Just changed oil in my 1999 4.3 liter mercruiser with Mobile 1 10-30 synthetic and a K&N oil filter. Showed good oil pressure when I warmed up the engine before the oil change and now that I have new oil and filter on and started the engine for initial warmup period it show's no oil pressure at the gauge. Engine sounds fine and oil level is up. Not sure if there may be goop in the sending unit or ?????????. Changed oil in a lot of engines and never had one not return oil pressure to the gauge. Scratching my head. Any ideas?