Yes, you can add to the cord. You should use 12/3 cord and a heavy duty plug. Use butt connectors for the splice, and seal it up with waterproofing tape.

You are burning up the plugs because the exposed contacts of the plug get corroded and don't make good contact in the extention cord. The resistance builds up heat and burns up the plug. Coat the new plug contacts with a dielectric grease, and put a cover over the plug contacts and you will never need to change the plug again.

Same holds true for the female end of the extention cord.

 

Thanks for your reply. Do you think if I used. 16/3 cord instead of 12/3 it would make a difference? I’ve tried looking up what the OEM was but can’t find that info.

Thanks

 

Not an authority, but my answer would be yes to splicing in a length of extension cord. As to type/rating, you would want to, at a minimum, match the gauge of wire used in the original block heater cord.

 

Best bet would be to splice in an extension cord with the sealed plug end.

 

I can't really recommend a smaller wire size without knowing what the wattage of the block heater is. If it is over 1500 watts you need #12 wire, if it is under 1500 #14 wire should work, it would have to be under about 1000 watts you could get away with #16 wire.

Bigger (smaller number)wire is always better. Smaller wire could build up heat, and burn things up, as you have discovered.

 

The oem and third party block heater for my '12 3500/6.0 are 400W, I doubt the '03 uses a much higher wattage one...
The cord for it is also indicated as being 18 gauge on rockauto...

A short, underhood extension that is 18 gauge is probably fine, but you want to still get one rated for outdoor usage. The longer external extension needs to be heavier gauge.

 

Don’t those cords screw into the block heater like on the big in line 6 diesels so maybe get a new cord and insert if possible

 

Yes, replacing the whole cord is probably the way to go, and then protect it. The one on my '04 3500 has been good for 9 Canadian winters so far... I should scrub some of the corrosion off the prongs though.

And it really only has to be used when the temps are below about -20C or so, and even then, it should still crank up fine if the engine and battery are in good working order.

 

I would use the 12/3 cord. It sounds like it is getting some usage/abuse. The heavier gauge wire will be a heavy duty cable covering too.