96 Deville runs at about 194 to 196 degrees while driving, but overheats to over 260 degrees when at idle. Like at drive throughs and such. What could be the problem?

 

What codes are displayed? I'd first suspect the cooling fans. At idle/very low-speed the cooling system depends on the fans, on the highway there is air-flow to remove the heat from the coolant.

 

we need more info ...

codes?
fans runnning?
mileage?
coolant maint history?
belt?
pump?
radiator?

 

Coolant is not circulating at low engine speed so that points to weak water pump in my opinion.

 

No Codes, I usually see steam coming from under the hood, from the water running from the overflow. I usually shut it down before it even tells me too. Afraid of damage to the engine. I was already leaning towards water pump, but drive long distances at a time and have no problem. I think my fans are running ok. I have about 144k on the Deville

 

A new pump wouldn't hurt, that's for sure! 144k....just broke-in good. Make positive sure you use the sealant tabs in the cooling system. A $2 insurance price.

 

Sealant tabs? Where do I get them?

 

The sealant tabs are required for use in these engines. Any GM parts will have them: GM #3634621. Auto parts stores the sell AC-Delco will have them: #10-108 and cheaper than the GM dealer.

 

Sorry Guys, looking back, I see I forgot to let you know what the culprit was. A bad relay. Replaced the relay and everything is working fine again. Seems the fans were not coming on when needed. Coming on at about 225 degrees now. Andon always when the compressor is engaged.