There is a very real danger of antifreeze in engine oils.

All coolant systems require the use of antifreeze, however have you ever thought of the danger of antifreeze in engine oils? Obviously this was never meant to be, but even the slightest internal leak can result in antifreeze (Containing Glycol) engine oil contamination.

 

What is the primary danger of antifreeze in engine oils?

Antifreeze contamination is common in engine oils and can greatly alter the properties of the lubricant. The danger of antifreeze in engine oils is that they cause a thickening of the oil, increasing the engine oil 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 also be compromised.

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.


Another danger of antifreeze in engine oils is that it forms 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.

Another danger of antifreeze in engine oils is the formation of black Sludge.

This common danger of antifreeze in engine oils can be observed in many ways. One is simply a rise in the oil’s viscosity or a thickening of the oil. This often produces what’s called black sludge (Also known as black mayonnaise), which is a thick gel or emulsion when mixed with the motor oil. Acids are formed like glycolic acid, formic acid and other organic acid types.

Flow is restricted as this black sludge 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 and car oil coolers. It is reported to be the No. 1 cause of premature filter failure in a diesel engine and overall poor lubrication.

How does antifreeze mix with the engine oil? 

There are several ways glycol can find its way into oil. If the cylinder 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.

How to overcome the danger of antifreeze in engine oils?

The first step to combating this problem is to determine if there’s 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 engine oil change after the leak has been fixed will ensure the danger of antifreeze in engine oils 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 indicating the danger of antifreeze in engine oils. 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.

To conclude: Regular checks on coolant levels will act as an early warning for any leaks in the system. It’s probably the only way to never experience the costly danger of antifreeze in engine oils.