Unwraveling Heater core issues

What is the best way to measure my heater core performance?

Not with an Infared gun.  An optical pyrometer AKA Infrared (IR) temperature gun cannot directly read air temperature.   Air is largely Oxygen and Nitrogen and these do not emit infared radiation.  At best you will measuret the emissivity of reflective surfaces around the air.

Emissivity is a measure of the efficiency in which a surface emits thermal energy. It is defined as the fraction of energy being emitted relative to that emitted by a thermally black surface (a black body). A black body is a material that is a perfect emitter of heat energy and has an emissivity value of 1. The emissivity of a surface will not only alter with regard to texture and colour but also with its actual temperature at the time of measurement. Since many people will ignore this information it is helpful to know that many vents are black plastic and the emissitity of black plastic is .95. 

So if I can't shoot everything with my $20 Harbor Freight Infared gun what do I do?

Try a common meat/cooking thermometer for your readings.

Why is a higher fan speed giving me cooler air?

Higher fan speeds tend to result in lower temperatures because reduced dwell time (residence time).

What is a reasonable expectation of a heater?

Most vehicles run 190-210 degree engine coolant through a heater core that then has air blown through it into the car's passenger "cabin".   The heater core outlet hose should be only 10°F–25°F cooler than the inlet.

Depending upon design and size, a heater core will typically produce air vent temperatures between 115 and 140 degrees. 

If you're not seeing that level of heat here is a list of consideratons and/or trouble shooting tips

• Your themostat should be at the spec of the engine.  if you lowered it you may have reduced your heater core output
• You have a failsafe thermostat, it could be failed in an open position
• You have air trapped in a thermostat
• Your coolant is low
• You mix your coolants and caused gel which clog a heater core
• You have sand in the block from your engine casting which can clog a heater core
• Your air intake is blocked
• Your plenum is blocked with debris, dirt, dust, mouse nest etc
• Your blend door actuator has failed
• Your blend door sound like its moving, it may be spinning the rod but not the door
• Your HVAC control module has failed
• Your resistor on your blower motor has failed
• Your inline valve is stuck in the open position
• Your water pump impeller has corroded and not circulating coolant
  
• If the engine is cold, the heater core will struggle to heat. The heat from a heater core comes from the engine so it has to be at operating temperature to generate heat in the cabin.
• If the inlet hose is close to the engine temperature e.g. 190-210 degrees, the thermostat is functioning. If the engine is cold and it does not warm up, then check your thermostat is not stuck open or lower than the intended specification.
  If the heater core outlet hose is ~10-25 degrees less than the inlet, the heater core is dissipating heat.
• If the heater core outlet temperature is significantly cooler than the inlet, then the heater core may be clogged/restricted and require and flushing the hoses and heater core.
• If the heated air is hot but airflow is not strong your blower may have failed.
• If there is not much heat, the engine is running at the expected temperatures and coolant levels are appropriate, you may have stuck blend door, malfunctioning actuator or a clogged cabin filter.

Not all components exist in all vehicles.  Please read this and think about it before calling us and asking us to read from the page to you.