Best Engine Stop Leak: Compare 9 Engine Oil Additives

#1 · Best Overall

1. Bar's Leaks OS-1 Oil Seal

• Weight: 1.1 lb

Best for: Broad engine-type coverage.

Why it ranks #1: Designed for engine oil burning and leaks, it lists gasoline, diesel, turbocharged, EcoBoost, hybrid, and racing engine coverage plus a leak-severity guide.

Compatibility with gasoline, diesel, turbocharged, EcoBoost, hybrid, and racing engines is Bar's Leaks OS-1's clearest distinction. That broad stated coverage lets owners of varied engine types consider one oil-seal treatment for leaking main seals and gaskets, while its description also addresses worn valve seals and guides.

OS-1 is specified for both gasoline and diesel engines, with turbocharged, EcoBoost, hybrid, and racing engines also named; that breadth helps buyers compare it across distinctly configured vehicles. Its stated targets include leaking main seals and gaskets, plus worn valve seals and guides, connecting the treatment to both leakage and oil-burning concerns. The product description gives a practical severity boundary: it identifies a candidate vehicle as one that does not consume more than one quart of oil per day.

Skip it if you need an additive explicitly specified for power steering, differentials, or hydraulic systems; ATP Automotive AT-205 Re-Seal lists those uses.

OS-1 fits owners seeking an oil-seal treatment across a broad range of engine types, including hybrids and turbocharged engines. Its own guidance sets a boundary at oil consumption above one quart per day, where this stated candidacy no longer applies.

Listed on Amazon as: Bar's Leaks OS-1 Oil Seal Engine Oil Burning/Leak Repair, 16.9oz, 1-Pack

#2 · Rear Main Seal Focus

2. Bar's Leaks Rear Main Seal Repair

• Weight: 1.1 lb

Best for: Rear-main-seal leak focus.

Why it ranks #2: Specifically targets rear main seal leaks while also addressing timing cover, cam seal, and other engine oil leaks; directions say many stop within 100 miles or two days.

Its specific focus on rear main seal leaks gives Bar's Leaks Rear Main Seal Repair a clear place in an engine-oil maintenance plan. The same product also lists timing-cover, cam-seal, and other hard-to-stop oil leaks, so buyers are not limited to the rear main seal alone.

The seal-restorer additive is described as restoring seal size, flexibility, and elasticity lost through engine heat and age, linking its mechanism to worn seals. Application is straightforward: add the entire bottle to the crankcase where engine oil is added, either at or between oil changes, without overfilling. The product is specially aimed at rear main leaks but also addresses timing-cover and cam-seal leaks; its stated expectation is that most leaks stop within 100 miles or two days of driving.

Skip it if you need a treatment explicitly listed for turbocharged, EcoBoost, hybrid, and racing engines; Bar's Leaks OS-1 names those types.

This is a fit for an owner targeting a rear main seal leak or another listed engine-oil seal leak and able to add it at the crankcase. Follow the no-overfill instruction and allow for the stated driving period.

Listed on Amazon as: Bar's Leaks Rear Main Seal Repair, 16.9 oz

#3 · Seal Elasticity Treatment

3. XADO Atomex Stop Leak

• Weight: 10.8 oz

Best for: High-mileage seal restoration.

Why it ranks #3: Its stated purpose is restoring elasticity in rubber seals and gaskets; the instructions call for pouring it into warmed engine oil at operating temperature.

Its seal-restoring components target the elasticity of rubber seals and gaskets, giving drivers a treatment aimed at oil leakage associated with aging sealing materials. XADO Atomex is a 250 ml motor-oil treatment for engine use, with instructions to pour it into the oil tank after the engine reaches operating temperature.

The focus on restoring seal and gasket elasticity makes this a targeted option when leakage is associated with those sealing materials, rather than a general-purpose fluid treatment. Its 250 ml bottle provides a defined treatment quantity, while the warm-engine instruction shapes the maintenance workflow: bring the engine to operating temperature before pouring the contents into the oil tank. The supplied information identifies engine-oil use, so buyers seeking treatment for other vehicle systems should look elsewhere.

Skip it if you need one additive for transmission, power-steering, or hydraulic systems; ATP Automotive AT-205 Re-Seal lists those applications too.

This suits an engine owner addressing leakage tied to aging rubber seals or gaskets who can follow the warm-engine application step. Its supplied use is engine oil, so it is not the pick for treating leaks in other systems.

