Sounds like air to me.
Have your mechanics bleed (rebleed?) your system.
Both at the thermostat and the radiator.
JC...

-------------- Original message --------------
From: Jamie Fitterer <fittdog8848@HOTMAIL.COM>

> I jsut had my vna in the shop and they replaced my rear heater core and O2
> sensor and while they were there I had them flush the old Prestone coolant and
> replace with Volkswagen cooloant. Now that I did this my thermostat is all over
> and pegging high temps. Is it possible that the flush made my thermo go tits
> up? If not any other suggestions as to why this went from a perfectly
> functionaing thermo to now a bouncy ball?"Prohibition will work great injury to
> the cause of temperance. It is a species of intemperance within itself, for it
> goes beyond the bounds of reason in that it attempts to control a man's appetite
> by legislation, and makes a crime out of things that are not crimes. A
> Prohibition law strikes a blow at the very principles upon which our government was founded."