I have a 2003 F150 with a 5.4 engine. It started running rough and I noticed oil in my coolant. I checked the dipstick and it is clean. I was just a little low so I added oil. When I removed the oil filler cap on the valve cover it was like a milk shack, but nothing in the oil pan itself. I am a loss I have had blown head gaskets before on other vehicles but nothing like this. Any advice?
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The white emulsion on the inside of the oil filler cap is caused by 'under bonnet thermals'. If the PCV is under performing then the fumes and humidity from the engine crank case are cooled and solidified by cold air entering the engine compartment. The cold air cools the cam cover/rocker cover and causes the emulsion on its inside.
Significant amounts of oil in the cooling system is symptomatic of a leak between the oil galleries and the cooling system galleries. The head gasket is one of the usual suspects but the list extends to the oil cooler, engine block cracks, head assembly cracks.
If you feel up to it drain the engine sump of oil into a suitable container and check the oil for water contamination. If there is no contamination you can always put the OK oil back into the engine.