I have a leaky heater core on my 1994 850. From time to time it'll leak large amounts of water/coolant onto my floor, emit steam, etc.; usually when the car is hot or I've driven a long distance. I've gotten to the heater core to take a look at it while it's leaking, and it leaks at one of the joints on the pipe going FROM the heater core; it's located underneath the core.

Does this mean that it isn't the heater core itself that is leaking, but that I'll just need to replace the O rings? When I bought her in February, the heater core had just been replaced, so I'm wondering if they forgot to do the O rings when they put the new one in.

 

It could be just the O-rings, but since you'll drain the heater core while accessing them, you should pull the core and test it for leaks.

 

If the core has not been replaced within 5 years, replace it. You can get nearly new ones from the jy. The one I pulled the other day had a 9/09 date on it. They usually last 10 years, if they are Volvo Cores.