Doing an engineering thesis, and I have presented a detailed summary of my data in the abstract. Is it ok for me to copy/paste entire paragraphs of my abstract to my conclusion without changing a word?
Yes, of course. There are no issues with this at all. Self plagiarism only occurs when you don't cite your own words from other publications. Within a single document there is no problem. The reason that we self-cite is to let readers easily find the original source. But that doesn't apply here.
OTOH, make sure that it doesn't read "awkwardly" when you do this. It is just a style consideration, though.
I'm assuming that your abstract is actually part of the thesis, say a preamble.
However, if the abstract is to be published separately from the thesis, you should cite the thesis in the abstract. But you would do that in any case.