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Cracked block

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Hey guys, I’ve been chasing a coolant leak for a few days now on my ‘89 2.5L. Finally found the smoking gun: CD59FA9F-38C8-48E1-BE9B-E1C63CFDBF4D.jpeg.e60f35e8b7b3c209fcf9edbc9042cb2c.jpeg


right above the driver side motor mount, it’s at least a two inch long crack. I’ve never welded cast before, but my brother has some experience, and we have access to mig, tig, or stick. Since it appears to be only the coolant jacket at this point, is it worth trying to weld the block? Or would that be a band aid at best?


it only has 56k miles, so I’m somewhat surprised, but it’s incredibly rust free for New England, so I had planned to keep this one happily in stock configuration, ie no drivetrain upgrades. If it makes more sense to swap the bottom end, so be it, but to sum up:


does anyone have experience welding a cracked block, and did it hold up long term?

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Could you fix it? Yes. It's not terribly uncommon to see old welded Chevy 348/409 blocks or Mopar Hemis. I have no clue on the longevity of the repair. But in order to do it, you have to pull the motor, clean it, and heat it a bunch before you weld it. If you wanted to keep the truck numbers matching, it may be worth trying, but it a 4cyl Comanche, I don't think it is worth the work and I would swap in a different block.

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I’ve had good luck in the past brazing cracked water jackets. It won’t be near of a shock on the casting that welding would, and the brass rod will be way more ductile. You’ll still need to warm up the area you’re working in, but again not near what you would trying to weld. The stress from welding can also crack something further into the block too. 

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Mine’s doing the same thing. I dosed it with a block repair in a can product and got about a year out of that. I looped the heater lines together to avoid filling the core but otherwise followed the instructions to a T.


Trouble is stress pulls the crack open when you’re accelerating. Made it tough to find my own leak because it only came out when I was on the throttle and the crack opened up. Brazing with brass is probably the best semi-permanent fix as a result. Welding can work, but you can increase internal tensions as it cools which might make it just pull apart again under engine load. 

There’s also a block repair system that’s more labour intensive but used somewhat commonly in heavy industry. You start just outside one end of the crack, drill a hole and tap it for a pipe thread plug. Install the plug with some sealant, crank it down as tight as you can. Drill another hole that overlaps the first plug, and keep repeating the overlapping plugs along the length of the crack until you’re past the other end of it. The drilling usually stops the crack from progressing and the pressure from the tapered plugs counteracts the tension that opened the crack. Overlapping the plugs ensures you get the whole crack and stops the plugs from spining loose under vibration, but also means you don’t get a second chance at tightening them if it still leaks after the fact. 

As an aside, late this fall I used a different stop leak because I was shipping it and didn’t want it making a mess for the shipper, and didn’t have the time for the thorough flush the block repair required, and didn’t want to dump water everywhere in the cold either. Bypassed the heater core again for the running period specified on the bottle and hooked it back up before parking. Started it up at -20°C a couple days later to load it and had zero heat. Block heater plugged right solid and no time to deal with it before it went on the truck. When I eventually flushed it out after it came back off the truck I mostly just pushed an entire bottle of stopleak goop out of the thing. Also it was leaking again right away when it came off the truck, probably because the crack wasn’t opened far enough to push the thick radiator stop leak into it. So maybe don’t use a goopy orange stop leak… don’t remember specifically which one it was though.

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I appreciate all the feedback. I think I’ll try the stop leak method for the time being. Then I’ll track down a decent used engine without having to rush.


I think with the amount of labor needed to weld/braze, I might as well just swap the engine. It’s also January. If I can put off an engine swap until the weather warms up, I’d prefer that.

 I’ve always been leery of those magic stop leaks and “head gasket in a can” things, but if I’m only trying to buy a couple months, I’ll give it a go. 

Thanks Guys!

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