1992 Cadillac El Dorado

Can anyone help please? I have a 1992 Cadillac Eldorado Touring Coupe with 4.9L engine with 233,000 miles on it. It has JUST started to KNOCK TERRIBLY EVERYTIME I start the engine. After about 5 minutes of running, the knock goes away. The engine DOES NOT overheat. My thoughts are that I am getting water mixed in the oil since I loose water quickly. Here is what my radiator cap looks like:

Here is what my oil cap looks like? I see some white on the cap, but when I look inside the engine or pull the oil dip stick, it all seems fine...

Here is the engine:

I have been told things like a head gasket, leak in a manifold, pull spark plugs to look for water, exhaust leak??? Can anyone please give me more information?? THANKS MUCH!! Marty
January 30, 2007.

The radiator, if the tranny cooler lines attach to it, can leak tranny fluid into the radiator! Check your transmission fluid! If you have a small bit of white oil on the cap, change pcv! As for the knock, connecting rod or wrist pin!

Aug 13, 2007.
Man oh man, if coolant is getting into the oil, the intake manifold gasket is leaking, remove the valve covers and pressure test the cooling sys to check this and if you have a knock from it replace the engine dont let someone replace the gasket it will cost you more in the long run

Sep 17, 2007.