Hey Scotty, I have an 07 Toyota Avalon with the 3.5L 2GR-FE engine, and currently has 217k miles. At around 190k miles I noticed that the coolant was emptying, and noticed that I can see smoke coming out of the exhaust even when it's at operating temperature. I took your advice and put some K-Seal coolant leak fix in it, and got some 30k miles of relatively trouble free driving. I have checked the coolant occasionally since then, and only recently did I notice it really starting to get low again. I can see it burning out of the exhaust and can smell a sweet smell. I don't have any oil dilution or any other sign of a coolant leak that is visible to my naked eye. It doesn't even leak or burn any oil in between oil changes either, and it looks perfectly normal every time I change it. I also can't see anything leaking on the ground where I park my car at home. What risk do I currently have of it diluting my oil and destroying my engine, and is there anything more I can do to extend it's life? Could I try another bottle of K-Seal? Or do you have any other suggestions?
Products like "K-Seal" are snake oil that might provide some temporary relief, might not work at all, and might plug up your heater core and cooling system. There is no reasonable expectation that a "mechanic in a can/bottle" product will effect a permanent repair. If you want an actual and lasting repair you need to replace the blown head gasket.
If there is no visible contamination, such as the oil turning milky, You can send an oil sample out to a lab (Blackstone, etc.) to see if you're getting any antifreeze in the oil and how much. Any such contamination will ultimately destroy engine bearings.
