Car Heater Blows Cold – Auto Service Tips Part 2December 4, 2010 11:23 am Consumer, DIY, How To Auto Repair
The standard heater core above is copper – some cores are aluminum .
© DenLorsTools.com Summary: This is part two of our exclusive car repair blog helping to troubleshoot car heater problems when they blow cold. The original article has been very popular in the colder months of the year. This repair article picks up where the first article leaves off. If you have not read the first part of the Car Heater Blows Cold article, I recommend reading it first.
One common complaint with the car heater performance; is the temperature of the air only blows warm for a few seconds and then starts to blow cold. This could be caused by a restricted heater core or a thermostat that is staying open – or the t-stat is opening too soon.
Clogged Heater Core
If the heater core is clogged up, the coolant in it may be hot initially. However, after the air blows through the heater core it lowers the temperature of the coolant inside of it. If the flow is restricted it will cool the coolant down to a point that results in the air blowing through the fins to NOT be heated as designed. Low coolant flow within the core can sometimes be deceiving because both heater hoses may feel hot to the touch. As talked about in part one of this article, one test is to check the temp of both hoses to see if they are both hot to the touch. If the core is completely stopped up, one hose will be cold. The possible curve ball to this test is that there may be enough flow to make the hoses feel hot to the touch, but not enough flow to maintain a high enough temperature when the heater is being operated. This may result in warm air blowing through the vents only for a few seconds. The easiest way to check for volume of flow is by removing both heater hoses and spraying water through the core with a garden hose. If only a trickle comes out, then a restricted core is confirmed. There should be free flowing water exiting the core when this is being done. Just as much water coming out as being sprayed in. Sometimes the heater core can be flushed to increase flow and other times the core has to be replaced.
If the thermostat stays open all the time, or opens too early (before the engine reaches the target operating temperature) the heater will not blow as warm as it should. If this is the case, usually after the car has ran awhile the vent temperature will increase gradually (at varying rates depending on the ambient temp). If it’s really cold outside the engine’s temperature gauge may stay on cold. If the engine’s temp never reaches 1/2 way or the normal range, the heater cannot be expected to heat up either since it operates by exchanging heat from the engine’s coolant. This is why warm air may blow for a few seconds when first turned on, but after the core is cooled off, cold air will come out of the vents. Also, many times if the thermostat is not closing correctly, a CEL (Check Engine Light) will be turned on with a fault code stored. The code that can be set is a P1281, see the articles below for tips on dealing with this code on the Jeep Grand Cherokee and the Chevrolet Trailblazer.
Related Thermostat Auto Repair Articles
Heater blows warm a little when RPMs are raised?
A common occurrence is the heat blows warm or “warmer” when the gas pedal is pressed slightly. When the engine is turning faster (higher RPMs) the water pump turns faster too. When the waterpump is pumping water faster there’s more water volume traveling through the heater core. A little increase in temp is normal. Extreme differences are felt when the system isn’t working as it is suppose to. As mentioned in part one of this article, air trapped in the cooling system can affect the heater performance. Bleeding the air out is the first thing to try in this case. What if the air is bled out, the heater core is not restricted, the thermostat is new, there’s not an actuator or door issue and there’s not much heat blowing out the vents? Next thing to investigate is the water pump. Sometimes though it is seldom; the water pump may not be pumping sufficiently. The water pump impeller may have rusted fins on the impeller. A special thanks to workshop.search-autoparts.com for providing the image of the rusty water pump. In the summer this pump would cause an overheat – in the winter it would cause the heater performance to suffer. One way to check for a problem like this is to do the following.
Measure three temperature readings from the car with an infrared thermometer.
1. Radiator temperature. 2. Engine block. 3. The vent temp with the heater on maximum.
The three temperature readings could indicate that the water is not flowing properly. A cold vent temp with a “warm” engine and a cool reading at the radiator is the main indicator.
A more direct way to check flow from the water pump is to remove the upper radiator hose from the radiator. Have someone start the engine for a few seconds to see if there is water pumping out.
The impeller on the water pump could come loose or can deteriorate from rust or electrolysis due to lack of maintenance or improper ground straps. Still would like more tips? See Car Heater Not Working? Troubleshooting, How to Fix Repair Tips.
Automotive Heater that plugs into car cigarette lighter – Review
What about the car heater that plugs into the cigarette lighter? There are several brands of these available on the Internet that provide the hope of a cheap fix for a malfunctioning car heater. Nice thought, but just like most things in life that sounds too good to be true it usually is, this one is too good to be true also. The heating element is very small and inadequate for making a real difference in the passenger compartment temperature. The fan doesn’t put much volume out and if it did, the air would not heat up even as much as it does. There are several models that have a slightly larger size, the problem is with those units they usually end up blowing a fuse. Larger fuse anyone? Not a good idea, this might melt wiring in the car and could likely be a fire hazard. There have even been some reports of these units melting! Save yourself the trouble and expense and work towards fixing the heater system your car came with.
Click the following for even more on car heater not working, with tips for troubleshooting problems.