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Cadillac Seville Not Quite Overheating

Q. The car is a 1992 Cadillac Seville 4.9 liter engine, automatic transmission and 135,000 miles. After replacing the radiator, heater valve, hoses, thermostat and the water pump the car continues to overheat. Not to the point of steam rising from under the hood but the engine temperature will say HI TEMP 259°. At that point the car is turned off to cool down.

Cadillac Seville Not Quite Overheating

There are no water leaks that we can see. When we check the radiator there is very little water missing. Any suggestions as to what could be the problem?


A. It is most likely an air bubble trapped in the cooling system. I would try bleeding the cooling system following this procedure.

Cooling System Bleed Procedure

  1. Fill cooling system with a 50/50 mixture of antifreeze and water, to just below the filler neck.
  2. Fill the coolant recovery reservoir to the specified fill mark on the outside of the reservoir.
  3. Run engine with the radiator cap removed until normal operating temperature is achieved.
  4. Set climate control to maximum heat and high blower.
  5. With engine running at idle, add coolant to the radiator, until it reaches the bottom of the filler neck.
  6. Replace the radiator cap. Arrows on the cap must line up with the coolant recovery reservoir hose.
  7. Cycle the engine to 5,000 RPM, then back to idle at least five times. This will help expel any air trapped in the system.
  8. Verify heater operation.
  9. Recheck coolant level in reservoir, add if necessary.

If it still is running hot, and with the work you have already done, I would have to say there is an obstruction in the block, the Coolant Temperature Sensor (CTS) is malfunctioning or the cooling fans are not coming on when they are supposed to. The cooling fan should go on low speed at 223°F and go off at 208°F.

The cooling fan should go on high speed at 226°F and go to low speed at 223°F. This operation is controlled by the PCM based on information from the coolant Temperature Sensor.

I would recommend checking the actual coolant temperature with a thermometer to be sure the gauge is accurate before looking for any problems.

Additional Information provided courtesy of AllDATA

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© 2005 Vincent T. Ciulla

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