next time you know it would do it, check the HP resevour. It is the box dead center on the top front of the motor....long thin aluminum thing right up top. take the little motor cover off, and there will be a plug on the drivers side of that resevour. Take the plug out and check the oil level in there. It should be 1 inch or less from the top....im betting your resevour is draining down on an incline...