block heater not showing ohms on multimeter but can hear 'kettle noise/hissing'

Joined
Sep 23, 2017
Messages
400
on my truck i was curious if my block heater was still working so i watched those youtube videos to test it and seems like a good method was the multimeter method.
they say to set the multimeter to ohms and then measure the resistance when hooked up to the hot and neutral on the plug.

well i did that a few times and it starts at 0 and then when my multimeter makes contact it jumps to some values and then drops back to 0 after 1 second. i tried changing connection and it does the same thing like it doesnt give a constant ohm reading. it just jumps to a random number and then back to 0.

however i did the ear test and when i plug it in, 2-3 seconds later i can hear a hiss/kettle noise from engine bay.

is there a reason my multimeter test isn't working? if so, what r some other tests i could try

thx!
 
Joined
Jul 7, 2014
Messages
2,249
Location
Winnipeg MB CA
There may be corrosion on the prongs of the plug, which is not allowing the probes of your multimeter to make good contact. You could clean up the faces of the prongs with sandpaper or a fine file and try again. Typically you're looking for 25 - 40 ohms, depending on the wattage of the heater. Anything under 1 or 2 ohms indicates a short, and infinity (O.L.) indicates an open circuit, which is almost always a bad plug on the end of the cord.

I changed one for a friend yesterday - it tested out OK intermittently, but when we opened it up, one prong was broken off its base, making only intermittent contact.

Because you're hearing it sizzle, it's almost certainly working fine. If you have a ScanGauge or equivalent, you can check the coolant temperature immediately after starting the engine - my block heaters typically raise the temperature from near ambient up to around 23°C after about 3 hours.

Good luck!
 

jalikaria24

Thread starter
Joined
Sep 23, 2017
Messages
400
There may be corrosion on the prongs of the plug, which is not allowing the probes of your multimeter to make good contact. You could clean up the faces of the prongs with sandpaper or a fine file and try again. Typically you're looking for 25 - 40 ohms, depending on the wattage of the heater. Anything under 1 or 2 ohms indicates a short, and infinity (O.L.) indicates an open circuit, which is almost always a bad plug on the end of the cord.

I changed one for a friend yesterday - it tested out OK intermittently, but when we opened it up, one prong was broken off its base, making only intermittent contact.

Because you're hearing it sizzle, it's almost certainly working fine. If you have a ScanGauge or equivalent, you can check the coolant temperature immediately after starting the engine - my block heaters typically raise the temperature from near ambient up to around 23°C after about 3 hours.

Good luck!

gret thanks so basically if it was 'short' then it wouldnt be sizzling/ working right? i paid attention for 30-45 seconds and the sizzling didnt go away and right when i unplugged it, i noticed it stopped. so i am certain the noise is from the block heater!
 
Joined
Jul 7, 2014
Messages
2,249
Location
Winnipeg MB CA
gret thanks so basically if it was 'short' then it wouldnt be sizzling/ working right? i paid attention for 30-45 seconds and the sizzling didnt go away and right when i unplugged it, i noticed it stopped. so i am certain the noise is from the block heater!
If it was shorted, it would trip the breaker.

If it was open, there would be no current flow, and so you wouldn't hear the sizzling.

Is your multimeter good? If set to Ohms, does it display close to 0.0 when the probes are shorted together?
 

jalikaria24

Thread starter
Joined
Sep 23, 2017
Messages
400
If it was shorted, it would trip the breaker.

If it was open, there would be no current flow, and so you wouldn't hear the sizzling.

Is your multimeter good? If set to Ohms, does it display close to 0.0 when the probes are shorted together?
yes i believe its good, i tested a nother device and it showed 30 ohms, ill try that 0.0 test and see whats up
 

JHZR2

Staff member
Joined
Dec 14, 2002
Messages
46,758
Location
New Jersey
My block heater plug was dirty enough that I got no reading at first... had to scratch through, then I got 6 ohms or some reading around that value, IIRC.
 
Joined
Sep 30, 2020
Messages
392
Location
Canada, eh?
stupid question but i wont get bruned or anythign by touching in that area right?
that's correct.

Only time you'd get "burned" is after the engine has been running.
I'd feel around the area after it's been plugged in for about half an hour on a stone cold engine.
You should notice one area (where the block heater is inserted) is noticeably warmer to the touch...it'll be "comfortably" warmer.

