haha ok it works both ways. during the time when the engine is running, it will blow a little oil into your cooling system, but you'll see some collecting in the radiator, i've noticed with these trucks you wont see much if any in the reservior. when you shut the truck off, oil pressure is 0 while coolant pressure is 16 or so. pressurized coolant enters the oil system, which is much more visible.

the usual is seeing more coolant in your oil.

unless your seeing coolant dripping on the ground, pressure testing the system isnt gonna show you anything other than it wont hold pressure. since 7.3's dont usually blow head gaskets (i got 309k on mine, heads never been off), ill put money on your oil cooler.

have you noticed the coolant level dropping? or find yourself adding coolant recently?

 

is the oil milky on your dipstick or just milky at the oil cap?

 

yea theres something i should've asked haha

if the truck's been sitting a while, you get condensation buildup inside the engine. as soon as you start putting some heat in it, what will look like blowby is really just steam and other junk.

if it's not drinking coolant, take if for a good highway run (like an hour or two) and that should clear that up then change your oil haha