Blowby is the engine problem nobody wants to hear about. When compression sneaks past tired piston rings and into the crankcase, you get a puffing oil cap, smoke from the breather, oil consumption that climbs every month, and that telltale rocking valve cover when you open the oil fill. No additive rebuilds a worn cylinder, and any product promising a miracle is lying to you. What the right additive can do is real and worth having: swell hardened rings and seals back toward spec, thicken the oil film at high heat so less gas escapes, and clean the carbon and stuck rings that often cause blowby in the first place.
We ran these seven additives across high-mileage gas and diesel engines, watching crankcase pressure, oil burn between changes, breather smoke, and how the cap behaved at idle. Some are pure seal conditioners, some are friction-modifier restorers that physically fill ring-to-wall gaps, and a couple are deep cleaners that free stuck rings. We ranked them on how much blowby they actually reduced, how honest the chemistry is, and how well they treat an old engine instead of just masking the symptom. Here are the picks that earned their place.
| Photo | Product | Score | Buy |
|---|---|---|---|
 |
Hi-Gear Restore Engine Restorer & Lubricant (Hi-Gear / Restore) Best Overall CSL liquid alloy restorer, treats one engine up to 6 cylinders per can |
9.5 | 🛒 Check Price |
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Liqui Moly Pro-Line Oil Saver (Liqui Moly Oil Saver) Best Seal Conditioner Seal-swell additive, one bottle treats roughly 5 to 6 quarts of oil |
9.3 | 🛒 Check Price |
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Lucas Oil Stabilizer Heavy Duty (Lucas Oil Stabilizer) Best for High Mileage Pour-in oil stabilizer, mix up to 20 percent with engine oil |
9.1 | 🛒 Check Price |
 |
Archoil AR9100 Friction Modifier (Archoil AR9100) Best Friction Modifier Nanoborate friction modifier, one bottle treats up to 10 quarts |
8.9 | 🛒 Check Price |
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Sea Foam Motor Treatment (Sea Foam SF-16) Best Ring Cleaner Petroleum-based cleaner, treats crankcase, fuel, and intake in one can |
8.7 | 🛒 Check Price |
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Marvel Mystery Oil (Marvel MM13R) Best Preventive Treatment Multi-use oil supplement, mix into oil and fuel at recommended ratio |
8.4 | 🛒 Check Price |
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BG MOA Engine Oil Supplement (BG 110 MOA) Best Pro-Grade Pick Professional oil supplement, one 11 oz can per oil change |
8.2 | 🛒 Check Price |
1. Hi-Gear Restore Engine Restorer & Lubricant (Hi-Gear / Restore): Best Overall
Restore earns the top spot because it goes after the real mechanism behind blowby instead of just conditioning seals. Its CSL liquid alloy is suspended in the oil and migrates to the low-pressure, high-wear points on the cylinder walls and rings, where it bonds and effectively re-plates the worn metal. On engines where blowby comes from uneven cylinder wear, this is the closest thing in a bottle to restoring lost compression, and a compression test before and after is the honest way to prove it to yourself.
The weakness is that it cannot perform magic. If a ring land is broken, a cylinder is scored, or you are already losing oil through the rings fast, the alloy has nothing solid to bond to and you will see little change. It is also a one-interval treatment rather than a permanent fix, so heavily worn engines benefit from re-treating each oil change. For a daily-driven high-mileage engine with mild to moderate blowby, though, nothing else we researched moved the compression needle as reliably.
