why - not 15W-40 oil for DD two strokes?

[bevans6]

That one I like.  Thanks for indulging my quest.  The DD has a lot of gear driven accessories, which promote shear, and the piston head cooling, which I understood  better yesterday when reading the DD manual, will be a key oxidizer of the oil and is quite different in thermal load than a four stroke.  Two solid differences that will indeed affect oil life and performance.

Thanks again,

Brian

[luvrbus]

Oil cools the 71 series piston head on the 92 series they are cooled by water and they don't have any more gear driven accessories than any other engine depends on the how the buyer ordered the engine.
Might be a good lesson for the guys running 60 series to stop the bull gear failures in those engines to use 40w fwiw


good luck

[bevans6]

by "accessories" I meant that the cams, all the pumps, the blower, the compressor, sometimes the alternator are all gear driven.  That's actually a lot of gears!

When I was running race Mini's  we changed the oil every two to three hours of operation.  The transmission shared the same oil as the engine and after three hours we could easily see a reduction in oil pressure.  The gears sheared the oil...


Brian

[TomC]

Brian-big difference in gear shear with full engine power going through the gear case of the Mini, compared to the 2 strokers where the air compressor takes about 5hp when running, 20hp to the blower, 300amp 12v alternator will max out at 6hp, and power steering pump 5hp continuous.  So that adds up to 36hp total on the rear gear train-plus running the camshafts (don't know the power consumption of that)-maybe another 20hp, so less then 60hp on the rear gear drive train-even with all the gear driven accessories.  Good Luck, TomC

[bevans6]

I continued to think about this after this thread died it's natural death, and posted on a forum for professional automotive engineers.  I got this reply, and it has the ring of truth about it.  it's important to note that sulfated ash components are largely a byproduct of detergent and other additives - so low sulfated ash content is another way of saying low additive packages including detergents - which are good in a four stroke, and not good for our two strokes.  Interesting that he says the issue is related to the piston ring area, not so much the valves.

anyway, here it is:

Romke:

the reason was fourfold.

first the fact that the original multigrade oils did not have very stable viscosity index improvers - they broke down quite fast from the original SAE 20W-40 to SAE 10W-30, resulting in lower wear protection than anticipated. Nowadays that problem has completely been overcome.   

The second reason was temporary shear, as already mentioned. That problem has also largely been overcome.

A third reason was that the use of viscosity index improvers in DD engines tended to give more deposits in the piston ring area. Nowadays it would be possible to use better quality base oils that require less viscosity index improver so that problem can be solved.

Finally the fourth reason was that conventional diesel engine oil contained quite a amount of metallic additives that also contributed to deposits in the ring belt area of DD two stroke engines.

DD therefore required a singlegrade engine oil with a restriction on the sulphated ash content. That requirement i reflected in the API CF-2 classification

It all boils down to the fact that DD engines have a different "oil appetite" then fourstroke engines.

That is also reflected in the contruction details of the engines: cast iron pistons are used because aluminium based pistons where not able to withstand the local heat induced stresses.   

[Busted Knuckle]

I continued to think about this after this thread died it's natural death, and posted on a forum for professional automotive engineers.  I got this reply, and it has the ring of truth about it.  it's important to note that sulfated ash components are largely a byproduct of detergent and other additives - so low sulfated ash content is another way of saying low additive packages including detergents - which are good in a four stroke, and not good for our two strokes.  Interesting that he says the issue is related to the piston ring area, not so much the valves.

anyway, here it is:

Romke:

the reason was fourfold.

first the fact that the original multigrade oils did not have very stable viscosity index improvers - they broke down quite fast from the original SAE 20W-40 to SAE 10W-30, resulting in lower wear protection than anticipated. Nowadays that problem has completely been overcome.  

The second reason was temporary shear, as already mentioned. That problem has also largely been overcome.

A third reason was that the use of viscosity index improvers in DD engines tended to give more deposits in the piston ring area. Nowadays it would be possible to use better quality base oils that require less viscosity index improver so that problem can be solved.

