Without a doubt. If the cylinders are filling up with water. Water does not compress.
It could if the coolant is leaking on to the top of the piston.
If water or oil is getting into a couple of cylinders, the plugs can be fouled and not sparking which can keep it from starting.
Happened to me. Termostat stuck closed. Changed thermostat. Test for possible blown head gasket. Happened to me. Termostat stuck closed. Changed thermostat. Test for possible blown head gasket.
Possibilities are low coolant, defective radiator, leaky hoses, blown head gasket...
You are getting pressure in your cooling system if they are not rusting out, could be from a blown head gasket or hopefully a bad radiator cap.
The heater generates heat by blowing air over a small radiator type device (heater core) under your dashboard. The device runs hot coolant through it continuously. If you have a blown head gasket, your coolant is being evaporated trough the firing chambers and tailpipe. When the coolant level is low due to evaporation, there is no water to flow through the heater core. Keep in mind if you are not certain that this is a blown head gasket, these models were notorious for a defective lower manifold gasket leak that caused it to lose coolant the same way a head gasket would.
Head gasket is probably blown. Water is passing out through exhaust. This is a common problem with subarus
Timing not set properly, carbon deposits in the combustion chamber, cracked head, blown head gasket, overheating.
External or internal leak. If there is no apparent external leak and you see white smoke then you have a blown head gasket.
Rocker gasket? If you are referring to a valve cover gasket, no it will do no damage as long as you keep the oil level full.
The noise you are hearing is probably the coolant boiling in the block. If you keep running the engine in that condition it will cause a blown head gasket or cracked head or both.
Sounds like you have a blown head gasket. If you get white smoke out through the exhaust, you may also have a cracked cylinder head.