I've only noticed this within the last 3 oil changes I've done or so. I'll drain the oil, put a new filter on, end up putting somewhere around 4.5 qts to fill it to the full line on the dipstick after starting it to fill the filter and circulate the oil around. Then a few days later, the oil level will be a good ways overfull, maybe like .25 qt or so. I just checked it the other day, and it was over. I checked it today, and it's just a hair over the full line. This has happened a few times to me, but I can't seem to find a good reason for it. The first time it happened I was sure I had a leaking injector that would dump some gas into the oil while off, but I pulled the rail with injectors, put a few pieces of paper under the injector tips, and kept fuel pressure on the injectors the whole day I was at at work, and not a drop leaked out of them. It's kind of irritating, considering at one point I drained the excess oil, restarted and got it to the full mark, only to find the oil was overfull in two days. It doesn't smell like gas like a leaking injector would, but my level mysteriously fluctuates. Do the oil molecules go have a party up in the head when I change the oil and drop down to the pan before I check it or what!? BTW, I'm a professional auto mechanic with about 7 years of experience in the field, so I know I'm doing the drain/fill procedure right. But this is boggling my mind...?

EDIT: BTW, it's a 97 GSR with stock internals save for a pair of CTR cams and boltons. No oil cooler, and no other mods to the motor that would cause different oil capacity...

 

what weight oil are you using?