How to Spot Check Your Car's Oil

It had been more than 5,000 miles since my last oil change and I was pretty sure my synthetic motor oil would survive the extended drain. Still, to ease my anxiety, I decided to do a little test on the oil - the blotter spot test using a business card from my wallet.

Within five minutes of spotting the card with oil from the dipstick, I knew something was horribly wrong. The heavy black soot in the oil was immobile, creating a sticky center on the card. This was not what I wanted to see and I knew it was symptomatic of an oil that had passed its prime.

Cause and Effect

Why did this happen? The main reason was my driving habits. I’m frequently away on business so my car sits in the garage most of the time. When I do drive, it’s usually short distances (typically 3 to 4 minutes to the office).

This causes moisture to build up in the crankcase (perhaps as much as 20 percent), which in turn, causes additive distress, loss of dispersancy and sludge. The condition was compounded by the fact that it was January (cold driving conditions hold moisture longer in the oil).

The Solution

A double oil and filter change was prescribed. I knew from the blotter test results that the oil in my engine had thrown sludge, and soot had dumped (lost dispersancy). An oil change brings in a fresh supply of detergents and dispersants. With the single oil change, these additives would have lifted up much of the sludge and carried them to the filter.

Consequently, the filter would have plugged within minutes, sending the oil into bypass and unfortunately, automobiles don’t have bypass indicators. By performing two oil changes, most of the sludge and deposits are discarded with the first oil and filter, enabling the second oil and filter to have normal service life. This was confirmed by another blotter spot test after the second oil change.

Aunt Minnie Drivers Give Synthetics a Licking

Even the very best motor oils cannot safeguard against sludge when free water is present. Within several minutes after starting an engine, the oil typically reaches the thermostat setting. This heat can drive off the moisture, even in cold winter conditions. However, it can sometimes take 15 to 20 minutes of continuous driving before the condensed moisture has dissipated.

When water accumulates in sooty used oil and remains in the engine for an extended time, the damage to the oil is irreversible. This is why short-trip “Aunt Minnie” drivers need to change their car’s oil more frequently.

How frequently? If you are a short-trip driver like me, consider performing a simple blotter spot test before a scheduled oil change in order to regulate the optimum oil change interval to your driving conditions and climate. If you see undispersed soot, characterized by an inability of the soot to wick outward into the card stock, this may indicate that you need to change your oil more frequently.

In contrast, if you see no structure (sticky centers, rings, etc.) on the card, you might consider extending your oil drain. Keep in mind: The optimum drain interval may change by season, age of the car and quality of filtration. Also, other oil properties may become impaired before dispersancy is lost.

Poor-Boy Oil Analysis

Laboratory oil analysis for personal automobiles is often too expensive. For those who are inquisitive and need to know what’s lurking in their oil, there are a few low-cost and simple alternatives:

Blotter Spot Test

Information about soot dispersancy, coolant leaks (glycol) and fuel dilution.

Crackle Test

Water contamination (fuel dilution may cause an interference).

Patch Test

Particles from the oil can be collected and examined with a top-lit microscope.

Used Filter Inspection

Information about wear debris, contamination and sludge.

Oil Drop Placed on Water Surface

When oil ages and becomes contaminated and oxidized, the oil drop spreads out over the surface of the water (instead of beading up like a new oil).

Viscosity Comparator

Information on changing oil viscosity influenced by shear down, soot load and fuel dilution.

The reasons for analyzing passenger car motor oils vary. One reason might be a need to optimize a scheduled oil drain interval as discussed above. Another reason might be as an inspection test of engine condition when buying a pre-owned car. Oil analysis might also be helpful in comparing the performance of lubrication alternatives, such as aftermarket additives, different oil viscosities, different oil filters, etc.

The common availability of onboard oil analysis sensors with dashboard indicators is in the near future. Several well-funded research efforts are currently underway offering promising new technologies.

Future automobiles may have the ability to analyze changing properties of oil on the fly, replace depleted additives and engage an assortment of cleansing and rejuvenation technologies. Besides its role in the development of oil films, the base oil would serve as a transient host for both additives and contaminants and would be recycled in the engine indefinitely.