Article from BusRide on why 2-strokes use single-grade oil.

[Barn Owl]

This is from the March '07 issue of BusRide.

http://www.busride.com/Page.cfm/PageID/8607

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A surprise find in the world of tribology    Christopher W. Ferrone

After many years of premature engine failures my frustrations turned to further investigation. For more than 25 years beginning with the Detroit Diesel (DDC) 92 series in 1981, I have researched ways to use quality lubricants and creative methods and intervals to extend the life of engine components.

In 1995, I joined forces with Detroit Diesel to assist with a failure modes and effects study using my empirical fleet data on Series 92 engines. That project lead to a technical paper, single source part number (23514770) repair kit, and a national ad campaign to assist operators with the care and feeding of their Series 92 engines.

As a result of emissions compliance the newer engines are 4-stroke cycle unlike the 2-stroke cycle of the 71 and 92 series. Other than the fact one is a 2-stroke and the other a 4-stroke, from a purely mechanical standpoint, these two engine types are similar in function and lubrication intervals.

Since the crank journal is constantly under load as compared to the 4-stroke engines, the 2-stroke engines require a single-grade oil with a higher viscosity. The boundary lubrication never has a chance to recover for 2-stroke engines.

In 4-stroke engines, the boundary lubrication does have a chance to recover during the non-loading turn of the crankshaft, which allows the use of multi-viscosity oils.

The use of single viscosity oil in 4- stroke engines can actually extend the life cycle with really no downside.

As our fleet became a mix of 2-stroke and 4-stroke engines, I was concerned with the accidental introduction of multi-viscosity oil into a 2-stroke engine, which, of course, would have led to a catastrophic failure. With this in mind, I called Detroit Diesel to discuss the use of single grade oil in a 4-stroke Series 60 engine. Told this would not be a problem, we began to replace engine oil in the Series 60 with single viscosity oil. Thanks to indoor parking, we can use XHD 40 weight oil in both the summer and winter. Where starting the engine in cold weather is a concern, simply use XHD 30 during the winter months. For fleets that still incorporate 2-stroke engines, this will not be an issue because they use a heavier single-grade oil anyway.

With any one cylinder/piston and main bearing journal, the 2-stroke journal is under load with every turn of the crankshaft. In a 4-stoke engine, the journal is under load every other turn.

A 2-stroke engine only uses single viscosity 30- or 40-weight engine oil. Oils for 4-stroke engines are generally multi-viscosity 15W-40. In some instances, the engine is acceptable to synthetic oils, which are outstanding for a number of reasons, but are very high priced compared to traditional engine oils.

Having used this oil in DDC Series 60, Cummins 5.9L and PowerStroke 4-cycle engines for more than 10 years, the engines have never experienced a lubrication failure or shown any negative effects. In fact, the PowerStroke engine currently has 483,000 original miles all to the credit of single grade oil — well beyond its projected life cycle of 250,000 miles. The Cummins 5.9Ls also have lasted well beyond the expected life cycle. My original Series 60 test engine has 375,000 city miles, in addition to thousands of idle hours, which equates to almost 1.2 million highway miles. I attribute the additional success of these engines and their extended life cycle to the use of single grade (XHD 40) motor oil.

Single grade oils are much less expensive than the synthetic oils recommended for 4-stroke engines. It is worth mentioning that in addition to extended engine life, specifically crankshafts and bearings, the peripherals such as turbochargers, air compressors and gear trains also benefit from the single grade oils. There is no need to keep two types of oils in the shop and run the risk of a mechanic accidentally pouring a multi-viscosity oil into a 2-stroke engine.

Though this has been an ongoing process in our operations for more than 10 years with the utmost success and simplicity, it is still advisable to contact the engine dealer to confirm single grade oils are acceptable before making the switch. 

People may think I am crazy, but I use XHD 40 motor oil in all of my automatic transmissions and power steering as well.

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Comments?

[H3Jim]

great article, and it sheds some light on why the 2 strokes do better with single grade oil. 

[Hi yo silver]

Thanks, L, for a very good article!

[gus]

This is my kind of expert. He has actually done what he writes about, very refreshing after so much of the bull that is published. And, he has finally explained why 2 strokers us single grade oil. I think I have read ten thousand words on this subject and not one has explained the "Why?".

Three cheers for Christopher W. Ferrone!!