Silicone can give/flex with the block expansion, Doesn't need any re-machining, costs a couple of bucks to perform, and is PROBABLY the best permanent fix, other than going with a later block, with the cost of machining.
I ordered them from what I considered "best" to "cheapest", you're supposed to try them in the opposite order. Personally, I don't think picking up another short block is that unrealistic, it's a good excuse to do a stronger build. But I've personally been using these types of problems as excuses to upgrade where my goal is to eventually go through the whole car.
I'm going to assume by "Silicone" you mean
some adhesive sealant, and not a silicone-based sealant specifically, in which case I might agree. Now, I'm admittedly a bit of a new-jack mechanic but sealants I know two things about — Silicone based sealants are not permanent (just read the tube on any Marine application Silicone, especially the 3M products which present a lay-persons scale of the adhesive strength), they are designedly removable, non-permanent sealants.
There are significantly more robust adhesive sealants, middle grades being based on polysulphide resins and higher grades being based on polyurethane and epoxy resins. JB Weld actually *is* one of those products, it's just a two part epoxy with steel-base resin (in the same sense as the poisonous copper-base paint we put on the bottom of boats). It will likely make handy-work of this little problem and it will stick for years and years to come without revisiting.
Silicone is the crap you use to seal your shower door. It's also the base used in most RTV sealants, which I trust for some odd things like sealing up my valley pan, but I just wouldn't stick on the opposite side of a water jacket because I don't like to come back and do the same thing over every season.
Another option I don't see mentioned is "Gorilla Snot" (commonly otherwise referred to as stove and oven sealer), I used this just recently to seal up an exhaust stud on my head which I had to heli-coil because I had snapped off an easy-out in it like a dumb ***. Here, have a pic:
Edelbrock makes a version of it under the label Gasgacinch. I originally used a high-temp sealant of brand I do not recall, as recommended to me by my local parts store. It failed under pressure and heat, so I pulled the stud and resealed it with gasgacinch I haven't had any trouble with it since. It sits right on the inside of the water jacket, exposed to all the heat and moisture you can imagine, and I know the thread to not be water tight as I've seen steam and water escape it when the previous sealant failed. Gasgacinch solved the problem.
You can get it on amazon
Again, I wouldn't bother with silicone for this application. I also wouldn't bother with any of those mechanic-in-a-can solutions. But hey, that's just me. I'd also probably be driving the car right now (if it wasn't for the aforementioned salt on the roads), dumping more coolant into it every other morning like I did on my car until I fixed all the various problems in my own cooling system and the water level finally tabled off.
. Mine is only 4 years old now but it's showing signs of being over heated and it's 1/4" wall.....but I've had it well over 500 a lot and there's been many times when I got in a hurry just to get it hot to start cooking and buried the gauge...which only slows me down waiting for it to cool down some lol. Had to replace the grate in the firebox already...
