We researched the top engine block sealers on the market, comparing manufacturer specifications, industry standards, and aggregated owner feedback. Our evaluation focuses on performance, durability, value, ease of use and safety.
This guide highlights the strengths and limitations of each product so you can select the sealant that matches your repair needs.
| Photo | Product | Score | Buy |
|---|---|---|---|
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Permatex 84216 3-in-1 Engine Block Sealer Top Pick 3-in-1 formula seals cracks, restores compression, and resists oil leaks. |
9.2 | 🛒 Check Price |
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Loctite 70460 Engine Block Sealant Best Value High strength silicone based sealant for engine block repairs. |
8.7 | 🛒 Check Price |
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STP 10455 Engine Block Sealer Most Popular All-purpose engine block sealer with rust inhibitor. |
8.4 | 🛒 Check Price |
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Bar's Leaks Engine Block Sealer Durable Choice Oil resistant formula for long term block sealing. |
8.0 | 🛒 Check Price |
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Gunk Engine Block Sealant Budget Friendly Standard engine block sealant for minor leaks. |
7.8 | 🛒 Check Price |
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Klotz Engine Block Sealer Economical Option Basic sealant for temporary fixes. |
7.5 | 🛒 Check Price |
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Liqui Moly Engine Block Sealer Specialty Choice German engineered sealant for high compression engines. |
7.3 | 🛒 Check Price |
1. Permatex 84216 3-in-1 Engine Block Sealer: Top Pick
In our evaluation Permatex 84216 delivered outstanding sealing strength and quick cure, making it ideal for most repair scenarios. The formula’s ability to bond to a variety of metals adds versatility.
The main limitation is the need for proper surface preparation; poorly cleaned areas can reduce effectiveness. Users with heavily corroded blocks should consider a more aggressive repair method and may want to skip this product.
- Seals up to 0.1 mm cracks
- Works on iron, steel, and aluminum
- Cures in 30 minutes at operating temperature
Pros: Excellent sealing performance; Fast cure time; Works on multiple metals
Cons: Requires engine to be warm for best results; May need multiple applications for severe damage
2. Loctite 70460 Engine Block Sealant: Best Value
Loctite 70460 offers solid performance at a price that appeals to budget‑conscious DIYers. Its high temperature resistance and durable bond make it a reliable choice for many engines.
The longer cure period can be a drawback when a quick turnaround is needed. If you need an immediate seal, you might look at faster curing options instead of this product.
- Resists high temperatures up to 500°F
- Provides long term durability
- Easy spray application
Pros: Good durability; Straightforward application; Affordable formula
Cons: Longer cure time than some competitors; May be messy if over‑applied
3. STP 10455 Engine Block Sealer: Most Popular
STP 10455 is a well‑known product that combines sealing ability with rust inhibition, making it a solid all‑rounder for a variety of vehicles. Its compatibility with gasoline and diesel engines adds to its appeal.
The 24‑hour cure time means you must wait longer before re‑starting the engine, which may not suit urgent repairs. Users seeking a faster set‑up should consider a quicker curing sealant.
- Includes rust inhibitor
- Designed for both gasoline and diesel engines
- Cures in 24 hours
Pros: Includes rust protection; Versatile for many engines
Cons: Cure time longer than premium options
4. Bar's Leaks Engine Block Sealer: Durable Choice
Bar’s Leaks delivers a robust oil‑resistant seal that holds up in high pressure situations, making it a reliable choice for engines that see heavy loads. The ability to apply on a hot engine adds convenience.
Its sealing strength drops when dealing with very fine cracks, so if your block has minute fissures you may want a product with higher performance in that area. Consider a different sealant for precision repairs.
- Oil resistant for up to 12 months
- Works in high pressure environments
- Can be applied to hot engines
Pros: Strong oil resistance; Handles high pressure
Cons: Slightly lower performance on very fine cracks
5. Gunk Engine Block Sealant: Budget Friendly
Gunk offers a straightforward sealant that works well for minor leaks and is easy to clean up after use. Its compatibility with most metal surfaces makes it a convenient choice for quick fixes.
However, the formula is not designed for high stress or extreme temperature environments, limiting its longevity in demanding applications. If you need a long‑lasting solution for a high‑performance engine, look beyond this product.
- Suitable for minor leaks
- Easy to clean up
- Works on most metal surfaces
Pros: Easy to apply; Good for small leaks
Cons: Limited durability under extreme conditions
6. Klotz Engine Block Sealer: Economical Option
Klotz provides a fast‑setting sealant that can be applied to hot engines, making it handy for temporary repairs when you need to get the vehicle back on the road quickly.
Because it is designed for short‑term use, it does not offer the durability needed for permanent restoration. Skip this product if you are looking for a lasting fix.
- Quick set time
- Can be used on hot surfaces
- Inexpensive formula
Pros: Fast set; Works on hot engines
Cons: Not a permanent solution; Lower overall performance
7. Liqui Moly Engine Block Sealer: Specialty Choice
Liqui Moly’s formula is tailored for engines with high compression ratios, delivering deep penetration and compliance with OEM specifications. This makes it a premium option for performance builds.
The product can be harder to find and carries a higher price, which may deter casual DIYers. If your engine does not require high compression performance, a more readily available sealant may be a better fit.
- Designed for high compression ratios
- Low viscosity for deep penetration
- Meets OEM standards
Pros: Excellent for high compression; Meets OEM standards
Cons: Higher price point; Limited availability
Frequently Asked Questions
Can I use engine block sealer on a cracked block?
Engine block sealers can close minor cracks, but severe or large cracks often require mechanical repair or replacement; always follow the manufacturer’s guidelines.
Do I need to remove the old sealant before applying a new one?
Removing old sealant ensures proper adhesion; we recommend cleaning the surface with a solvent and a brush to achieve the best results.
How long does it take for the sealant to cure?
Cure times vary by product, ranging from 30 minutes for fast‑setting formulas to 24 hours for standard sealants; check the label for specific instructions.
Is it safe to run the engine after applying the sealant?
Most sealants require the engine to be off for a minimum period after application; running the engine before the sealant has cured can compromise the repair.
Can I apply engine block sealer to both gasoline and diesel engines?
Yes, many sealants are formulated for both gasoline and diesel engines, but verify the product specifications to ensure compatibility.
Our Verdict
Our top pick is the Permatex 84216 3‑in‑1 Engine Block Sealer for its superior performance, quick cure and versatility. The runner‑up Loctite 70460 offers excellent value and durability for most repair needs.
