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.

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I have a 2002 Dodge Dakota 4.7l 4x4. I recently replaced the radiator because of a crack in one of the tanks. After that it began to overheat. I since then have replaced the thermostat, fan clutch, both hoses and the cap to try and solve it. So far it has seemed to not get hot over the past few weeks but I still smell coolant from outside the truck. I see no signs of leaks by the radiator and hoses. I checked the overflow and some coolant was steaming from inside, making it the place where the smell of coolant is coming from. Also my heater works great when I’m driving, but when I stopped for a minute my heater started to blow cold even though it was on the hot setting, then as I began driving it got hot again. Then cold one last time as I parked before I turned it off. Still not overheating, sat at normal running temp the entire time. I’m just wondering if it’s not a heater core problem, or possibly a heat gasket. Exhaust sort of smells sweet but I’m not positive.

My car has 164000 miles.
My car has an automatic transmission.

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.

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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.

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