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My use of single weight engine oil: A follow up

By Christopher W. Ferrone

Photo 1: A sample of the removed main bearings makes a case for single multi-viscosity engine oil.

In an earlier column [BUSRide, March 2007, Safety and Maintenance; A surprise find in the world of tribology] I discussed our use of single weight engine oil I use in four-stroke cycle engines, specifically the DDC S-60 motors. This column is in response to the comments BUSRide readers posted to that article.

Most of the comments were from “bus hobbyist” with little or no experience with DDC engines. Comments ranged from “Who cares?” to an “urban myth diagnosis.”

The express purpose of that article was to bring to the attention of professional motorcoach operators that despite Detroit Diesel Corporation (DDC) recommending 15W-40 wt (multi-viscosity) engine oil in the S-60 engine, we use 40wt (XHD) oil with no problems at all. I called DDC and asked if that would create warranty issues, and they stated it would not. Now 14 years later and five million accumulated (collective) miles, I am happy to report that the project was successful — and I can now show BUSRide readers the direct proof.
Here is my reason for using the 40wt (XHD) oil in the Series 60 engines — as well as my Cummins and Ford PowerStroke engines. In 1997 my entire fleet featured DDC Series 92 and 71 engines, for which Detroit Diesel mandated the use of single weight engine oil to prevent catastrophic failures. My fear was we could make a catastrophic mistake of our own during maintenance by adding the wrong oil to a particular engine. To simplify this, and to eliminate the risk, I decided to go with single weight oil across the entire fleet regardless of the engine type or its manufacturer.

Photo 2: The connecting rod bearings are largely undamaged and show very little wear relative to their mileage and age.

Yes, I was aware, and still am, that 40wt oil may have start-ability issues in the cold. But hold on. I live in Chicago, the city that claims to have invented winter.
Although we have 100 percent indoor parking, to this day we have never experienced a problem related to temperature with this oil.
Simply stated, a multi-viscosity oil use spolymers to modify its behavior. As the temperature changes it actually acts as two different weight oils. The polymers are coiled when the oil is cold, which allows for better oil flow through the engine. As the temperature increases, the polymer chains unwind to prevent thinning of the oil.
Some examples of the success of 40wt oil in a four-stroke cycle engine are our PowerStroke engine with over 500,000 original miles. Our four original DDC S-60 engines have a combined total of 172,000 engine hours and 4.3 million miles.
As a preventative maintenance measure, we recently changed the main and connecting rod bearings on the four original S-60 engines. Photo 1 shows a sample of the removed main bearings. Photo 2 shows a sample of the connecting rod bearings. As you can see, these bearings are largely undamaged and show very little wear, relative to their mileage and age.
Photo 3 shows a main bearing from an engine with an oil pump-related problem. The damage is not to the extent the bearing would be spun. During the engine-hours the oil pump was manifesting its failure, the 40wt oil was providing additional protection that single weight oil would not have.

Photo 3: The damage to this main bearing is not so extensive the bearing would be spun.

So one conclusion is that in addition to long term engine protection, single weight oil can also provide protection during internal engine failures. Lastly, single weight oil delivers another benefit during lube oil dilution. During a failure related to the fuel system as diesel fuel is entering the crankcase a single weight oil will assist in maintaining oil pressure until technicians can determine the cause of the failure fuel issue and make the repair.
Operators should refer to the owner’s manual for details, and discuss with the manufacturer if single weight oil is appropriate for use in their engines.

Christopher W. Ferrone is president of Americoach Systems Inc., Glenview, IL, an engineering firm specializing in transportation, technology, analysis and safety.

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Posted by on Jun 1 2011. Filed under Safety. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry

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