When the catalytic converter fell off, I debated whether or not to give up on the Honda. Tunex told me I had a head gasket leak and it would cost over $1600 to fix. But with Tory Mesmer's help, we checked for coolant or anything else in the oil and found none. And even after added dye to the coolant I couldn't see any evidence it was leaking outside either. And, just in case, I put in some head gasket sealant.
I then spent a couple hundred bucks replacing the ignition coils and spark plugs, and replaced the thermostat, the temperature sensor and the temperature switch (I did all these myself to save money.) I still overheated later, but then found I needed to "burp" the radiator and was low on oil. It was then working fine. I felt like I had licked the problem and could get at least another year out of the car. The catalytic converter is a very pricey thing, but I thought $900 would now be well spent.
Oops.