I HAVE NOTICED THAT WHEN THE ENGINE IT HOT ...THE BOTTOM RADIATOR HOSE IS SLIGHTLY SWOLLEN. Does this affect the opening of the thermostat; seeing that the pressure might be somewhat diminished by the flexibility of the hose?
A thermostat is mostly a bimetallic part that will open the waterway from the radiator to the engine block when the temperature is high enough. This has nothing to do with the hose. However, if the hose is swollen then I'd suggest you change it asap as it sounds like it's about ready to burst.
SOURCE: overheating 1999 cadillac deville
THIS SOUNDS CRAZY BUT, ON SOME OF THE OLD SCHOOL CARS, THEY HAVE A CLUCH FAN.. AND IF ITS BAD, THE CAR WILL OVERHEAT WHEN DRIVING AND COOL DOWN AT IDLE.. I DONT THINK THE CADY HAS A CLUTCH FAN, BUT I BET ITS IN THE FAN.. GOOD LUCK KEITH..
SOURCE: 1997 eldorado still runs hot
Are you sure it's not air locked? Run it with the rad cap off and keep watching the water level. It might go up and down and then finally drop. Maybe even try letting some air out of one of your heater hoses if you can.
SOURCE: my 2000 cadillac deville keep running hot when i
OK, check that the 2 fans are turning on when it gets to operating temperature. If not, replace the 3 or so relays that control the two speed fans on your car.If that doesn't solve the problem, then you may have to buy new fan motors and also have the harness replaced if necessary to make it cool reliably.
I had this problem on a 1997 Cadillac Deville Limousine that overheated over 157 deg. F and went into its limp mode for cooling the engine off by allowing 1/2 of the cylinders to circulate fresh air into the engine in case all antifreeze would leak out or the car would overheat.
Don't run the Northstar engine too long, more than 45 min. at a time in this limp mode.
Good luck on this repair of your Northstar Engine.
SOURCE: my 1999 cadillc deville delegance
IF COOLANT SYSTEM BEEN BLED AND PLENTY COOLANT IN COOLANT SYSTEM. THE IGNITION TIMING LATE OR VALVE TIMING LATE TIMING CHAIN WORN WITH A LOT OF SLACK JUMPED A TOOTH ON CRANKSHAFT GEAR TEETH OR ENGINE CYLINDER BLOCK WATER JACKETS CLOGGED ENGINE BLOCK NEED FLUSHING. IF ENGINE OVERHEAT WHILE SITTING IDLING LONG TRAFFIC LINE COOLANT FANS NOT TURNING ON.COULD HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR FAULTY COOLANT FANS RELAYS OR BLOWN FUSE.PCM FAULT.CHECK ENGINE OIL IF IT LOOKS LIKE MILK SHAKE YOU HAVE BLOWN HEAD GASKET.
SOURCE: I had my engine rebuilt along with the coolant
Hello Darryl, have you checked the accuracy of the gauge and confirmed the engine is actually over heating? Check the cooling fan Assembly to ensure they are fully operational. The shop that rebuilt your engine should of never released the vehicle if the engine was running hot after it was rebuilt & installed. If it fails from excessive heat, your warranty is worthless. I hope this information is helpful. 
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