Can anyone shed any light on why this might have happened to my 98 Subaru:

Went for a drive, parked up put the heater on, steam came out through vents, since then I have had a overheating problem and the heater doesn't work properly.

Can't feel any water on the inside of the car on the carpets and have ensured there is sufficient water in the engine!

 

That same thing happend to friends vw bora ones can't remember what the problem was.
I think they said it was something to do with the head gasget but i am not sure.

good luck

 

Possably the heater matrix is leaking, are you losing any coolant from the engine (just check the header tank)

Tony

 

id check the matrix mate and get it looked at before u do any damage to the engine

 

i had the same check your water as mine kept going turned out to be my head gasket