After verifying that the heater is not performing well enough, the engine coolant level needs to be checked for the proper level. The coolant should be at the full mark on the reservoir tank as well as in the radiator. Warning: Never remove the radiator cap or a pressurized coolant reservoir cap while the engine is hot to avoid having hot and pressurized coolant released onto your skin, which will cause injuries and burns. If the cooling system is found to be low, then the vehicle should be inspected for leaks.
The coolant level is full on this radiator. This system uses extended life coolant that is red in color. The coolant reservoir should also be checked and filled to the full cold
This heater core is badly deteriorated and caused a leak in the duct box. The driver of the vehicle noticed that the windshield was fogging up and coolant was leaking from the duct box drain
This heater core developed a slow coolant leak that caused a light fog on the windshield when the heat was turned on. A pressure test was performed on the cooling system and caused coolant to drain from the duct box drain
Checking the Cooling System for Leaks
1. Look for signs of coolant on the various parts of the engine and cooling system. The coolant will be affected by gravity, create a downward trail, and then drip onto the ground. Be sure to find the exact location where the coolant is exiting the engine or cooling system component.
2. A pressure test is sometimes necessary to aid in locating leaks in the cooling system. This device uses a pump to add pressure to the system, which will often make the leak easier to see. Be sure to only add pressure that does not exceed the radiator cap pressure rating, which is usually around 15 psi.
3. On leaks that are difficult to locate, coolant dye can be added to the cooling system to aid in locating the source of the coolant leak. After installing the dye to the system, the engine should be operated for several minutes to circulate the dye. A black light is used to increase the visibility of the dye.
4. A block tester tool can be used if an internal coolant leak is suspected. This tool uses a chemical that changes colors if it is exposed to combustion gases. This tool provides a positive way to test for blown head gaskets or cracked cylinder heads.
