if i accidentally hooked a heater core line up to a vacuum line would it be the cause of coolant in my oil?

 

Welcome to the forum

What engine?

No, unless you left it that way for awhile, but engine wouldn't run very long

Vacuum line goes to intake manifold which has no connection to oil area of an engine
But if left that way coolant could run down inside the intake and sit on a piston, then leak down past the rings into the oil pan

There is a PCV hose and Breather hose that hook to valve cover(s) these lead directly to oil area, and are larger hoses, like heater hose size

 

4.0l v6 ohc 03 ranger

I did new timing and refreshed the entire engine except for the heads. The heads were never touched. Everything was torqued and sequenced to specs. I tried starting it the night before the issue and the battery was dead. Left it on the charger and tried starting. Battery was junk and needed to charge overnight. It became pressurized and leaked gas out of one injector. Fixed the oring and tried again the next afternoon. Only had it run for a second before smelling antifreeze. Looked in dipstick and had coolant. Drained it all from block.

 

So the engine was pulled out to get to rear timing chain

And which hose to the engine had the coolant from heater core?