I have installed a zerostart freeze plug block heater on my 67 190xt and recently my 68 190xt because neither had the special port.  I also installed a zerostart in my 7010, which has the special port and the plate install.  My 67 190XT was done 6 years ago and no problems of a meltdown.  My 7010 was replaced by me I think 2 years ago.  None of them have burnt up or stopped working so I think that is quite odd.  I have used them quite a bit.  

I don't think you will want to put in a 400 Watt version.  It will not get hot enough in a few hours.  After installing a 600 Watt in my 68 190xt, it struggles to get the block warm when the temp goes below 20 degrees.  I measured the temp on the heater side and it was 45 degrees, but on the opposite side, it was like 30 degrees.  The outside air was 10 degrees.  

Here's a couple of ideas to consider:

1) Measure the output of the voltage of the receptacle you are using?  Is it 120+ volts?

2) Are you using the same receptacle every time or do you use different ones?

3) Could you be using an inferior extension cord?  I use a heavy duty 12 awg cord on mine.  Does the short pigtail cord have damage to it causing overheating?

4) Orientation is important but most of them will only orient one way.  190xt has the element going to 3PM position for freeze plug but you are using the port.  You can only put it in one way from what I remember on my 7010.

5) When I did a search on the Allis part number, I got the 1000 watt block heater come up and not a 1500 watt version.  Could you be buying the wrong part number and that element is touching the metal?  I think 1500 watt will have more element extending into the block.  Zerostart model that is compatible with 7010 engine is 350-0014 and is 1000 watt.

6) The other possibility is that your coolant is low and not completely covering the element.  This will cook them quickly.

7) I didn't know this but the AI bot said if you leave them plugged in 24/7 it can also cause them to fail.  I have left mine plugged in all night because I wanted to use it the next morning.  It suggested no more than 3 hours at a time.

Electrical things can be quite elusive so good luck.  I really like using the block heaters but at about $130 a pop, that sucks to see them stop after short term use.

I ordered one from agco for my 8010, it goes in a port just above the starter,. I don't know how the engine is configured in the payloader, the starter may be on the opposite side??? 

I didn't fully understand your original post, I think.  Sounds like you don't have the normal port for a block heater.  You have a 1 inch threaded plug opening which means you can use an immersion heater.  I looked at Zerostart and they have a 1 inch 1000 watt immersion heater plug (8600090 model) that is 3/4 inch shorter than the 1 inch by 5 inch long, 1500 watt model, assuming you are using that model.  Wonder if that is worth trying?  Seems to me that touching the metal may be the most likely culprit since everything else you mention seems to not be the problem.  You could stick something in the hole and determine how much clearance you have.

I always unplug my heater before starting but haven't waited very long.  Good luck.  It is cold and snowy here in Indiana this week. I am guessing you could use it to move some snow around.

Good to know you got it started!  I have about 12 to 14 inches of snow here and continues to blow and drift and I imagine you do as well in Illinois.

I would try the 1000 watt just to try something different and a 12 awg cord but that is your call.  It is hard to do the same thing over and over and expect different results.

Here is what it looks like from ZeroStart parts catalog.  So, it is a loop.

Here is the cordset that it uses too.  Looks like it is a 16 gauge wire.  So, 12 or even a 14 gauge extension cord depending upon how far the distance is to the receptacle, would work.

I would bet you're right except the guy on the phone had it in his hand and said it was a single element. It'll be delivered today so we shall see....

Is the picture posted 90 degrees off?

SteveM C/IL wrote: Easiest plan B is put a tank heater on but I don't like where it needs positioned Drain plug on side of block up to tstat hsg. I may pull that filter etc off to see what.

Seems like it is going to be a lot of work to go to a Tank Heater.  Wouldn't the 1000 watt heater be less heat and less likely to boil the coolant?  Is that worth a try or did the rep say that won't work at all?  Was the rep a Zerostart tech person?   Does it make sense to ask them?  I know you have burnt up every one you tried so I understand why you don't want to try the 1000 watt version or maybe even the 400 watt version.  

SteveM C/IL wrote: Talked to zerostart engineer. He wasn't comfortable with 1000wt at that location. A 700 maybe but cost add up burning em up doing trial and error. A tank heater could mount on frame rail and have about 20 inches of hose for both inlet and outlet. Literature on tanks say to keep out of weather. It would be somewhat under fender and I plan to keep it under roof so that might be okay. I just like "clean" installs. Sometimes your choices are limited. The tank i looked at was recommended for up to 26? qt system. Mine is around 34qt. It was 1500wt. This is getting complicated....

That's good to know you completely explored that with Zerostart.  Given how complicated things are getting, I might blow another $130 on the 700 watt version, then go to the tank heater after that.  I had a tank heater and while it worked, it took 3-4 times longer to heat up.  Of course, tank heater is better than no heat at all.  It is crazy how big of a rats nest this has become but old equipment always has it's challenges.  I know you will whip it.  Good news is that you can take a picture and post it now when you finally get success. 

SteveM C/IL wrote: the latest....put a 1000wt heater in my loader. Straight version like the 1500 i've burnt out. If this fails I'll have to modify my f/filter mount and use the bent one like a tractor uses. It's a 1000wt.  Certain it would work but just couldn't help myself and tried this first. Experience is a great teacher.

I think it is worth a try given the level work for the other plan.  Hope it works!

I got one of them magnetic heaters somewhere but the time or two I put it on my 220 pan it didn't heat worth a crap. Was on for several hrs and pan wasn't warm enough to tell a difference. The Allis heater for a 301 is 1000wt and there's 2 members at least  here that use them and they don't fail so I'm thinking maybe this straight heater will be ok. They are both in the same water jacket just the tractor one is in the "middle" and mine is in the front end where a tractor water pump feeds the block. I would rather have plenty of heat because when it's zero and it's in a tin shed,I want it to START!!! I can't say how effective a 700wt heater would be.

I had, basically, the same experience with the magnetic heater. I bought to put on my subcompact tractor for extreme cold weather. After being on for over two hours, the oil pan still felt cold, but maybe not quite as cold as the rest of the engine.

I ended up giving it to a neighbor who put in on his water pump in the barn for his beef cows.

Lots of folks seem to trash-talk lower rad hose style for not heating as effectively because the thermostat isn't open and you don't get natural convection, and it has to heat the rad coolant. But I have and use half a dozen or so of each type, and notice minimal (if any) difference. The lower rad hose ones are cheap, readily available (I've ordered two this winter off Amazon - arrived the next day), can be installed in minutes with no additional hoses/fittings, and are easily replaced if they do ever fail.

I will say to avoid the magnetic heaters. They do work. But they're veeeery slow compared to either the inline rad hose or freeze-plug type.

Thank you for the valuable insight, I have been contemplating installing some type of coolant heater on my Model C and have been wavering between the various types; your real-life experience most useful