Stop the insanity, save the thermostats!

By Jody Treadway on Jan 27, 2014 at 5:08 PM
  1. Jody Treadway

    Jody Treadway Croc wearing fool Moderator

    Mar 20, 2005
    Hendersonville, NC
    Catchy title got your attention didn't it? Once again I have been beckoned by Mr and Mrs NC4x4 for a wee bit o' tech. Enjoy...

    Each year as the outside temps drop, 2 things happen. People complain about crappy fuel mileage and million of perfectly good thermostats are tossed in the trash can of the shop. Together we can end this mindless abuse of thermostats. It seems whenever a lack of heat issue is posted that someone also throws out the proverbial "replace the thermostat" reply. Not so fast Einstein.

    Before condemning the thermostat, let's actually diagnose the issue. The following is how I successfully diagnosed a lack of proper heat on my wife's 1998 Jeep ZJ.

    #1 thing was to make sure the coolant level is filled up to spec. The radiator was full as was the overflow reservoir. Next thing I did was start up the engine and let it get to operating temperature. It took about 10 minutes for the gauge to reach 210 degrees. What does this tell me? I tells me the thermostat is not stuck open. Had it been, the engine would have never warmed up so quickly nor would it had climbed up to 210 degrees with a stuck open thermostat. Now what?

    Next I used my very specially calibrated temperature measuring device, my hand. I grabbed one heater hose and took a mental note of how hot it felt. Then I grabbed the other heater hose and checked it's temp. One was the same temp as the upper radiator hose and the other one was barely lukewarm. Revelation 3:16 states God's disdain for the lukewarm and I feel the same way about lukewarm heater hoses.

    Now we're getting somewhere. There is obviously a restriction in the heater core. Call O'Reilly Auto and order a heater core while taking 3 hours of my day to replace it? Of course not, I have axles to build and my wife isn't a paying customer. I did what I have done so many times over the years. I flushed the heater core with a garden hose. Here's how to do it:

    Pinch off both heater hoses just so you limit the amount of coolant that leaks out. Then remove the hoses from the heater core. They may be retained with either hose clamps or spring loaded quick lock fittings like most late model cars use. With both hoses removed I simply connected the hose to the heater core inlet and (Andy Griffith voice on) "Lawd, you shoulda seen what came out of that core. It was the awfullest mess of crud and sediment I have ever seen." I flushed it both directions until only clear water was exiting the core. Once I reconnected the hoses and topped off the radiator it was time to crank it up. The results? Both hoses are the same temperature and the heat output is what it should be.

    You see, unless the counter girl at the Advance is super cute, take a little time to actually find what's wrong with your vehicle. Maybe it needs a thermostat or a water pump, but why throw around money guessing?

    You'll see a few pics from my 20 minutes out in the parking lot of my shop today. Ask away with any questions.
    IMG_20140127_102348_470 (1).jpg IMG_20140127_102512_640.jpg IMG_20140127_103156_706.jpg IMG_20140127_103254_456.jpg
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    1. rodney eppes
      rodney eppes
      Been looking for som goood Clips, Man.:smokin:

    2. 2010nctaco
      Dumb question, but did you flush it with just a garden hose? I'm going to be probably doing this on my dad's xj before long as he is without heat.
      And thanks!
    3. Jody Treadway
      Jody Treadway
      Yep, disconnect the hoses and flush it both directions. You'll see "crud" shoot out of it.
    4. mommucked
      Great advice sir, I would add it's also a good idea to turn the heat on briefly/occasionally in the summer to circulate the coolant in the core, and likewise run the AC now and then briefly in winter to make seals and O rings last longer. I blew up my AC cause I only used it when it was REALLY hot before learning this.
    5. frankenyoter
      Nice work! And well said too!
      mommucked likes this.
    6. /dev/yj
      Thanks Jody - I've been freezing my a$$ off in the Dodge and will give this a try once Snowmageddon has past and temps climb back to where I can safely run the hose!
    7. Croatan_Kid
      You're a damn genius Gump! :D I can always tell when a thermostat dies in my Silverado. It'll get to the half way point on the gauge and that's it. Otherwise, it's good to go!

      Never had a problem with my heat, but I let my AC go all to crap. Probably my fault because I never use it, but last summer it would hold a charge for about a week if I used it every day. I know it drops because my fans won't kick on high because the clutch isn't kicking in. That being said, AC work is about the only thing I don't do myself and I'm dreading dropping the cash to fix it. :(
    8. Lurch830
      Exactly what I had to do to my old Ranger, of course half the problem was the water pump vanes were pitted/corroded enough that it didn't have the force to push the coolant to the heater core. Checked that by running one of the heater core hoses into a bucket & firing her up.
    9. Jody Treadway
      Jody Treadway
      Good point. Basically all Jeeps (aside from earlier XJs and older models that used a heater control valve) have constant flow through the core to keep it circulating. Also, some people may not know that running your defrost actually runs your AC compressor. This was a strategy employed by manufacturers to make defrost work better and to keep AC compressors alive longer too.
    10. Silverado_Express
      Just a good tip I've learned along the years, if your hoses are the kind that slip over the heater core tubes and have clamps, be gentle when removing them. Use either a big angled pick type tool like the one shown in the first picture or slit the hose longways where it is pushed over the tubes. Too much force can cause the tubes to twist off or crack from the heater core body. Especially on old or corroded heater cores.
      Great informative post, most people don't think about a stopped up core.

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