It's not uncommon for an engine to go undetected during a seizure. In fact, it happens more often than you might think. Here are some tips on how to seize an undetected engine:
1. Check the oil level first. If the oil level is low, it could be the cause of the seizure.
2. Next, check for any external leaks. If there are any, they need to be fixed before proceeding further.
3. Once you've ruled out those two potential causes, it's time to take a look at the spark plugs. If they're fouled or damaged, that could be the cause of the seizure.
4. Finally, if all else fails, you may need to remove the head and inspect the pistons and cylinder walls for damage.