What Capt Solo said plus: 1) emulsified oil means coolant in getting into the oil and the engine may get damaged, 2) besides a head gasket either the head or the block can be cracked. Much more expensive than a head gasket. 3) starting off in the morning, if you are emitting a lot of white smoke...
I just can't believe I can get the Shield and G19 plus 5 mags mounted in there and still have room for anything else. That's why the Fort Knox box is on the rear floorboard, attached with a grade 70 transport chain. Which ever firearm is left in the vehicle goes in the Fort Knox when parked...