The Fuel tank is always the size of all the MXC your miner ever mined. So as the M2 Pro continues to mine MXC tokens, your Fuel tank itself is also growing in size. Which means that if you remove 500 MXC tokens from a fuel tank that is 500 MXC in total size, your Fuel score will drop from 100% to 0% (which means a 80% drop in mining performance).
However, as the M2 Pro continues to mine MXC tokens over the months, and accumulates (for example) 99,500 more MXC tokens, you will now have a Fuel tank that is 100,000 MXC in total size, and which is currently filled with 99,500 MXC tokens. This will mean your Fuel score will have grown to 99.5% (i.e. 99,500 / 100,000). Which would have minimal affect on your mining performance. But as you can see, you will never return to a true 100% (until you replace the removed MXC) --but you will get pretty close.
Another way to refill your Fuel score (even to 100%) is to purchase MXC from an exchange. MXC is listed on many exchanges including gate.io, Kucoin and crypto.com.
So the general rules of thumb when it comes to MXC and Fuel are:
- You're free to remove your MXC whenever you want, and
- Be aware that doing so will impact mining performance by up to 80%.