So I recently bought a car in bad condition I did a self check kit on the radiator for the head gasket and the fluid did turn yellow but I realized the thermostat was stck closed and wouldn't open which I think would be the reason it turned yellow because the thermostat was stopping anything from getting in and out of the radiator so I've replaced the radiator and booked a mechanic to come fix the thermostat just wanting to see if this adds up to anyone who knows what they're talking about with this or if its still the head gasket
If the color changed there is exhaust gas in the coolant - bad head gasket.
If you took all of the steps and you siphoned out enough fluid to not mix up the coolant and the mixture in the tube, your head gasket is blown. A stuck thermostat will cause that.
stuck thermostat is a cause of overheating. Blown head gasket is a symptom/result.
