Use of MoS2 in a rotary engine. 2

[dalcazar]

Hi guys, sorry to bring up an oil additive topic on here, however I've had very little luck getting coherent answers to the question as to whether or not it's safe to use Liqui (Lubro) Moly's MoS2 additive in a wankel engine, specifically on my rx8. I aim to decrease wear, especially on the apex seals, as well as all the engine internals.

I haven't found anyone who has been willing to try this product on wankel yet, if I do so, I might be the first person to try it who has posted any information on the web about doing so.

First off, I contacted liqui-moly themselves in germany and got an email back from them quickly stating that it would be fine to use in a wankel. A query on the main rx8 forum for the internet got cautious responses of "try at your own risk" which is valid. The specific reasoning being that it could either:

a) cause the oil metering pump to fail by filling it with heavy metals.
b) cause the CAT to fail.

My main problem with any of these opinions is that they are merely speculation on behalf of people who may or may not know what they are talking about. I have confirmed directly with liqui-moly that the product is entirely compatible with CATs and will not damage them in any way, however the possibility of either the oil metering pump or the oil injection ports in some way clogging are a valid concern that I can't dismiss out of hand even though I would lean away from it being a problem of any kind.

So I ask you experts, is there anything to substantiate the calls for caution? The MoS2 product is a colloidal suspension with an average particle size of 0.3 microns?

Would the use of the MoS2 product be considered worthwhile in wankel engines?

 

[patprimmer]

While the average particle size is interesting, of more interest would be the largest particle size and say the average particle size of the biggest 0.1% of particles.

What is the pore size of your oil filter. Does it have a bypass.

What is the size of your oil injector port nozzles.

What does Mazda recommend.

Is engine wear normally a cause of premature failure or do the wear surfaces normally outlast other parts or normally outlast the car.

Regards
Pat
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[evelrod]

To my knowledge moly is no longer in general use as an IC engine oil additive...too many problems with clogged filters and, in some cases, oil passages (particularly in the cylinder heads of small block 260/289 Ford in my personal experience).
I have a neighbor that has an RX8 that is well over 100k miles and, aside several trips to the dealer for a variety of failures over the years, doesn't smoke or anything visible to me. He has all his maintenance done at a dealership.
Pick a dealer recommended lubricant or one of the top synthetics and perform the recommended service at the appropriate intervals and you won't need any additives.

Pat, do you remember the graphite additives?

Rod

 

[MikeHalloran]

The last place I used Molykote was on a distributor advance pivot pin in a Ford distributor, way back when Fords had distributors. It's not super-high pressure or super-high rubbing speed, but it does move a lot, and I found that the Moly acted as an abrasive, and made the hole bigger and the timing less stable.

I have as a result come to regard Molykote and related products as excellent solutions, for something that has to not move for extended periods of time, and then just has to work, once, or for a very limited number of cycles.

Given the multiple millions of USD that Mazda put into apex seal development before coming up with a solution that worked, and widespread reports that it does work, I'd be reluctant to try to homebrew an improvement on the official Mazda parts and lubricants.





Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Mike said-
"I found that the Moly acted as an abrasive...."

From time to time I have heard that MoS2 behaves as an abrasive at high temps or in the presence of moisture.


This 1953 NACA paper seems to have been able to make Moly powder misbehave when lubricating steel.
"For the case of lubrication by unbended MoS2 powder,wear increased as humidity was increased."

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930083561_1993083561.pdf

Note incresed friction is not necessarily the same as increased wear.

Other on line sources suggest that MoS2 oxidizes to MoS3 when temps exceed 400 C, but most also say MoS3 is not particularly abrasive by itself.

 

[patprimmer]

Rod

I never used moly or graphite as engine oil additives and stopped using them as gear box oil additives probably 40 years ago.

I always use a good synthetic engine oil and don't change it as often as I should.

I use molly grease as an assembly lube on flat tappet cam lobes and as a lube when specified to torque down nuts on studs. I never use it elsewhere, especially where heat is involved. I used it once to my regret to try to increase the life on the front wheel bearings on a car that had a front wheel bearing life problem. It failed very quickly due to heat from the disc brakes.

