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Junior Member
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Discussion Starter #1
1989 7.3 idi Natural Aspirated (not a powerstroke) no turbo. New rebuild, shop replaced old freeze plugs when the block was cleaned, checked for cracks and honed. Freeze plug on right side over the engine mount blew out. Has anyone had luck with the expanding rubber plugs? The alternative appears to pull the engine again for a freeze plug repair.
 

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Discussion Starter #2
No responses on this.

This engine uses core plugs as opposed to freeze plugs. Core plugs are dome shaped wavers while freeze plugs are cup shaped.

Since one failed, I have no confidence in the rest of them and so I will remove the engine from the truck and replace all seven plugs on the engine.

(I didn't think the rubber plug was a good idea either!)
 

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Smart move if you have the time. When one fails the others should at least be watched close. On my lil VW the block heater used rubber o ring with a clamp that failed alot. Never liked it.
 

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Discussion Starter #4 (Edited)
I work alone and it takes me while to do big jobs because I tend to be very critical of my own work. I started on trucks and then worked on airplanes for a military career. Airplanes are all about clean and precise engine work. That has stayed with me especially when I work on my own stuff.

What I have learned: Core plugs are dome shaped wafers that fit snugly in the orifice intended. Once the plug is seated it must be dimpled in the center of the dome. The dimple causes the diameter of the plug to increase in size thereby creating a very tight fit. Literature that I found stated that a properly installed core plug may not act as a freeze plug and may not pop out in the event of a block freeze.

What I found when I pulled the engine: All seven of the core plugs were installed and virtually beat to a "reverse dome". This causes the plugs to fit loosely in the bore. Once the dome is dimpled beyond flat, it causes the plug to begin to retract in size. A dimple about the depth of half the height of the dome is good. More than that is not better! After installing the first plug, I sacrificed it by removing it. I found that the one I installed with a smaller dimple was much more dificult to remove than the plugs that were installed beyond "flat". I installed all new plugs in the engine and am ready to drop the engine back into the hull.
 

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Discussion Starter #5
:knight
I have a few hours on the engine since installing new core plugs. So far no signs of leaking. I'll start using it as daily driver until I have a couple hundred easy miles on the rebuild. Then I'll load it down and give her whirl!
 

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Discussion Starter #6
After 300 miles of break in: no signs of leaks from the engine. Runs strong, light diesel smoke on accelleration (normal), easy starting at 30 degrees f. Pulled about 8000 lb trailer, nothing came apart! ran at 50 to 60 mph for 20 miles with trailer and no probles with heat or power. I think I got it!
 

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Good to see it working for someone. Clean professional work is hard to find. Sounds like you will be your own best mechanic. I love driving my 85 even more than the 99PSD. Something about the sound and smoothness. The old truck cannot be broken. Other than hitching up a 15000 pound trailer to a truck that had been sitting for 4 years causing the tranny to blow nothing serious goes on the rig. Congrats on a job well done.
 

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4,247 Posts
You are correct, lots of shoddy workmanship out there. Core plugs are about the easiest thing to install, about all you need to worry about is clean surfaces, a small amount of sealant applied to the bore and prudence with placement. Obviously the machine shop could not get that simple task correct.

I was going to suggest performing this in-frame, but I think your results will be better having taken the engine out again.
 

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Discussion Starter #9
I am glad i took the engine back out. There is a total of seven plugs. Two on the right side, three on the left side, and two (one at the rear of each bank of cylinders) on the rear under the bell housing. All seven were over dimpled and were potential faillure points. The engine (which I rebuilt) is back in the truck and I am real pleased with the results. 12 mpg just like when it was new. C-6 three speed transmission, and a 410 rear end does not make a high mpg possible. I would have to either change the rear end ratio, or put in a high/low gear box to change the ratio. With higher gears, I would do better in the mpg area, but it would suffer when hauling a load. I think I will put up with the low miles to keep the towing capacity. It is a 1989 f-350 in pretty good shape. Unless I could find a used two speed gear box not too expensive, I am not inclined to start modifying the truck with big ticket items, it works well the way it is.
 

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YEOW! I'd be pretty p!ssed with 12 MPG as I am used to about 20 in our F-250. Granted it's a manual but still, we can pull anything that doesn't tear the GN ball out of the bed.
 

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Discussion Starter #11
John G:
I bought the truck new in 1989. Then fuel was about $.50 a gallon so it was not an issue. Now at nearly $4.00 per gallon that hurts. There are no signs that I am burning excess fuel. The idi turbo charged engine uses different rods with larger piston pins and bushings to take the turbo load. I kept the internals stock so a turbo may be too much for the original rods. When I took the engine down it was because of leaking water at the head gaskets. The radiator was partially plugged and I got the engine really hot a couple of times. I suspect that is when I spoiled the head gaskets. Put on a new radiator then the heads started leaking on the next run. New lower end bearings, all new seals, got the injector pump overhauled and installed re-manufactured injectors, and new "o" rings in the engine oil cooler (you helped me with that) and got the block cleaned and honed (that is where the core plugs were don incorrectly). Now it is all back together and runs the way it is supposed to. Top speed (hamer down) is only 67 mph. It has never been faster. In the days of 55 national speed limit this was not a problem. Now I cruise at 60 right around 3000 rpm. The C-6 tranny is a sluchbox and does not have a locking torque converter so a solid hook up to the rear wheels never hapens.
 
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