I looked up the MSDS on one those flush products one time.. it was mostly stoddard solvent. in other words,high quality mineral spirits or paint thinner ..which by the way also seems to be the main ingredient in wd-40 , along with some 'light' oil. Ever since, I've just used a pint of mineral spirits, or kerosene , when I wanted to flush an engine. I do keep some wd-40, or similar product, around, just because the spray can is handy ..... If the engine is very badly gunked up, disassembly is the only way to get it clean. If the rings are just 'mildly' stuck, pouring some some solvent in the plug holes and letting it soak several days will sometimes unstick them. Kroton oil is the best I've ever used for this, but can't seem to get it anymore. Heard it had a carcinogen in it. Marvel mystery oil seems to have the right combination of oil and solvent to cling to parts long enough to do some good. I'm sure there are other brands out there as good. None will fix a serious mechanical problem. The oil additives that 'stop smoke' seem primarily to boost the viscosity.....running heavier weight oil will accomplish the same thing. I once put 70wt aircraft oil in a 6 cy ford engine with bad rings to see what would happen....it quit smoking , noticably at least, and the oil pressure went up some .....but it obviously isn't a fix. My experience with 'seal softener's is that they are a waste of money. If seals are that old and dried up, they probably are covered in a nice layer of gunk that will prevent anything you add to the crancase from having much effect on them. well, I've ranted enough on this topic ...:)
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