It comes with miraculous claims. No one seems to really know, but I read here somewhere by someone in the oil industry saying they investigated it, and it did not work well in an engine. In a gearbox, that might be something different. I tried using some once, and I am sure it gummed up the oil filter. Probably it is o.k. if you have a cheap paper filter, but with a PureOne filter, the pores are so tiny that I am sure they got gummed up. I still have the filter, but I haven't opened it up to inspect for the MoS2 paste. That is why I don't use it in an engine anymore.
Yellow metals meaning the softer metals. Tin, Copper, etc. Poor choice of words I guess, I've seen moly and yellow metals mentioned somewhere IIRC, I just can't find it. Love that search engine. Also would it be good or bad for bearings? Oil companies such as RL use a lot of it, others use little or none. The new ultra fine moly should easily pass through a filter without getting trapped or clogging it up.
So is Molybdenum Disulfide really harmful to yellow metals in an engine?
I'm not sure how many brass parts are in an engine. Maybe some bushings? There are brass parts in manual transmissions. The corrosion issues that are potentially caused by moly may be related to high heat.* Those high temperatures are usually not seen in street-driven cars.
*Maybe someone can confirm that GL-5 fluids contain moly, which is the ingredient that can cause issues in transmissions calling for GL-4 fluid. I am not sure about this!
I've read that, heat isn't really an issue with automotive applications. Then I read just the opposite, and it was supposed to be bad for yellow metals. I chatted with someone from a company that sells it (naturally he would be bias), but he said it was no problem as long as the UF grade is used. I wonder if it can stay suspended, or if it settles out? Then comes the confusion!
Why not just buy an engine oil with moly already blended into the formula? That way you can be assured that it will not leach or corrode yellow metals. An example would be Schaeffers #703:
FYI, many bearings are made of bronze which is also a "yellow" metal due to it's brass content (aprox. 70%).
Of the various bronze alloys, not all are considered yellow metal. There is such a thing as "white bronze" (copper/tin/zinc alloy). Neither is all brass considered yellow metal. To say bronze contains brass is not correct. Both, bronze and brass are copper alloys. With copper being the main component. Bronze is an alloy containing copper, tin, possibly lead, and often phosphorus or manganese (to harden the alloy). Brass is an alloy of copper and zinc, but may contain other metals, for example lead or bismuth. How corrosion resistant brass and bronze are depends on the exact composition of the alloy.
IIRC tin and zinc are white metals. I had forgotten about copper in babbitt, although aluminum is quickly replacing it for that application so not all engines will have copper in the bearings.
back on target, anyone got a source stating moly. d. is harmful to the materials used in an engine?
The terminology "yellow metal" and "white metal" is somewhat arbitrary and also depending on the context in which those terms are used. For example, if I buy casting metal, "yellow metal" metal refers to any brass or bronze alloy that is literally of yellow color due to its composition. Normal casting bronze, is not a "yellow metal."
The term "white metal," in the context of casting metals, refers very specifically to alloys of tin that may contain bismuth, antimony, tin, lead, cadmium, and zinc. Another term used for "white metal" is "pot metal" or low-melt alloy," which is a common base metal in jewelry and tool production.
Terms may be used differently by people depending on the field in which they work. There is no reason to believe that a term like "yellow metal," which is commonly used by artists and craftsmen is used in the same manner by a metallurgist dealing with alloys created for industrial applications.
What's my point? Terms like "yellow metal" are very vague. A modern, sintered bronze bearing is not composed of the same components that make up a 4,000 year old bronze axe blade. One "yellow metal" alloy may well resist corrosion much better compared to another. For example, bronze holds up very well to saltwater, common brass (There is actually "naval brass") not so much.
I made an inquiry to a company that sells it, and they state it is harmless to an engine. They went on to say some of it might settle out of suspension but quickly goes back into suspension as soon as the engine is started up again. They also stated their ultra fine MoS2 will not get trapped by the oil filter since the average particle size is small enough to simply pass through the filter.
They supply product to oil companies for blending, but couldn't provide anymore information due to agreements they have with the oil companies. They said you can add 1 teaspoon - 1 tablespoon to a 5 qt sump, (thoroughly mixing it into oil first). I have no idea how many ppm that would be. It interested me, and could be worth further investigation, although I'm not sure where I'm headed it with it.
The top post in this thread shows my used-oil test results in 2006 and 2007. The 7th column shows Mobil Delvac 5w40 with a 300 ml can of Lubro-Moly MoS2 added.
Tin did rise from 0 to 7 ppm, but this was well within safe levels. Other wear metals -- iron, copper, and aluminum -- were reduced.
Based one what I considered satisfactory results, I used the LM MoS2 later on, but only 150 ml per fill, which is about 4.5 quarts/liters. I do not have any more test results, however. I no longer have a local source, and haven't ordered any online. I still recommend it.