While we here at EngineLabs try to deter our readership from cutting corners, there is no denying the fact that “stop leak” additives are here to stay. From the U.S. military’s widespread usage of Marvel Mystery Oil during World War II to the advent of the undeniably ubiquitous line of products claiming to be a “repair in a bottle” line the shelves everywhere you look.
However, being that most drivers are entirely too busy (or flat-out “mechanically challenged”), conducting an engine teardown just to replace a gasket or a few leaky O-ring seals is completely out of the question for them. Being that gasket, seal, and O-ring replacements also require a significant amount of financial investment, the appeal of an inexpensive quick fix remains quite alluring to many.
But do these self-proclaimed “stop leak” products actually work? If so, how well? And perhaps more importantly, what happens when they don’t work as advertised? Will they bludgeon our precious seals faster than a boatload of money-hungry Alaskan fur traders in the late 1800s?
I guess we’ll just have to find out…
Putting Stop Leaks to the Test Via Unbiased Gumption
Not too long ago, Todd over at Project Farm LLC released a comparison video, where the unbiased (and outright enthusiastic) YouTube product tester pitted fourteen engine stop leak products against one another. A video that the clever content creator claims were intended purely for “entertainment purposes,” and did not influence the contents being placed in shopping carts across America.
But before meeting Todd’s contenders, his methodology for testing these products must first be examined. Which in true Project Farm fashion, are equal parts effective, well-illustrated, and strikingly simple.
The goal of the test was straightforward: Compare a handful of stop leak products and determine their ability to condition/soften hardened rubberized engine components, with brand-new parts like gaskets, O-rings, and seals being the primary focus.
Resistance to evaporation during normal engine operating conditions while providing adequate lubrication and cooling was also taken into consideration, as was viscosity in cold conditions, and wear and tear on metal-to-metal contact points.
Meet Your Quick-Fix Contenders
As with any Project Farm comparison test, a slew of products were selected, with Todd opting to put fourteen additives through the proverbial gauntlet this time around.
While there are a ton of other oil additive options to choose from out there, time constraints kept Todd’s findings focused on some of the more common products you’d find down at the local auto parts store, along with a few online oddballs thrown in for good measure.
Some of these products proclaim that they are intended purely for engine oil enhancement and seal repair purposes. Whereas others boast that they have the power to fix leaks and lubrication issues within differentials, transmissions, power steering systems, hydraulic units, and more.
In the case of this particular Project Farm test, Todd’s contenders included:
- ATP AT-205 “Re-Seal”
- Bardahl “NoSmoke +Stop-Leak”
- Liqui Moly “Pro-Line Oil Loss Stop”
- Lucas “Engine Oil Stop Leak”
- Bar’s Leaks “Engine Oil Stop Leak Concentrate”
- Lubegard “Seal Fixx”
- Hapco “Pro-Seal”
- Blue Devil “Oil Stop Leak”
- XADO “Engine Oil Stop Leak Concentrate”
- Seal Lube “Seal Expander”
- Promeko Inc. “Snake Oil”
- CD-2 “Heavy Duty Sealer”
- Justice Brothers “Engine Stop-Leak”
- Wynn’s “Engine Oil Stop Leak”
Todd’s Testing Procedures Explained
According to his introduction within the video, Todd’s key focuses remained zeroed-in on the following considerations:
- Oil viscosity
- O-ring “rehabilitation”
- Impact on new O-ring resilience
- New engine component safety
And like any mad scientist worth his salt, Todd began his testing with a control. In this case, this meant using a 40ml dose of full synthetic Pennzoil 5W-30.
For the metal-to-metal comparison test, a simple belt-driven lathe and grooved wheel making contact with a steel pin was the tool of implementation. After measuring the diameter of the groove and the energy exerted via the use of an energy usage meter, each oil additive was put to work.
During testing, a 50/50 blend of stop-leak and the aforementioned motor oil was implemented in 30-second testing increments to prevent excessive damage from poorly performing products.
Each test was then followed by an inspection with a microscope and a set of calipers to confirm the effectiveness of the product in regard to reducing (or increasing) wear-and-tear on the metal pin contact point. Furthermore, a new mixing straw was used for each brand to eliminate any cross-contamination between products.
In between each round of testing, splashes of brake parts cleaner and a quick resurfacing of the test wheel with sandpaper removed any residue or grooves leftover from the previous round. Thus guaranteeing a fresh surface after each round, regardless as to how much metal was shaved off, steam was emitted, or splashing occurred.
Viscosity Freezer Testing
After conducting the metal wear test, Todd placed each blended test sample into a freezer to see if those claims that “engine viscosity will not be affected” were true or not. Naturally, there were some clear winners and failures, with a 24-hour cooldown period in the freezer resulting in certain products performing better than the straight motor oil, while others merely turned to sludge, or worse yet, became frozen globs.
O-Ring and Heat Testing
While all fourteen blends were chilling in the deep freeze, the O-ring testing portion of the gauntlet was taking place. Naturally, brand new gaskets were utilized, all of which were first measured and then dropped into 100-percent straight stop-leak test cups for 48 hours at room temp. Todd explains that he did not blend the additives with the motor oil for this stage due to the separation that was observed with certain products.
