THE ENGINE THAT ANSWERED QUESTIONS

A 1940S CATERPILLAR OIL TEST ENGINE

Special thanks to Lee Fosburgh at Cat Historical, Braden Reddall at Chevron, and Jim Rush!

It’s easy to forget how much engineering goes into a quart of oil. We all know how much depends on that oil. What many don’t know is how the advancement of diesel engine technology stumbled in the early 1930s and how the development of new lubricants put it back on track. Along the way, special diesel engines were built to develop and test those lubricants.

In the 1920s, the growing diesel engine market faced a major ring-sticking and piston-deposit problem. It was not new, nor was it exclusive to diesels, but diesels had the most severe form. As diesel power density and RPM capability moved higher, the problems grew worse. Behind the scenes, the engine manufacturing and lubricant industries pointed fingers. But two companies rose above the rivalry and set an example of how cooperation can solve wide-ranging issues and produce a compounded result. That was a pun, and you’ll get it in a minute.

Problems and Solutions

So what were the problems? In as few as 300 hours, the rings on a diesel piston could become so gunky they’d stick in the ring lands. The piston skirts gummed up as well. A gradual loss of compression was the first symptom, and the resulting influx of combustion byproducts into the crankcase from blow-by caused other types of wear and failures. If left for too long, severe ring, piston, and cylinder wear resulted.

The root cause was oxidized lubricant in and around the ring packs. The base oils of the era had a very low tolerance to temperature. The heat of combustion caused oil on the cylinder walls and pistons to oxidize and turn gummy. This was a problem in all engines of the time, but because diesels had higher combustion temperatures than the average low-compression gasser, the problems occurred sooner and with more intensity. Oxidation residue alone could stick the rings, but that gummy residue served as a binder to grab carbon from combustion and contamination from the intake air and turn them into a nasty, destructive paste.

The fuel oils of the period played a big part in this problem. With few standards in place, fuel oil was of inconsistent quality and operators were not always well educated on sorting the good from the bad, or the right from the wrong. Yes, the “RTFM problem” existed even then! The poor-quality fuel oils tended to create excessive soot, carbon, and deposits, which gave the oxidized oil more to grab. It didn’t help that the injection systems of the day were imprecise.

A perfectly maintained diesel operated in a clean environment using the best fuel and lubricants available had a chance, but few land-based high-speed diesels in those days were used that way. Sooner or later it came time to tear the engine down for cleaning and do so before too many hard parts were eaten up. Some operators would add chemical detergents to the fuel and oil just prior to a lubricant change, and this would occasionally clean up things enough to stall a teardown. None of this was even close to being optimal — and everyone knew it.

A Gummy Caterpillar

By 1931, Caterpillar’s chief engine designer, Art Rosen, had finished the hard work on that company’s first diesel engine, the D9900. It was a masterful design and one of the most advanced diesels in the world, but its impact was blunted by the fuel and lubricant issues that were giving everyone in the growing diesel industry fits. Rosen was a proactive guy, so he started an in-house lubricant research program in 1933 and reached out to lubricant suppliers. Among the several oil companies he contacted was Standard Oil Company of California (now Chevron Corporation) in Richmond, Calif., just 20 miles down the road from the Caterpillar test lab in San Leandro. This led to a collaboration between Rosen and a research engineer at Standard Oil named George Leonard Neely.

Say Hello to DELO

In the 1920s, Standard Oil Company of California had seen the need for improved lubricants and began an active program to develop them. According to Neely, they had accidentally discovered a compounded mineral oil with anti-sticking qualities as early as 1925 when researching another product.

First, what’s “compounded oil”? It’s oil that contains solid or chemical additives blended to produce a desired effect. Yes, all of today’s oils are compounded, but that term isn’t commonly used outside of test labs. In the 1920s, compounded lubricants were new, and scientists were learning what existing chemicals could be used to improve lubricant capabilities and create new ones. At this point, the lubricant industry had only recently evolved past organic lubricants — like castor bean or animal-derived base stocks — into mineral oils refined from petroleum. At this point, the lubricant industry hadn’t devoted much time to the specific needs of the diesel engine.

