It seems like my 8 month old heater core on 99 V70 is start leaking. What could cause this to fail so quickly?
Thanks for the help.

 

Was it an aftermarket heater core?
If so, that can be one answer, if it's a Volvo core either the install was incorrect or something else bizarre happened but it should still be under a parts warranty

 

If the setup is the same as in my 98 V70 T5, there is an O ring kit that is required to perform a proper installation. If someone other than the dealer performed the repair, and was not aware of this, it could be the root cause of your leak. Hope this helps.
Regards,