Finally the fourth reason was that conventional diesel engine oil contained quite a amount of metallic additives that also contributed to deposits in the ring belt area of DD two stroke engines.

DD therefore required a singlegrade engine oil with a restriction on the sulphated ash content. That requirement i reflected in the API CF-2 classification

It all boils down to the fact that DD engines have a different "oil appetite" then fourstroke engines.

That is also reflected in the contruction details of the engines: cast iron pistons are used because aluminium based pistons where not able to withstand the local heat induced stresses.  

Brian this is one of the most important reasons according to a old DD expert who taught  (tried too teach me anyway!) me a lot a long time ago! I wasn't a great student on the listening part and don't recall all the details. But one of the reasons he gave was that the multi oils aren't/weren't able to keep up with keeping the pistons cooled and led to piston failures quite often!
Now bear in mind I have no actual documentation of this, but the man that told me that has forgotten more about 2 stroke DD's than I or most of us will ever hope to know!
FWIW  BK  

[junkman42]

My youngest son just got back from Iraq for the 3rd time in 6 years!  He is a motor pool NCO and told Me that the US Army uses nothing but multi grade oil in all of their diesels!  The hemet which is a very large multipurpose wrecker has a 8V92 which is run on multigrade oil and JP8 for fuel in the hottest and most engine wrecking enviroment one can imagine!  These wreckers are run day and night at what My son refers to as boot down!  Funny enough his opinion is that the old detroit is a no problem engine and it and the electronic allison never has a problem.  His opinion of the cats and cummins and the inline detroits they use is not positive.  Interesting how a young diesel person favours the old over the new.  His thoughts are based on real hands on experience and not hear say.  So multi grade will not work.  Would be interesting to see if research would reveal what the military has to say about the multigrade oil debate in regards to 2 stroke diesels.  Regards john

[Busted Knuckle]

John,
Interesting and relieving to hear!
But keep in mind that the Military is known for rebuilding and replacing componets long before they wear out or break in most instances! (not saying all the time!)
So their engines & equipment aren't worn out like most average bus we as busnuts use.
  BK 

[luvrbus]

John, Cole would love that about the Army guys and the 2 strokes he is a believer in the young guys and laughs when people say all the 2 strokes guys gone.
The Army guys and girls can rebuild the engines in the dark so I was told.
FWIW I know several on this board that use 15/40 and have for years in their 92 series and never get into this oil debate it works for them I guess.  

good luck

[robertglines1]

I checked with my oil supplier and he said that shell oil's book said straight 40 with the other specks. The price difference is about 30%more than 10W40. About $30.  I think I will play it safe for that..

[bevans6]

Here is what the military thinks, for those who are interested.  MIL-PRF-2104H


http://www.wbdg.org/ccb/FEDMIL/prf2104h.pdf

Two stroke (92 series) starts around page 8.  It's way over my head, mostly   

[Len Silva]

My military days were more than 40 years ago, but I bet things haven't changed that much.

Motor pool boss: "That engine doesn't sound quite right, order me a new one".

"OK Sarge, it'll be here next Tuesday".

No different than ordering a box of spark plugs.

[junkman42]

Len, the comments I made were provided as information for thought only.  Any engine failure causes a report to be generated and can result in someone having to pay for the damage!  I also entered the service in 1959 and did not find the rampant waste that You did.  Your average militarty  NCO in this day and age posses a college education.  The fact remains that the US ARMY is running the 8V92 series engines in the dammed desert with multi-grade oil and with no problems.  Just food for thought and nothing more.  Need any cheese with that whine?  Regards John

[TomC]

I've heard that the military doesn't run their engines more then 2,000hrs before overhaul (that's like 80-100,000 miles).  Any engine should last that long even with 2 strokes using 15w-40.  It has been proven over and over again that to get maximum engine life out a 2 stroke-I mean getting close to a half million miles out of it, you have to use a single viscosity 40 weight oil.  What the government does with their deep pockets is really of no concern of us considering we all have to pay for overhauling the engines straight out of our pockets.  Personally-I'll stick with my Delo 100 sae40 weight.  Good Luck, TomC