Q: Truck doesn’t overheat but I can see coolant in the overflow steaming and my heater will change from hot to cold all the time.

Hi Bryce. Thanks for contacting us today. An overheating issue like you’re describing is often caused by some sort of obstruction in your heater core - especially if the air is cool instead of hot sometimes. However, it is more likely that you’ve got air bubbles trapped in the coolant system. When replacing any cooling system component, it’s vital to correctly bleed the system as recommended by the specific manufacturer. If this is not completed or done right, it can cause the type of overheating you’re experiencing. I think the best thing to do is to have a professional mechanic come to your location and complete an overheating inspection. This will allow them to isolate the root source of your problem, so the right repairs can be made.

You may have a clogged heater core that may be prohibiting the outer linings of the heater core to get hot. As you know, the heater core is a series of tubes that the coolant runs through that generates the heat from the warm coolant after circulating through the motor. These tubes can occasionally develop a buildup on the inner walls such that when the heater core is "flushed" this buildup on the inner walls of the lines remains and still allows the coolant to flow through the heater core. It is important to note that when the heater core is "flushed" it is possible to get good flow through the heater core while the inside walls of the heater core remain caked with buildup. As a result, the buildup on the inner walls prevents the temperature from rising to its capability due to the insulating effect of this buildup on the inner walls which will prevent the necessary heat transfer to properly heat the inside of the car. I would recommend having an expert from YourMechanic come to your location to diagnose and replace your heater core.