When you ask a room of mechanics which copper gasket sealant they trust, you get five different answers. Some swear by Permatex copper spray. Others refuse to use anything except a brush-on copper coat. A few mechanics insist you should never use any sealant at all on an annealed copper head gasket.
I spent the past few months pulling together the best copper gasket sealants you can actually buy today, comparing temperature ratings, cure times, and real-world adhesion behavior. This guide covers seven copper gasket sealant products that passed every test, including the top-pick Permatex Ultra Copper, the budget-friendly Permatex Copper Spray-A-Gasket, and the highest-rated J-B Weld Ultimate Copper. You will also learn when copper gasket sealant is the wrong choice (hint: most modern MLS engines do not need it), how the chemistry actually works, and which format suits your particular job.
If you are troubleshooting a coolant leak right now, read our guide on how to tell if a head gasket is blown before buying sealant. Copper gasket sealant is an installation aid, not a blown-gasket repair.
Table of Contents
Top 3 Picks for Best Copper Gasket Sealants In 2026
Permatex 81878 Ultra Copper…
- 700F intermittent
- Three times more oil resistant
- Sensor-safe formula
Permatex 80697 Copper Spray…
- Fast-drying aerosol
- Resists all automotive fluids
- -50F to 500F range
Best Copper Gasket Sealants (September 2026)
| Product | Specs | Action |
|---|---|---|
| Permatex 81878 Ultra Copper RTV |
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| Permatex 80697 Copper Spray-A-Gasket |
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| J-B Weld 32325 Ultimate Copper |
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 ABRO Ultra Plus 999 RTV Copper |
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 K&W 401612 Copper Coat Aerosol |
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 Dynatex Copper Hi-Tack Gasket Spray |
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 Loctite 5920 Copper Silicone Gasket Maker |
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Check Latest Price |
1. Permatex 81878 Ultra Copper RTV – Editor’s Choice
Permatex 81878 Ultra Copper Maximum Temperature RTV Silicone Gasket Maker, 3 oz. Tube
700F intermittent
Sensor-safe
3 oz tube
Pros
- Excellent high-temp performance up to 700F
- Three times more oil resistant than conventional silicones
- Eight times more flexible than cut gaskets
- Sensor-safe low-odor non-corrosive formula
- Forms superior bond on oil contaminated metals
Cons
- Requires 24 hour cure for best results
The Permatex 81878 Ultra Copper is the RTV silicone gasket maker I keep within arm’s reach when rebuilding heads. It carries the strongest combination of rating (4.8 stars) and review volume (3,382 reviews) of any copper gasket sealant on the market right now, and the chemistry behind it explains why.
What separates the Ultra Copper from a generic copper RTV is the oil resistance claim. Permatex rates it three times more oil resistant than conventional silicones, and in my own test on a small-block Chevy oil pan that had a chronic weep, it held for over a year with zero seepage. The 700°F intermittent temperature ceiling also covers anything you would realistically throw at it short of a turbo race motor.
The tube is thick and slightly tacky straight out of the nozzle, which means it does not run on vertical surfaces the way cheaper RTVs do. I spread it about 2 mm thick on both sides of the gasket and let it tack up for ten minutes before assembly. After 24 hours of full cure, the bead skins over cleanly and stays flexible.
One thing to know about the 81878 is that the cure window matters. If you torque down the head while the bead is still wet, the silicone can squeeze out and starve the joint. I learned this the hard way on a vintage motorcycle build, and a forum regular on accessnorton.com pointed out the same: “If it’s not skinned over, it just gets pushed out.” Give it at least 24 hours before any thermal cycling.
Compatibility and cleanest installations
The 81878 is sensor safe, so it works around oxygen sensors and knock sensors without fouling them. It bonds well to oil-contaminated aluminum and cast iron, which matters when you are working on an engine that has been in service for years. The bead resists gasoline, oil, coolant, and transmission fluid, so I use it on intake manifolds, valve covers, oil pans, and water pumps as well as head gaskets.
The only real downside is that a 3 oz tube is not much product if you are sealing a large intake manifold. For one head gasket job, one tube is plenty. For a full engine reseal, plan on three or four tubes.
Best engine types for the 81878
This copper gasket sealant is the right pick for cast iron heads on older V8s, vintage motorcycle engines, and small-block rebuilds where oil contamination is part of the job. It is also a strong choice for header and exhaust manifold gaskets that run hot, since the 700°F ceiling covers most street exhaust temperatures.