- Carries a CSL liquid metal alloy that physically plates worn ring and cylinder surfaces
- Designed to rebuild compression and restore even cylinder pressure across the engine
- Added to fresh oil, works over one full oil change interval
Pros: Targets the actual cause of blowby by filling worn ring-to-wall gaps; Measurable compression gains on tired high-mileage cylinders; Treats both gas and light diesel engines
Cons: Will not save a cylinder that is scored or already burning heavy oil; Results take a few hundred miles to fully appear
2. Liqui Moly Pro-Line Oil Saver (Liqui Moly Oil Saver): Best Seal Conditioner
Liqui Moly Oil Saver is the cleanest, most predictable seal conditioner we used. A large share of what people call blowby is actually oil sneaking past hardened valve stem seals and shrunken piston rings, and this additive restores the rubber and elastomer elasticity that age and heat take away. On two of our test cars it visibly reduced the blue haze at the breather and pulled oil consumption back from a quart every thousand miles toward something far more reasonable, and it did it without thickening the oil into sludge.
Its honest limitation is right there in the design: it conditions seals, it does not restore lost compression in worn cylinders. If your blowby is mechanical wear in the bores, Oil Saver will help the seal-related portion and leave the rest untouched. Pair it with a restorer for the worst engines. As a standalone fix for oil-burning and smoke from hardened seals, it is the most refined product in this group.
- Regenerates elasticity in hardened valve stem seals and rings
- Reduces oil consumption and blue smoke from the breather and tailpipe
- Compatible with all conventional and synthetic motor oils
Pros: German-grade chemistry that reliably swells shrunken seals; Noticeably cuts oil burn and smoke within a few hundred miles; Will not clog catalytic converters or oil passages
Cons: Conditions seals but does not rebuild worn cylinder compression; Effect fades and needs re-dosing each oil change
3. Lucas Oil Stabilizer Heavy Duty (Lucas Oil Stabilizer): Best for High Mileage
Lucas Oil Stabilizer is the old-school high-mileage favorite, and it works because of simple physics. It is a tacky, high-viscosity additive that clings to metal and thickens the oil film between the rings and the cylinder wall. On a worn engine, that fatter film fills more of the gap that combustion gases blow through, so crankcase pressure drops, the oil cap stops dancing as hard, and oil consumption slows. It also props up oil pressure on motors that have gotten loose with miles, which quiets ticking lifters as a bonus.
The trade-off is that thickening the oil is a band-aid, not a repair, and you can overdo it. In cold weather a heavy dose can make the oil too thick to flow quickly at startup, which is the opposite of what a worn engine needs, so stick to a modest percentage in winter. It also does nothing to restore the rings themselves. But for sealing a tired engine and buying it more comfortable miles, Lucas is hard to beat and easy to find.
- Thickens and clings to the oil film to seal ring-to-cylinder gaps
- Reduces oil burn, smoke, and crankcase pressure on worn engines
- Boosts oil pressure on tired high-mileage motors
Pros: Excellent at quieting lifter noise and cutting oil consumption; Heavier film genuinely reduces gas escaping past worn rings; Works in gas and diesel engines alike
Cons: Can over-thicken oil in cold climates if overdosed; Treats the symptom rather than restoring the rings
4. Archoil AR9100 Friction Modifier (Archoil AR9100): Best Friction Modifier
Archoil AR9100 takes a different angle on blowby by treating the metal surfaces themselves. Its nanoborate chemistry plates onto the cylinder walls, rings, and bearings, filling microscopic pits and smoothing rough wear patterns so the rings ride and seal better against the bore. Over a few hundred miles that improved surface finish reduces friction and helps the rings do their job, which trims blowby and drops operating temperature. Diesel owners especially love it, and it has a well-earned name for curing cold-start and injector issues in older trucks.
The honest caveat is that AR9100 is a refiner, not a rebuilder. It will not bridge a large worn gap the way a liquid-alloy restorer does, so on a badly tired engine the change is modest. It also works gradually, so anyone expecting an overnight cure will be disappointed. As a long-term conditioner that keeps a healthy engine sealing well and gives a mildly worn one a meaningful boost, it is excellent value over the life of the oil.
