So I’ve decided to roll the dice and try one of the several head gasket sealer additives available at your local autoparts store. After a fair amount of online research, I went with one of the cheapest options: K&W Block Seal and followed the method described by Austin of TrustMyMechanic: . Austin says his garage has used this product on hundreds of vehicles over several decades with an 80% success rate doing his special procedure (instead of following the directions on the can).
First I drained and flushed the old coolant. K&W isn’t compatible with antifreeze so you have to remove as much coolant as possible. After the fourth flush using tap water with the heater controls turned to full HOT, the coolant coming out the radiator was totally clear (although it still reeked of exhaust). So I flushed a fifth time just to be sure.
I mixed the can of K&W into 3/4 gallon of hot distilled water which I’d heated up on the stove burner. Our volvos don’t have radiator caps so I removed the top coolant hose from the radiator and poured the mixture directly into the radiator. The radiator slightly overfilled before using all the mix; I probably have about 12 oz. left over. I then reattached the top coolant hose and filled the overflow tank to the MAX mark with distilled water.
I started the car with the reservoir cap off and let the car idle for about 15-20 minutes. I was able to add maybe a cup of distilled water as the level in the reservoir dropped. Per Austin’s instructions I took the car for an easy 15 minute drive. The next morning the coolant level was at the MIN mark so I topped it up with distilled water. When I started the car, it fired up with no misfires.
Austin recommends you drive the car for 500 miles with the K&W mixture before draining, flushing and replacing with regular coolant. I drove about 100 miles yesterday with no misfires. Also the backfire I was starting to get every time I took my foot off the gas seems to have mostly disappeared. After four good starts with no misfire, the CEL has turned off and the car is now running as well as it ever has.
The preliminary results would indicate the repair is working, at least for now. No CEL means the car stands a good chance of passing inspection although it still needs exhaust work. I’m driving around with the heater controls set on full COLD hoping to minimize the K&W mix’s flow through the heater core. My concern, of course, is that the sealer could end up plugging the radiator/heater core. Austin recommends not removing the thermostat and states he’s not had an issue with K&W fouling up the cooling system.
So now I just need to drive another 400 miles, watch the coolant level, be careful not to overheat the engine (since the radiator only has water in it), and hope the CEL doesn’t come back on. If the engine continues to run great, maybe I’ll flush out the K&W after 250-300 miles instead of doing the full 500 miles. We’ll see…