What is the correct color of engine oil? Do you know what color it should be? The color of the oil in your car’s engine can reveal quite a bit, but it might not reveal what you expect it to. If you want to know if the fruit on your peach tree is ripe, you look at the color. When it has completely changed from green to yellow, your peaches are ready to be picked. But engine oil is not fruit. Contrary to what you may have been led to believe, you cannot tell if it is time for an oil change simply by looking at the color of your oil. That is not to say that its color is unimportant. In fact, the color of engine oil can give you some clues about its condition and, more importantly, the condition of your engine.
What color should engine oil be, and why does it change?
When you think of engine oil, what color comes to mind? Many people associate engine oil (also called motor oil) with images of oil that they have seen on television. Black. But while crude oil is often called “black gold” (in fact, crude can be black, though not always), engine oil that has been refined from crude is not black.
Actually, fresh engine oil straight from the bottle is a translucent amber color, not much different from the color of honey. But it does not stay that way for very long. You see, the normal heat cycles from your engine – upwards of 200 degrees Fahrenheit during operation and back down to air temperature when it is not running – cause your oil to darken naturally. It transitions from honey color to caramel in pretty short order, in just a few hundred miles.
There are other, perfectly normal reasons that your engine oil changes color. For instance, certain additives in the oil are susceptible to darkening, adding to the change. In addition, oxidation that occurs when oxygen molecules interact with oil molecules makes the oil darker, similar to when a cut apple turns brown when left exposed to oxygen on the countertop. These changes happen whether the oil is regular oil or synthetic oil.
Perhaps the most stark change to the color of your engine oil comes as another normal result of engine operation: soot, the byproduct of incomplete combustion. Often associated with diesel engines, soot is produced in gasoline engines as well, especially modern gasoline direct-injection engines.
As you well know, at least you do if you have ever built a bonfire, owned a fireplace, or watched Mary Poppins, soot is black. And when soot mixes with your engine oil, it turns the oil black. But contrary to one motor oil myth, black oil is not necessarily bad oil. Engine oil can be blackened from soot and still be completely fine with many miles of useful service life left. That is because soot is an extremely fine powder not capable of harming your engine. A strand of your hair is more than seventy times larger in diameter than a particle of soot. Even if particles of soot clump together, your engine’s oil filter will catch them. But the oil will still become black.
Engine oil colors that cause concern
Now, just because it is normal for your engine oil to change color over time, even a short time, that does not mean that all color changes are normal. And even though black oil can be perfectly fine for use, when considered with other factors, black oil could tell you it is time – past time – for an oil change service.
Your oil will start out clear and honey-colored. It will transition to a caramel brownish color and then to a dark brown or black. But what are other colors to be on the lookout for? Colors that can reveal problems with your engine? When you check your oil, beware these telltale colors on the dipstick:
1. Milky or muddy brown
The oil on your dipstick should not have a creamy or milky appearance. If it does, that is a sign of a couple of problems. The lesser of the two is condensation. As your engine warms up, moisture in the air inside the crankcase can condense into liquid form on all of the cold components inside. That liquid mixes with the oil and turns it a milky brown color. The condition is more common with vehicles driven frequently for short distances, when there is not enough time for the engine to heat up fully and burn off the moisture before it gets into the oil. This is not an indication that there is something wrong with your engine so much as an issue with your driving habits.On the other hand, if the dipstick looks milky or muddy and you notice white smoke coming from the exhaust pipe, there could be a bigger problem, the most common of which is a failed head gasket allowing engine coolant (antifreeze) into the crankcase, into the oil. When this happens, you might also notice a slight syrup smell coming from the exhaust, and your engine might run roughly and even overheat. The check engine light might come on to signal an engine misfire. Your vehicle should not be driven if these symptoms are present. Significant engine damage can result from overheating! Besides, these could also be symptoms of a more involved problem, such as a cracked or warped cylinder head.