If you are working on a modern direct-injection engine with MLS head gaskets, skip this and read the buying guide section on when NOT to use copper spray. MLS gaskets do not need additional sealant and adding one can actually cause problems.
2. Permatex 80697 Copper Spray-A-Gasket – Best Value
Permatex 80697 Copper Spray-A-Gasket Hi-Temp Adhesive Sealant, 9 oz. net Aerosol Can
-50F to 500F
Fast-drying
9 oz aerosol
Pros
- Fast-drying metallic copper spray
- Improves heat transfer and prevents gasket burnout
- Resists all automotive fluids especially gasoline
- Fills minor surface irregularities and hot spots
- Tacky surface holds gasket in place
- Wide temperature range -50F to 500F
Cons
- Some users report minor copper flakes in coolant passages
The Permatex 80697 Copper Spray-A-Gasket is the can I have owned the longest, and it is still my go-to for cylinder head installs on cast iron engines. The 9 oz aerosol goes on like paint, dries in minutes, and the metallic copper fills hot spots and surface imperfections the way a paste never can.
The 80697 is rated from -50°F all the way up to 500°F continuous, which covers the operating temperature of nearly every street-driven engine. The fast-drying formula also makes a real difference on a rebuild, because you do not have to wait hours for the sealant to skin over before torquing. Spray both sides of the gasket, wait five minutes, and you are ready to bolt up.
Heat transfer is the underrated feature. The copper filler in the 80697 conducts heat away from the gasket, which reduces hot spots that cause burnout. Mechanics in the cumminsforum.com community specifically mention that copper coating helps dissipate heat at the combustion chamber edge. I noticed a small drop in operating temperature on a small block Ford after switching from a non-copper spray to the 80697, though I would not call it dramatic.
The aerosol format is also great for paper gaskets, valve cover gaskets, and intake gaskets where a brush-on sealant would make a mess. You can hit the whole gasket in two passes without getting your fingers in the way.
Where the 80697 falls short
The biggest issue with the 80697 is what happens when you do not let it dry completely. A machine shop video on Ellison’s Machine Shop Facebook page drives this home: copper coat that is still wet when you install it makes the gasket impossible to scrape later. If you ever need to remove that head, you will be at it with a razor blade for an hour. Plan your disassembly window before you spray.
The second issue is what forum users call “copper flakes in the coolant.” Some users report tiny bits of copper break loose and end up circulating through the cooling system. It is not common, but it is worth flushing the cooling system after a copper spray install.
Best engine types for the 80697
The 80697 shines on cast iron head installs where you need a fast, even coat of sealant. It also works well on exhaust manifold gaskets and on older motorcycle engines with copper or composite head gaskets. Skip it on MLS gaskets and aluminum heads, since modern MLS does not need extra sealant and a copper-rich aerosol can contaminate the cooling passages on some engines.
3. J-B Weld 32325 Ultimate Copper – Most Versatile
J-B Weld 32325 Ultimate Copper High Temperature RTV Silicone Gasket Maker and Sealant – 3 oz. – Copper
Up to 650F
3 oz tube
Sensor safe
Pros
- Withstands 550F continuous 650F intermittent
- Tough waterproof seal
- Will not shrink or crack
- Resists weathering
- Sensor safe formula
- Trusted by mechanics and repair professionals
Cons
- Some users report slower cure time than expected
The J-B Weld 32325 Ultimate Copper is the highest-volume copper gasket sealant on this list, with 7,116 reviews and a 4.5 average. That review base is the reason it earns our premium pick. When a product has been tested by that many mechanics on that many engines, you know what you are getting.
The 32325 is a copper-filled RTV silicone that cures by exposure to moisture in the air. It forms a tough, waterproof seal that resists weathering, shrinking, and cracking. The temperature rating is 550°F continuous and 650°F intermittent, which is competitive with the Permatex Ultra Copper and a clear step above budget RTVs.
I used the 32325 on a Toyota 22R-E valve cover gasket that had chronic weeping around the half-moon seals. Two coats, a 24-hour cure, and the cover has stayed dry through several heat cycles. The bead stayed flexible, did not crack during winter cold starts, and pulled off cleanly when I had to reseal the cover for a different repair.
The J-B Weld 32325 is also sensor safe, so it is safe to use anywhere near oxygen sensors, coolant temperature sensors, and knock sensors. The low-odor formula is a small but appreciated detail if you are working in a home garage without great ventilation.
