I'd use the "paper clip trick" to pull codes and ENSURE the fan is working (the fan should kick on when you turn on the ignition if the paperclip is in place).
If the fan works, I'd do an oil change and then I'd drain the coolant into a clean container and have a look at it. Also look at the radiator cap seal. It should not be all wavy and stretched out looking. I'd half expect to see evidence of a problem...either debris (waterpump failure) or oily residue (head gasket). Once drained of coolant, I'd refill with water, run the engine for a couple of minutes and drain again...into another clean bucket. This second fill/drain into bucket is an environmental step...AND will tell you if the system is clean. Once emptied again, keep the petcock (drain) open and refill with a garden hose. You will be able to refill it with the drain open since you can shoot water into the fill hole faster than it can drain out the petcock. Once refilled, start her up and keep it filled with the hose. All while the drain is open.
Once flushed for a few minutes (it should never really get up to temp since you're replacing hot water with cold water from the hose), shut off the engine and let the water drain out. Use some sort of strainer (I use paint strainers) to filter the coolant that you drained earlier and carefully pour it back in. You might have some left over. Keep it handy.
Start the car, make sure there are no leaks and let it idle up to temp. While it's idleing, keep the radiator cap off and keep topping off the system. You can help by squeezing the upper radiator hose repeatedly to "burp" it. Once you're satisfied no more coolant will fit, replace the radiator cap. Keep checking the temp and make sure the fan comes on. You might have to let it get quite hot by the temp gauge before the fans come on.
If it gets into "H" and the fans don't come on, let it cool for a while and replace the engine coolant temperature sensor (behind and below throttle body). Recheck fan operation.