Radiator Sealent--What makes it tick?

I’ve had a leaky radiator in my Suburban. I’ve added some radiator sealant to the cooling system as a temporary fix. I got to thinking–how does it work? I’ve seen some that seem to be made of copper; others almost look like sawdust mixed with some other mysterious active ingredients. Is it physical? Like a particle fills in the hole? Or is it chemical? Or both?

My understanding is that it depends upon who makes the stuff. Some of them claim to work by physically plugging the hole, while others claim that the heat of the radiator causes them to melt and seal to it. Supposedly you can achieve the same effect with black pepper and raw eggs, but I’ve never tried it.

I would consider the fix to be very temporary. I’ve never had any of the various additives (save fuel system cleaner) work for more than just a few days at best, if at all. Many of the radiator additives have the annoying habit of clogging up the internal passages of your radiator, which is bad if you want to keep your car running. If you can see the holes in the radiator, and they’re not too hard to reach, JB Coldweld is an excellent (and inexpensive) way to patch those holes.

I’ve heard that radiator sealant can be a bad thing to use. Not only does it clog up the leaks it is supposed to fix, but it also clogs up working lines through the radiator, and worse, the cooling paths through the engine block.

I’m not a mechanic, and I don’t know how true this is, just passing it on.

I used it 3x.

The 1st time it stopped the leak and no adverse side effects happened, till I changed the antifreeze then the leak came back.

The 2nd time I tried it again, and again it stopped the leak again w/o any problems, till car was retired.

The 3rd time I tryed it in a different car which antifreeze was disappearing from w/o any hint as to where it was (I assumed it was into the engine). It didn’t stop the leak but stop heat from comming out of the vents. Car was also retired.

I only used the silver sawdust type, mainly because it worked the 1st time.

My mechanic calls it a can of “Last Rites.”