The Effects of Glycol Contamination in Engine Oils

Wes Cash, Noria Corporation
Tags: contamination control, oil analysis

The drive home started just the same as all the other ones had. I was a freshman in college at Oklahoma State University and was driving home for Christmas break. Like any other teenager, the last thing on my mind was checking the fluid levels in my car (my dad always told me to, but I seldom remembered) before I started the six-hour drive to rural southwest Kansas.

I had driven about two hours when I noticed the temperature gauge on the dash was beginning to rise. Not knowing why this was happening, I pulled into a gas station to check the radiator. After letting the car cool down, I opened the radiator cap and filled the radiator with water and antifreeze, never once wondering why it was low. Starting down the road again, my car sputtered and died. After a very slow trip to a local mechanic, we discovered the intake manifold had cracked, allowing the coolant to flow into the engine block. This fluid being on top of the pistons could have easily resulted in bent rods or blown valves. It can also have very detrimental effects in oil.

Glycol contamination is common in engine oils and can greatly alter the properties of the lubricant. Antifreeze causes a thickening of the oil, increasing the viscosity and not allowing it to flow as readily as before. This can lead to boundary conditions in parts of the engine that require a less viscous fluid to properly lubricate and protect them. It also creates an acidic environment within the oil, resulting in corrosion within the system, especially on copper surfaces. The additives within the oil can be compromised as well.

These images illustrate the formation of oil balls.

Once contaminated, the oil continues the same route of flow, from the sump, into the crankcase, through various parts of the engine and through the filter. With the added glycol, these filters become plugged sooner, which can cause reduced flow and eventually, once the bypass pressure is reached, a condition in which you are no longer filtering your oil. This allows particles that normally would have been filtered out to remain in the system, disrupting the lubricating film and resulting in surface damage to components.

Antifreeze also mixes with oil to form small globules called oil balls. Although very small, typically 5 to 40 microns in size, they can cause big problems. These balls are abrasive and create surface erosion. A common place to see this would be on the inside walls of the cylinder, where the oil balls could cut and gouge into the wall. They can produce all types of surface fatigue and lead to lubrication failures in areas of very tight tolerances.

Beware of Black Mayonnaise

The effects of coolant and antifreeze contamination are many. One is simply a rise in the oil’s viscosity or a thickening of the oil. This often produces what’s called black mayonnaise, which is a thick gel or emulsion when mixed with the oil. Acids are formed like glycolic acid, formic acid and other organic acid types. Flow is restricted as this black mayonnaise moves throughout the engine. It can occlude to the walls and narrow passageways, and interfere with oil flow, causing partial or total starvation where the oil is intended to go. It is very common for glycol and these emulsions and gels to completely block flow-through filters. It is reported to be the No. 1 cause of premature filter failure in a diesel engine and overall poor lubrication.

In my case, the culprit for this contamination was a cracked manifold, but there are several ways glycol can find its way into oil. If the piston heads are warped or cracked, contamination would be allowed into the system. In more severe cases, cavitation wear provides a straight path for ingression. Cavitation occurs when an air bubble implodes against a hard surface, resulting in a pitting action. As it becomes more aggressive, this can cause a hole or crack in the cylinder wall.

Though very small, oil balls
can cause big problems.

The first step to combating this problem is to discern that you have a coolant leak. Periodic checks of fluid levels are the easiest way to do this. If you notice levels beginning to change, try to find the coolant leak. Fixing the leak should be your first priority. Otherwise, any actions you take to clean the oil will be in vain. For most engines with small sump volumes, an oil change after the leak has been fixed will ensure that any contamination has been mitigated by new oil.

In systems with large volumes of oil, small leaks can be hard to detect. Oil analysis can reveal glycol in several ways. A patch test can show sludge or precipitates associated with this type of contamination. A blotter test is another simple test that can expose the presence of glycol. If the oil appears thick and doesn’t wick into the blotter paper very well, glycol contamination could be a possible culprit.

Although many years have passed since my breakdown on the road home, the lessons it taught me are still useful today. Simple inspections on all types of machines provide invaluable information as to their condition as well as reassurance that they are operating in a reliable manner.

62% of lubrication professionals say glycol contamination has caused problems for their company’s equipment, according to a recent poll at


About the Author

Wes Cash is the director of technical services for Noria Corporation. He serves as a senior technical consultant for Lubrication Program Development projects and as a senior instructor for Noria's Oil Analysis I and Machinery Lubrication I and II training courses. He holds a Machine L...

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