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Q: In a 2003 Cadillac CTS at idle position, it does blow hot air but once driving, I only feel cold air coming through the vents.

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In a 2003 Cadillac CTS at idle position, it does blow hot air but once driving, I only feel cold air coming through the vents. Coolant level is fine, dont think a leak is in the radiator. I've felt the hoses and they're hot, but once on the road, cool. I felt the heating core by accessing it through the inside of the glove box, in idle its warm, semi-hot but once driving, cool. Stuck. Help? :)

My car has 114000 miles.
My car has an automatic transmission.

Hi there. It is possible that you have an obstruction of engine sludge or debris inside the heater core. This typically will cause elevated engine temperature and heaters to not work as well during operation; or specifically - when the heater control valve is opened during operation. It’s also possible that the heater control valve is not working as intended; which might explain the cooler air during engine operation. I would first suggest reading this article which explains some of the common symptoms of a failing heater control valve. If these are common with your issue, it’s probably best to have a professional mobile mechanic come to your location and complete a heater is not working inspection to determine the source of this issue.

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