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Does the engine temperature gauge get up to normal operating temperature? It should be straight up, or half way. If not the thermostat is stuck open or opening to soon and must be replaced.
If the engine temperature is correct your symptoms are consistent with a plugged heater core or possibly a failed dual coolant flow valve.
The core of the heater core is not only a group of tubes, but the tubes are filled with a mesh material similar to steel wool. It takes very little resistance to overcome the low pressure from the engine. On a properly functioning system the temperatures of the two heater hoses is typically fairly close with only a slight reduction in temperature. Typically when I replace restricted heater cores the coolant often appears perfectly clean. When I cut open the core and then it has a chance to dry out, small particles consistent with the appearance of sand are found in the mesh material.
The amount of flow going through the heater core is very hard to determine and the apparent resistance can be deceiving. If you try and remove the heater hoses and check for flow, you will not be able to determine the “flow” as the coolant is “drawn” (sucked) through the core by the water pump. This way there is flow through the heater core even before the thermostat has opened. If you run water through the core or blow through it, it may appear not to be restricted, again “deceiving”.
I suggest you try to confirm the core blockage as follows. Fully warm the engine to operating temperature. With the temperature set to maximum heat shut off the fan so that no air flows through the system. Drive the vehicle at slow speeds or run at an elevated idle for a few minuets. Turn on the defrosters at maximum heat and turn the fan on high. If the heat appears hot at first, but then rapidly diminishes, the core is likely the cause. If however there is no heat the dual coolant control valve may be at fault.
The dual coolant valve regulates the flow of engine coolant to each half of the heater core
. Two electric solenoids, Which are individually actuated by the heater control module, are the control elements. The valve contains five ports:
inlet port - coolant from the engine
outlet port - coolant to driver side of heater core
outlet port - coolant to passenger side of heater core
return port - common coolant return from heater core
outlet port - coolant return to engine
The next step would be to remove the valve and check for flow restriction. Would this be within your capabilities? Or are you just looking for a better idea of what might be going on before you bring it into the shop?
If there does appear to be a restriction in the heater core to further confirm, you can try back flushing (flushing backwards) the heater cores with a water hose. Observe the expelled water, especially in the beginning, for any evidence of contamination. Use a clear hose that you buy from the hardware store and run the fluid into a clean bucket. This may give you increased performance, but typically will not be 100%.
I hope I have answered your questions and addressed your concerns. Should you have further questions on this matter, please do not hesitate to ask. I want you to be 100% satisfied with my answer.
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Jake “The Auto Doctor”