I have a 2000 XJ that has about 6000 on a rebuild, new pistons, water pump, and head was inspected and cleaned professionally but now it has a lot of blow by and leaking out out of valve cover. When driving it will push the oil fill cap out of valve cover and spray oil every where. I hate to think it is rings and am looking for other ideas before i tear engine down again.

 

Well, assuming your PCV valve is working correctly..... But even if it is, that king of blow by is rings or valve guides. Usually rings. Sorry about that.

Even if you have been running stupidly rich and washing the cylinder walls with raw fuel, I don't think you could wear out the rings in only 6k miles.

I'd say that something in that rebuild was not done correctly. No way to know what until you pull it apart.

 

It may not be blow-by. If the valve lash wasn't set up properly, one or more lifters may be bottomed and causing a constant flow of oil to be splashing inside the valve cover. If this is what's going on, the rest of the rockers aren't getting the oil they need. Take the valve cover off and start it up, but wear a raincoat!