Fixing Head Gasket Leaks and Small Cracks
There are several block sealer products out with sodium silicate in them, the most popular being the K&W brand. The alchemists called sodium silicate "water glass" since it turns to glass when dried. When added to coolant, first it is sucked into a crack by the intake suction, then the exhaust blast dries some of it out and turns it to glass, making the leak smaller. This continues with each stroke, the leak getting smaller and smaller as concentric layers of glass are laid down, until the leak stops leaking. Genuine MOPAR antifreeze, recommended in Chrysler owners manuals, contain a small amount of sodium silicate to stop internal leaks as they develop. Hence, leaking head gaskets and cracked heads are usually only a problem if you haven't been using genuine MOPAR antifreeze as Chrysler recommends.
Here are the major complications:
1. Most products add metal to the mixture to strengthen the glass, so that it is more durable. Products without metal produce a "town car" result, where the fix may only last a year or so, provided that you don't take it on the highway and heat it up.
2. They often clog up the heater cores, so it is best to disconnect the heater when treating the car, and for a period following treatment.
3. As indicated on the label, it is very important to flush all of the antifreeze out before treating, and flush all of the block sealer out before replacing the antifreeze. I reuse the old antifreeze for a few hundred miles, then flush and replace it and reconnect the heater.
4. I believe that you should drive the car hard during treatment, to get the the crack to shift in any way it can to fully fill it in. However, I first drive gently to mostly seal the crack, then vent any gas in the head, then put the pedal to the metal to finish the job. I suspect that the Higway Patrol wouldn't let them put this on the can.