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Message: <blockquote data-quote="Tazza" data-source="post: 13847" data-attributes="member: 82">Sounds like your hydraulic pump is worn. As the oil warms up it gets thinner, thinner oil means it by-passes easier. You could pull the pump off and check it for internal wear. It will most likely be a vane pump, scratches that run around the cam plate are fine, the biggest issue is what looks like chattering marks. If there are marks your problem is the vanes are un-able to stay in contact with the cam plate at all times to generate pressure. They sort of skip over the top, this is where your pressure would be going if its worn. Wear on the front and rear housings can be an issue too.The only way to test it short of pulling the pump is to get it pressure and flow tested. They remove the high pressure hose and attach a test unit to load the system down and check flow rates. Never just stick a pressure gauge here, there is no relief valve and you will do damage to yourself or the pump.</blockquote>