Think of a resume as something like a fish eye lens - you want the most detail in recent work and relevant technology to achieve the ambitions of your next position. Avoid detail that either is in the far distant past, or isn't relevant.
I mention this since it sounds like your resume is getting full - if this is your only job in your industry, you may want to keep the detail and cut something else that isn't relevant to working in your industry first.
Over time, it matters less whether it was full time or part time and more what the position was - generally, prior to graduation, students are treated as "co-ops" or "interns" and most people I know couldn't clearly delinate a difference. When someone graduates they generally get a title reflecting the more permanent role (Software engineer, vs. Software engineering intern).
Using the metaphor of a fisheye lens, I'd handle it this way...
Less than 5 years from the start of the internship
Date of start of 1st coop - Present, promoted to , company name
After 2 internships and some part-time work while finishing formal education, I was promoted to . Work included the following projects... and highlight any big differences between the coop work and the full time permanent work.
1996-2001, Intern promoted to Member of the Technical Staff, GTE
Assignments included the Labs, Corporate Headquarters, and CyberTrust Systems
Originally hired for a summer internship, I was invited to a full time elite recruitment program and eventually placed into a full time role as a software engineer. Work assignments included internship work on static help pages, and dynamic front ends in web applications, assignments in performance analysis, demonstration lab administration, and software developmet, and final placement doing full lifecycle software engineering on a certificate authority in C, C++, and SQL.
At one point, 8 or so years into my career, I mashed up 3 different companies into one time span, because all three were in the same building, on the same basic technology, with the same people, and my goal was continuity. So there's really no one way to render some of this.
When you're within 5 years of the work, and within 5 years of graduation, prospective employers are trying to figure out what work you did as an intern vs. what work you did as a full time permanent employee. The supervision level and scope of responsibility tend to increase greatly after graduation, so resume reviewers will likely try to make sense of it.
More than 5 years ...
Reduce the description much more. Stick with dates and the most interesting parts of the work, and the final position held at that company.
Date of start of 1st coop - Present (or date of departure from final position), , company name
2-3 sentences on the major contributions and technologies used. Highlight technologies that are relevant to what positions you are now applying to.
Example (same position as before):
1996-2002, Member of the Technical Staff, GTE
Highlights included performance analysis on the GTE backbone, and diverse Cybertrust PKI products. Key technologies used: C/C++, SQL, UNIX, Oracle, X509, OCSP
If I'm in a position where I'm selling myself to manage SW development of another identity management solution, I may go into more detail on that part of the work, or if I'm doing something related to data analytics, I may beef up the performance analysis work description to be more hitword compliant with what position I'm looking for. After 5 years in the field, I'm not too concerned with the descrepancy between start date and graduation date, since what I've done in the 5 years SINCE graduation is much more important.