use a vacuum/pressure pump (I have a mighty-vac I use to bleed brake systems) that would work well, you should be able to pinch the supply line up where it enters the tank on the motor, and pressurize the other line where it connects to the motor crankcase, and see if it leaks down. If it does, find the leak and you will have solved your problem.2008 Pantera Classic2014 Mercury Pro XS 200
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