SIXSLUG

What should my ohm meter read if the circuit is good. I am trying to see if the block heater in my tahoe is bad but I think the antifreeze may be affecting the reading.

Thanks, Kurt

1-2-3

Depends on the setting of the meter and the resistance of the heater. It the reading never changes, the heater element is broken into at least two pieces. if it goes to all zeros, then it's probably shorted. Depending on it's rating you will get diffrent readings. it will never end up being exactly to spec.

I beleive the elements in out trucks are somewhere around 800 watts, but I don't know what the resistance reading would be to obtain that rating.

I'd say if your getting some kind of number from the readout, then you should be ok.

if your having issues, I'd suspect the cord. They get the most amount of abuse. Take a reading from prong to prong, and if it's open, remove the plug and read from terminal to terminal on the heater itself.

jrs_dodge_diesel

If your meter reads all 0.000's than its shorted and and needs to be replaced. If the display reads 0L, then the circuit is open and the heater should be replaced (this is assuming you are measuring just the heater, not the heater and cord).

The anti freeze should not affect the readings very much.

Here is the resistance in Ohms, that your heater should read (using Ohm's law for my calculations), depending on how many Watts it's rated for :

500W - 29.2 Ohms
750W - 19.2 Ohms
1000W - 14.4 Ohms
1250W - 11.5 Ohms
1500W - 9.6 Ohms

There is some leeway in the measurements though. For example the block heaters in our Rams are rated for 750 Watts (should read 19.2 Ohms). The last time I measured my heater it read 22 Ohms. So, nothing is perfect.

And as 1-2-3 mentioned the cord is a very common culprit in block heater problems. Try to take your readings from the heater itself. Also check the cord by itself.

Hope this helps.

Jim Lane

Also check from each prong to the engine block and make sure it has not corroded and shorted to ground.

I have boiler elements do this all the time.

SIXSLUG

Thanks guys, I should have noted this is the block heater in my wife's Tahoe. The dealership installed it over a year ago and won't warrant it even though I don't think it has ever worked. It's up behind the starter and a pain to get at. Everything on the outside looks good. Thanks for all the info!

Kurt