Don’t Judge A Motor Oil By Its Color

Used motor oil analysis provides the complete picture about what’s happening inside your engine

Common questions about oil analysis:

  • My motor oil turns black, do I need to change it?

Common sense says you should change it, however, oil color doesn’t always reflect performance. In fact, when motor oil turns black, it’s a sign that motor oil is doing its job.

Motor oil naturally darkens during use of the vehicle on a daily basis. During your drive to work, your engine reaches normal operating temperature (195 degrees F to 220 degrees F) heating the motor oil. Then you park the car and the oil cools. This process repeats itself throughout the day. This continual process, heats and cools the oil, naturally darkens the oil.

In addition to your daily activities, normal oxidation can darken the oil. Oxidation occurs when the oxygen molecules interact with the oil molecules and cause chemical breakdown, the same process happens when iron turns to rust.

Soot also causes oil to turn black. While we associate soot with diesels, today’s direct injected gasoline engines can produce more soot than older diesels without exhaust treatment devices. While individual soot particles are too small to cause engine wear, particles can accumulate into a larger wear-causing contaminant that cause lead to engine wear before they lodged in the oil filter.

Just because the oil has turned black doesn’t necessarily mean its reach the end of its service life. Motor oil contains detergents and dispersant additives designed to clean contaminants like soot and prevent them from depositing onto metal surfaces. Oil that has turned black is an indication the additives are doing their job

  • My motor oil fields gritty should I change it.

When checking oil levels, some motorists like to rub oil between their fingers to check for particles. Grid or other contaminants can mean the oil has chemically broken down, but this is unlikely, especially with top shelf synthetic oil. More likely, the oil filter has filled with contaminants and unfiltered oil is bypassing the filter and circulating through the engine. The oil filter is designed with a bypass valve to ensure the engine receives oil even if the filter is fill. While dirty oil is preferable to no oil, it’s not a long-term plan for success, in this case, change the oil and filter.

  • My oil looks like chocolate milk

This means water or engine coolant has contaminated the oil, typically due to a head gasket leak. We all know that water and oil don’t mix. When they combine in your engine, water droplets suspended in the oil and alter its appearance until it looks frothy or like chocolate milk. The presence of water leads to foam bubbles, which rupture when pulled between engine parts during operation, leaving metal components unprotected against engine wear. It also forms sludge, which can clog oil passages and ruin the engine. In this case, see a mechanic as soon as possible.

  • My motor oil looks or feels too thin.

Smell your dipstick. Oil that has lost viscosity is often due to fuel dilution. You can usually smell gasoline or diesel fuel on the dipstick in such cases. Fuel dilution occurs when gas or diesel wash past the piston rings and contaminate the oil in the sump. It reduces oil viscosity, which reduces the oils ability to prevent engine wear. It also leads to the formation of harmful varnish and sludge. Fuel dilution can occur if you idle your engine excessively or to a mechanical defect. It’s also common in some direct-injected engines.

While it’s possible to get a rough idea what’s going on inside your engine due to oil color, you need to perform oil analysis to really find out what’s going on inside your engine. By chemically analyzing a used oil samples, a qualified lab can tell you if the oil contains excessive wear particles, water contamination, fuel dilution and more. Ultimately, the report will tell you if the oil is suitable for continued use or not. It’s a cost-effective way to get the most out of your oil change and your engine.