Should you use anti-seize on exhaust manifold bolts?
One question that is frequently debated by automotive technicians is, “do you put anti-seize on exhaust manifold bolts before putting them back into the engine head?”
We’re going to break down the pros and cons of using compounds and grease like anti-seize on your bolts and studs between repairs or maintenance.
The first thing to understand, is that there are numerous products on the market,each having a special use and application. For example, automotive formulas may contain aluminum, copper and graphite which are combined with grease. These formulas work great in high temperatures with copper and graphite combined with a high-quality grease, for example, on hot engine fasteners and bolts.
However, it is important to note that these additives will react harshly with moisture and wreak havoc – so avoid using them on marine engines at all costs! There are marine formulas of anti-seize that will have a rubber-cement type viscosity which are crafted to prevent the corrosive effects of water and metal interaction. These marine-based formulas unfortunately do not have a high heat tolerance, so in areas such as exhaust manifold studs or turbocharger mounts, they would be very ineffective.
Another factor to consider is the temperature the exhaust manifold is exposed to.
On average, an exhaust manifold on gas and diesel engines will reach temperatures as high as 800 - 900 degrees under a medium load. The exhaust can reach 1,000 - 1,200 degrees under a heavy load and even higher on integrated turbochargers and at high throttle. Different formulas are engineered to withstand different temperature levels. Some anti-seize formulas will simply evaporate once the exhaust reaches these peak temperatures.
Which type of anti-seize should I use?
• Silver Grade Anti-seize: Fortified with graphite and metallic flake. Inert and will not evaporate or harden in extreme cold or heat. Can withstand temperatures up to 1600°F.
• Copper-based anti-seize: Fortified with copper and graphite in a grease. Can withstand temperatures up to 1800°F.
• Nickel Anti-seize: Copper-free. Recommended for stainless steel and other metals. Can withstand temperatures up to 2400°F.
Our Two Cents:
Utilizing the correct compound can be an excellent way to prevent seizing, galling and corrosion in areas that are regularly exposed to high temperatures. They are rust and corrosion inhibitor which can give you the upper hand the next time you remove your exhaust manifold. Just consider the application. If you are reusing exhaust manifold bolts (which we don’t recommend), apply a metal fortified anti-seize to your manifold bolts. If you’ve just removed the broken bolts and ready to complete the repair, chase the threads clean and use fresh OEM bolts for best results. Although there’s no real need for applying anti-seize, it can rarely hurt as these types of repairs are often done several times throughout the life of the vehicle and with a lucky draw of the card, you might just be the one to do it again.