Have a 97 deville with the northstar engine. Bought the car for a steal from a local auction. Only has 79k original miles. Problem is, it's overheating.. Cannot figure out what the problem is.. The water pump is workin fine, replaced both radiator hoses, flushed the radiator/refilled w/ dex-cool. Replaced thermostat. Did compression test on radiator and block and head gaskets are fine and the coolant has no leaks whatsoever. The only thing left I can think of is possibly the temperature sensor is going bad, however I don't think that's the case since I ran into soooo many posts of northstar engines overheating. Just at idle the temperate gets up around 220 sometimes.. and just going down the highway you can't get 2 blocks before it reaches 260-270 degrees. Any help would be greatly appreciated. Thanks for any and all help.