Welcome, I'm Chris (aka Moose) I'm an independent contractor here at Just Answer.
Can you go into better detail on this " When I turn the heat on it is fine at first but then cools off after a few seconds on the drivers side stays hot the entire time. The passenger side if fine."
I cannot tell which side has the issue?
I assume you have auto climate control where as you can change the left and right temp independent.
If you have one side getting heat then it is not the heater core, there is only one and 2 blend doors.
Thanks for asking your question and letting me try to help you.
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