What’s the difference between Loctite 515 and 518?
The main difference between Loctite 515 vs. Loctite 518 is that Loctite 518 is better for use on aluminum flanges and can replace Loctite 515 for most applications. However, Loctite 518 is generally a faster-setting anaerobic adhesive and it may tend to cure too quickly on very active metals like brass.
- Loctite 515 Vs 518: Specs & Uses
- Directions for Loctite 515 (Loctite 515 Gasket Maker & Flange Sealant)
- My Hands-on Test of Loctite 518 (Loctite 518 Gasket Maker Flange Sealant)
Loctite 515 Vs 518: Specs & Uses
⏰Fixture Time+Maximum Gap Fill Length
Loctite 515: 15 minutes, 0.25 mm
Loctite 518: 10 minutes, 0.25 mm
🌡️Optimal Storage and Operating Temperature
Loctite 515: 8°C to 28°C, -55°C to 150°C
Loctite 518: 8°C to 28°C, -55°C to 150°C
🛠️Common Uses
Loctite 515 can be used to seal engine case halves; secure the dipstick tube on a Chevy automatic transmission; Sealing with Rubber Gaskets; used by Lawnboy to seal crankcase halves of their 2-cycle mower engines without a gasket
Loctite 518 is suitable for rebuilding motorcycle engines, such as the 1970 BSA race-bike; used as an alternative to RTV (Room-Temperature Vulcanizing) sealants for various applications, including sealing flanges, threads, and engine cases.
Technical Info
Directions for Loctite 515 (Loctite 515 Gasket Maker & Flange Sealant)
✅Pros: Loctite 518 Equivalent
It also works great for putting an outboard motor back together after a rebuild. It is a great choice for a sealant between two metal flanges that are both nice and flat. It definitely won’t fill any big gaps, but that’s not what it’s for.
Applying Loctite 515
Valve Plate Gasket Leakage
I have an old Speedaire air compressor that had a leak from the valve plate gasket, and it was no longer available for replacement. The gasket is subject to high compression and excessive heat. After attempting to make a replacement from gasket material, which nearly worked but still leaked minutely, I assembled the compressor using Loctite 515. It has performed flawlessly with no leaks.
Loctite 515 Flange Sealant
Leaking flange seals on a Carrier 30RB 🫧
Using the combination of crowd favorite Loctite 515 and silicon-filled protection blocks. I shouldn’t have to worry about leaks again!
Water Pump Install
I also tested Loctite 515 with Klean ‘N Prime primer on a water pump install, too. I was installing a pump on a Ford 5.0, so there were several layers and several opportunities to leak. I had tried NAPA 80062 High Tack because that is how my dad always did it, and it gave me less than acceptable results.
Next, I tried 
Permatex ( hondabond vs permatex ), which also gave me less-than-acceptable results. Finally, I tried Loctite 515 with Klean ‘N Prime primer. I followed the instructions to the letter, and the result was no leaks!! What a relief. Another nice thing about this product is that any over apply or messes don’t harden and can even be cleaned up the next day.
💬 FAQ of Loctite 515
Q: Can I use Loctite 515 for a diesel exhaust manifold block off plate with high temperatures?
A: Loctite 515 can only resist temperatures up to 300-350 degrees F, so it is not recommended for use on exhaust manifolds. Metallic gaskets are the only suitable option for creating a proper seal for those high temperatures.
Q: Can I use Loctite 515 to seal around the leak for automatic transmission fluid around the dipstick tube on a Chevy automatic transmission?
A: While Loctite 515 is primarily designed for preventing air leakage between torqued metal surfaces, it may work for securing the dipstick tube if it can be secured and not move around. However, JB Weld may be a better repair option. You can see my test here: alum bond vs jb weld 
Q: Can Loctite 515 be used with a rubber gasket for an oil pan?
A: Loctite 515 can work without a gasket and may work well with a rubber gasket, although it takes a while to dry and its effectiveness may depend on the two pieces’ thermal expansion rates. However, I am not 100% certain of its effectiveness with rubber gaskets, as it did not work for me with an exhaust gasket.
