The Lisle Coolant Fill Funnel to Remove Trapped Air

Image The Lisle Coolant Fill Funnel to Remove Trapped Air
By Dennis Bandy Copyright  

In this article we discuss using the Lisle coolant fill funnel to remove trapped air from cooling systems and diagnosing other potential heater performance problems particularly in Nissan vehicles. It should be noted that air trapped in cooling systems can affect any vehicle's ability to keep the engine cool and the heater's ability to heat the passenger compartment. Air enters the cooling system when replacing water pumps, radiators or if there is a small gradual leak and then the system is topped off. Although other car's can have heater performance problems, it seems that Nissans tend to trap air in cooling systems more than others. So tips in this article can be helpful when working on other makes as well. 

Factors that may cause poor heater performance
 Low Coolant
Malfunctioning Thermostat
Flow inadequate, possible restriction
Doors in the heater/evaporator case not operating as designed
Air trapped in cooling system

First Check the Coolant Level
If the coolant is low enough, this alone could be the problem. In many cases with Nissans, only a slightly below full coolant level could be enough to cause poor heater performance. The coolant could be low enough to affect the heater however, not low enough to cause the engine temperature to rise above the normal range. Pressure test the system to make sure there is no leak, even a drip can cause enough coolant loss to affect the heater performance, due to air pockets being introduced. If the heater does eventually work after the vehicle has been ran for an extended period of time, the thermostat could be stuck in the open position. This allows the coolant to flow continuously, preventing the engine from reaching operating temperature quickly. As you may know, a stuck closed thermostat presents a much more urgent problem than heater performance (it can cause overheating).
Check for Flow and Possible Restrictions
Particularly if the cooling system on the car you are working on looks like it has been neglected, there is a chance there could be a restriction in the radiator or the heater core. On rare occasion, the fins of the impeller on the water pump could be rusted to a point that it is no longer pumping the coolant. If the impeller is plastic and not subject to corrosion, it is possible for it to stress crack an come loose from the shaft.
If equipped, verify heater control valve operation and control cable adjustment to make sure the valve is being opened completely (this is a common problem with 1996 to 1999 Honda's). Use an infrared thermometer or feel the heater hose temperatures at the heater core. If the hoses are both warm, the coolant is flowing through the heater core. The temperature blend cable or actuator should be checked for proper operation, the blend door may not be moving fully or at all. If there is a major difference in the temperature of the two hoses, there is a possibility there is air trapped in the heater core or at some portion of the cooling system, preventing the flow through the heater core. Some models have one or more bleeder valves to purge the air out of the cooling system, refer to the service manual for the specific vehicle. The use of a coolant fill funnel like the Lisle LIS24680 works wonders in purging the air from cooling systems. The Lisle coolant fill funnel allows coolant to fill the void as the air slowly works its way to the surface. The air is removed when the heater is blowing hot air and there are no more air bubbles surfacing in the coolant fill funnel.
Suggestions for diagnosing heater performance on Nissan & Infinity vehicles, air trapped in cooling systems can decrease heat out-put...