Q: No Water Flow on 2005 GMC Yukon XL 1500

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Temp gauge was bouning from overheating to below normal temps. Pulled Themostat to see if it was sticking, car then overheats in minutes. Replaced with new thermostat, still the same. Radiator hose line and heater core lines soft, no water in them. Reservior bottle full.
(1) Answer
You may have an air pocket in the cooling system, try bleeding the air from the cooling system. You may also have a problem with the temp gauge. It's hard to diagnose without seeing the vehicle, I suggest you tow it to a shop and have a mechanic look at it. The one thing you don't want to do is overheat your engine and cause thousands of dollars of damage. Have a professional look at this.