I'm sure the opinions go in both directions but lets hear them.

I recently picked up a 1987 GTA as a weekend driver/project/toy. It has the 5.7 TPI and the Odo shows 120K miles but honestly I think the engine has been pulled out and overhauled. This engine just runs way to smooth to have 120K miles on it.......

......but...I am not sure of that. So should I do an engine oil flush? I have heard of it being bad on really old engines as it removes gunk that might have been keeping oil from leaking on a bad seal.

When I check the oil on the dip stick I do see some tiny grains of particulate. Nothing solid, it disintegrates when I rub it between my fingers. I think it might be carbon.
The oil however seems very clean and when I look into the valve cover through the oil fill it looks fairly clean in that I don't see sludge.

So......oil flush before I change the oil or just change the oil and leave it alone?

 

I bought a 91 Formula with 150k on the 305...
I've used the Gunk Engine Flush (gray plastic bottle) a number of times during oil changes and no ill effects that I'm aware of...
New injectors made it run smoother too

 

If it runs good then don't bother. Run a quality synthetic with proper levels of zinc and let the synthetic do the slow cleanup of varnishes, etc.

Engine flush is a last ditch effort to get an engine that's been severely neglected to behave (lifter noise problems, etc). If your engine runs fine then you only risk knocking a bunch of crud loose all at once and causing a problem where there wasn't one before.

Remember the golden rule - if it's not broken don't fix it.

My 86 LB9 runs awesome with just plain synthetic. I have only fixed those items which were broken - leaking seals, stretched timing chain, and bad valve stem seals. Otherwise just leave it alone. The slow flush that is a natural result of proper frequent fluid maintenance is much less drastic and less likely to result in some kind of clogging of passages or filters.

GD

 

In addition to what GD said,

Marvel Mystery Oil - Sludge build-up in newer and older engines can result in lower performance and life expectancy. Marvel will prevent sludge build-up from occurring in new engines and removes sludge from older engines. In newer engines, Marvel protects against scoring or seizing and creates a highly polished, wear resistant finish on engine surfaces. Your new engine will remain clean and your older engine will thank you for cleaning the insides.

 

MMO is pretty decent stuff - used by the military in WWII. I have had as good or better results from the Amsoil engine flush or Rislone also.

Generally talking about sticky lifters here. There's not many other reasons people generally add this stuff to the crankcase. Although I did get a variable valve timing system working again for a customer with a Chevy Colorado 4 cylinder that was disgusting inside.

GD

 

Great info thanks.....and yes I am one that likes to follow the golden rule...."if it ain't broke don't fix it" so thank you for reminding me of that. And no, the engine has no lifter noise even after the engine has not run for days.

As for oils....I usually use Royal Purple in all my vehicles. My daily driver is a 2008 Escalade EXT which I also use to pull my boat (short distances) and travel trailer and the travel trailer is typically really long hauls and the 6.2 LS in the Caddy runs like a dream.

So I'll go ahead and leave the GTA alone and do the oil and filter change as normal. I actually already have the Royal Purple oil and filter ready to go. Just wanted to put out some feelers on the flush thing first.