After battling mysterious coolant loss for months now, I added a $45 bottle of Bar's Head Seal, their top end HG-1 product. So far, confidence is high. For some quick history, I had already replaced the plastic thermostat housing with the metal upgrade, new thermostat, new top & bottom radiator hoses, new expansion tank and new cap. Replaced all screw type hose clamps with FI type band clamps. Pressure tested and would hold 15lbs forever. However, the sumbitch still wouldn't go 20 miles without the 'Low Coolant' light coming on and need of topping off. Recently I pulled the right front inner fender cover to inspect the recovery bottle and found I was blowing bubbles when hot at idle. CRAP! NOT a good sign!

Typically, this is 'just' a bad head gasket but the '99 4.0L V-8 is also well known to have issues with bad cylinder liners. Either way, bad news and basically a 'kiss of death' for my $5,000 car I just bought in April. Again, at the end of my rope and out of money, the Bar's Head Seal was my Hail Mary pass. So far, I'm happy to report so far so good. Added to the coolant expansion tank, ran for 15 min as directed. Completely cooled, topped up a bit and then ran for another 15 minutes at 1,200rpm per the instructions. Cooled and level checked fine. Huh! Have since run two more complete heat cycles to be sure and am happy to report NO coolant loss and NO bubbles in the recovery tank either. I will do a 40 mile road test this afternoon. If successful, that will be a new record!

Now I have no real idea what this stuff is or exactly how it works... and am not sure I really want to know! Sure, the 'real mechanics' on here will scoff at stuff like this but if this stuff works like its looking, I don't care!

 

If it works and doesn't block the heater core, it's a success. But your comment about the cylinder liners is misplaced. The problem with nikasil was erosion due to high sulfur levels in the fuel, and that's ancient history. Those liners will out last steel.

 

The way I understood all of these kind of stop leak products to work is actually rather brilliant and simple. They contain tiny fibers (in this case perhaps carbon fiber), that get caught and pile up as they migrate through the leak. If you've ever had to auger a wad of hair out of a shower drain, its the same concept. Be advised that these products have been known to cause cooling system issues if too much product is used, or if a subsequent owner adds more, unaware that a previous owner, mechanic or in some cases, yes, even the factory OEM had already added a stop-leak product to the system. Now that you've done it once, if the leak ever does come back or a new one appears, don't add any more.