thanks for the input Richard, on this last oil change im now using quaker state high mileage FS 5w-30, and i do have some SEA FOAM i was thinking about adding to the fuel tank, but haven't got that far yet.
I wouldn't expect immediate results. Most oil detergents do the work of softening the deposits while the car is parked after the car has run long enough to get to normal operating temperature, and then remove them during the first few minutes to half an hour the next time it's started. It really doesn't do very much good while the engine is running after the first half-hour or so. It needs time to soak.
My Soul's oil burning started suddenly enough that I thought something might be mechanically broken, but a quick dip of the borescope revealed that it was just carbon deposits around the rings. I was about ready to do a piston soak (it would be relatively easy on the 1.6) or paying the dealership to do one (which would have been even easier), but I decided to give the high-mileage oil a try first.
Most people associate seal reconditioning with high-mileage oils, but most of them also have enhanced detergent packages on the assumption that older engines have more carbon buildup. I was skeptical, but the first oil change with the high-mileage oil did show some small improvement. The second showed much more improvement, with roughly a pint lost compared to almost a quart before the switch. This one looks like it will lose even less than that.
In the past, I would use an oil with both C and S ratings (generally Rotella or Delvac) to clean engines, especially if I bought a used car with a questionable maintenance history. Gads, did I dislodge a lot of gunk. I had to keep those OCI's short for fear of clogging the filters. Old, poorly-maintained engines can hold ponderous amounts of sludge and gunk.
I'm the original owner of my Soul, however, so I decided not to go that drastic route. Most oils with both C and S ratings barely qualify for the S in terms of ZDDP content (which can shorten the life of the CAT). They're also more prone to foaming in high-revving engines. So it's not something I actually liked doing.
Thing is, I've always strongly preferred using decent oil and not adding anything to it, to using an additive whose compatibility with the oil manufacturer's additives is unknown. Because the additive packages are proprietary, there's no way for me to know exactly what I'm mixing. Given the choice, I'd rather use the Delvac or Rotella than an additive whose contents are a trade secret. But I'd rather use neither if I can avoid it.
So far, the high-mileage, API SP / ILSAC GF-6 Castrol Edge seems to be doing the job gently, but consistently. I think it was the right choice.
One thing maybe I should have done was shorten the OCI's for this experiment. It's entirely possible that the detergents offgas relatively quickly. But the label claims a 10,000 drain interval, so I decided to just stay with my nominal 3,750-mile OCI.
As for the GDI, that really has more to do with the valves than the rings; but an induction system cleaning for the valves will have some incidental benefit for the rings if the soak time is long enough. But so will a fuel system cleaner with a respectable amount of PEA. In fact, I think the combustion chamber and ring cleaning probably is more of a benefit than the fuel system cleaning per se
unless the car is showing signs of an actual problem in the fuel-delivery system.
I presently use Gumout Regane High-Mileage Fuel System cleaner around the same time as every oil change unless I use it in between, which I do when I have no choice other than to buy non-TOP TIER gas because of where I happen to be. I carry a bottle of the Gumout around and add it to that tank of gas. That's pretty rare, though, now that Sunoco finally got TOP TIER certified.