Q: Is Loctite 515 rated for contact with gasoline?
A: Lawnboy has used Loctite 515 to seal the crankcase halves of their 2-cycle mower engines without a gasket, and other OEMs have recommended it for certain sealing situations that involve contact with gasoline.
Q: What is the oil resistance of Loctite 515?
A: Loctite 515 works well with oil, coolant, and similar chemical components.
Q: Do you need to use Loctite primer/activator when using Loctite 38655 515 Gasket Maker on a gearbox cover?
A: Loctite 515 works on its own, but it is important to ensure that both surfaces are very clean. It is also recommended to let the seal cure for 24 hours.
Q: Will Loctite 515 work with hydraulic fluid, and how much pressure can it hold?
A: Loctite 515 is suitable for use with hydraulic fluid, and it can withstand several thousand psi on fine threads and close tolerance flanges. However, the thicker the gap, the easier it is to leak, and gaps larger than <.015” are too big.
Q: Can I use Loctite 515 for assembling a tractor carburetor?
A: It is not recommended to use Loctite 515 or any type of silicone or flexible sealers on a carburetor. The best option is to use the correct gaskets, or if they are no longer available, find similar gasket material at an auto parts store and make gaskets using the old gaskets as a pattern. Loctite 515 is designed for use in transmissions, gearboxes, and similar applications.
4 reviews
📣🔥 Share it to easily keep track of the answers!
Leave a Reply
My Hands-on Test of Loctite 518 (Loctite 518 Gasket Maker Flange Sealant)
✅Pros: Loctite 518 Flange Sealant
I was a bit hesitant at first, as some reviews had mentioned that Loctite 518 wouldn’t cure properly without primer. However, I followed the directions carefully, cleaned both surfaces thoroughly, and applied a thin coat to each side using a small paintbrush. I then assembled the crankcase and let it set for a couple of days.
Testing Loctite 518 Flange Sealant
Testing LOCTITE 518 for engine case closing. Short block is done and checked deck height.
Success
I wanted to ensure that the product had cured correctly, so I disassembled the crankcase to check before completing the assembly. To my relief, everything looked fine, so I cleaned both surfaces again, resealed, and reassembled the crankcase. I let it sit for a week before running the motor, and I’m happy to report that there were no leaks after multiple runs.
Seal the Crankcase with Little Volumns
I was impressed with how little product was needed to seal the crankcase, and I’m sure that one tube will last me for many more small engines. However, I must admit that Loctite 518 is a bit pricey compared to RTV. Nevertheless, Loctite is much cleaner and seals just as well, if not better. I even used it to seal a case and on a jet ski pump.
Applying Loctite 518
How Long Does Loctite 518 Take to Cure?
30min to 24h
❌Cons: Loctite 518
The only downside is that it can be hard to find without ordering online, and you also need to order the activator separately for non-active metals like aluminum. But if you have a race car, you’ll definitely need this stuff!
FAQ of Loctite 518
Q: What is the low and high temperature range on the 518
A: Loctite 518 red anaerobic flange sealant is compatible with metal materials with a 4 hr cure time. Delivers great performance with a shear strength of 1100 psi and tensile strength of 1200 psi. Minimum to maximum operating temperatures are -65 F to +300 F.
I’m Ronald Stevens, a Mechanical Engineer obsessed with adhesives, glue, and all things sticky! My passion began in childhood when I’d always be the one playing with glue during arts and crafts. And I’d spend hours researching and experimenting. Happy reading, and remember: stick with the best, and you’ll never be stuck in a mess!
Feel free to contact me and join our discussion:
Is it safe to use Loctite 515 on plastic engine parts, such as the cylinder on a chainsaw?
Unfortunately, Loctite 515 is not recommended for use on plastic. This product requires the presence of metal ions to fully cure, so it is not the ideal choice for sealing plastic engine parts.
Can I use picture 518 on plastic oil seal into metal hub, will it cure?
I would not recommend it. Loctite 518 is designed for metal-to-metal sealing applications. Using it between a plastic oil seal and metal hub is not the intended use.