Used a can of sea foam today. Nasty stuff, don't drink it. I pour it into the intake to clean injectors. I wouldn't hesitate pouring a can in the crankcase. I've also used straight kerosene. Did no harm.
My test is to get a heavily deposited engine part (oil filler cap, dipstick, drain plug) and dip it into the snake oil in question. Kerosene doesn't do much. Sea foam works quicker than MMO.
I have a number of well used, low cost, low tech vehicles. One thing I do to keep the lower end shiny is occasionally run a quart of transmission fluid along with the balance of crankcase oil. (I read your post, I do it anyway) No trailering or heavy loads, just an hour of easy highway speeds. Disperses the gunk and grit. Then do a regular oil change. This is regular procedure, so if you've got serious rattles, try the following.
If the trooper is really grungy (or if you're not the original owner) remove the oil pan and clean it out. Look at (remove?) the oil pump pickup and clean out any screens. A clogged intake screen can starve the pump and top end of oil, leading to death rattle. Be sure to have a new pan gasket on hand, and gently clean the mating surfaces. (I like Brake Cleaner, but it gets $$$)
ALSO, my Rover is really finicky when it comes to filters. It hates the popular orange filters, but runs great on with a Wix. Some motors develop different pressures.
Speaking of pressures, check and clean all the breathers, vents and valves (e.g. Positive Crankcase Ventilation valve).
Finally, in the Grey cold north, I go to a thinner oil in the winter (5W-30). I've also heard that synthetics are easier to pump.
User a good filter (try a Mobil-One, and don't feel bad about running through two changes [8000 miles]) Clean your sump and intake (after running the snake oil) and let's hear what happens.