2. Mixed with metallic particles
When you hold the dipstick up to the light, you should never notice tiny metallic particles in the oil. If your oil looks a bit like metal flake paint, there is a problem. Metallic particles in the oil are created when, usually because of poor maintenance, insufficient lubrication is taking place and moving metal components inside your engine, hundreds of them, wear away and cause debris. It is possible that the oil is not moving freely inside the engine and lubricating all the parts. This is really a snowball effect. If you do not pay attention to changing your oil on time, it breaks down and thickens up, making it harder to lubricate as it should. Less lubrication means more friction and metal to metal contact between components. And that leads to damaging wear.
3. Dark and thick
The engine oil in your vehicle is meant to be of a particular weight or viscosity. That means, it should have a certain consistency. The viscosity of oil (also referred to as its weight or grade) is its resistance to flow, its thickness. If the oil is too thin (low viscosity), it will not hold up to the stresses inside your engine. If it is too thick (high viscosity), the oil will not be able to make its way into all of the tight spaces in your engine.When oil is new, it is rated at a given viscosity (ie. 5W-20 or 0W-16) to be matched to the recommendation of your vehicle manufacturer for your car, truck, or SUV. But over time – mainly due to thermal breakdown, but also because of contaminants that make their way into the oil – engine oil begins to not only change color, but it gets thicker. This process of thickening happens naturally, inevitably. That is why it is necessary to change your oil on a regular basis.Therefore, if your oil is dark (which you now know is normal) and it is thick in consistency, it is getting old and should be replaced. This is particularly true if you can feel grit in the oil. The longer oil is in service, the thicker it will get. Eventually it will turn to sludge that cakes up on engine components, clogs passageways, and destroys your engine. Really, you should be getting oil changes long before it gets thick enough to cause problems.
If not by color, then how do you know when to change your oil?
So, if it is important to replace your oil before it gets dark and thick, but you can’t tell just by looking at it (and, after all, who can measure the thickness anyways), how do you know when it is time?
Well, barring the problems mentioned earlier with milky, metallic, or thick black oil, there are only two ways to tell if your oil is any good. Neither are by its appearance. It might be common to assume that black engine oil is worn out or contaminated, but the only way to really know for sure is to submit a sample for a chemical analysis. Remember, black oil is normal, but it could also be beyond its useful life. You cannot tell by looking at the color. If you want to know if the oil in your engine has gone bad or is still good, you need to get it tested.
Of course, few people are interested in that level of scrutiny or want to put in that kind of effort several times each year. So, absent an oil analysis, there is but one way to know when to change your oil. Check the vehicle owner’s manual.
You see, the manufacturer has designed your engine to work with a specific type and weight of oil. They tell you so in the manual. And they tell you how often to change it. Most manufacturers have one recommendation for “normal” driving conditions and another for “special” or “severe” conditions, such as driving on dirt roads, in stop and go traffic, or the frequent short trips mentioned earlier.
If you want to ensure that you are keeping your engine full of fresh motor oil, do these three things:
- Start with a quality engine oil product, such as Mobil 1, and avoid no-name or generic brands.
- Check the level frequently. Weekly is ideal; bi-weekly at least. And check it before you head out on long trips. Top it off with the proper type and weight oil when it gets low.
- Change the oil when the manufacturer recommends you do so, paying attention to whether your habits fall into the “normal” or “special” category.
The level and condition of your engine oil is the number one issue for maintaining your car. Unlike a peach, it does not ripen with age, it deteriorates. But, also unlike a peach, you cannot tell just by looking at it.
Columbia Auto Care & Car Wash | Author: Mike Ales | CopyrightThis article is intended only as a general guidance document and relying on its material is at your sole risk. By using this general guidance document, you agree to defend, indemnify and hold harmless Columbia Auto Care & Car Wash and its affiliates from and against any and all claims, damages, costs and expenses, including attorneys’ fees, arising from or related to your use of this guidance document. To the extent fully permissible under applicable law, Columbia Auto Care & Car Wash makes no representations or warranties of any kind, express or implied, as to the information, content, or materials included in this document. This reservation of rights is intended to be only as broad and inclusive as is permitted by the laws of your State of residence.