Should the engine be cold or warm when I check the oil?

The important thing here is that you do actually check you oil regularly. It’s a basic home maintenance chore, but one that too many car owners ignore.

That said, it doesn’t really matter whether you check the oil hot or cold, as long as you do it the same way each time. That’s because cold oil will contract a little, while hot oil will, thanks to thermal expansion, appear as though the level is a little higher. All engines use a little oil, so what you’re checking for is any change in the engine’s drinking habits that could indicate engine wear starting to show up. That’s why it’s best to check it the same way every time.

You’re also right in suggesting that the oil takes a little while to make its way back into the engine’s sump when the engine stops. Checking it straight after a drive means it won’t have all returned to the sump and you’ll get a low reading on the dipstick. So, leaving it for a few minutes is the way to do it. Also, you shouldn’t trust a dipstick reading when the engine has been run but not reached full operating temperature. Cold, thick oil won’t drain back into the sump completely and, again, you might have a low reading on the stick.