Why isn’t my jeep heater working?

A common call for help we get is… “My heater isn’t working right in my Jeep… and I am driving with my mittens on.” So this year if you run into trouble… give us a call or drop us an email, then come by the shop and we will get you fixed right up!

An introduction to heating and cooling systems

How does your heater work?  As your water pump circulates coolant to keep your engine at the correct temperature, that water travels in a path that goes from your motor, past your thermostat, to your heater core, to your radiator (to be cooled by air coming through the grill or from the fan), before returning through the engine.  (there are variances to this, but you get the gist)

What is a thermostat? A thermostat is really just a fancy valve with a spring, that opens or closes depending on its pre-set temp. So if its a 195 degree thermostat that means it stays closed and keeps the coolant trapped in the engine block until that 195 degrees is reached. Once it opens it allows the coolant to enter the radiator to be cooled off, then circulate back through the motor (via the water pump) until the proper temperature is reached.  Then the thermostat closes, and the process repeats.

What is coolant (antifreeze) and why can I just use water?  Antifreeze is there for a few reasons. It helps with heat transfer in the radiator, it stops your coolant from freezing in wintertime and it helps to inhibit corrosion. Water expands when it freezes… and water freezing inside your motor is a bad thing… trust us!  Well unless you would like a new motor.

Pro-Tip: Do not drink antifreeze, it might taste good, but it’ll kill ya.

Common reasons for help calls.


My Motor is running cold and never comes up to temperature.

This is usually caused by a stuck open thermostat, and is the easiest problem to solve.

My Motor is running hot – Possible causes, in order of ease to diagnose and fix.

Low coolant levelthermostat problems with jeep wrangler
Air trapped in coolant system.
Fan Clutch Bad/Fan Shroud Broken/ Fan does not flow enough CFM.
Stuck Closed Thermostat.
Clogged Radiator
Malfunctioning Waterpump.
Clogged Coolant Journal in the motor – This is obviously the worst case.

My heater isn’t working – Possible causes, in order of ease to diagnose and fix.

Low coolant level
Air trapped in coolant system
Clogged Heater Core – Essentially your heater core is a little radiator with a fan behind it. If you are not getting heat, that means that the hot coolant from your engine block is not circulating through the heater core. This is also why if your motor is overheating you can crank the heater to help cool it off.

If you are experiencing problems, post below, email us, or call the shop to set up an appointment. Contact us!

Fun resources: Want to calculate the volumetric expansion of freezing water inside an engine block?  Click Here!

<script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <!-- Responsive --> <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-5460472681587901" data-ad-slot="6752537473" data-ad-format="auto"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script>