Hi I'm Harrier,

Recently I had my my air system refilled by mechanic, car idled 20-30 min.
Driving from mechanics car and air cond. ran fine for about ten minutes, car
temp then went to 255, with all the alarm bells & chimes, including oil use life
dropping to zero/replace???????

Car is a 1999 Deville

Not good. Are the electrical rad cooling fans working?

Check Purge line, there should be steady flow at idle, if that all checks out get a Block test (Hydrocarbon test) done, to check for exhaust gases in the cooling system. also if your A/C is on your fans should kick into high speed pretty much right away.

If all other instruments went bonkers, I suspect something else besides cooling system at fault.

I suggest hooking car up to a scanner to view live data vs what'* seen on the instrument cluster.

its factory that the oil life monitor goes down to zero, the PCM tells it to because it thinks when the engine gets overheated it wrecks the oil'* life, also there will be a message something along the lines of "engine overheated - Idle engine" and "A/C shut down" check engine light appears as well. all normal.

Also check for airflow. You may have a dirty condenser or radiator.

Something just doesn't smell right....and I just took a shower....