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1989 Cadillac Deville Overheating No Heat

CADILLAC DEVILLE
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JACKANDBUDLIGHT
  • MEMBER
  • 1 POST
I have a 1989 Cadillac coupe deville, 4.5 V8 it has 103,316 miles on it. It is over heating and has no heat. I replaced the radiator, thermostate, hoses, no water or antifreeze on the oil stick. I also replaced the radiator cap and pressure tested the system, it held good at 16 pounds. ??????????
Jan 23, 2007 at 11:23 AM
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SQM
  • ✓Experienced Mechanic
  • 6,383 POSTS
Hello,

The heater not working is likely due to an issue with the heater control valve.
The control valve is located next to the blower motor under the hood (see diagram).
It is a vacuum controlled actuator. Inspect that valve. Make sure that the vacuum hose is connected and the hose has suction.
The valve can also fail in the inside and be stuck shut. This will not allow coolant to flow and you will have a non working heater.

https://www.2carpros.com/articles/car-heater-not-working

As for the overheating issue, check the radiator cooling fans. Make sure they are operational.

Please let me know of any questions.
Thank you.
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Sep 16, 2021 at 3:56 AM
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Suggested Repair

Inspect the vacuum-controlled heater control valve beside the blower motor; confirm the vacuum hose is connected and has suction, and replace the valve if it is stuck shut. Also verify that the radiator cooling fans operate.

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Conversation Summary

A 1989 Cadillac Coupe DeVille with a 4.5 V8 overheats and produces no heat after the radiator, thermostat, hoses, and radiator cap were replaced. The system held 16 psi and no coolant was found on the oil dipstick. The expert advised checking the heater control valve and its vacuum supply for the no-heat issue, and confirming that the radiator cooling fans work for the overheating.

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