98 s-10, 6cyl. Overheats, blows cold air, replaced thermostat, still does the same thing. Radiator OK, full, no leaks in hoses, nothing leaking at all. The temp. gauge will then go back down, and it will blow warm/hot air like it should. This happens most often when idling at a red light or stopped in traffic, and occasionally when driving

. Reverse flush the cooling system, including the heater core. Phosphate scale and/or corrosion has likely blocked the heater core and radiator. It wouldn't surprise me if you needed to replace the radiator. This link should help:

https://www.askmehelpdesk.com/cars-t...tml#post235973

Afterwards, refill with a 50/50 mixture of the recommended antifreeze and distilled water.

. Test the radiator fan:

https://www.askmehelpdesk.com/cars-t...ml#post1642158