If you've blocked your car out for your own use, it will show as 'available' for that time period when you are logged in. This is because it is available to you. If any other member is logged in and viewing your car's profile, they will see it as unavailable.
If you would like to confirm that your blockout was successful, go to your car's dashboard and check the calendar there, rather than on its public profile page. You should see your booking/blockout in your car's calendar.
You can also try logging out of your account and viewing your car's public profile page. If your blockout was successful it will show as unavailable to a logged out user.