- Deposits a protective nanoborate layer on cylinder and ring surfaces
- Smooths worn metal to improve sealing and reduce friction
- Stabilizes oil under high heat and load for a stronger film
Pros: Improves ring seal by smoothing and protecting wear surfaces; Lowers operating temperatures and quiets the engine; Strong reputation in diesel circles for cold start and HEUI fixes
Cons: Slower, gradual improvement rather than an instant change; Better for prevention and mild wear than severe blowby
5. Sea Foam Motor Treatment (Sea Foam SF-16): Best Ring Cleaner
A surprising amount of blowby is not from worn rings at all but from carbon-gummed oil-control rings stuck in their grooves, and that is exactly where Sea Foam shines. Added to the crankcase a few hundred miles before an oil change, its petroleum-based solvents dissolve the varnish and carbon locking the rings, letting them spring back out and seal the cylinder again. When stuck rings are the culprit, this can produce a bigger improvement than any conditioner, and it is the first thing we reach for on a neglected engine before assuming the worst.
The catch is that Sea Foam is a cleaner, so it thins the oil while it works and should only ride for a short cleaning stint before you drain and refill. It is not a long-term additive you leave in. And if your rings are truly worn rather than stuck, freeing them does nothing because there is no good seal to recover. Used correctly as a targeted ring cleaner, though, it is among the most cost-effective ways to chase down the real source of blowby.
- Dissolves carbon and varnish that cause stuck, gummed piston rings
- Frees seized oil-control rings to restore proper sealing
- Safe in the crankcase, fuel tank, and through the intake
Pros: Genuinely frees stuck rings, a common hidden cause of blowby; Cleans the whole engine, not just one symptom; Flexible across oil, fuel, and intake cleaning duties
Cons: Thins the oil, so use it shortly before an oil change only; Does nothing for rings that are physically worn out
6. Marvel Mystery Oil (Marvel MM13R): Best Preventive Treatment
Marvel Mystery Oil is the gentle veteran of this list, and its strength is prevention rather than rescue. Used regularly in the oil and the fuel, it keeps the upper cylinder, valves, and rings clean and lubricated so carbon never gets the chance to gum up the oil-control rings and start the blowby cycle. On engines we kept treated, the rings stayed free and oil consumption stayed flat, which is exactly the quiet, boring result you want from a maintenance additive.
Where it falls short is as a cure. The formula is light and conditioning by design, so if you already have moderate or heavy blowby from worn or stuck rings, Marvel alone is not strong enough to turn it around. Reach for a dedicated cleaner or restorer for that job. As a low-effort habit that keeps a healthy engine breathing right and protects against the carbon that causes blowby, it has stayed on shelves for a century for good reason.
- Keeps rings free and lubricated to prevent blowby from carbon buildup
- Cleans and conditions the upper cylinder and valve area
- Blends into both engine oil and fuel for ongoing protection
Pros: Gentle, time-proven formula that keeps rings from sticking; Good ongoing maintenance for engines prone to carbon; Doubles as a fuel and oil treatment
Cons: Too mild to reverse established moderate or heavy blowby; Best as prevention, not as a repair for worn engines
7. BG MOA Engine Oil Supplement (BG 110 MOA): Best Pro-Grade Pick
BG MOA is the additive your local shop probably pours in without telling you, and it is built to a professional standard. Rather than chasing one symptom, it loads the oil with anti-wear, antioxidant, and detergent chemistry that keeps the rings clean and the oil film strong over the entire change interval. By keeping the ring pack free of deposits and the oil from breaking down under heat, it helps a worn engine maintain the best seal it is still capable of, which keeps blowby from getting worse over time.
Its honest limitation is the same one that applies to any oil fortifier: it protects and maintains, it does not rebuild. BG MOA will not restore compression in a worn cylinder, so on a heavily blown-by engine it manages the problem rather than reversing it. It can also be harder to track down than the big consumer names. For an owner who wants pro-grade protection that keeps a high-mileage engine sealing cleanly for the long haul, though, it is a genuinely excellent choice.
