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J b weld cracks

has anyone had, good success with j b weld would it help with a small crack on the head. up around the coolant temperature sending sensor.

Cracks require certain measures to ensure they do not continue to propagate. The first step is to relieve the stress riser and that is commonly done by drilling a hole at the end of the crack. Then you need to provide a way to penetrate the crack to allow the stitching process. As much of a fan as I am for JB Weld, this is not the right solution to this kind of problem. First, it is hard when cured. As the head expands and contracts, this will likely break the epoxy bond. Drilling, grinding and welding cracks is the only real way to repair something like this and that is usually cost prohibitive compared to simply replacing the head. To fix it right, it has to come off and by then, it’s usually better to just replace it than to invest in fixing it…

thanks twin turbo, going to bone yard today.thanks

Good to hear.
The only way to repair a crack in a cast part subject to mechanical stresses and thermal cycling is welding. And even that’s not guaranteed. The Heat Affected Zone (known as HAZ) around the weld is then subject to possible failure.

I read many years ago that JB Weld was originally made to repair cracks in flathead Ford engines on farms because farmers did not want to spend money on antifreeze and an unexpected cold snap woutd crack engines that had not been drained. I don’t think the modet T and A 4 cylinder flatheads had pressurized cooling systems.

I still remember when these miracle “glues” starting appearing and my Dad using a two part epoxy to glue a patch in a snowblower crankcase. It was astounding, especially compared to the stuff available up to that point.

Looks like JB-Weld came into existence in the mid-late 60s. Check out the wiki article. Interesting stuff:

I used JB Weld to repair a vertical crack, about 2" long, in the left side of the block of the 20R engine in my 1979 Toyota truck. The truck had been neglected when I bought it for $50. There was a green stain coming out of the crack, so I suspect it was too-weak antifreeze that had frozen and cracked the side of the engine block.

I Dremeled the crack a little deeper and wider, cleaned the block vigorously, then mixed the JB Weld and applied it with a putty knife. The area never leaked again in the decade or so I had the truck, before its frame broke from rust. RIP old truck.

I have to say if you are going to try JB Weld, the quick stuff pales in comparison to the original stuff.

Other than the time to do the experiment, little harm done by trying JB Weld. Epoxy’s are similar chemically to plastics, so verify the version of the product will stand up to cylinder head temperatures. There’s several types of JB Weld products, and there’s probably a version that’s designed for higher temperatures than the company’s standard product.

There’s a big difference between a block crack and a head crack IMO. That’s why I wouldn’t even attempt it and I’m not known for being conservative in this regard… :wink: