Front of radiator behind front grille. Good luck Reread your question not quite sure if you wanted in car or outside temp sensors. In car in top dash panel
If it is the Northstar engine which I believe it is, it is inside the motor under the intake manifold.
the top of the carborator
under the lower intake manifold
The cabin air filter on a 1991 Cadillac DeVille is located under and slightly behind the glove compartment. All the air which enters the cabin is filtered through it to remove most contaminants.
4.5 liter=frnt bottum of the engine 4.6 liter= under the intake manifold
its stamped on top of the intake manifold
The coolant temperature sensor in a 1998 Cadillac Seville STS is in the engine compartment. It is located on the intake manifold.
It is under the intake tube from the air cleaner. You have to remove the air box to get to it. GM had a great idea with this placement .....
My 01 deville had a cracked intake boot, between the throttle body and intake manifold, it would only leak when eng was hot.
Sitting right on top of the engine between the heads.
top of intake behind fuel rail
The 1998 most likely has a Northstar engine. On this engine the starter is under the intake, and the intake has to come off for replacement.