Block Cracked?
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4wd Low
Joined: Jan 2018
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Block Cracked?
I just got a 73 F100 with a 390, 4 speed. I decided to save a lot of time and pull the engine and replace all gaskets, since someone had covered every seam with gasket maker. The engine ran fine, but with a wicked exhaust leak. So we had some hard freezes at night, but temps in the 30's during the day, but a couple of mornings at 15 degrees. So a few weeks later I drained the oil, very black but no water, and the water had no oil in it. But my concern is that the knucklehead had only water in the coolant system, I had topped the radiator off before the cold snap with anti-freeze, but the block had only water in it. Now I am fearful that the block or heads cracked. Will I be able to see all possible crack areas or will there be a hidden water jacket?
Cargo Master
Joined: Jul 2010
Posts: 2,099
Likes: 8
From: York, Pa
You're probably fine but a FE is very very thin by the front freeze plug on the passenger side. My orig 390 did not push a freeze plug out when it should have and cracked the block. Even if yours cracks like mine did they can be fixed. We used lock and stitch method and worked perfect.
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4wd Low
Joined: Jan 2018
Posts: 12
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You're probably fine but a FE is very very thin by the front freeze plug on the passenger side. My orig 390 did not push a freeze plug out when it should have and cracked the block. Even if yours cracks like mine did they can be fixed. We used lock and stitch method and worked perfect.
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
Over the years I have seen a freeze crack something a lot more often than I saw freeze plugs pop out And 15 is getting down there where things would freeze unless it was in a shed. Not sure on a 390 but a lot of those old center oiler 427 boat engines were prone to cracking in the lifter valley when not drained properly. Before you tear it down, do a good pressure check. Leave it pumped up for an hour or so if you can.
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Fleet Mechanic
Joined: Aug 2004
Posts: 1,311
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From: Nevada
Water
I bet your fine. My truck was run by the PO for years on just water, which was very evident when I took off the heads and replaced the freeze plugs... Took hours to flush the rusty gunk out of the block 
.... If you suspect it has been run on water for a long time, flushing the block and replacing the plugs would be highly recommended.... Water + Cast Iron = heartache
.... If you suspect it has been run on water for a long time, flushing the block and replacing the plugs would be highly recommended.... Water + Cast Iron = heartache
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Cargo Master
Joined: Jul 2010
Posts: 2,099
Likes: 8
From: York, Pa
Mine was only noticeable once it was run and up to temp. Just sitting in the garage cold it was fine. I would think it would take a pretty good stretch of cold to break one. I'm guessing the water might get slushy but not do damage if it's a night or two.
More Turbo
Joined: Sep 2003
Posts: 514
Likes: 27
You guys are whistling in the dark. my first engine was given to me. It was just overhauled and they filled the cooling system with water to start and run. Ma called them in for supper and they didn't drain the engine. it froze overnight. In the morning the head had a big crack in it. That's why they gave me the engine.
Also you may call them freeze plugs or frost plugs but they are not for that. The holes they plug are put there to drain the core sand out of the block after it is cast. If one is pushed out and relieves a freezing situation you are just plain lucky.
OP, I'd check that engine for coolant system leaks before putting any more money into the block.
R.
Also you may call them freeze plugs or frost plugs but they are not for that. The holes they plug are put there to drain the core sand out of the block after it is cast. If one is pushed out and relieves a freezing situation you are just plain lucky.
OP, I'd check that engine for coolant system leaks before putting any more money into the block.
R.
Cargo Master
Joined: Jun 2014
Posts: 2,216
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From: Central Florida
The term "freeze plug" is a misnomer. They are not designed to protect the block from the expansion of freezing water though sometimes they do just that. They are actually "core plugs" which are necessitated by the casting process which involves sand that must be removed after the block or cylinder head is cast. That sand is poured/flushed out through those holes in the casting. After block machining, those holes are plugged with core plugs so that coolant can be retained in the block.
Thus, we shouldn't depend on those plugs to protect the engine from the expansion of freezing water.
Thus, we shouldn't depend on those plugs to protect the engine from the expansion of freezing water.
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
The term "freeze plug" is a misnomer. They are not designed to protect the block from the expansion of freezing water though sometimes they do just that. They are actually "core plugs" which are necessitated by the casting process which involves sand that must be removed after the block or cylinder head is cast. That sand is poured/flushed out through those holes in the casting. After block machining, those holes are plugged with core plugs so that coolant can be retained in the block.
Thus, we shouldn't depend on those plugs to protect the engine from the expansion of freezing water.
Thus, we shouldn't depend on those plugs to protect the engine from the expansion of freezing water.
Like I said, I've seen way more cracked engines than I have pushued out "freeze"plugs.
15 is plenty cold enough to crack a block if it stayed the cold for a while.
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