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.