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Discussion Starter #1
Hey guys, I have an 1984 International school bus with a 6.9 diesel engine. The block heater on the passenger side core plug recently started leaking coolant. Long story short, I'm debating on whether or not to replace the heater with just a regular brass core plug or if I should buy a new block heater. This isn't my daily driver and will most likely be parked all winter. I really don't think that I'll need the block heater but if it needs to be moved/used how hard are these engines to start cold soaked to lets say 20 degrees? Also, I think I read somewhere that there were a bad batch of blocks from International because of the heater the block heater. Any truth to that?
-Brad
 

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My IDI won't start worth a damn without the heater in cool weather. But it's fine all summer so if you really don't intend to use it during winter you should be fine.
 

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My idi would fight if it was cold soaked, but it would start after a couple glow plug cycles. The key to cold weather starting is maintaining your starting system, you gotta have GOOD batteries, cables, and glow plugs. That being said a block heater helps tremendously. I would put a frost plug in it. Those internal heaters are worthless, get an external heater 750-1000w like a Phillips & temro or equivalent. They're much better. I have a 750w on a timer in one of my trucks, in 3 hours my coolant is 100*f. And they're not much more than a internal block heater.
I haven't heard that yet, I think a lot of the early 6.9 block issues were due to poor castings/materials, and in both the 6.9 and 7.3s the usage of wrong coolant is another contributing factor to the cavitation issues they had.
 

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You might get away with replacing the O ring. Usually that is causing the leak. Do not use a brass plug on the heater hole, or any hole on the IDI. They will fail. Use only stainless steel. You can get them from Ford or Corn Binder.

Early 6.9's had a weak spot near the heater. You will see a crack radiating from the heater hole if this is the issue. This was corrected in the 85 model year. Only the 7.3 IDI's are know for cavitation.
 

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Discussion Starter #5
Wow, I didn't know they used an O-ring to seal it. I'll have to try and remove it and check that out. I have the motorcraft/beru glow plugs with the relay operated off of a pushbutton and the system works fairly well. I also use just regular green coolant and test strips to monitor the Ph, freezepoint, and additive levels. I knew I was loosing coolant somewhere but didn't think much of it, until I noticed it dripping when I was setting the pump timing.
 

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To remove the heater loosen the screw just enough to get the heater out. If you completely remove the screw you will drop the toggle inside the block.:(
 

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My block heater fell out on the way to work one day. I didn't need it so I just popped in a neoprene expansion plug. It was a lot easier to reach than I would have expected. It's been several months and it's still leak free. You can get new heaters at most auto parts stores, usually start at $15 and up.
 
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