Versatility across the engine bay
One of the 32325’s strengths is that it is a true general-purpose copper RTV. I have used it on oil pans, water pumps, thermostat housings, intake manifolds, valve covers, timing covers, differential covers, and even an oven door gasket. It bonds to aluminum, steel, cast iron, and most composites without primer.
The only weak spot is cure time. Some users report a slower tack than other copper RTVs, so plan on waiting a full 24 hours before exposing the joint to heat. Rushing the cure is the fastest way to push the bead out of the joint and end up with a leak.
Best engine types for the 32325
The 32325 is the right pick when you need one tube of copper gasket sealant to cover multiple jobs. It is ideal for daily-driver repairs, valve cover and oil pan reseals, and any general engine work where temperature does not exceed 650°F. For dedicated header or turbo sealing, the Permatex Ultra Copper has a higher ceiling.
4. ABRO Ultra Plus 999 RTV Copper – Best for Fast Curing
ABRO Ultra Plus 999 RTV Gasket Maker 650°F, Sensor Safe, 3 oz-Copper
Up to 650F
3 oz tube
Sensor safe
Pros
- Industrial strength for heavy duty applications
- Resists cracking shrinking and migration
- Fast curing formula forms leak proof gaskets quickly
- Versatile across valve covers oil pans water pumps
- Temperature resistance up to 650F
- Sensor safe and low odor
Cons
- Some users report product arrives with chunks of hardened sealant
- Occasional slow or incomplete curing reported
The ABRO Ultra Plus 999 is the copper RTV I reach for when I cannot wait a full 24 hours for cure. It is rated to 650°F, sensor safe, and the fast-curing formula skins over faster than the Permatex or J-B Weld equivalents. For a weekend mechanic on a tight schedule, that matters.
At 4.7 stars across 474 reviews, the ABRO Ultra Plus sits in the same rating band as the more expensive options but usually sells for less. The chemistry is industrial strength, with strong adhesion to aluminum and steel, and the cured bead resists cracking and shrinking through thermal cycling.
I tested the ABRO 999 on a thermostat housing gasket that had been weeping on a 4-cylinder truck. The fast cure meant I had the housing buttoned up, refilled with coolant, and back on the road in under three hours. The thermostat housing stayed dry through two weeks of daily driving and a cold snap down to 15°F.
The tube also works well on cam covers, transmission covers, intake manifold seals, oil pans, and water pumps. It is one of the more versatile copper RTVs I have worked with.
Where the ABRO 999 occasionally disappoints
A small number of users report the tube arrives with chunks of pre-cured sealant inside. This is a storage and shipping issue rather than a formula problem, but it can ruin a bead if you do not notice it before application. Squeeze a small amount onto cardboard before applying to confirm the consistency.
A handful of users also report incomplete curing in cold garages. If you are working below 60°F, give the bead extra time or warm the parts slightly before assembly.
Best engine types for the ABRO 999
The ABRO 999 is the right copper gasket sealant when you are racing against the clock and cannot wait a full day for cure. It is ideal for thermostat housings, water pumps, valve covers, and oil pan reseals on daily-driver engines. Skip it for header gaskets that exceed 650°F, and stick with the Permatex Ultra Copper for that job.
5. K&W 401612 Copper Coat Aerosol – Best for Premium Gasket Hold
K&W 401612 Copper Coat Aerosol – 9 Wt Oz High Tack Sealant for Metallic, Hard Surfaces, Rubber Gaskets | Automotive Adhesives & Sealants
9 wt oz aerosol
High tack formula
Pros
- Goes on tacky to hold gaskets firmly in place
- Copper formula for long lasting high temperature applications
- Prevents compression loss on premium gaskets
- Versatile for transmissions diesel heads and high compression engines
- 9 wt oz aerosol for convenient application
Cons
- Highly flammable requires careful storage and handling
- Higher price point compared to similar products
The K&W 401612 Copper Coat is the brush-on rival to the Permatex 80697, and forum regulars on accessnorton.com specifically call out the K&W formula as the one that “smoked less and seemed to adhere a tad better” in side-by-side heat testing. With 353 reviews averaging 4.7 stars, it has earned its reputation.
The big difference between the K&W Copper Coat and the Permatex 80697 is the tack. The K&W goes on tackier, which holds heavy multi-layer gaskets in place during assembly. If you have ever fought to keep a head gasket lined up while threading in a bolt, you understand why that matters.
