10' 4.2 V8 Rattle
 

I have been chasing down a fairly consistent engine ticking/tapping. The engine is always silent upon startup for the first 5-10 seconds whether the engine is hot or stone cold. A little background, I have tried many oil viscosities from thinner to thicker with no change at all. I have since replaced the oil with 502 spec 5W40 that's called for in the manual. I've replaced the valley pan gasket, anti-drainback valve and oil jet, air filter.

If I remove the oil filler cap the ticking disappears... I used a stethoscope and I was able to isolate the noise to the passengers side valve cover. If I position the scope and then pull the oil cap I can hear the tick
dissapear and reappear when the cap is replaced. I can only assume that the noise is valvetrain related? If I pull the hose that leads from the drivers valve cover to the oil separator there is a good amount of pull (vacuum) from the separator and if I plug the hole in the valve cover it builds substantial positive pressure? Does anyone know if this condition is normal?

Does that sound like the oil separator is functioning properly? I've already had it off and replaced the diaphragm with a new one from RKX.

Anybody have any idea???