Loctite 518: The Unsung Hero Behind Leak-Free Flange Seals
Loctite 518 Review: The Hidden Hero of Flange Sealing
When it comes to reliable flange sealing, few products have built a reputation as solid as Loctite 518. Whether you’re a mechanic, engineer, or DIY enthusiast, chances are you’ve encountered leaks, flange distortions, or gasket failures that just wouldn’t quit. That’s where Loctite 518 comes in—a game-changing anaerobic sealant that simplifies your life and ensures zero leaks, every time.
In this deep-dive review, we’ll explore everything about Loctite 518: what it is, how it works, where it shines, and how to apply it step-by-step. We’ll even compare it to Loctite 515, discuss cure times, temperature resistance, diesel compatibility, and the best places to buy it. Let’s get into it.
What Is Loctite 518?
Loctite 518 is a medium-strength, anaerobic flange sealant designed specifically for machined metal surfaces. It cures in the absence of air (anaerobic) when confined between close-fitting metal parts, forming a flexible, chemical-resistant seal that prevents leaks of oil, coolant, fuel, and gases.
Think of it as a modern replacement for traditional paper or rubber gaskets. Instead of relying on pre-cut gaskets that often fail over time, Loctite 518 fills all the microscopic gaps and surface imperfections between metal flanges—creating a 100% leak-proof seal.
Where Can You Use Loctite 518?
Loctite 518 is perfect for rigid iron, steel, or aluminum flanges—common in:
- Gearboxes and transmissions
- Engine covers and oil pans
- Water pumps and compressor housings
- Hydraulic and pneumatic systems
- Gear housing covers and differential covers
- Industrial pumps, compressors, and valve assemblies
Basically, anywhere you have two machined metal surfaces that need a reliable, flexible, and pressure-resistant seal.
How Does Loctite 518 Work?
Loctite 518 cures when air is absent and metal ions are present. Once you apply it between flange surfaces and assemble them, it starts to cure from the inside out. Within minutes, it forms a tough polymer that resists pressure, vibration, and chemicals.
Because it’s anaerobic, it won’t harden until the parts are assembled—meaning you have ample working time to align your parts correctly before it sets. Once cured, the seal is permanent but serviceable, and disassembly is still possible using standard hand tools.
Loctite 518 Technical Highlights
- Color: Red
- Base: Methacrylate ester
- Viscosity: Thixotropic (doesn’t run or drip)
- Temperature Range: -55°C to +150°C (-65°F to +300°F)
- Cure Time: Fixture time around 25 minutes on active metals (e.g., steel, iron); full cure in 24 hours.
- Gap Fill: Up to 0.25 mm (0.01 inch)
- Resistance: Excellent chemical and thermal stability; resistant to oil, diesel, coolant, and transmission fluids.
Loctite 518 vs Loctite 515: What’s the Difference?
Both Loctite 515 and 518 belong to the same family of flange sealants, but they have subtle differences that affect performance:
| Feature | Loctite 515 | Loctite 518 |
|---|---|---|
| Gap Filling | Up to 0.125 mm | Up to 0.25 mm |
| Temperature Resistance | Up to 150°C | Up to 150°C |
| Viscosity | Medium | Thicker (thixotropic) |
| Surface Compatibility | Works best on active metals | Works well on both active and inactive metals (e.g., aluminum, stainless steel) |
| Ease of Use | Flows easily | Less mess, non-drip formulation |
| Cure Time | Slightly faster | Slightly slower but more stable |
In simple terms, Loctite 518 is an upgraded, more flexible, and versatile version of 515—ideal when working on aluminum or uneven flange surfaces.
Is Loctite 518 Diesel Resistant?
Yes. Loctite 518 is highly resistant to diesel, engine oils, coolants, and hydraulic fluids. This makes it a top choice for automotive and industrial applications where fuel or oil exposure is common. Once cured, it forms a non-brittle seal that resists vibration and temperature changes without cracking.
Loctite 518 Cure Time
Cure time depends on the metal type, temperature, and gap size. Here’s a general guide:
- Fixture Time: 25 minutes (steel) / 1 hour (aluminum)
- Functional Strength: 4–6 hours
- Full Cure: 24 hours at room temperature
You can speed up curing using Loctite 7649 Primer N—especially on inactive metals or in low-temperature environments.
Step-by-Step Guide: How to Apply Loctite 518
Using Loctite 518 is simple, but correct application ensures long-term reliability. Follow these steps:
Step 1: Clean the Surfaces
Ensure both flange surfaces are clean, dry, and free from oil, old gasket, or debris. Use a surface cleaner like Loctite SF 7063 to remove contaminants.
Step 2: Apply Loctite 518
- Apply a continuous bead (about 1.5 mm wide) around one flange surface.
- Go around bolt holes to maintain complete coverage.
- Avoid excessive application—Loctite 518 spreads evenly when tightened.
Step 3: Assemble Parts
Join the parts immediately and tighten bolts to the manufacturer’s torque specifications. Don’t wait too long, as curing starts once air is excluded.
Step 4: Allow to Cure
Let it cure at room temperature for 24 hours before putting the system into full operation. For faster results, use a primer or apply light heat (not exceeding 50°C).
Step 5: Test for Leaks
After curing, pressurize the system or fill it with the appropriate fluid to check for leaks. If applied correctly, you’ll have a flawless, long-lasting seal.
