I've experienced really long delays getting a good reading. Last time I changed mine, I put 6 1/2 quarts in, so I knew it should be good. After warming it up, it only read half full. I resisted adding more because I knew 6 1/2 should be enough. I checked it everyday and after 3 days of it reading half, I was getting ready to top it up, but didn't. On day 4 I checked it and it reads full and still does 3K miles later.