Moly in Oil

[PCT1981]

On another forum these statements are being made. Any truth to them? I do not remember hearing any of this.
"I use there gear oil,good stuff and haven't had any problems.I wouldn't recomend using the engine oil since it has a high moly content which is bad for our tighter tolerance engines".
"I quit using their motor oil when i read about the moly. Performed just fine but moly builds up after years of use and I didn't want to take the chance".
"Moly is a processed mineral that is similar in appearance to graphite. Moly has good lubricating properties when used either by itself (in dry power form or as an additive to oil or other lubricants). Particles of the Moly can come out of suspension and agglomerate. Over time this may actually clog or partially clog oil filters or oil lines and the remainder normally settles in the bottom of the oil pan. This seems to be more likely when using extended drain intervals".

 

[bruce381]

moly disulfide 'solid" yes true
Moly dithiocarbamte "soluble" no not true
bruce

 

[JHZR2]

lol... sounds like someone spouting off hearsay and half-truths...

JMH

 

[mechtech2]

I wish the moly would build up after years of use.
That could be great!
But automotive engine oil type moly does not do this.

 

[jpr]

Here's something I've been puzzling over -
From a sample of 61 VOA's found here, there seems be about three broad categories of moly content -
* oils have basically no moly
* oils have moly content in the range of 174 to 54 ppm
* oils that have a huge moly content of about 600 to 800 ppm -

The only oils in the last category are Redline oils and the Motul 300V 5W-40. The 300V is Motul's "race" oil and unlike many of their other products does not carry any API or ACEA rating. Similarly, none of the Redline oils have API or ACEA approvals.

To what extent, if any, do you think the high moly content is related to the lack of API or ACEA certifcation?

 

[ChiTDI]

Originally Posted By: mechtech2
I wish the moly would build up after years of use.
That could be great!
But automotive engine oil type moly does not do this.


Yeah that would be terrific. Permanent ball bearings on moving parts.

There used to be a good explanation of molybdenum on the home page of BITOG, don't know if it's still there.

 

[JAG]

Moly in whatever form contributes to sulfated ash which is capped by most oil specs. Other additives like detergents and ZDDP also contribute toward sulfated ash so the formulator has to balance the additives that have different functions. If they load up on ZDDP and detergents (like CI-4+ HDEOs), there is that much less moly they can put in the oil.

If the oil doesn't have chemical limits imposed on it, the formulator could blend 800 ppm moly, 3000 ppm calcium, and 1500 ppm zinc. I do wonder what the sulfated ash content of current Redline motor oils is. It has to be relatively high.

As an aside, a big reason some oils use magnesium detergents in place of calcium is that the former contributes less sulfated ash per TBN number. They are trying to stay under the capped value on sulfated ash.

 

[jpr]

I guess the appropiate follow-up question is what's the consequences of an elevated sulfated ash content?

If I understand correctly, lower sulfated ash levels are beneficial to reducing engine deposits and particulate emissions. On the other hand, higher sulfated ash content offers an increase in TBN.

So pumping up the moly and disregarding the API/ACEA sulfated ash limits would seem more sensible for a race engine where emissions are not really a concern and the engine is likely tore down frequently, making deposits a non-issue as well.

Is that about right?

 

[JAG]

That's about right IMO but the deposits matter must be defined. Oils with higher sulfated ash will produce more ash-like particles when burned, as happens in the combustion chamber. They tend to adhere to piston tops, valve heads, piston ring packs, spark plugs, and of course also go flying out with the exhaust stream. But many of the additives that contribute to this ash also contribute to overall engine cleanliness so the ash-deposit relationship is a complex one. Also, ash layers can only get so thick on many part surfaces before they reach a near steady-state condition since they get eroded off when thick enough. My opinion is that a high ash oil may build up ash deposits more quickly but I can't believe that the steady state amount of ash on parts is directly proportional to the oil's sulfated ash content.

An interesting thing is that some engine's need high ash oils to cushion the valve seats which is what leaded gas used to do.

One last thing interesting thing is that detergents (contributor to sulfated ash) have been found to help decrease the poisoning of cat. converters caused by phosphorus in ZDDP. Diesel particulate filters are another matter...ash plugs them up.

 

[jpr]

Originally Posted By: JAG
An interesting thing is that some engine's need high ash oils to cushion the valve seats which is what leaded gas used to do.
That would be the flat tappets on the older Porsche and VW engines correct and why the guys over the Pelican forum get so steamed up about the API SM oils?

Other than that though, I would think the general idea would be that less ash buildup is better than more. The complex part then is choosing the right balance of trade-offs.

I did see one article about low-SAPs oils that attributed at least some of their good performance in extended use to the fact that the lower detergency levels were offset by the lower sulfated levels reducing the need.