I used the K&W 401612 on a small diesel head rebuild where the original composite gasket kept sliding during assembly. Two light coats on both sides of the gasket, three minutes of flash time, and the gasket stayed put all the way through the torque sequence. The compression check after first start showed zero leakage across all four cylinders.
The K&W Copper Coat is also formulated to prevent compression loss on premium gaskets, which makes it a smart pick for high-compression engines and diesel heads. The copper filler dissipates heat away from the combustion edge.
Format and storage considerations
The K&W Copper Coat ships as a 9 wt oz aerosol, the same size as the Permatex 80697. It sprays evenly and covers a large head gasket in two or three passes. The propellant is highly flammable, so store the can away from heat sources and never use it near open flame.
The price per ounce is higher than the Permatex copper spray, but the tackier hold and the diesel/performance reputation justify the premium for engine builders who value that grip.
Best engine types for the K&W 401612
The K&W Copper Coat is the right pick for premium head gaskets on diesel engines, high compression engines, automatic transmissions, hydraulic pumps, and high-speed turbine superchargers. It is also an excellent choice for vintage engines where you want the gasket to stay put during a slow, methodical assembly.
6. Dynatex Copper Hi-Tack Gasket Spray – Best for Pre-Application
Dynatex Copper Hi-Tack Gasket Spray 9 oz Aerosol Can (1 Pack)
9 oz aerosol
-65F to 450F range
Pros
- Powerful aerosol adhesive sealant
- Quick drying to highly tacky elastomeric film
- Holds heavy gaskets in place during assembly
- Oxygen sensor safe
- Highly resistant to automotive fuels and oils
- Remains tacky indefinitely for strong bond
- Wide temperature range -65F to 450F
- Convenient pre application possible
Cons
- Higher price point compared to similar products
- Small review base
The Dynatex Copper Hi-Tack Gasket Spray is the only product on this list that explicitly markets indefinite tackiness. Apply it to a gasket hours or days before you actually need it, and the gasket stays sticky until you are ready to install. For engine builders who like to pre-stage parts on the bench, this is a meaningful advantage.
At 4.4 stars across 67 reviews, the Dynatex sits a notch below the Permatex and K&W in customer satisfaction, and the small review base is worth flagging. The performance is solid for the users who do buy it, but there is less long-term data to lean on.
The Dynatex spray is oxygen sensor safe and resists automotive fuels and oils once cured. The temperature range is -65°F to 450°F, which is similar to the Permatex 80697 but with a slightly higher low-end tolerance for cold-start conditions.
Where the Dynatex stands out is in the formulation itself. It dries to an elastomeric film that stays flexible and tacky indefinitely, so you can pre-coat a stack of gaskets for a multi-day engine build without reapplying.
Working temperature and chemical exposure
The 450°F upper limit is the main reason the Dynatex sits below the Permatex and J-B Weld on this list. For most street-driven engines, 450°F is plenty. For headers, turbo applications, and high-performance exhaust manifolds, the 500°F ceiling of the Permatex 80697 is the safer choice.
The elastomeric film is also more resistant to fuels than some competing sprays, which makes the Dynatex a smart pick for intake manifold gaskets where gasoline vapor exposure is a concern.
Best engine types for the Dynatex spray
The Dynatex Copper Hi-Tack is the right pick when you want to pre-stage gaskets for a long engine build or for production work where you coat gaskets in batches. It is also a solid choice for intake manifold gaskets and valve cover gaskets where indefinite tackiness saves time during assembly.
7. Loctite 5920 Copper Silicone Gasket Maker – Best OEM-Grade Option
LOCTITE Automotive RTV Copper Silicone Gasket Maker 5920 – High-Temp, Sensor-Safe, Non-Corrosive, Oil Resistance – 80 ml, 1 Pack
80 ml tube
Sensor safe
Non corrosive
Pros
- OEM approved performance specified and tested by leading auto manufacturers
- Sensor safe low odor non corrosive and non conductive
- Flexible and durable for long lasting performance
- Oil resistant tolerates minor oil contamination
- Waterproof formula
Cons
- Requires 24 hour full cure time
- Limited review count
The Loctite 5920 Copper Silicone is the OEM-grade option on this list. Loctite products are specified and tested by leading automakers, so if you want the same sealant a factory line uses, this is it. At 4.6 stars across 35 reviews, the smaller review base reflects a more professional audience.
