What tense to use when writing a thesis?
The answer to this question varies across disciplines. Your dissertation presumably falls within some academic discipline. Look at other papers in the same discipline, and see what tenses they use. For example, unlike your suggestion, in math papers the abstract is usually present tense. 

If some of the premier journals in your discipline have a style guide, look at these style guides and see what they say. 

The journal Nature, in which the majority of articles are in the  sciences, has the following suggestions for verb tense (I've left out a few of their examples):


  Past tense 
  
  Work done  
  
  
  We collected blood samples from . . .
  Consequently, astronomers decided to rename . . .
  
  
  Work reported 
  
  
  Jankowsky reported a similar growth rate . . .
  In 2009, Chu published an alternative method to . . .
  
  
  Observations  
  
  
  The mice in Group A developed, on average, twice as much . . .
  The conversion rate was close to 95% . . .
  
  
  Present tense     
  
  General truths  
  
  
  Microbes in the human gut have a profound influence on . . .  
  The Reynolds number provides a measure of . . .
  
  
  Atemporal facts  
  
  
  This paper presents the results of . . .
  Section 3.1 explains the difference between . . .
  Behbood's 1969 paper provides a framework for . . .
  
  
  Future tense 
  
  Perspectives 
  
  
  In a follow-up experiment, we will study the role of . . .  
  The influence of temperature will be the object of future research . . .