How to lubricate a treadmill belt

When to check

When the manual’s service interval comes round. Many makers give it in hours of use or months.
When the belt feels different underfoot, or the machine shows a lubrication reminder.
After moving the treadmill, or after a long period unused.

Treadmill oil of the type your manual specifies. GlideX Treadmill Oil comes in 30, 60, 100 and 200 ml bottles with a nozzle-tip cap.
A clean, dry, lint-free cloth.
The manual.

Switch off and unplug. Never work on a treadmill that is plugged in.
Check the belt and deck. Wipe away dust and old residue from the belt edges and the visible deck with a dry cloth.
Lift the belt. Raise one side of the belt edge to reach the deck underneath. Some machines need the belt loosened first; the manual explains how.
Apply along the deck. Place the oil in a line along the deck under the belt, near the centre. Use the amount your manual gives. Repeat on the other side.
Spread it. Plug back in and walk slowly for a few minutes so the belt spreads the oil across the deck.
Wipe off any excess from the belt edges and the floor.

Too much oil. More is not better. Excess can run off the deck and gather dirt.
The wrong product. Use the lubricant type your treadmill maker specifies.
Oiling the top of the belt. The oil goes between the belt and the deck, never on the running surface.
Skipping the manual. Intervals and amounts differ between machines.