This product did not fix the small head gasket leak on my 2005 Civic. The fine print on the guarantee requires a shop to diagnose and replace the head gasket in order to make a claim. Me personally seeing the bubbles go away in my radiator, after head gasket replacement isn't enough. It did plug up my heater core and overflow tube and caused me more work in the end.
As a former engine machinist and current mechanical engineer, I highly recommend you don't put this in your cooling system.

Had a pesky head gasket leak into cylinder #2 in yet another late 90's, 4.6_liter Vortex V-8. My engine symptoms were within the stated guarantee guidelines, so I purchased this latest Bar's Leak HG-1 HEAD SEAL product from Amazon AND followed the directions to a 'T'. Well...This 'Miracle-In-A-Can' almost immediately eliminated my head gasket issue! No more coolant odor, no more water vapor from the exhaust pipe AND Increased/Restored Compression! Absolutely amazing!!! Further, since introducing this product into my cooling system back in mid September of 2017, my engine remains restored to a leak free condition. AAA+++THANK YOU!

Omg ! My head gasket went out in my truck .. I was very skeptical and broke so I purchase on a Hail Mary .. to this day my truck is still running strong (knock on wood ) 2,600 hundred miles give or take

One day all-of-a-sudden our 3.8L engine of this 1994 Mercury Sable began to overheat whenever the car was driven for about 25 minutes especially up any long steep grade or in stop-and-go traffic on a humid rainy day. My mechanic who is shop owner and quite competent kept our vehicle for 6 weeks and reluctantly gave up after replacing the thermostat (twice) plus the water pump plus the radiator's electric fan plus the radiator, and after running very many tests. He had other mechanics also trying to solve what he said was only the 2nd mystery in his 20 years of business that he could not solve. Their final diagnosis (including a cooling system expert) was that even though this car passed 3 different head gasket tests, they believed this car had a very rare type of head gasket failure, one which if you were to go to the expense of inspecting the head gasket you would not see any problem visually, but that under certain conditions air compression would leak into the cooling system and create a temporary air pocket which defeated the cooling circulation.

Since this car has only 55,000 original miles on the engine and still looks good, we looked for an 'alternate therapy'. So I tried this HG-1 Bar's Leak Head Seal, following the instructions exactly, being careful to do this on a completely cold engine in the morning. Believing that after adding the product there is a necessary 'healing period', I have perhaps been overly cautious and have driven the car normally but gently for the next several weeks, and never for more than 1 hour at a time. My wife and I are holding our breath as we are amazed that the analog temperature gauge which had been going over halfway up the scale in 15 minutes now stays almost on the bottom of the scale even after 45 minutes. This engine has never ran so cool. Bar's Leak claims that with the liquid ceramic plus carbon fiber it is a permanent fix. Time will tell. But so far, we are pleasantly surprised, if not amazed.

Used it on a 2004 Chevy Impala with a leaky head gasket. The car would use up coolant and overheat after about 20 - 30 miles of driving before needing to have more coolant added. I was skeptical, but the cost to replace the head gasket was way more than the car was worth. So, I had nothing to lose except the cost of purchasing this product. After following the instructions, it appears to have solved the problem - for now. I've driven the car about 500 miles since treatment and it hasn't overheated yet. As far as I can tell, the coolant level in the reservoir hasn't gone down at all either. For my situation, it was worth a try and it seems to have paid off.