I only use graphite where I need non sticky dry lube, like on brake callipers where the disc pads bear and slide.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[evelrod]

I agree. I've stopped using moly based grease for anything. Now use Mobil 1 synthetic (the red stuff) for wheel bearings and 'whatever'. I use a cam assembly lube from Isky and a 'custom blend' engine assembly lube. I still use the ARP lube on all my engine's studs/bolts etc. But that' it.

My dad used an engine oil that contained 'moly' and graphite in the 60's in a 260 Fairlane...that's the one I refer too. I've never used anything but Castrol, Mobil 1 or, Red Line for the last 50 years

Rod

 

[izzmus]

Speaking as someone who does not have to worry about catalyst life, a half-ounce of decent two-stroke oil per gallon of fuel will go a long way towards seal life. Power, too. In an engine that did not have the metering pump, I noted power gains at up to 3 ounces per gallon of fuel, at which point I stopped testing.

I'm not entirely sure that a half ounce per gallon would affect catalyst life all that much. Assuming 20mpg, that is a quart of oil burnt per 1280 miles, not unreasonable.

 

[drwebb]

Nowadays there are a number of oil soluble molybdenum derivitives that are commonly used in engine oils. I happen to have the IOM's 2009 survey of North American motor oils open and looks to me like about 133 of 250 oils surveyed have 10-300 ppm molybdenum in them- so you may in fact already be using a soluble moly-fortified oil. What concentration of Mo will this product impart to your oil, and what is the benefit of having it in sub-micron solid form rather than soluble form?

Much like ZDDP, moly-based antiwear additives function primarily in the boundary lubrication regime, such as protecting sliding cam/tappet interfaces. Isn't one of the advantages of the Wankel engine a paucity of these energy-sapping high-wear interfaces? What benefit would be expected from loading up on anti-wear in an engine that's already milder in this respect than mainstream oils are designed for?

BTW, there is a lubrication engineering forum, although pretty dusty at the moment.

 

[dgallup]

Nice find drwebb. I always thought IOM was the Isle of Man.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[swall]

Arco Graphite is the graphite containing motor oil from the '60's that I remember. I never used it -- always found the black color somewhat disconcerting.

 

[evelrod]

The reason I mentioned the Arco Graphite oil was because my dad used it in his '64 260 Fairlane engine and after he died I inherited the little Ford. When I got it home and pulled the heads because of obvious oiling problems, I found the entire oiling system was almost totally clogged. I'm not talking ~100 micron filters here, more like 0.25" oil galleries....... Hardening of the arteries, automotive style.

I don't use MoS₂ any longer (even though I still have some on the shelf) and only use powdered graphite on door locks and such sometimes with a silicone spray for the latches.

@ drweb, I asked my Red Line rep and he said no moly. In your survey does it list Castrol 20W-50 as having any? That's the only non synthetic oil I use any longer.

Rod

 

[drwebb]

I don't believe any API oils contain MoS2. There's more sophisticated chemistry available now that is better able to achieve any benefits without complications of settling.

 

[pwildfire]

I think you are worried about the wrong things. The concern with using alternative oils in a Mazda rotary engine is not with damaging the metering oil pump, it is that many synthetic or modified base oils are not designed to be combusted and therefore produce harmful deposits when burned. Typically this causes carbon/sludge buildup on the rotors which eventually causes the apex seals or side seals to stick into their slots, producing low compression. I would venture to guess that at least 20% of 'blown' rotary engines suffer from this issue and have no physical internal damage at all.

The company that makes the oil should be able to give you a report on the combustion byproducts that will show if there is an unusual amount of ash created. If not it is likely OK to use.

Another possibility to consider is that if you want to use the oil but are concerned about it, you can eliminate the MOP system and premix your fuel with TCW3 two-cycle oil, which is formulated for combustion and therefore produces a reliability advantage even over the stock system.

I personally run a hybrid system on my cars where I have modified the metering oil pump to pump 2-cycle oil from a dedicated container. This is the best of both worlds, as you are burning the right oil, but don't have to worry about mixing or forgetting to mix, and also are burning the appropriate quantity whereas premixing adds too much oil at low engine speeds.