2003 kia sorrento


I have a car problem, and being a retired backyard mechanic I they to fix most things myself. My problem is a 2003 KIA Sorrento which only gives heat when moving above 40mph. I replaced thermostat, it has no visible leaks, blend door seems to work. I’ve thought about loose water pump belt, bad W/P impeller, water control valve and all the horror stories found on Internet about Kia’s. I can’t find a repair manual which doesn’t help. Hoping someone might have some words of wisdom or just an idea. I live in Mastic NY


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