1990s Engine oil

[Coral58]

I've got a 93 Sixty Special,about 80,000 miles. I've been using semi synthetic oil the past two oil changes, over 8 years,  just a fair weather car,some shows or tours.
 Should I stay with the same type of oil or go to full synthetic, would it tend to leak more?
Still has factory gaskets.

Ivan

[TJ Hopland]

I have never had the impression that one leaks any more than the other.  If you got a leaker its gonna leak either way.  I liked the blends for a while because they got me the range or grade I wanted and they seemed like a good value but now the prices seem to have got a lot closer so I'm usually just going full syn.   

[David Greenburg]

Oil questions seem to be like a a number of other topics these days where everyone has an opinion, theirs  is the only one that's right, and the rest of us are fools. There's a lot of disinformation and misinformation out there put out by people or companies with an agenda. That said, I think the idea that synthetic oil will cause leaks in older engines has been disproven. The most definitive discussion of oil for older cars that I have come across is a discussion by Richard Widman. While it focuses on his experience with Corvairs, the information is useful for any older car, and importantly, warns that there is a danger of "too much of a good thing" when it comes to additive levels like zinc and phosphorus. 

https://www.widman.biz/uploads/Corvair_oil.pdf

[TJ Hopland]

It seems like many of the 'bad' things about synthetic like leaks and not mixing it came from its early days in the 1970's.  I guess those first few generations of synthetics were quite different than what we have to work with in the last 20 or so years.   

[Jeff Rosansky CLC #28373]

My understanding is that it is better at cleaning the insides than the old oils and that one of the reasons for leaks is that little openings are plugged up with crap, synthetic cleans the crap, and exposes a leak path that is already there.
For that reason, if you go full synthetic, I would do your 1st oil change sooner rather than later because it may break crap loose inside the engine.
But, as stated above, that may just be an old wives tale and may be untrue.

[TJ Hopland]

The detergent packages have improved over the years in all the oil unless you are seeking out a non detergent oil so if you put any modern oil in something that is crusty its going to do some cleaning.  That is one reason I don't use any sort of flushing additive in the oil of a new to be engine, you don't want to break it all up all at one time.

I would not extend my change interval because I was going with a blend or full synthetic unless you were to do an oil analysis and the analysis said it was still good to go.  For the typical person its not worth the extra time and expense to do the analysis vs just changing it likely early.  If you were running a fleet racking up a bunch of miles daily then the analysis is worth it to find that perfect balance between wear and frequency of changes plus they can tell if an engine is starting to wear based on finding engine bits in the oil.