But it only does it when its warm. I had it plugged in at work tonight, and when I came out 2 hours later, the light up cord was out. So I figured it tripped the GFCI, which it did. I tried to reset it a few times, but it wouldnt with the heater plugged in, so I unplugged it and went back inside. When I went to leave, I plugged it back in to see if it worked and it did. Figured there was some snow shorting it out earlier and it shook loose when I fired her up. Drove home and plugged it in with the engine up to temp and pop goes the GFCI. So now I'm guessing the heater has a short somewhere, but only when its warm. Anybody else have this problem?

 

It's possible the cord to the block heater is shorting out, check for defects.

 

Your GFI is sensing current flow between the ground and neutral. Like said above, check the cord from plug to heater. The extension cord you are using, is it the same cord or different cord?

 

Two different extension cords. I just thought it was strange that it only did it when it was warm. I'll have to ohm it out tomorrow when I get a chance (both warm and cold). So much for hoping the GFI at work crapped out. They tend to do that on occasion. (oh, and it trips when it senses a currend difference between the line and neutral of more the 5-10 mA. electrical work is one of my many skills)

 

The block heater needs a 20A circuit. Unless your GFCI looks like -l l its only a 15A device and most likely circuit too. When you add the extra resistance of an extension cord, everything heat up and can trip the GFCI even without a short. All electrical cords have a small amount of leakage, and the longer the cord, the higher the chance for nuisance GFCI tripping.

Even though the OEM block heater is only 1000W and should in theory only draw around 12A, the three times I checked mine with an amprobe, it was drawing 18A-21A. In my experience as an electrical contractor, block heaters are best in a regular grounded receptacle.

I would check the entire length of the block heater cord for chaffing, especially the plug, behind the bumper and at any bends. Wipe it clean so you can see it better. Then, check it for continuity between the hot and ground and between the common and ground. If all tests out good, make sure you at least use a 12 gauge extension cord and you should be fine.


Austin

 

In residential use, a 15amp GFI can be installed on a 20amp ckt. I don't have the nec in front of me right now, but it is in there. with the block heater cord, definetly use a 12awg ext cord. Not the cheap 16awg problems will happen, melted cord caps for sure.

 

and check your block header cord for defects right at the bumper end.

I know more than one guy who has replaced his due to damage/defect/wear & tear..

I slobbered [soldered] a new end on mine rather than replace the whole cord, because I'm a cheapass

 

The block heater works perfectly fine on a 15A circuit. That's what I have at my home. And also I have it plugged into a GFCI outlet as well.

Your best bet is the plug at the end of the block heater cord. That is the first to go. Chop it off and get a Marinco outlet from Bass Pro Shops or any other marine or boating store.

Here's the Marinco plug: http://www.basspro.com/webapp/wcs/st...003000_200-3-4

And here's the mod: https://www.ford-trucks.com.com/cont...r%20Plug%20Mod

 

Weak GFCI plug itself. We have them go bad all the time. When the heater starts getting warm it's kicking the plug. If you want to go that far, change out the plug for a new one and see if that fixes it. I'd just change it out for a regular plug and be happy.
Joe

 

I suspect moisture and contamination. Do they salt the roads where you live? Could be salt on the plug (on the truck, since you have already ruled out the extension cord). When it's cold and frozen, it may not conduct as much or at all, but when it gets a little moist, it could conduct enough stray current to the ground pin to trip a GFI. The plug itself may warm up enough to melt any snow or ice that is on it.

Your block heater should work fine on a 15 amp circuit, as others have said. A heavy cord is good to minimize loss, and in particular to keep the plug contacts on each end cool. However, a lighter cord will not cause it to draw more current, it will cause it to draw less.

The very first thing I would try would be to clean the plug on the truck very thoroughly. I would use rubbing alcohol on a Q-tip to clean the face of the plug, between the contacts. I would also use a Scotchbrite pad to clean the tarnish off of the prongs of the plug.

A good inspection of the cord assembly on the truck is also advisable, as has been pointed out, paying particular attention to areas around bends and sharp edges.

 

Well tonight it works fine. My dad had the same problem with his and simply changed the end. I've been meaning to crawl under and check the cord, but i hate the cold. Guess I know what I'm doing tomorrow.

 

Wow, look at all the electricians. Yes, I am certified 15 years.

 

Haha, yeah. I'm still learning, but my dads a master electrician for about 20 years. Thanks for all the suggestions guys.

 

These block heater cords fail at the plug connector. Look over where you plug the extention cord in at an look for signs of the plastic melted around the connector pins. If it has you'll need to replace the cord or cut off the end and put on a new connector that is water tight. What I did on mine was go to home depot and buy a short heavy duty extention cord, cut off the female end and splice in onto my block heater cord using butt splices, heat shrink with the meltable liner to seal it and then put liquid electrical tape over that. I am on my third winter with it now and no more GFI trips.

 

Not to dis Austin, but here in Wisconsin I am pretty sure code does not allow you to have a non-GFI outlet in the garage let alone outside. READ - I am a Certified Crop Advisor, but in writing an offer to purchase a house I learned from a home inspector that all outdoor outlets must be GFI. Maybe he was full of ___.

BTW - Mine will kick my GFI out if there is snow in the plug. Especially if I hook two cords together. That was a bad day...running cords across the lawn down to the road...bad deal.