My car has apparently has a blown head gasket...
The options at this point are basically:
put $5k into an 8 year old car with 120k mi that is otherwise in good shape (with a 2 year warranty on the new engine), or
spend $15k on a newer (used) car -- which will essentially be an unknown quantity in terms of what kinds of problems it may have.
How do you decide which is the better course? (In my case, I've got a trustworthy mechanic to do the work.)
Edit: In the end, we decided to replace it. Sold the car to the mechanic, who tried to revive it, failed to do so, and is now stripping it for parts....
Thanks to all for the helpful advice.