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Lack of heat and rough running car

Ray jumped to a conclusion of low coolant.

Is it possible poor running engine and a resulting low vacuum are causing the heat blend door to close and open when they shouldn’t? A tune up might be needed but don’t go looking for head gaskets and cracked cylinders or head gaskets.

Possible? Sure. But every time I’ve seen this situation in the real world, adding coolant solves the problem (well, symptom).

If she goes to add coolant but it’s already full, hopefully she’ll be smart enough to bring the car to someone.

I had a similar problem with an older Cherokee a few years ago where the radiator finally gave out. The real problem was that the water pump had no blades on the impeller, so no water would circulate at all. Replacing both the water pump and the radiator and the jeep is still going.