I am having a site with education niche. My site is getting around 3000 uv per day from google... if i add content from other niche like "health" or "mobile", do it will affect my site ranking ???
It depend upon site structure.. If you are adding extra pages then it will not affect your previous ranking..
i have planned to do something like starting a separate blog in my site... this won't affect others... but it is completely unrelated to education niche... so i got feared...
If you are concerned, then why don't you use its subdomain .. it will be treated as diff. site for Search engine.
It will make your site irrelevant to eduction niche since your new posts will stay on the homepage for a while and on the sitemap till they are deleted.
For my personal experience yes, but then if you can get some reputable backlinks all back to normal, but it was my personal experience...