By the early 1930s, Standard Oil was made aware of ring-sticking issues in diesels, and Neely began cogitating the problem. He referenced those experiments done earlier and found aluminum dinaphthenate was good at curing ring-sticking issues. Standard Oil didn’t have a test engine at the time, so he bought a Lauson one-lung gasser for tests and found a compounded formula that not only prevented ring sticking, but also could reverse the process on engines already gummed up. This was in 1933, just before Art Rosen entered the scene.

Rosen and Neely were a bit cagey with each other at first, but once an offer of some experimental compounded oil was made, Rosen had a truck on the way to Standard Oil before the phone line cooled off. This began a series of tests at Caterpillar’s lab, many of which Neely attended. It didn’t take long to prove the concept, and before long, Cat had a new engine oil from Standard Oil that they marketed exclusively for their products.

Something Neely coveted at the Cat test facility was a single-cylinder Cat diesel oil test engine. By 1934, he had acquired one for the Standard Oil lab, which had embarked on a process to develop and market a line of diesel oils for general consumption, eventually called “DELO”: Diesel Engine Lubricating Oil. When copper-backed crankshaft bearings appeared, the original DELO formula was found to be corrosive to copper, and the oil was updated for 1935. Research continued and by 1938, a very advanced- for-the-day DELO formulation had been achieved. That was just in time to support some of the huge diesel developments coming just prior to and during World War II. The evolution of DELO has continued to this day, and no doubt many of you are running Chevron DELO as you read this.

Say Hello to SCOTE

During the process of lubricant development, Standard Oil’s experimental lubricant was tested in Cat diesels like the D9900, and it went into lab test engines. Rosen felt strongly that bench tests were one thing, but engine tests were another — and maybe of more importance. Since using production engines was expensive and complex, the lab developed single-cylinder oil test engines.

These test engines had to be quickly disassembled with combustion configurations easily altered, such as cam timing, injection parameters, combustion chambers, exhaust restriction, intake restriction, and so on. To quantify test results on known components, they used as many common wear components from production engines as possible, like pistons, liners, connecting rods, bearings and more.

It isn’t clear from our research exactly how and when Rosen’s test lab built the first iteration of the SCOTE (Single Cylinder Oil Test Engine), but it’s mentioned in documents as early as 1933. According to Rosen and Neely’s later writing, the first generation SCOTE had a 5.75 x 8-inch bore and stroke, the same as the Cat D13000 engine and several other derivatives. In production form, that bore and stroke came around 1935. One of Cat’s production diesels in that 1931-34 period had a 5.25 x 8-inch bore and stroke, making the early SCOTE history a little muddy. Since the smaller and larger bore engines were of similar architecture, it’s probably not a big deal.

Caterpillar was one of the first engine manufacturers to research and create lubricant standards for their engines, and it began offering a line of oil test engines to the petroleum industry starting in the 1930s. It was all on the down-low as far as the public was concerned, but from then on, few were the lubricant industry test labs that didn’t have and use a Cat SCOTE.

This topic is so obscure that even the Caterpillar archives could offer very little information on SCOTE before deadline. We got a bit from Chevron (which evolved from Standard Oil) and some from SAE International. Beyond certifying oil for use in Cat engines, the SCOTE also developed into something used to establish more generic ASTM test protocols for lubricant standards beyond those necessary for Cat. There was, and is, a maze of ASTM lubricant standards that change often with the development of new technology. The SCOTE were (and are) used in specific ways to determine the lubricant standards for the industry to set more general guidelines.

SCOTE have a useful lifespan. Not so much their actual operational life — they are infinitely rebuildable as long as parts are available — but their application to testing in a specific era. The 1D model began to be replaced by the 1Y73 SCOTE starting around 1950. The 1Y73 is also long obsolete and was supplanted by the 1Y540 in the 1970s. The 1Y3700 appeared in the 1990s. It’s still current and there are several variations. It can be configured many ways, including with the latest combustion chamber types, overhead cams and electronic injection.

SCOTE Survivors

Once a SCOTE becomes obsolete, it usually goes for scrap. They have little use outside a lab. A few escape the scrapper and have been used to power generators and the like. More commonly an engine collector saves one and turns it into a display piece. Jim Rush is such a collector, and his restored 1D SCOTE has been seen at shows since 2000. We took pictures of it at the 2018 Tri-State Show in Portland, Ind., and observed a lot of “What the hell is that?” activity around it. Jim gets hoarse taking about it.