Just installed after market oil pressure gauge and sending unit in 70 351 w. In order to install, I had to use bushing and short nippleto install. When I fired it up, pressure went right up to 60 lbs and then settled to 52-53 steady. As soon as I put it in gear. it drops to 20lbs. I realize I need to put a mechanical gauge on it, but why would putting it in gear make it drop/difference?
Any thoughts?