How can I test a thermostatically controlled block heater cord?

Tiny
MARVINJOHNSON9
  • MEMBER
  • 2009 FORD F-150
  • 116,000 MILES
Thermostatically controlled block heater.
Friday, August 11th, 2023 AT 9:28 AM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,924 POSTS
Testing a thermostatically controlled block heater cord on a 2009 Ford F-150 involves checking its functionality to ensure that it's working properly. The block heater cord is designed to keep the engine block warm in cold weather, aiding in easier starting and reducing wear on the engine. Here's how you can test it:

Materials Needed:

Multimeter (voltmeter or continuity tester)
Extension cord (if necessary)
Access to an electrical outlet
Steps:

Visual Inspection: Start by visually inspecting the block heater cord and plug for any visible damage, fraying, or exposed wires. If you notice any damage, it's recommended to replace the cord before testing.

Check for Continuity (Ohmmeter Test):

Set your multimeter to the continuity (ohms) mode.
Unplug the block heater cord from the vehicle.
Place one multimeter probe on one of the prongs of the plug and the other probe on the corresponding prong.
If there's continuity (a complete circuit), the multimeter will beep or display a low resistance reading. This indicates that the cord's internal wires are intact.
Test for Voltage (Voltmeter Test):

Plug the block heater cord into an electrical outlet.
Set your multimeter to the AC voltage mode.
Carefully insert one probe into one of the prongs of the plug and the other probe into the corresponding prong.
If the block heater cord is working properly, the multimeter should show a voltage reading. The voltage may vary depending on the design of the block heater, but it should be around 120V AC.
Feel for Warmth: After the block heater cord has been plugged in for a while (usually at least 15-30 minutes), carefully touch the engine block in the vicinity of the block heater. It should feel warm to the touch if the block heater is functioning correctly.

Temperature Testing: If the ambient temperature is below freezing, you can also monitor the temperature of the engine block with an infrared thermometer. Measure the temperature before and after the block heater has been plugged in for some time. You should see a noticeable increase in temperature if the block heater is operational.
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Friday, August 11th, 2023 AT 4:09 PM
Tiny
MARVINJOHNSON9
  • MEMBER
  • 3 POSTS
When plugged the block heater cord into a power outlet the thermostat on the cord gets considerable warm. Is this normal? Outside air temperature is approximately 70 F.
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Sunday, August 13th, 2023 AT 8:58 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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It sounds like the block heater is bad, the cord should not get hot. A little warm is okay but hot is telling us the internal heater could are bad and drawing too much amperage.
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Monday, August 14th, 2023 AT 11:30 AM

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