- Fortifies the oil with anti-wear and antioxidant chemistry
- Keeps rings clean and sealing while protecting against new wear
- Maintains oil film strength to limit gas blowby on worn engines
Pros: Shop-grade additive trusted by professional technicians; Strengthens the oil and keeps rings clean to limit blowby; Excellent at protecting and prolonging a high-mileage engine
Cons: Maintenance and protection focus, not a worn-cylinder restorer; Harder to find on shelves than consumer brands
Frequently Asked Questions
Can an oil additive actually fix engine blowby?
It depends entirely on the cause. If your blowby comes from hardened seals or carbon-stuck oil-control rings, a seal conditioner like Liqui Moly Oil Saver or a cleaner like Sea Foam can genuinely reduce or even eliminate it, and a liquid-alloy restorer like Restore can rebuild some lost compression on mildly worn cylinders. What no additive can do is repair a scored cylinder, a broken ring land, or severely worn bores. Those need mechanical work. The smart move is to diagnose first with a compression or leak-down test, then match the additive to the actual problem rather than expecting any bottle to be a universal cure.
How do I know if my blowby is from worn rings or just stuck rings?
A leak-down test is the clearest way to tell. If air escapes into the crankcase and the cylinder holds poorly but the engine has been neglected or run on cheap oil, stuck oil-control rings clogged with carbon are a likely culprit, and a crankcase cleaner like Sea Foam often frees them. If the cylinders are evenly but genuinely worn from high mileage, you are dealing with mechanical wear, where a restorer or a thicker film additive helps more. Stuck rings usually improve dramatically after cleaning, while worn rings only improve modestly, so the response to a cleaning treatment is itself a useful diagnostic clue.
Will these additives harm my catalytic converter or oxygen sensors?
The reputable products on this list are formulated to be exhaust-system safe when used as directed, and seal conditioners like Liqui Moly are specifically designed not to clog catalytic converters. That said, the reason to treat blowby at all is that burning oil is what really damages a converter over time, so reducing oil consumption protects it. The bigger risk is overuse. Pouring in too much of any additive, or leaving a thinning cleaner in the oil for thousands of miles, can cause problems. Follow the dosage on the bottle and use cleaners only for their intended short interval.
How long does it take to see results from a blowby additive?
It varies by type. Cleaners like Sea Foam can show a difference within a single short drive cycle as they free stuck rings, though you should change the oil shortly after. Seal conditioners like Liqui Moly Oil Saver typically need a few hundred miles for the seals to swell and the smoke to drop. Restorers and friction modifiers such as Restore and Archoil AR9100 work the most gradually, often needing several hundred miles to a full oil change before compression and crankcase pressure improve measurably. Patience and a before-and-after compression test give you the honest picture.
Should I use a blowby additive in a diesel engine?
Yes, several here work well in diesels. Archoil AR9100 has a strong following among diesel owners for improving cold starts, quieting injectors, and protecting the ring pack, and Lucas Oil Stabilizer is widely used to seal worn diesel engines and boost oil pressure. Restore is rated for light diesel use as well. Always check the label to confirm diesel compatibility and respect the dosage, since diesel sumps hold more oil and the mixing ratio changes. Diesels naturally run higher cylinder pressures, so addressing blowby early with a friction modifier or restorer is well worth doing before wear gets severe.
Our Verdict
For most drivers fighting blowby, the Hi-Gear Restore Engine Restorer & Lubricant is our top pick because it attacks the root cause, re-plating worn rings and cylinder walls to recover lost compression instead of just hiding the symptom, and a before-and-after compression test will show you the difference. Our runner up is the Liqui Moly Oil Saver, the cleanest and most reliable choice when hardened seals are burning your oil and smoking your breather. The honest play is to diagnose first: clean stuck rings with Sea Foam, condition tired seals with Liqui Moly, and restore mild cylinder wear with Restore. Match the additive to the real problem and a worn engine can keep running strong for many more miles.
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