Review on Genuine GM (12378255) Fluid 3634621 Cooling System Seal Tablet - Pack of 5: Effectively Stops Leaks, 4 Grams per Tablet by David Hashman

I work on Pontiac Buick GMC and Saturn in the 90's and 2000's. I know these pills. Historically they were used to seal porous heads. Since then I've driven over a million miles to work in several Chevy vans and in all of those miles I've found multiple leaks in the cooling system. Some of these are catastrophic. This is exactly the case with my current 2006 with 380,000 miles. I love this man and recently replaced a flex plate because it cracked. If you're unfamiliar with this, it sounds like the pistons are flying out of the engine and it's just a cracked flexible plate. However, when I returned to the coolant leak after replacing the flex plate, I noticed a small coolant leak coming from the back of the block. To my dismay, I found that the outer cylinder head bolt number was leaking out of the bolt head rather than through the gasket. I also had a very small side reservoir leak on the radiator that I was aware of but didn't fix immediately. With those two leaks, I was regularly using about a liter every 500 miles. I was also concerned that the leak would only get worse and possibly even enter the cylinder. So before I disassembled the van or put a motor in it, which were my only two options, I remembered these pills and decided to use them. And just as I remember, they are a business! They just work. They covered about 6000 km. Coolant leaks through the radiator reservoir and cylinder head bolt have stopped. I've heard people say they need to be smashed and put in, it really isn't necessary. They have been designed to fall as full granules. You just have to make sure the engine is cold and throw them in the radiator or expansion tank. Then take it on a nice, long, easy city and highway ride for a solid 15-20 miles. Bring to operating temperature. Then park and let cool overnight. They work. However, remember that in the event of a catastrophic failure of more than one cylinder head bolt thread or a small side leak from the radiator, nothing is likely to last for too long. but if it's minor league even in a box with a 46 cylinder head, I highly recommend trying them out before you give up!