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ok- so I pulled the freeze plug trying to match the bolt head and yes indeed the "locking arm" for lack of a better name, broke! the screw appears bent too. even though it's brass, that would still take some force!
I agree with all the above, the idea being to determine if it failed simply because of age/corrosion OR comma, something else - stuck (closed) thermostat, for example. There are other possible causes, none of them very good.
Other BAD cause would be too much water, not enough antifreeze and froze overnight on a cold night. If that's the case, that block heater could be the very least of your problems. If nothing else is visually wrong, then get a plug in there and pressure test the system and pray it holds.
Upon further inspection, I noticed something odd- if you look at the last photo and this one at the break carefully you will notice no fresh break, no clean brass. Only the look of metal that has been long exposed. perhaps this didn't take as much force as we are guessing to blow out the plug/ block heater?
Looks like a problem that was quite a while coming based on the fracture surface. It could have been caused by improper torque, a defect in the part, heat/cool cycles, vibration, etc. If there was that little material still holding on, normal system pressure (12-14 psi) would be enough to force the heater out of the block.
A stuck thermostat would not cause an increase in cooling system pressure. Only a defective radiator cap would have any effect, but even so, other things would break before busting this retaining tab in two from pressure alone. If the coolant froze in the block, that could certainly force it out, but a crack in the block or heads would also be extremely likely.
A stuck thermostat (closed) while not as common seems to me would raise pressure dramatically inside the block. It would tend to overheat. Why is the radiator somehow different? Heater hose is always flowing, I guess.
A stuck thermostat (closed) while not as common seems to me would raise pressure dramatically inside the block. It would tend to overheat. Why is the radiator somehow different? Heater hose is always flowing, I guess.
Pressure is virtually the same in the whole system, regulated by the cap. The block heater retainer simply failed. It is old. Replace it with an e pansion plug or new heater and drive another 20 years.
Seems to me all it would take would be for that bolt to be over-torqued ONE time, which would bend and weaken that toggle / locking arm. Coulda happened, say, 10 years ago, setting off a ticking time bomb, that just happened to tick down to zero yesterday (...should old acquaintace be forgot...). I wouldn't agonize over the analysis; it's a replaceable part that failed. Plan of action would be determined by whether you WANT a block heater. Coupla weeks ago, a bunch of brand new KAT's brand block heaters of this type went up on eBay cheap. May still be some left.
Rather than over thinking the situation why not replace the heater or install a freeze plug. While you're at it a new radiator cap and thermostat is cheap. You will already need coolant no matter what.
I couldn't get replacement parts on new year's day, but yesterday I got out and sourced another block heater. Cleaned the hole and installed the new part with only a coating of antifreeze for lubrication. I recommend having a blunt tool to tap the heater into place because you really need it to get the new part to fully seat.
anyhow I filled it up, checked oil and fired it off....
seems like I'm Ok, but I will want to take it to a pro for a radiator pressure test and cylinder leak test.
I'm checking the oil and antifreeze on every trip I make for the moment. I will change oil and flush and refill antifreeze the next semi-warm day i get- and change the thermostat too. Any other advice?
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