How many ohms resistance should a block heater have?
Set a multimeter to the “ohms” setting, then touch one probe to each of the prongs on the block heater plug and read the resistance. An ideal resistance reading will be about 20 to 30 ohms, but if there is a “0” or infinite resistance, the block heater is not functional.
What is the resistance of a block heater?
Yes 20-25 ohms gives you ~650 watts, which is about right for a Dodge Cummins block heater (I heard about 700W).
How do I know if my block heater is bad?
If the ohm reads open (infinite resistance) at the plug, you can slide under the truck and unplug the wire from the heater itself, and ohm it at those prongs on the heater. If that shows the 14-ish ohms, then the heater is probably good and the cord is bad.
What temperature does a block heater turn on?
A general rule of thumb is to plug in your engine block heater when the weather reaches -15° C or lower, just to be safe. If you drive a diesel vehicle, you may need to plug in the engine block heater before temperatures drop that low.
Do block heaters go bad?
It’s just a big heating element, a big resistor. Just like a heating element in an electric dryer or electric stove (or a glow plug, for that matter), it can fail over time.
Is it bad to leave a block heater plugged in overnight?
One thing that most can agree on is that the maximum amount of time you should leave the engine block heater plugged in for is four hours. Any more and you’re just wasting electricity. You should also plan for plugging your vehicle in for at least two hours to ensure it will start.
What can go wrong with a block heater?
Coolant can leak from the block heater and come in contact with the cable terminals, possibly causing a fire. The heaters are used to keep the block warm in extreme cold temperatures. GM says it has reports of 24 fires potentially caused by the problem from Dec. 3, 2019 through May 28, 2021.
