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Block Heater

JD 5020

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As Rick said, screw in just in front of the starter, has a wide slot and you might want an air impact. I had to use an impact and a little heat around the hole. Screw in is pre 81 or 84 not sure, after that its expansion plug type. Be prepared to drain down alot 10 to 12 gallons of antifreeze in a large clean container so you can use it over. Might as well fix anything that leaks or might leak soon while it's drained down. I replaced my heater hose shut off while I was at it, it was dripping. The cost was 45.72 at the dealer. Well worth it. I think it is the most brutal thing you can do to a diesel is a very cold start. Hard on the starter, all the cold parts,and I can't see how it would throw oil when it is that cold.

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Alot of the new block heaters are push in despite the threaded block hole. Pre 81 has a toggle screw to fasten and 81 and up has a plate with 1 bolt to fasten it to the block. (Reference Zero Start brand...)

You can also use a remote tank type heater that functions as a pump (due to temperature differential) to circulate the water through the cooling system. Kats, or Zero Start brand both market them and they are easy to install by tapping into the water lines. I've used them for over 20 years without problems.


Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.



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  • 5 years later...

Just grab that square plate and slip the element out of the block. It does down, so you will have to wiggle it around.

There is an insert screwed into the block with a shoulder on it. There is a ring behind the shoulder that the element plate bolts to(with a rubber gasket). I had to remove mine completely when I installed the screw on filter housing.

To remove the screw in bushing, I had to heat and chisel it out.

What was left:


New plug:


No room behind new housing:


BTW, I never really used the block heater. I'm one of the lucky ones, even at 18* temperature, I was able to get her to fire up WITHOUT ether or heater. Crank, wait, crank, wait..............Zoom it came to life. Guess I got a good one? But I do have 12v starter and GOOD batteries. It wings that lil motor over like nothing. I originally put FOUR 12v batteries in it, but a few years ago I finally had to replace them I just put two and it still starts very easily.



1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"


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Yeah, I gave it a little pry to break the gasket loose and she came right out...tested good on the bench at 10 ohms (I thought I tested it in the truck?!?!?!?) Anyway, my cord may have a SLIGHT leak to ground, enough to trip the GFCI, or my GFCI is weak, any way it works great on another house circuit!

At the end of the day I learned something, and it didnt cost anything...

Thanks for the help


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  • 10 years later...

Revisiting an old thread.

I am wanting to replace a not working square, bolt on heater adapter with a conventional style heater element.  Like the 81 and newer trucks have, mostly for ease of future replacement and parts availability down the road.

Can this be made to happen with the existing water jacket plug/bushing that is currently housing the bolt on heater, OR should I use one of the other water jacket plugs?


Im thinking something like this might work.


Edited by Full Floater
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