Either the inside of the rad is plugged, so you need to flush it, or the vanes are plugged with dirt, bugs, leaves, etc. You will need to pressure wash it from the inside of the engine compartment. Your water pump could be shot.
when overheating occurs at highway speeds the cause is usually. a radiator or coolant circulation problem, Check for a restricted or clogged radiator.
The DeVille could have low transmission. Or the internal transmission bands or valves could have failed. The transmission will most likely need a rebuild.
uotside temp sensor in front of the radiator has gone bad
O2 sensor, and catalytic converter can be ruined. You can also cause internal damage to the engine, depending on what the problem is. Have it repaired.
There are several things that can cause your Cadillac Deville to have transmission problems. The most common transmission problems are worn transmission gears.
check radiator for small leaks or cooling lines which would most definitely cause it 2 steam when running after awhile
Absolutely
8 to 12 miles per gallon . cause i own one "D
1 of a 100 but the 1st to check . BAD THERMOSTAT
Heater core has failed.
dirt in the speed snsor bad speedo head in the dash
Heater coil