What Thermal Paste Should You Use on a Hub Motor Heat Sink?

The short answer: use the thermal paste that comes with every HubSink (it is also sold separately), put it on the HubSink piece and the outside of the magnet ring (never inside the motor), clean the surface first with something that leaves no oil, and heat cycle the motor on the first rides so the paste seats. Here is why each of those matters, and the mistakes that quietly cost you cooling.

What thermal paste does on a hub motor heat sink

A metal fin pressed against a metal magnet ring looks like a perfect contact. Under magnification it is not. Both surfaces have microscopic hills and valleys, and the valleys fill with air, which is a poor conductor of heat. Thermal paste fills those valleys with a material that conducts heat far better than air, so heat can pass from the motor shell into the fin and out to the airflow.

Without paste the fins still help, but a lot of the heat has to cross an air filled joint. With paste the joint stops being the bottleneck. That is the whole reason it is part of the installation.

Where the paste goes (and where it does not)

• On the HubSink pieces and the outside of the magnet ring: spread evenly across each of the six pieces. The install guide says to use the entire 5G tube evenly across the pieces.
• Not inside the motor: thermal paste does not go inside the motor. Inside the motor you want Statorade ferrofluid, which bridges the air gap between stator and shell.

How to apply it, step by step

1. Clean the magnet ring. Clean the outer surface of all dirt and oil before applying paste. Do not use petroleum based cleaners (WD40 and many automotive degreasers). Their oil is engineered not to evaporate, fills the microscopic valleys and significantly reduces how well any paste works afterwards.
2. Do not touch it after cleaning. Oils from your fingers can stop the paste filler from contacting the metal. Fingerprints can be as thick as 0.005 inches, which is enough to matter.
3. Test fit first. Check the pieces around the hub with the included nuts and bolts before any paste goes on.
4. Coat the piece, then fit it. Apply paste to the HubSink piece, push it down between the spokes and give it a slight twist so the paste coats the whole joint.
5. Work around the hub. Leave the fixings slightly loose to an equal amount, then go around a few times, taking out half the gap each time, until every piece is tight and even.
6. Heat cycle it. Turn the amps up and ride so the hub gets as hot as possible on the first few rides. Tighten again and repeat. The paste seats and the alloy pulls tight to the hub.

The full process, including the QS273 beta notes, is in the HubSink installation guide.

Common thermal paste mistakes on hub motors

• Cleaning with WD40 or a degreaser that leaves an oily film.
• Handling the cleaned ring with bare fingers.
• Skimping on paste so some pieces have dry patches. Use the whole tube across all six pieces.
• Putting paste inside the motor. It belongs outside.
• Skipping the hot rides and the second tighten. The first heat cycles are part of the installation, not an optional extra.
• Expecting paste alone to cool the motor. Paste only helps the shell to fin joint. The other bottleneck, stator to shell, needs Statorade.

What other riders try

On the Endless Sphere HubSink thread, riders mention a few variations. One suggested a 2mm silicone thermal pad as a substitute for paste on a smaller diameter motor where the fit was loose, and another suggested paste between every layer when adding an aluminium shim under the fins. These are rider ideas rather than our recommendation, and the standard install with paste is what the guarantee and the testing are based on. See the thread.

Paste, Statorade and fins: how they fit together

Heat has to travel from the windings to the shell, then from the shell to the air. Statorade fixes the first step and HubSink fixes the second, and thermal paste is what makes the second step work properly. In Grin Technologies testing on a Cromotor, HubSinks improved shell to air cooling by 50 to 60%, and added up to 20% more total heat flow on top of Statorade (Grin results). Read more in why ebike hub motors overheat and the cooling methods compared.

Find your motor

Cooling guides by motor: QS205, MXUS, Leaf, 9C, Crystalyte, Cromotor and QS273. Compare Statorade, HubSink and vented covers.

Thermal paste FAQ

Can I use any thermal paste on a hub motor heat sink?

The job of the paste is to fill the microscopic gaps between the fin and the magnet ring so heat can cross the joint. A tube of thermal paste comes with every HubSink and is also sold separately if you need more. The install guide says to spread it evenly across all six pieces using the whole 5G tube. If you use something else, choose a proper thermal compound that stays in place and does not dry out or run at motor temperatures.

Does thermal paste go inside the hub motor?

No. The paste goes on the HubSink piece and the outside of the magnet ring. It does not go inside the motor. The thing that goes inside the motor is Statorade ferrofluid.

What should I clean the magnet ring with before applying paste?

Use a cleaner that leaves no oil. Do not use petroleum based cleaners such as WD40 or many automotive degreasers. Their oil is made not to evaporate, fills the microscopic valleys in the metal and reduces how well the paste works.

Why does my motor get hot on the first rides after fitting HubSinks?

That is deliberate. The install guide says to get the hub as hot as possible on the first few rides so the paste seats properly, then tighten again and repeat for a few rides. Performance increases as the paste fills the gaps and the alloy pulls tight against the hub.

Is thermal paste the same as Statorade?

No. Thermal paste joins the HubSink fins to the outside of the motor shell. Statorade is a ferrofluid that goes inside the motor and helps heat move from the stator to the shell. They fix different bottlenecks, which is why they work best together.

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