Oh, and the "sizzling" sound you hear is perfectly normal.
 
Joined
Aug 13, 2017
Messages
2,716
Location
WY
What are block heaters? 1500 watts? 120 Volts....in a pure resistive circuit is near 10 ohms.
 
Joined
Nov 20, 2006
Messages
26,822
Location
MA, Mittelfranken.de
First of all set the ohms to a low value. A reading of 0 is fine in this case it tells you there is continuity between both poles, if the heater element had burned out there would be no 0 just a blank screen.
 
Joined
Jul 7, 2014
Messages
2,249
Location
Winnipeg MB CA
What are block heaters? 1500 watts? 120 Volts....in a pure resistive circuit is near 10 ohms.
1500 W is really high. I think you might see 1000 W for a diesel.

The one in my friend's Nissan Versa worked out to be c. 375 W.

Your calculation is correct, though - a 1500 W block heater, @ 120 V, would be about 10 Ohms.
 
Joined
Jun 26, 2003
Messages
11,876
Location
Illinois
on my truck i was curious if my block heater was still working so i watched those youtube videos to test it and seems like a good method was the multimeter method.
they say to set the multimeter to ohms and then measure the resistance when hooked up to the hot and neutral on the plug.

well i did that a few times and it starts at 0 and then when my multimeter makes contact it jumps to some values and then drops back to 0 after 1 second. i tried changing connection and it does the same thing like it doesnt give a constant ohm reading. it just jumps to a random number and then back to 0.

however i did the ear test and when i plug it in, 2-3 seconds later i can hear a hiss/kettle noise from engine bay.

is there a reason my multimeter test isn't working? if so, what r some other tests i could try

thx!
Resistance rises as it heats up. It will start close to zero and rise. If you run it and then unplug and measure, you should see a higher value.

You probably need to measure current. If you have a killawatt to measure current, use that instead.
 
Joined
Jul 7, 2014
Messages
2,249
Location
Winnipeg MB CA
Resistance rises as it heats up. It will start close to zero and rise. If you run it and then unplug and measure, you should see a higher value.

You probably need to measure current. If you have a killawatt to measure current, use that instead.
The resistance will start at its rated value, and will stay pretty close to that. Remember, it's immersed in coolant, which will not get much warmer than room temperature. I tested this a few years ago, and the resistance only rose 10% or so.
 
Joined
Jun 26, 2003
Messages
11,876
Location
Illinois
The resistance will start at its rated value, and will stay pretty close to that. Remember, it's immersed in coolant, which will not get much warmer than room temperature. I tested this a few years ago, and the resistance only rose 10% or so.
Perhaps. Still, I think measuring current is more accurate for heaters. I.E. if I know the current and the voltage, I can calculate the resistance.

But as long as it's not infinite, it's probably good...
 
Joined
Nov 20, 2006
Messages
26,822
Location
MA, Mittelfranken.de
He says he can hear it making noises like a working one would and he may not have the ohmmeter set on a low enough setting to do 10 ohms.
I said in this case, he gets activity on the meter before it is zero and it is sizzling, I sure sounds like it is working, a simple temp probe will tell.
How can you have a dead short in a heater circuit? I would think it either dead shorts to ground or it burns out and has an open but I am not an electrician so I defer to someone who is.
 
Joined
Aug 13, 2017
Messages
2,716
Location
WY
He says he can hear it making noises like a working one would and he may not have the ohmmeter set on a low enough setting to do 10 ohms.
I said in this case, he gets activity on the meter before it is zero and it is sizzling, I sure sounds like it is working, a simple temp probe will tell.
How can you have a dead short in a heater circuit? I would think it either dead shorts to ground or it burns out and has an open but I am not an electrician so I defer to someone who is.
Well we know it isn't zero ohms as that would immediately trip the breaker. I imagine the resistance is being mis-read and you noted the sizzling sound which is coolant boiling of the surface of the element. I guess I am not understanding the OP's issue.
 
Joined
Feb 25, 2015
Messages
1,545
Location
Sask, Canada
A neat way to check if your block heater is working, plug it in for an hour and then go put your hand on it. If it warm it works. If its cold it doesn't. Other than that......
 
Top