Depends.
If you know why it stopped, and you've fixed the problem, and know it's not likely to happen again, then no need for a pan call.
If you don't know what the problem was, you managed to start it again, and have no idea if it will continue to run, then yes a pan, or even a mayday would be appropriate.
Engines fail for a reason. If you don't know what the reason was then you probably haven't fixed it, and you have little reason to think that it will continue to run after the restart.
Don't be worried about blocking the frequency. It won't be blocked for long. Once the controller knows about your plight, they can continue to use the frequency as normal if they feel that's appropriate. If they don't feel that's appropriate they can swap to another dedicated frequency. In case, blocking the frequency should be the least of your concerns at the time.
dp