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  #1  
Old 02-19-2008, 09:30 AM
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block heater

Does anyone have a test procedure to see if a block heater is in working order? OK, I know I'll get posts that say to just plug it in, but here's the deal. I recently bought an 85 300d and the plug is cut off the cord coming out of the block heater. I have learned through the years that sometimes people do things for a perfectly good reason (like the shorted tach that I replaced in my first car, causing the ignition to short out and the car not to run for three weeks till my mom pointed out that the car quit running the same time I replaced the tach). Anyway, I'd like to test it before I replace the cord and try using it.
thanks,
ben

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Old 02-19-2008, 09:40 AM
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I'm sure you could test it's resistance and there's some figure which would indicate if it was ok or not. I think it would be easier to attach a plug, plug it in and see what happens. Can't see what harm it would do besides blow a breaker if it's shorted out.
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Old 02-19-2008, 09:45 AM
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Strip back the insulation and test it with an ohm meter. I believe they are rated at 450 watts which is about 4 amps at 120V, so using V=IR you should see about 30 ohms across it, but the resistance does change as it heats so it may be lower when cold...it will probably be either shorted or open if it is nonfunctional but if you get a reading between shorted and open, or around 30 ohms it probably is OK to try plugging it in.
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Old 02-19-2008, 10:27 AM
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Aren't block heaters like $30-$50? I've never done this so maybe it's more work than I'm imagining but wouldn't it just be easier/safer to buy a new one and put it in?
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Old 02-19-2008, 11:28 AM
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Originally Posted by herring View Post
Aren't block heaters like $30-$50? I've never done this so maybe it's more work than I'm imagining but wouldn't it just be easier/safer to buy a new one and put it in?
Why replace it if it works? Someone may have just cut the cord because it was dangling and got damaged. It's a lot less work to splice a plug onto an already installed block heater than to replace it. They can be a PITA to get out.
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Old 02-19-2008, 11:33 AM
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Either get a dummy plug for the end that's cut, or just get a new cable. If it's already there, it probably works. The best way is to try it. What's the worst that can happen?
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Old 02-19-2008, 12:19 PM
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Quote:
Originally Posted by nhdoc View Post
Strip back the insulation and test it with an ohm meter. I believe they are rated at 450 watts which is about 4 amps at 120V, so using V=IR you should see about 30 ohms across it, but the resistance does change as it heats so it may be lower when cold...it will probably be either shorted or open if it is nonfunctional but if you get a reading between shorted and open, or around 30 ohms it probably is OK to try plugging it in.

Why would you need to strip the insulation??? Resistance can be checked at the plug prongs. You need series to check current.

If you really care to find out if it is working buy a Kill-A-Watt. They are $30, but they have other uses. You plug it into the extension cord and then plug the heater into it. It will tell you how much power, current, etc you are using.

-Jim
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Old 02-19-2008, 12:21 PM
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Originally Posted by Jadavis View Post
Why would you need to strip the insulation??? Resistance can be checked at the plug prongs. You need series to check current.

If you really care to find out if it is working buy a Kill-A-Watt. They are $30, but they have other uses. You plug it into the extension cord and then plug the heater into it. It will tell you how much power, current, etc you are using.

-Jim
I think the OP said the plug was snipped off....
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Old 02-19-2008, 12:27 PM
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Originally Posted by Jordan G View Post
I think the OP said the plug was snipped off....
Thanks...I'll take my crow served well done.

In that case, check each wire to the engine block with a volt meter set on resistance. It should be infinate. Check wire to wire. I don't know what it should be, but will check it tonight.

A new cord is only about $15 + shipping, but I agree you should do some testing first. You can also take just about any left over power cord and a couple of wire nuts, and wire the thing up for a test. If it pops the power strip or the circuit breaker you know you have a problem.

-Jim
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  #10  
Old 02-20-2008, 09:37 AM
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I tested with an ohm meter last night and got infinite resistance at the cut end of the cord. I'll test again at the heater end when I've got a minute to get greasy, but I'm guessing its shot. I've read that they can be a real PITA to remove so I'll probably just skip it. Besides, I live in Atlanta where it doesn't get too cold, and even in the 20s the car fires on the first crank.

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