Loctite 518 vs Loctite 5188: Are They the Same?
While they’re similar, Loctite 5188 is a newer, more flexible formulation designed for modern engine materials, such as cast aluminum. It performs better where thermal cycling and vibration are issues.
In short:
- Loctite 518: Great all-rounder for rigid metal flanges.
- Loctite 5188: Enhanced flexibility and adhesion—better for modern engines.
If you’re sealing aluminum or composite housings, Loctite 5188 might be your best pick. But for standard metal flanges and heavy-duty sealing, 518 remains unbeatable.
Advantages of Using Loctite 518
✅ No need for traditional gaskets – Eliminates paper or rubber gaskets and all their alignment issues.
✅ Seals instantly against low pressure – Prevents early leaks during assembly.
✅ Resists vibration and temperature extremes – Ideal for automotive and industrial environments.
✅ Easy disassembly – Despite forming a strong bond, it can still be removed with regular tools.
✅ Reduces inventory – One product seals a wide range of applications.
✅ Non-corrosive and non-toxic – Safe for various metals, including aluminum.
✅ Long service life – Resistant to oil, diesel, and coolants, ensuring reliable performance for years.
Disadvantages (Few but Worth Mentioning)
❌ Not for large gaps – Loctite 518 is designed for close-fitting flanges only (up to 0.25 mm).
❌ Requires clean surfaces – Any oil or dirt can prevent proper curing.
❌ Not suitable for flexible plastics or rubber gaskets – It’s made for rigid metal parts only.
Real-World Case Study: Loctite 518 in Action
Case: A local garage had recurring issues with oil leaks on aluminum transmission housings. Conventional paper gaskets kept failing due to surface distortion and vibration.
Solution: The mechanic switched to Loctite 518. After cleaning the flanges and applying a thin bead, they reassembled the housing. The result?
- Zero leaks after 24 hours.
- No gasket compression over time.
- Easier future disassembly.
The shop later standardized Loctite 518 across multiple engine and gearbox repairs.
This case perfectly demonstrates how Loctite 518 reduces downtime, eliminates leaks, and improves reliability in real-world applications.
Loctite 518 Equivalent Products
Looking for a reliable replacement for Loctite 518?
- Here are the best options to match its performance and sealing quality.
- 🔧 Direct Equivalents (Anaerobic Flange Sealants)
- These products work the same way as Loctite 518 — they cure without air and are ideal for sealing metal flanges and close-fitting parts.
- Bondloc B518 – A direct, affordable alternative to Loctite 518.
- Permatex 51031 – High-temperature anaerobic flange sealant with similar strength.
- MX18 Flange Sealant – Specifically designed as a Loctite 518 replacement.
- Loctite 574 – Suitable for rigid metal flanges, offering strong sealing.
- Loctite 515 – An earlier version of 518, still trusted for similar use.
- 🧩 Other Compatible Options (RTV Silicone Gasket Makers)
- While not true anaerobic sealants, these can also seal flanges and gaskets in less demanding applications.
- Permatex 82180 (Ultra Black) – Flexible, oil-resistant RTV sealant.
- Permatex 82194 (Ultra Grey) – High-torque RTV gasket maker.
- Loctite SI 5980 – High-performance RTV silicone for durable sealing.
- Dirko HT – Heat-resistant, oil-proof RTV sealant for engines and gearboxes.
- Loctite High-Flex Gasket Maker – Silicone-based sealant for flexible joints.
- 💡 Recommendation
- For a true “like-for-like” replacement, always choose a product labeled anaerobic flange sealant and compare key properties:
- Operating temperature range
- Oil and fluid resistance
- Cure time and gap-filling ability
- This ensures performance equal to or better than Loctite 518 in your sealing applications.
Always confirm the manufacturer’s technical data before substituting.
Where to Buy Loctite 518
You can find Loctite 518 easily online or at local distributors. Trusted sources include:
- Henkel official distributors (such as Lasap Kenya for industrial users)
- Amazon, eBay, and Jumia
- Local automotive and hardware stores
- Industrial supply outlets (e.g., RS Components, Grainger, or Motion Industries)
When buying, look for authentic Henkel packaging—fake sealants often perform poorly.
Expert Tips for Best Results
- Always apply Loctite 518 to metal-to-metal joints only.
- If working in cold weather, use a primer to speed up curing.
- Avoid over-torquing bolts after curing—it can break the seal.
- Store the tube in a cool, dry place, tightly closed.
- Apply a small test on inactive surfaces to confirm adhesion before full use.
Final Verdict: Is Loctite 518 Worth It?
Absolutely. Loctite 518 is one of the most dependable flange sealants on the market. It replaces gaskets, simplifies repairs, and ensures a clean, professional seal every time. From engine covers and gearboxes to pumps and compressors, it’s the go-to choice for professionals who hate leaks and rework.
If you want a reliable, easy-to-use, and cost-effective solution for sealing metal flanges, Loctite 518 is your best bet.
Key Takeaways
- Loctite 518 is a medium-strength, anaerobic flange sealant for metal surfaces.
- Works on aluminum, iron, and steel—perfect for engines, gearboxes, and pumps.
- Offers excellent oil, diesel, and coolant resistance.
- Fills gaps up to 0.25 mm and cures without air.
- Outperforms many traditional gaskets and rivals like Loctite 515.
In short: Loctite 518 helps you say goodbye to leaks and hello to lasting reliability.