What to do when your heater has low output.

[jonmark1985]

Alirght I see alot of the same questions this time of year, so I figured I would make a sticky to help people out with their heating system.

Probably the first place to start is how the heater system works on the convetional automobile. Early cars used a shroud over the exhaust manifold, and a blower motor that blew warm air off the engine into the car. These systems were inefficent and dangerous. Later on auto manufacturers began using engine coolant to heat the interior of the car. The exception to this was the Volkswagen, being that the car was air cooled the cars may have had a gas heater installed that was used to keep inside temperatures suitable.

Today almost all modern cars use a liquid cooled engine. The start of the system is water. Distilled water should be used, rain water or other types of hard water are terrible for a cooling system. Some sort of antifreeze, wether is orange, green, or clear is also used. Antifreeze extends the operating temperature of water in both directions. It keeps water from freezing a temperatures below 32° and from boiling at temperatures above 212°. Antifreeze in its pure state will freeze far earlier than it will when it is mixed with water. Ranges can vary on the amount that it is mixed with water, but 40/60 to 60/40 ranges are appropriate. Antifreeze also serves as a lubricant for the water pump and a rust inhibitor for the entire system. Types of antifreeze should never be mixed, and if a person is switching from on type to another type, they should flush the entire system.

The radiator is what does the work of the cooling system. It is a heat exchanger for the liquid in the system. The radiator uses the cooler air passing through it to chill the coolant in the system. If the radiator's fins have debris between them, or if parts of the radiator are blooked off then the cooling system will be greatly comprimised. The radiator system on many modern cars is a sealed system, and checking the level is done at the overflow tank.

The overflow tank is an addition to the capacity of the radiator, Over the past 30 years it has only began to be used. Due to higher costs, and trying to cut overall vehicle weight, car manufacturers have begun to use lighter and smaller radiators. The auto manufacturers then added overflow or expansion tanks to increase the amount of coolant in the system. Today on modern cars this is the only way to fill the system. At cold termperatures usually the coolant will be at a low level in the overflow tank, and at high temperatures the level of coolant will be near the top. Filling up the overflow when the vehicle is cold, will only cause the overflow to overfill and run over when the vehicle warms up. On the side of the tank should be the appropriate marks.

The radiator cap serves to pressurize the sytem, therefore increasing the top boiling point of coolant. Early radiator caps were at a low operarting pressure, due to larger radiators and "lesser" build quality. When car manufacturers cut down on radiator size they upped to pressure of the cooling system to handle the harder cooling challenge. Modern caps run up to 18 psi. A radiator cap should never ever ever be opened when a system is hot, being scaled myself I can warn you that it doesn't take that much temperature or pressure to really hurt. A radiator cap also serves as a protection to the cooling system, when the car reaches an overheating temperature, the cap will vent off all excessp pressure. The best advice in this situiation is to just stand back and let the car boil over, steam makes for very bad burns.

The water pump moves coolant throughout the system. Most water pumps are of the vane type, and don't build much pressure throughout the system. very seldomly a pump will actually wear out, sometimes the vanes actually do wear to nothing. Usually the cause for water pump replacement is the front seal of the pump leaking. Most water pumps have "weep hole" so that coolant can escape, if you see coolant leaking out under the snout of your water pump this is probably what is happening, at this point the pump needs to be rebuilt or replaced.

All modern liquid cooled cars should use a thermostat. The thermostat is generally located in the path of the upper radiator hose. The thermostat is what keeps the coolant at a set operatiing temperature. Many modern automanufacturers run thermostats at the 200° range, this keeps emissions down and mileage up. Thermostats can bind up and not open properly, wether they don't open up at all causing the car to overheat, or they stay open and the car's coolant doesn't reach a suitable temperature. Thermostats can be tested in a pot of water on your kitchen stove. Using a thermometer you can see what the thermostat is operating at when it opens.

The bypass hose usuall runs from the intake manifold to the water pump. When the thermostat is closed this hose allows coolant to still circulate and warm up inside the block.

Hoses, this sounds too simple, but I decided to throw this in. They move coolant through the system to its various destinations.

The heater control valve allows coolant to travel to the heater core. At lover vehicle temperatures this doesn't not usually operate. This allows the car to build a decent temperature faster. Early valves were mechanicaly operatered through the heater controls and a linkage. Moderen vavles use vaccuum. A vaccuum swith will open up and let intake manifold pass to the heater controls inside the car at operating temperature, then when the operator turns the heat on vaccuum will pass to the heater control valve and allow heat to flow to the heater core.

The heater core is just like a mini radiator. It transfers the heat of the coolant into the atmosphere, however, the heating system utilizes this heat to heat the car. Usually when a heater core fails it will leak, these can be a nightmare to change and some involve removing the entire dashboard. Ford Pickups on the other hard are generally easy to change. Another problem can be a heater core getting plugged up. Coolant wont flow through the heater core at all making it useless.

The blower motor moves air along the heater core, and through ducts to heat the car. Blower motors generally have more than one speed, this is controlled through a blower motor resistor that varies the voltage sent to the blower motor.

The final part of the heating system is the duct work. This varies wether the warm air goes to the winshield, dashboard, floor vents or all three. Usually flaps in the system are controlled by vaccuum, and the operatiing control uses this vacuum to send vacuum to the approprirate flap.

OK, so what is happening when your cooling system isn't working properly. Probably the eaisisest place to start is to check the coolant level, if the level is low or has air pockets in it, this system just won't work. Then check to see if the blower motor is working. At highest speed the blower motor resistor is usually bypassed, if a blower motor works at these speeds, but not at lower speeds then a bad resistor is usually the fault. Then probably the next place to check is the heater hoses. With the car warm, feel the hoses after the heater control valve, they should feel warm with the heat turned on, as coolant will be passing through to the heater core. If this isn't happening you need to find the obstruction in the system, wether is the heater control valve is jammed, the valve isn't recieving vaccumm, the heater core is plugged, or a heater hose is stopped up. If these feel warm, then the next suiatble place to check is the thermostat. Remove the thermostat and either try another one, or put in a pot of hot water and heat it on the stove top. The thermostat will open at its operating temperature.

Ok, so lets stay you're having problems with the defrost or the floor heat. A person needs to then check that the flaps are opening correctly in the duct work of the system, if they are not, then you need check for vaccum as these ducts.

Well thats enough typing for one night.