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How do you test a block heater?

Discussion in 'Shop Talk' started by emmett518, Jul 10, 2021.

  1. emmett518

    emmett518 Senior Member

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    What is the easiest way to test an engine block heater? I’d rather know now that it needs fixing than on a freezing day with 24 inches of snow in the driveway.

    thanks
     
  2. Truck Shop

    Truck Shop Senior Member

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    Make sure the coil is submerged in water.
     
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  3. Vetech63

    Vetech63 Senior Member

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    Plug it in and see if it works lol
     
  4. skyking1

    skyking1 Senior Member

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    yes you can hear them, hear the sparks in the plug as you plug it in.
     
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  5. Truck Shop

    Truck Shop Senior Member

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    If you smoke it should produce enough sparks to lite-up.:oops:
     
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  6. emmett518

    emmett518 Senior Member

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  7. emmett518

    emmett518 Senior Member

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    The kind of reply I was looking for was something like

    “If you plug it in in the summer with a cold engine, you should see coolant temps rise 30 degrees in 1/2 an hour. Or something like that.

    No idea if the temp sensor for the dash gauge is in the block, a hose or the radiator. Will the gauge show the effects of the heater if you don’t run the engine to circulate the coolant? If it’s in the block, how long will it take for the heater to change the coolant temp?
     
  8. skyking1

    skyking1 Senior Member

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    Good luck with getting your required reply. If it sparks at the cord and draws juice, that heat is going into the engine. If it does not it is a bad unit or wiring. There is no spec for reading a gauge.
    I plug them in a minimum of 4 hours before startup, or set a timer to do it for me. If it makes that crackly noise and dims the lights I have never been disappointed with the results.
     
  9. 1693TA

    1693TA Senior Member

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    These are a simple resistive coil using the engine coolant to disallow it burning itself open, along with a thermostatic switch sometime(s) to regulate the temperature.

    What is the wattage of the unit in question? 120VAC, or 240VAC electrical supply?

    A multimeter is what you need to measure the coil resistance set on the appropriate ohms scale for the coil under test.
     
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  10. JLarson

    JLarson Senior Member

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    If its in the water I plug it in with a splitter cord and amp clamp it, amps, f**k it run it, no amps, block heater no worky.

    My more common interaction with block heaters is taking them out and plugging the hole here though lol
     
  11. Delmer

    Delmer Senior Member

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    A core plug block heater will typically be 400 watts. A "killawatt" is a handy plug in electric meter that's about $20 at menards, you can plug that into your extension cord, plug the heater into that, and see if it's drawing about 400 amps. The sparking when you plug it in is good enough though, they either work or not. Best way to judge from the heat of the block would be on a cool morning, plug it in and in a half hour the head should be warm to the touch.
     
  12. willie59

    willie59 Super Moderator

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    Agreed, it's simple to test. Block heaters are resistor elements so all you have to do is an ohm test at the plug where you plug in the AC cord with an ohm meter. If you read infinity then you have an open circuit, either the cord is bad, or the plug connection at the heater, or the heat element is bad. As for the ohm reading you get, well, that depends on the wattage of the element, but you should see something between 10 to 35 ohm depending on the wattage.
     
  13. Delmer

    Delmer Senior Member

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    Two reasons that an Ohm test is less than ideal for this. First, cheap multimeters aren't accurate for ohms. Second, a burned out element can have a reading less than infinity due to coolant filling the gap between the burned wires.
     
  14. willie59

    willie59 Super Moderator

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    That's true. I'm only saying, if an element is good you're going to get an ohm reading depending on the wattage of the element. For example, a 1000 watt 120VAC element is going to read around 14 ohm. Lower watt elements will read higher. Without knowing the wattage of the element, if you check it with an ohm meter and get a reading of 14 ohm or higher it's likely a good element. Anything lower than 14 ohm would be suspect and should be investigated further.
     
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  15. Truck Shop

    Truck Shop Senior Member

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    Or like one shop here in town did-ran it in the shop plugged it in--burned the shop and dump truck in it to the ground.
     
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  16. JLarson

    JLarson Senior Member

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    Proved the heater worked and pissed the insurance company off, two birds one plug lol
     
  17. DMiller

    DMiller Senior Member

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    Can vary as to wattage, from the 110w inline can types to 170w for my tractor as a core plug replacement, my Super Duty Powerstroke is right at 250w and the old Cummins heaters I was used to replacing were around the 400w size.
     
  18. Truck Shop

    Truck Shop Senior Member

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    Cord shorted at heater connection, breaker never popped.
     
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  19. Willie B

    Willie B Senior Member

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    It should have wattage printed on it. You need a short cord with individual conductors. I use a flat air conditioner extension cord with hot conductor separated with razor knife.
    Check with an ammeter. Amps X volts = Watts A watthour is 3.4 BTU per hour.
    A BTU is defined as heat needed to raise 1 LB of water 1 degree F from 70 Degrees F.
    A lot of calculating there, and that's before we figure how much energy needed to heat the iron, or how much is lost to the atmosphere.
    It is unlikely it is thermostatically controlled, so plug it in, give it an hour or two, see if it gets warm.
    As an electrician, I get calls often about block heaters tripping GFCIs 90% of these problems are solved with a good extension cord.
     
  20. Thirty5D

    Thirty5D Member

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    400 amps?