In some cases you may see crawls never end, such as when you upgrade Sharepoint to a later version. In such cases you want to check the health of the search service application.
Checking the health of your search server service application
- Open SharePoint 2010 Central Administration.
- Click Manage service applications.
- Click Search Service Application.
- Scroll down the page to see the applications components. Identify if they are in an Online status.
- If you see any failed components, check the Search Server logs for exceptions.
%ProgramFiles%\Common Files\Microsoft Shared\Web Server Extensions\14\LOGS