Here's my case study: 2007 Toyota 4Runner 1GR-FE V6, bought used in 2017 with 162K miles and poor maintenance with OCIs at 20-30K miles by the original owner. Main timing chain was worn and elongated causing P0016 bank 1 camshaft timing correlation error. I bought it cheap as a project assuming the engine would need replacement, ended up just replacing the timing components at 182K miles after a year of long highway work commutes and short OCIs with various synthetics including Rotella T6, Valvoline High Mileage, Pennzoil Platinum HM, QSUD, and M1 0W40. Occasionally added MMO toward the end of a few OCIs as a flush. When I pulled the bank 1 valve cover to check timing manually back in 2017, there wasn't significant sludge accumulation other than small clumps on bolt caps and other non-washed areas...just varnish everywhere.
Since the timing chain replacement 89K miles and 4 years ago, I've been running 5K mile OCIs with various high mileage synthetics (and a few runs of Valvoline MaxLife blend) and flushing the oil pan every other oil change, put the passenger side on ramps which places the drain plug low and dipstick high as shown in the pics. Placing a paper towel across the drain pan prior to pushing flush oil down the dipstick tube shows sludge flakes every time, the dirty paper towel pic attached is the pan wash at oil change just prior to this fill at 269K miles. This is what I've been seeing each time for the past 4 years...not sure if I'm pushing a channel through a bed of sludge on the pan floor, or it's old sludge breaking loose and washing into the pan.
The engine runs fine, but uses ~0.5 quart of oil by 5K miles and I suspect oil control rings may be stuck and/or piston drain holes clogged. Goal of the experiment is to see if the oil consumption can be mitigated by reducing sludge.
I bought 2 quarts of HPL Engine Cleaner, and added it to the Valvoline High Mileage Synthetic 10W30 at 270,118 miles at the prescribed ratio. Just drained it at 270,686 miles (568 miles on the additive, 1732 miles on the oil) and the pics tell the story. The oil had gone from light amber on the dipstick when the EC was added, to dark brown. The Fram XG3614 filter cut pics show just a few specks of solids (I usually see much more sludge particles in filter cuts), and the usual gray outlines of the FilterMag bars.
I collected a sample to send to Blackstone & will post results. Also poured the drained oil+EC through a coffee filter as shown in the pic after washing with isopropyl alcohol, just to see what else came out (drain pan was cleaned prior to drain). This took hours to finish one small pour into the funnel + filter at a time.
Observations:
1) During the EC run, I had two instances of startup clatter for ~1 second after the first 100 miles or so, then no further issue for the remainder of the 568 mile run. Heard this previously with defective oil filter ADBVs, but this XG3614 filter had been quiet for the first ~1200 miles prior to the EC. Possibly a lump of sludge broke loose inside the cylinder head passages and caused #2 timing chain tensioner(s) to bleed down, or a VVT actuator lock pin to temporarily malfunction. No further noise for the remaining ~300 miles.
2) This is the least amount of sludge I've seen in the oil filter can. The coffee filter from the drainage is remarkably clean with just a few flecks of sludge, I'll get another pic after the alcohol evaporates. EC seems to have dissolved much more sludge than HM synthetics, driving it into solution as the oil got really black really soon in the OCI.
3) I want to avoid/minimize timing chain pin & bushing wear due to the dissolved abrasive particles, so I shortened the run and sacrificed the oil + EC earlier than the 2K mile goal. Still have another 1qt bottle of EC, plus the remaining ~1/3 of the first bottle, so there will be another EC run in the future.