As the O-rings soaked, a standard strip of gasket material and a bunch of brand-new O-rings were dropped into a beaker (a.k.a. coffee pot) of motor oil that had been heated to 350°F for 2 hours.
A quick durometer test showed a much harder O-ring, with a material circumference that was about 6-percent thinner than prior to the heat treatment that had just been implemented. After throwing the heated O-ring seals back into a blend of each product with the motor oil, everything was weighed once again and reheated for two hours to see if any of the rings could recover.
After weighing, results showed that the straight synthetic motor oil only lost 0.02 grams during the entire 2-hour heat cycle. Now as for the additives and how they faired, this side of the examination was pretty polarizing. Heavily evaporated products provided respectable O-ring protection, while heat-resistant samples didn’t do much if anything for the rubberized rings.
As the final results chart above clearly illustrates, unheated O-ring soak times were also intriguing, as many products didn’t make a bit of difference in the durability or size of the new ring in question, while others did help the rubber to slightly soften and expand.
Being that gaskets are just as important and widely utilized as O-rings within a combustion engine, this form of material too had to be put through its paces. While we are not entirely sure as to what type or thickness of gasket was used, Todd explains that it was an unused item that had merely been cut into strips for usage.
While the whole O-ring boil side of the experiment was taking place, those strips of boiled gasket returned their own round of results. A quick poke with a pick and a press resulted in the scales showing a few products out in front in the gasket puncture test, with others performing miserably.
Torture testing complete, and findings all tallied up, the top performing stop leak additives included SealLube (which coincidentally was also the priciest product tested) and ATP’s AT-205.
Whereas the SealLube didn’t do well when it came to reducing wear, it practically dominated in almost every other category, including the O-ring comparison test, heat comparison showdown, and viscosity rankings.
The only other product that was able to best SealLube was the AT-205, which came out on top thanks to its superior wear resistance and O-ring rejuvenation capabilities.
Now as for the rest of the pack… let’s just say that they either did an alright job, or flat-out failed to deliver when it came to lubing up those dark black donuts or reducing heat-related wear and tear.
If you want to see all of the raw data, make sure to watch the video. We’ll post up our takeaways from each of the fourteen findings below and let you mull over what was discovered. Either way, we tend to steer clear of stop-leak type products in general, instead opting to fix things the proper way, and therefore view these types of tests for what they are intended to provide: Pure entertainment.
- ATP AT-205 “Re-Seal”: Settled at the bottom of the container and needed remixing prior to testing, and was literally steaming hot after the metal wear testing stage was complete. However, it managed to redeem itself by returning the O-ring almost to its original size and making it even softer than new. It also scored very well in the freezer viscosity test, earning it the top spot as the overall best-performing product.
- Bardahl “NoSmoke +Stop-Leak”: Very thick and therefore performed extremely well in metal testing and did not evaporate under heat, but didn’t do diddly-squat for O-ring repairs.
- Liqui Moly “Pro-Line Oil Loss Stop”: Provided less wear on the wheel and lowered friction, but evaporated a lot during heat testing. And while it did soften the O-ring slightly it did not restore its circumference, and almost froze solid during viscosity testing.
- Lucas “Engine Oil Stop Leak”: Requires a 1:4 blend ratio with motor oil and did alright, with O-ring testing being very close to that of the Bardahl stop-leak. Viscosity testing and heat treatment were just alright, as were gasket puncture test results.
- Bar’s Leaks “Engine Oil Stop Leak Concentrate”: Created more friction and wear and zero change to O-rings after heat testing. A middle of the road contender that did more harm than good overall.
- Lubegard “Seal Fixx”: Kept separating from the motor oil and caused loads of damage and evaporation, but did help restore some O-ring circumference and returned the ring to its original hardness level.
- Hapco “Pro-Seal”: Medium amounts of damage despite blending well with the oil, and served as a decent O-ring restorer.
- Blue Devil “Oil Stop Leak”: Separated almost immediately and created a reasonable amount of friction, it also boiled off a lot during heating, but helped some during O-ring testing. Another product that seemed to provide more risk than reward.
- XADO “Engine Oil Stop Leak Concentrate”: Only product on the roster that was made in Ukraine, which performed poorly in the metal friction stage, with mediocre evaporation and O-ring results.
- SealLube “Seal Expander”: Most expensive product tested ($35), and didn’t do well at all in regard to wear, but dominated in almost every other category, including the O-ring comparison test, heat comparison test, and viscosity ranking.
- Promeko Inc. “Snake Oil”: Pretty significant wear damage, but surprisingly, not the worst either, even though it didn’t help O-rings at all after not boiling off one bit.
- CD-2 “Heavy Duty Sealer”: Lots of damage to the metal pin, but little evaporation and slightly softened O-ring results, even though it couldn’t help the seal expand much in size.
- Justice Brothers “Engine Stop-Leak”: Became very hot and vaporized into steam, with the same metal pin damage ratio as the CD-2 product. It also boiled off the most during O-ring testing, yet somehow restored the O-ring’s size and softness to near original specs.
- Wynn’s “Engine Oil Stop Leak”: Made in Belgium, and blends well with motor oil, but it created the largest wear scar at 9.35mm during metal testing. However, it did fairly well during O-ring heat testing, and was dead center in the gasket puncturing challenge.