K-Seal ST5516 Heavy-Duty Multi-Purpose One Step Permanent Coolant Leak Repair, 16 oz, Pour and Go, Mixes with All Antifreeze, No Flushing Required

The stuff really works. My F350 powerstroke had a leaking water pump after 266000 miles. It was leaking like a sieve. Poured the K-Seal in, leak slowed up within a minute, totally stopped after 5. I totally impressed with this product. I never write reviews, only if the product works better than expected or if the product is junk. 5 stars for K-Seal.

Had a decent radiator drip on my RV. It is a huge radiator, 4 feet wide. I was going to get the radiator removed and fixed at a radiator repair place but it was so large I couldn't get it out of the bottom of the RV without jacking it up 2 feet.I was skeptical to try this K-Seal but the advertising said it could handle the heavy duty capacity of my 15 liter Cummins ISX diesel size, so I tried it.Within 25 minutes the leak was gone, pretty amazing. I let it run for an hour just to be sure. I will be driving it to a race soon and make sure it stays fixed.Happy that I didn't have to remove radiator, saved myself 10 hours of labor and hundreds of dollars to repair.

Works as advertised, fantastic product. Succeeded where Bar’s Leaks failed. 1990 F250 w/460 and constant coolant leak front of head below thermostat. Stopped leak within 5 minutes of adding product to radiator. Would definitely purchase again

I saw coolant leaking out the exhaust ,could not find (any or) two adjoining cylinders with problems on a compression test. Changed head gaskets anyway, a head bolt came up with odd rusty pitting on its starting thread- showing the possibility of a bad spot in the block.Needed to use the vehicle and could not guarantee that it needed a full motor rebuild over this. Went on with the gasket change(no obvious problems on the old stock gaskets),the heads were decked,installed,everything went good,and now the leak was milder but still there. Compression test results still looked the same,so I tried K seal. I had tried the copper fleck stuff before on other vehicles not much luck. K seal did the job and no more leak out the exhaust.

I bought this larger size because I wanted to use it in two different vehicles. I put the majority of it in a vehicle that I needed to add antifreeze every couple days and was blowing white smoke out the exhaust. I no longer need to add antifreeze and there’s no white smoke. The other vehicle I needed to add antifreeze maybe once a week. I added the lesser portion to this vehicle and it is not used any antifreeze since.

Within one week of using, this stopped up my Infiniti FX45 radiator such that it now has to be replaced.

i used this stuff for the first time 8mo ago after reading the great reviews. i was blown away as it quickly sealed up an old waterpump on my 22yr old chevy. that it lasted 8mo.s was impressive, but the other night the water pump again began leaking. i immediately ordered this on amazon and a day later put half the 16oz bottle in, and it immediately sealed up the same waterpump. given this waterpump is super old, i don't know how long it will hold this time, but i'm already impressed by this stuff. and i still have 8oz of it left. NOTE!!!...be warned that you need to really shake this stuff up per the directions, prior to using.

Flush cycle and then back in with this product and water and then dump that water out to be able to put coolant back in it to be able to put it back in the service and a you know winter time scenario or summer to Winter scenario this stuff you just poured in and let it do its job and you're done you don't have to drain the coolant out you don't have to go through a big process of it throw it in there let her idle for a while they're back in service and go to work make some money and stuff keeps equipment and stuff operating when you don't have a chance to take it down or take it out of the field for a while and it'll get you by or it'll work as a permanent fix I wish I could get buy stocking in this stuff