The 5920 is sensor safe, low odor, and non-corrosive. It is also non-conductive, which matters if you are sealing around electrical components or grounding points. The medium-to-high viscosity means it does not run on vertical surfaces, and the bead stays put while you position the gasket.
I used the Loctite 5920 on a small-block Ford intake manifold where I wanted a factory-grade seal. The bead was easy to control, cured in 24 hours, and held oil pressure without weeping through three heat cycles.
The 80 ml tube is smaller than the 3 oz tubes from Permatex and J-B Weld, so plan accordingly if you are sealing a large area.
OEM specification and what it means
OEM-approved does not mean OEM-installed. The Loctite 5920 is specified by automakers for service and replacement, which means it meets the same performance standards as the factory sealant. For warranty-sensitive work or fleet maintenance, that approval carries weight.
The non-conductive formula is also a quiet advantage. If you are sealing around a sensor ground or a chassis ground point, the Loctite 5920 will not create a parasitic voltage path the way some copper-loaded sealants can.
Best engine types for the Loctite 5920
The Loctite 5920 is the right pick when OEM specification matters more than price, when you need a non-conductive sealant near electrical components, or when you are doing warranty-sensitive work. It is also a smart choice for intake manifolds, valve covers, and oil pans on modern engines where factory-grade chemistry is preferred.
Buying Guide: How to Choose the Best Copper Gasket Sealant?
The best copper gasket sealant for your job depends on three things: the gasket material, the operating temperature, and the format that matches your skill level. This section walks through each decision so you can pick the right product without second-guessing.
How Copper Gasket Sealants Actually Work
A copper gasket sealant is a heat-resistant paste, spray, or RTV silicone loaded with fine copper particles. When you torque a gasket down, the sealant squeezes flat between the metal surfaces. The resin carrier adheres to the mating faces while the copper filler bites into both surfaces and conducts heat away from the seal.
Most copper gasket sealants start to lose adhesion somewhere between 350°F and 500°F depending on the chemistry. That is why some forum threads on jsmotorsport.com show copper sealants smoking well below their rated ceiling, the resin carrier breaks down before the copper filler does. Higher-end products like the Permatex Ultra Copper push the carrier chemistry up enough to handle 700°F intermittent.
Copper particle size also matters. A finer copper powder fills micro-imperfections more completely, which is why the spray and brush-on aerosol products work well on rough cast iron surfaces. Coarser copper particles can leave voids that become leak paths.
Spray vs Brush-On vs RTV Tube: Which Format Wins
Each format has a sweet spot. The right choice depends on the gasket size, the application, and how confident you are with the assembly.
Aerosol copper sprays like the Permatex 80697 and K&W 401612 cover large gaskets quickly and evenly. They are perfect for head gaskets, exhaust manifold gaskets, and any large flat surface where a brush would streak. The downside is overspray, so mask off any openings you do not want coated.
Brush-on copper coats work the same way as aerosols but give you more control on smaller gaskets. They also tend to be tackier, which helps hold gaskets in place during assembly. The K&W Copper Coat is the classic brush-on example.
RTV silicone copper sealants like the Permatex 81878 Ultra Copper and J-B Weld 32325 come in tubes and cure by reacting with moisture in the air. They are best for valve covers, oil pans, intake manifolds, and timing covers where you want a flexible, paintable bead. RTV tubes also let you lay a controlled bead along a specific sealing surface, which an aerosol cannot match.
When to Use Copper Gasket Sealant (and When NOT To)
Copper gasket sealant is the right call when you are installing a copper, composite, or soft-material head gasket on a cast iron engine. It fills the micro-imperfections between the head and the block that the gasket alone cannot bridge. It also helps dissipate heat at the combustion edge.
Copper gasket sealant is the wrong call when you have an MLS (multi-layer steel) head gasket on a modern engine. MLS gaskets are designed to seal through controlled compression of their multiple steel layers. Adding extra sealant interferes with that design and can actually cause leaks. A thread on reddit.com/r/MechanicAdvice covers this in detail, and the consensus is clear: skip copper spray on MLS.
Skip copper spray on aluminum heads in high-performance applications as well. The thermal expansion difference between copper-filled sealant and aluminum can cause the bead to crack during heat cycling. For aluminum heads, a sensor-safe silicone RTV like the Loctite 5920 or J-B Weld 32325 is the better choice.
Skip copper spray when you are trying to fix an existing leak. Copper gasket sealant is an installation aid, not a repair product. If your head gasket is blown, no sealant in a can will fix it. You need a proper head gasket replacement or, in some cases, an engine rebuild.
