Multiple warnings

History: On the advice of the dealer, the original owner paid to have the 'short head bolt problem' fixed. ($5,000.00)
I was told this after the sale was completed, so even though they didn't have paperwork showing it, I can see no reason why anyone would disclose this information (at that point) if it wasn't so. The original owner was elderly and had passed. Sale was made by her niece.
Problems: Multiple 'Information center' messages.
First one came at idle saying 'change oil'. I had just changed the oil and reset the information to 100% at 63124 miles. I did another reset and all was well.

A couple days later while sitting at a traffic light, 'service soon' light came on. At the same time 'idle engine' came on very briefly.
After that message disappeared, a new one saying 'engine overheating' came on. Temp gauge was at normal (center of gauge). Suddenly it jumped two notches and immediately went back to normal. I mean really fast!
When the traffic light changed, I turned off the A/C, turned on the heater and proceeded down the road until I got home. (About 15 miles) No other issues (other than the service soon light staying on).
After engine was cool I checked fluid levels. All normal.
The next morning the 'service soon' light was off. I noticed that the A/C fan would not blow, and changing to settings made no difference. I turned off the engine and restarted it. A/C worked fine.
Yesterday I drove it about two blocks to the store and came home with no warning lights. Everything working properly. Engine temperature gauge never got above 1/4. (Half of normal)
Backed into driveway and 'service soon' light and 'change oil' notice came on again.
Hoping a computer reset would fix it, I disconnected the negative battery cable, turned the key to 'on' and waited 10 minutes. Reconnected everything, started engine and put it in drive without moving.
Short ride this morning brought it to average temperature, but never above normal (half). After stopping and restarting engine, "Idle engine and engine overheating" warning came on briefly. Temperature gauge said normal. Made one more stop and nothing happened.