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Intermittent Heat/Erratic Temp Gauge - Bad Head Gasket?

scraigwoodyscraigwoody Member Posts: 1
edited March 2016 in Ford
My Expy started having intermittent issues with the temperature gauge sometimes showing cold when I knew the engine was warmed up (and no heat). I thought it was a bad thermostat and took it to the shop and they did a test and found gasses in the cooling system or something -- said it was for sure a bad head gasket. Does that sound right? Everything I read suggests other possible issues...


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    Mr_ShiftrightMr_Shiftright Member Posts: 64,481
    Well if they did a chemical test and it registered positive for combustion gases in the coolant, that's a pretty good test---but you should have other symptoms as well, such as fairly rapid overheating (in most cases), loss of coolant, and possibly steam out of the exhaust pipe.

    Another test would be to pressurize the cooling system and extract the spark plugs and "read" them for coolant deposit.

    Maybe they bungled the test---you'd better be pretty sure before you tear into the engine.
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    Replace the Engine Coolant Temperature “Sender”, not Sensor unless desired. If a 4.0 6 E, the sender is orange, non-threaded and held into the thermostat housing (lower) next to the sensor (gray). The sender is your issue from my experience, as it controls the gauge based on the sensor reference voltage as 0-Overheating has a voltage reference that is +/- reference voltage for 180 degrees operating temp (mid location of gauge needle). So lower than reference voltage on a working gauge should show a low temp and as the engine warms the voltage compared to the reference voltage increases until operating temp. Then, under overheating conditions the voltage (drop) compared the reference voltage will increase causing the needle to rotate into the “H” region. That’s what makes the gauges analog. Newer gauges work similarly, however, the ECU has an analog to digital converter that can provide seven segment or lcd displays. Regardless, a bad sender would be the #1 place to look. If you can get a PWM OBDII Monitor for apple devices, or VPeak using Bluetooth for Android os devices provides an inexpensive way to monitor your gauges like engine coolant temp. The thermostat may be rated at 160, 174, 180, or 192 deg F. Don’t be confused that your engine will run at these temps, the temp rating is simply the temp the thermostat will open. Use Dash Command App, $9.99 and best of the current available. Also has many abilities including reading DTC’s , setting PIDS, and clear codes. Very powerful tools, as they either support analog gauges or offer PID gauges that are not part of the display system of vehicle. Any questions just shoot me a message. I hope your problems have been identified and corrected. The sender and sensor are often misunderstood by parts stores with the sensor, big difference and both need to work properly. Hope this helps as I would not drive a vehicle without the monitoring system which also work with “footprint-less” tuner plug in devices using a splitter. Where I use a custom EEPROM flash with a Chip Your Car plug in tuner. Both operate simultaneously using the splitter and displayed through Dash Command on a IPad mini. PWM or Pulse Width Modulation aka WiFi that you select on the device. There are both standard PIDS to select as well as add on determined by green for standard and red for upgraded options. Fuel, air, temp, sensors, and more are the titles for each PID within the aspect of interest. A great example is MPG’s, older vehicles don’t have display capability like newer vehicles but having the Dash Command interface allows customization of dash boards to contain specific gauges which draw data directly from the ECU, so the sender could be bad, however, you’ll get an accurate digital or Needle style gauge to monitor engine coolant temp, however, the sensor must work as well as the t-stat. My 180 deg t-stat operates between 176 deg and 190 deg. Sitting at idle will provide higher temps 188-190 vs driving ranges from 178-185. Awesome and endless applications, as this just scratches the surface of the capabilities for on board monitoring which is a inexpensive and ensured form of a redundant as well as comparative form to determining proper analog gauge display.
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