Why Does Diesel Engine Oil Break Down?

Why can't oil last forever? Why do we have to change our oil so often?

Many vehicle owners have asked this question. Manufacturers, too, wish that it were possible to eliminate oil changes because making time for an oil change is probably a vehicle owner's number one inconvenience.

The problem is, oil breaks down and is no longer able to keep your engine operating as optimally designed. Hence the need for an oil change regimen.

When we first wrote about this topic last fall we shared how understanding  oil chemistry and composition helps us understand the limitations of engine oil. This is why OEMs have recommended drain intervals, and also explains why ignoring these can cause us to risk voiding warranties. 

But there are additional reasons oil deteriorates and can cause engine failure if ignored. Machinery Lubrication published a helpful article by Jim Fitch of the Noria Corporation titled "Four Lethal Diesel Engine Oil Contaminants" that addresses this issue of oil breakdown. The bottom line here is that there is considerable value in periodic oil analysis, as we have noted elsewhere.

What follows is an abbreviated summary of the four destructive forces that can damage the integrity of your oil, potentially leading to the catastrophic failure of your engine. A link to the complete article can be found at the end of this story.

The Four Lethal Forces

Glycol
Radiator fluid with glycol can get into the oil a variety of ways, from blown head gaskets to defective seals to cylinder heads. According to one study, glycol was found to be present in 8.6 percent of 100,000 diesel engine samples tested. 

Even a small amount of glycol can cause serious issue. A 0.4 percent glycol coolant in the oil can cause soot to coagulate, leading to a dump-out condition resulting in sludge, deposits and oil flow restrictions. The article cites numerous other issues and they are all bad.

Fuel Dilution
It is fairly common to have minor fuel dilution occur with frequent starts or excessive idling. Severe dilution (2 percent or more) indicates a more serious causes like leakage or fuel injector issues. 

In cold temps fuel dilution can cause waxing that results in low oil pressure or oil starvation. Fuel dilution can also thin out the oil so that it is no longer adequate to protect against wear in the combustion zone. Severe dilution undermines the effectiveness of oil additives. These and other issues are amplified when using a biodiesel lubricant.

Soot
Soot is a by-product of combustion that is present in all diesel motors. The presence of soot is normal, but when present in abnormally high quantities it is indicative of other problems that need to be addressed.

Combustion efficiency is directly related to soot production. Things to look at include poor ignition timing, excessive ring clearance or a plugged up air filter. 

Fitch details a host of other concerns that can crop up when you have soot issues inside the engine. 

Water
Though we can't live without water, it is also quite destructive, especially inside your engine. As the saying goes, oil and water don't mix. Too much water will result in that greasy slop that is not going to be fixed with an oil change. It also increases the corrosive power of acids inside the engine and attacks additives. 

* * *

The article closes by noting that total engine failure is something that happens over time as a result of the cumulative effect of one or more of these forces. This is not, the author notes, the some total of all that can go wrong in an engine. Dozens of other factors may lead to what seems like a sudden death. Usually, however, there are all kinds of warnings that we put off addressing or fail to notice.

Oil analysis is your best early warning system, though some of the signs of trouble can be observed as you do routine maintenance. 

Links

Four Lethal Diesel Engine Oil Contaminants

Champion Brands Offers Free Oil Sampling Kits for Diesel Engines

How Oil Analysis Helps You Diagnose Engine Health

Diagnosis is the process of identifying the nature of an illness or other problem by examining symptoms. In the Year of Covid, diagnostics has been much discussed in the news. Developing accurate diagnostic tools was an essential first step in the battle against its spread. 

Diagnosing engine wear may not be as life and death a matter as the coronavirus, but the concept of oil analysis operates on the same principle You use tools that have been designed to help identify things that are going on that you can't see. In other words, the data you can read will help you see that which is hidden from view, much the way x-ray machines hep doctors identify broken bones and ultrasound identifies what is happening in our internal organs.

This week an article by Karl Dedolph in the January 2021 edition of The Shop magazine goes into detail about the benefits of oil analysis for racers. Dedolph, director of racing and performance products for Champion Brands, begins by comparing oil analysis to a dyno. "Our complete oil analysis kit with mailer and sample bottle is just like using a dyno to measure horsepower," he writes.

The article discusses how sophisticated the process has become, using spectrometers to identify the metals and fluids found in a sample. Each element has its origin, enabling trained specialists to recognize where the wear might be occurring inside the engine and how serious it is. 

In addition to explaining what oil analysis is, the author addresses some common misconceptions about performance aftermarket oils and fluids. 

You can find a digital copy of this  article here in the January online edition of The Shop.

Related Links

Things You Can Learn from Oil Analysis

Champion Offers Free Oil Analysis Kits

Things You Can Learn from Oil Analysis

The other day I wrote about the 2021 Cummins engine that is going to have a 100,000 mile oil change interval. The caveat is that it is actually an 85,000 mile change interval unless you do routine oil analysis. 

Now the truth is, with the kind of money we spend on a diesel, the cost of oil analysis is just pennies. Why not take care of your equipment and make it last? Oil analysis is one of the best ways to do this. 

You can see rust on a truck body, the visible outer shell of your machine. But what's happening on the inside? Oil analysis uses science to determine the condition of your oil. It will also provide clues as to the condition of your engine, whether you have smooth sailing ahead or macabre mayhem. Dan Arcy, in a 2019 Fleet Equipment story, describes it as an "early warning system." And it is.

In short, what Cummins is saying is that oil analysis has real value. It's a cost effective tool for extending the life of your equipment. 

What a good oil analysis does is identify wear metals in the oil. The experienced lab has vast quantities of historical data which enables them to identify what is going on based on the wear metals in your oil. Arcy notes that high levels of iron might point to cylinder wear. Unusual levels of chromium, aluminum, copper or tin will help identify other problems. 

Some wear is normal. An experienced lab will point out for you what is not normal, and what this means.

Your oil analysis report will also give you insights into the fluid itself. Do you have glycol in the oil? Water? Is your viscosity correct? Have you had fuel dilution? 

Silica is a nasty and unwelcome guest in any engine. You can also find copper, potassium or lead as well. Each item on the lab report is there to teach you something.  

According to Mike Wyant of PetroChoice, the two most common problems are dirt (inadequate or improper filtration) or water (leaking through seals.) Each of these require attention, the sooner the better.

Click here to see a sample of a 2015 report from PetroChoice. 

Photo Credit: Science in HD