When is the best time to check the oil level for my car. When the engine has been running for a while? When it is cold? I checked it after it had been sitting all night and was told that was wrong.
Leave it to settle for half an hour after it has been running - when you've been for a drive - this gives the oil in the engine block time to drain back down into the sump to give you the true level. If you do it when cold, the volume is affected by temperature so it may appear lower than it really shoud.
Let the engine run for a while making sure the car is on level ground switch off, leave for 10 mins to let oil drain back to the sump remove dip stick wipe clean and re-insert dip stick and check level.
Well, officially the best time is to check the oil is before you start the engine. This would prevent serious damage if for whatever reason your car had lost oil. Then follow above guide! :)