You've never see an old vehicle blow a substantially "bluer than normal" cloud. That's what I'm talking about.
> Blown gaskets on ICE engines like E25s leak both oil AND coolant, no?
This is way, way too broad of a statement. The Subaru EJ25 tends to leak oil externally from the valve covers. When they have head gasket problems it tends to be combustion gas into coolant which blows the coolant out the expansion tank until equilibrium is reached. Typical head gasket failures cause some degree of that but coolant mixing with oil is more typical. Many V engines have intake gaskets that can leak coolant into the intake or oil or both.
Regardless, if you can taste coolant in the exhaust the car is basically at the point of "fix it now"
> I might be mixing up blown heads with cracked manifolds which often go hand in hand since temp extremes in engines fissure cast parts like the manifold.
A sizable minority of cars don't even use cast manifolds anymore. While it's possible for cast manifolds to crack in a way that makes them leak that's rare and it's more common for them to crack their mounting tabs off. Steel exhaust tubing can and does sometimes break after many years of vibration, say nothing of rust.
While cylinder heads can crack it usually takes the kind of overheating that requires major work to fix in order to make it happen so just about nobody is driving around with a cracked head.