Listed on Amazon as: XADO ATOMEX Oil Additive Stop Leak Engine – Restore Seal and Gaskets, Treatment for Car Engine High Mileage or Rear Main Seal, Best Stopper Leaks Reseal (Bottle, 250 ml)

#4 · Six-Quart Treatment

4. Lucas Oil Engine Oil Stop Leak

• Weight: 2 lb

Best for: Large-capacity oil treatment.

Why it ranks #4: The one-quart bottle treats up to six quarts and is listed for petroleum, semi-synthetic, and full synthetic motor oils in compatible internal-combustion engines.

A one-quart bottle treating up to a 6-quart capacity gives Lucas Oil Stop Leak a clearly stated scale for larger oil systems. Its seal and O-ring conditioning, combined with friction- and wear-reducing components, makes it a fit for buyers seeking both leak treatment and engine-part support.

Lucas Oil says its seal-swell agents condition hard and shrunken seals and gaskets, addressing the sealing materials behind oil leaks. The formula also conditions O-rings and contains components intended to reduce friction and wear, linking leak treatment with engine-part support. A quart treats up to a 6-quart capacity, so the bottle size and dosage guidance help owners plan an application. It is listed for internal-combustion engines compatible with petroleum, semi-synthetic, and full-synthetic motor oils.

Skip it if you need a compact 8-ounce additive explicitly listed for several fluid systems; ATP Automotive AT-205 Re-Seal lists that multi-system use.

This suits owners of internal-combustion engines using petroleum, semi-synthetic, or full-synthetic motor oil who want seal conditioning plus friction and wear support. Its one-quart treatment quantity is tied to capacities up to six quarts.

Listed on Amazon as: Lucas Oil 11100 Engine Oil Stop Leak – Top Off Additive – 1 Quart

#5 · High-Mileage Formula

5. STP High Mileage Oil Treatment

• Weight: 15.2 oz

Best for: High-mileage friction support.

Why it ranks #5: Formulated for vehicles over 75,000 miles, it combines seal and gasket rejuvenation with ZDDP anti-wear additive and a high-viscosity oil treatment.

Formulated for vehicles with more than 75,000 miles, STP combines a high-viscosity oil treatment with ZDDP anti-wear additive. That pairing gives high-mileage drivers a product intended to cushion moving engine parts against metal-to-metal friction while also rejuvenating seals and gaskets to address leaks.

The high-viscosity formula creates a thick cushion between moving engine parts, while the included ZDDP serves as an anti-wear agent; together, those features target friction and protection in a high-mileage engine. STP also says its stop-leak treatment rejuvenates seals and gaskets and helps address engine leaks, noise, and smoking. The 15-ounce bottle is specified for car use, making this a focused choice for older passenger vehicles rather than a listed multi-system treatment.

Skip it if you want an additive explicitly listed for diesel, turbocharged, hybrid, and racing engines; Bar's Leaks OS-1 lists those engine types.

Choose this STP treatment when your car has passed 75,000 miles and you want friction cushioning alongside seal-and-gasket treatment. Its supplied application is high-mileage car engines, so it is less clearly matched to other vehicle types.

Listed on Amazon as: STP High Mileage Oil Treatment + Stop Leak, Improves Car Oil, 15 Fl Oz

#6

6. ATP AT-205 Re-Seal

• Weight: 1.21 lb

Best for: Multi-fluid rubber-seal treatment.

Why it ranks #6: The 8-ounce bottle treats a six-quart capacity and works with conventional or synthetic oils, though its stated coverage also extends well beyond engines.

Compatibility with conventional and synthetic oils, ATF, gear oil, power-steering fluids, and hydraulic oil makes ATP Automotive AT-205 Re-Seal unusually broad in its listed fluid applications. Its rubber-seal and gasket focus gives buyers with leaks across several vehicle systems one treatment option to evaluate.

AT-205 targets rubber seals and gaskets in engines, transmissions, power steering, differentials, and hydraulic systems, which helps owners consider it beyond an engine-only leak treatment. Its listed compatibility spans conventional and synthetic oils, ATF, gear oil, power-steering fluids, and hydraulic oil. The stated dose is one 8-ounce bottle for a 6-quart capacity, adjusted accordingly, giving buyers a capacity-based mixing reference. The formulation also states it contains no petroleum distillates and will not over-swell or break down seals.

Skip it if you want a treatment specifically marketed for vehicles over 75,000 miles with ZDDP; STP High Mileage Oil Treatment + Stop Leak lists both.