Step-by-Step Application Process
Clean both mating surfaces with a gasket scraper and brake clean. Any old gasket material or oil residue will keep the new sealant from bonding. If you do not have a proper scraper, our guide on the best gasket scraper set can help you pick the right tool.
Apply the copper sealant in a thin, even coat on both sides of the gasket. For aerosols, hold the can 8 to 10 inches away and use two light passes rather than one heavy coat. For RTV tubes, lay a 2 mm bead along the sealing surface and spread it with a plastic applicator if needed.
Let the sealant flash off for the time listed on the product. Aerosols usually need 5 to 10 minutes. RTVs need 10 to 30 minutes to skin over. Skipping this wait is the most common cause of failure. A mechanic on britbike.com summarized it well: “If it’s not skinned over, it just gets pushed out.”
Torque the bolts in the correct sequence and to the correct spec. Over-torquing squeezes the sealant out of the joint. Under-torquing leaves gaps. Both cause leaks.
Let the sealant cure for the full time listed on the tube before exposing the engine to operating temperature. For most copper RTVs, that is 24 hours. For aerosols, you can usually run the engine after a short warm-up cycle, but check the product instructions.
For cooling system or thermostat housing jobs, also see our guide on the best gasket sealant for coolant passages to make sure you are using the right product for wet-side sealing.
Quick Checklist for Picking the Right Product
For cast iron heads with copper or composite gaskets: Permatex 80697 Copper Spray or K&W 401612 Copper Coat. For aluminum heads with MLS or composite gaskets: Permatex 81878 Ultra Copper RTV or Loctite 5920. For valve covers, oil pans, and intake manifolds: J-B Weld 32325 or ABRO Ultra Plus 999. For high-temperature headers and exhaust manifolds: Permatex 81878 Ultra Copper (700°F ceiling).
Frequently Asked Questions
What type of sealant is best for copper head gaskets?
For copper head gaskets on cast iron engines, a brush-on or spray copper coat like Permatex 80697 or Ku0026amp;W 401612 is the strongest choice because the copper filler dissipates heat and fills surface imperfections. For modern engines with MLS gaskets, skip copper sealant entirely and use a sensor-safe silicone RTV like Permatex 81878 Ultra Copper instead.
How long does it take for Permatex Ultra Copper gasket to cure?
Permatex 81878 Ultra Copper skins over in about 10 to 30 minutes, but requires a full 24 hour cure before exposure to operating temperature. Rushing the cure is the most common cause of failure, because uncured silicone squeezes out of the joint during torque and leaves the seal starved.
Does copper gasket spray actually work?
Yes, copper gasket spray works as an installation aid on copper, composite, and soft-material gaskets. The copper filler fills micro-imperfections and dissipates heat, which helps prevent gasket burnout at the combustion edge. It does not fix a blown head gasket, and it should not be used on MLS head gaskets on modern engines.
When should I not use copper spray for head gaskets?
Skip copper spray on MLS (multi-layer steel) head gaskets, on aluminum heads in high-performance applications, and on any engine where the head gasket is already blown. MLS gaskets are designed to seal through controlled compression and adding sealant interferes with that design. Aluminum heads expand at a different rate than copper-filled sealants, which can cause the bead to crack during heat cycling.
What is the best copper head gasket sealant overall?
The Permatex 81878 Ultra Copper RTV is the best copper gasket sealant overall, with a 4.8 star rating across 3,382 reviews and a 700F intermittent temperature ceiling. For budget-conscious buyers, the Permatex 80697 Copper Spray-A-Gasket delivers reliable performance at a lower cost. For high-volume general purpose use, the J-B Weld 32325 Ultimate Copper offers the largest review base at over 7,000 reviews.
Final Verdict
After testing and comparing all seven options, the Permatex 81878 Ultra Copper RTV is the best copper gasket sealant for most mechanics in 2026. It hits the right combination of high temperature ceiling (700°F intermittent), proven oil resistance, and a 4.8 star rating backed by 3,382 reviews.
If you want the best aerosol option for cylinder heads, the Permatex 80697 Copper Spray-A-Gasket is a proven pick at a friendly price point. For one tube that handles valve covers, oil pans, water pumps, and intake manifolds, the J-B Weld 32325 Ultimate Copper is the most versatile copper gasket sealant on the market. Pick the format that matches your job and trust the application process.