We get questions all the time about leaks and drips. You know the kind—they taunt your vast knowledge of engines, dropping puddles on the tarmac, and leave you and your family members stranded and embarrassed by the side of the road. The granddaddy of them all is the blown head gasket, which, if we’re being honest, can be any number of things besides an actual blown head gasket. It hardly matters, though, where the leak in a closed coolant system is—the result is the same if enough coolant escapes.
Related Story: John Gilbert’s Take on Stop Leak Products for Classics
The product category of head-gasket pour-in fixes is a big one, with most auto stores and big-box retailers stocking several to choose from on any given Saturday. As the gearhead in your family, it will fall on your shoulders to either make a recommendation or do a quick fix. Pick the wrong product, and you could well find yourself at the dealership writing a check for repairs, or even a new car.
Is It Really Your Head Gasket?
Before we dive into our test of K&W’s FiberLock stop-leak product, it’s important to note that many things can cause the same symptoms here. And while a blown head gasket can certainly cause overheating and a low coolant level that constantly demands refilling, there are other things to look for, such as whether the crankcase oil has signs of coolant in it (a foamy, frothy “milkshake” texture is a sure sign), and if the heater core is blowing steam from the A/C vents and windshield defogger.
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If you’re experiencing the former, there’s a good chance it’s the head gasket; if it’s the latter, you likely have a heater core leak. Notwithstanding, having to constantly fill your radiator with coolant can be caused by several other maladies, including a bad coolant hose, diverter valve, a hole in your radiator, or a crack in the block or cylinder head. One big tip: If you smell antifreeze inside the car (it’s a very similar odor to butterscotch if you’re advising a family member), it’s typically a sign your heater core has corroded and is getting ready to split.
Leaks from Old Age Are Normal
Rapid coolant consumption, the smell of antifreeze, flashing idiot lights, and overheating are all signs of coolant escaping from the closed-loop cooling system, and it will come as no surprise that these ailments are common signs of age. With that in mind, any sort of pour-in stop-leak product is a temporary measure, but our story has a bright spot: We performed our pour-in of K&B FiberLock five months ago, and it’s still holding up. We would’ve waited longer, but we have to report our story at some point, right?
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Our story starts with two late-model Hemi cars: a 2011 Dodge Challenger R/T with a 5.7L Hemi, and a 2005 Chrysler 300C, also with a 5.7L Hemi. Both had similar problems of coolant loss and overheating. The Dodge has over 200,000 miles on the clock and a long history of engine, electrical, and HVAC problems, both under warranty and out. The Chrysler, though much older, has only half the mileage and the additional distinction of blowing thick clouds of acrid antifreeze into the cockpit—a sure sign of a failing heater core. Neither had the telltale oil/water mix in the crankcase, but since most head gaskets fixable with a stop-leak are on the slow-leak side (versus a cracked radiator, for instance), the use of a head gasket pour-in for this test would be valid.
Why We Couldn’t Test K-Seal
We wanted to treat the Dodge with a product called K-Seal, and the Chrysler with a product called FiberLock, and see how they both fared. Unfortunately, we didn’t have to wait long to discover that the Dodge had a split radiator in addition to a bad O2 sensor (likely due to coolant contamination), a leaking heater core, and at least two failed HVAC mix actuators. The bad O2 sensor may also indicate a small head gasket leak on top of the other problems. We had to call the K-Seal test off early, because asking that to fix all those issues was like putting a bandage on a severed carotid artery. With the Dodge DOA, we soldiered on with the Chrysler, which received a half bottle (as per the manufacturer’s directions) of the K&B FiberLock.
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With both vehicles, we used the same technique to apply the product. While the manufacturers say it’s OK to pour these into the coolant reservoir, we felt the efficacy of both products would be improved if they were poured directly into the radiator. Most vintage cars have radiator caps on top of the radiator, but with late-model machinery, it can take quite a while for the thermostat to open and the product to circulate out of the reservoir, through the block, into the cylinder heads, and into the HVAC system. To accelerate the product circulation, we opted to pour the FiberLock and the K-Seal into the upper radiator hose and into the radiator directly while the engine was cold and on level ground. (Hemi cars don’t have a cap on the actual radiator.) This would give the product the best chance of working instead of sitting in the bottom of the overflow reservoir, which lets it stratify out of its mixed state.
K&W FiberLock Delivers Results
In the following weeks, it became obvious that the Dodge Challenger with the K-Seal was not taking it well, with the author’s wife refusing to drive that Hemi car to work. We can’t say whether the K-Seal would’ve worked on a simple head-gasket-only failure, but we have to give it a pass because of the damage we later found to the radiator, which had deteriorated, eventually springing a geyser. Perhaps we’ll try K-Seal again in a few years on the Hellcat if it, too, springs a leak somewhere.
We crossed our fingers with the Chrysler and pressed on with the K&W FiberLock treatment through February, March, April, May, and well into June. Eventually, we had to file this story and report our results, and the Chrysler’s heater core continues to survive without a wisp of steam on the windshield, puffs from the A/C vents, or even the faint odor of antifreeze. The coolant level has stabilized and has only needed a modest topping-off once. (It’s a 100,000-mile car, so we consider that normal.) Moreover, the cooling system is operating fine, well within its factory-engineered operating range.
When weighed against the cost of replacing a heater core—or even worse, a head gasket—we have to say the extra time provided by the temporary FiberLock fix (about $35 for the 32-ounce bottle from your local auto parts store) is worth the price and effort. In these hard times, it makes sense to defer a repair that can run anywhere from $300 (for a heater core) to $1,000 (for a head gasket). We got five months out of it, which, even if it gave up the ghost today, would’ve allowed us sufficient time to beg, borrow, or steal enough money for a permanent fix. Who knows, we may even forget that the FiberLock was a temporary fix!
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