AT-205 fits owners addressing rubber-seal leaks across multiple listed vehicle systems and fluid types, especially when one treatment needs to cover more than engine oil. Use its 6-quart dosage reference as a starting point and adjust for capacity.

Listed on Amazon as: ATP Automotive AT-205 Re-Seal Stops Leaks, 8 Ounce Bottle (2 Pack)

#7

7. BlueDevil Oil Stop Leak

• Weight: 4.8 oz

Best for: Gasoline and diesel leak sealing.

Why it ranks #7: This 8-ounce liquid is intended for engine oil leaks and is listed as compatible with gasoline or diesel engines; the supplied details give no treatment capacity.

Compatibility with gasoline and diesel engines, paired with a stated non-clogging formula, sets BlueDevil Oil Stop Leak apart for buyers seeking broad fuel-type coverage. Its pour-in application is described for the leaking component’s oil sump or crankcase, keeping the stated workflow direct.

BlueDevil instructs users to pour the recommended amount into the leaking component’s oil sump or crankcase, so the application point is clearly identified. The product is described as compatible with gasoline or diesel engines and as non-clogging, which gives owners of either engine type relevant compatibility information. Its claims also describe a permanent seal that remains sealed after miles of driving. Use the recommended amount; the supplied details do not specify a numerical dosage.

Skip it if you need an additive with a stated 8-ounce dose for a 6-quart capacity; ATP Automotive AT-205 Re-Seal provides that reference.

BlueDevil suits gasoline or diesel engine owners seeking a pour-in oil leak treatment with a stated non-clogging formula. The supplied information names the sump or crankcase as the application point but gives no numerical dose.

Listed on Amazon as: BlueDevil Products 49499 Oil Stop Leak – 8 Ounce

#8

8. STP Engine Stop Leak

• Weight: 15.1 oz

Best for: Minor-leak viscosity support.

Why it ranks #8: A straightforward 14.5-fluid-ounce option that helps stop minor oil leaks and includes a viscosity enhancer, but its listed use is limited to minor leaks.

A viscosity enhancer is the central feature of STP Engine Stop Leak, which is described as helping stop minor oil leaks. The product also lubricates moving engine parts, offering a simple engine-oil treatment for owners seeking leak support alongside lubrication rather than a broader multi-system application.

STP says normal engine heat can cause oil seals and gaskets to shrink, dry out, and crack, providing context for its minor-leak focus. Its viscosity enhancer fortifies the oil, while the stated lubrication of moving engine parts adds a second engine-oil function. At 14.5 fluid ounces, the bottle gives buyers a defined product quantity. The supplied description supports a modest-leak use case, not a claim that it addresses every leak severity or other vehicle systems.

Skip it if you need a treatment that lists rear main, timing-cover, and cam-seal leaks; Bar's Leaks Rear Main Seal Repair names those targets.

This STP option fits an owner addressing a minor engine-oil leak who also wants an oil viscosity enhancer and lubrication for moving parts. Its stated scope is minor leaks, so it is not presented as a solution for every leak severity.

Listed on Amazon as: STP Engine Stop Leak (14.5 fluid ounces)

#9

9. Liqui Moly Oil Leak Stop

Best for: 300 ml oil-leak treatment.

Why it ranks #9: The listing identifies a 300 ml oil leak stop product, but supplies no further application, compatibility, or treatment-capacity details to assess its fit.

A 300 ml format is the concrete distinguishing detail supplied for Liqui Moly Oil Leak Stop. The title identifies it as an oil leak stop product, making it a straightforward listing for shoppers seeking that category in a measured bottle, though no application directions or compatibility details are provided here.

The product title identifies Oil Leak Stop as its function, while the 300 ml specification gives buyers a clear quantity to consider when selecting a bottle. Those are the only supplied product details beyond its Liqui Moly brand, so they support a basic category-and-volume comparison but not claims about engine types, seal materials, or application steps. Buyers should treat this as a sparse-information option and rely on product-specific directions for use rather than assuming a workflow from the title alone.

Skip it if you need stated directions for adding treatment to a warmed engine; XADO Atomex specifies that workflow.

This listing suits shoppers who want a Liqui Moly oil leak stop in a stated 300 ml quantity and can consult its product directions. The supplied details do not establish compatibility, treatment method, or supported engine types.

Listed on Amazon as: LM 1005 Oil Leak Stop 300 ml