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Hello everyone and welcome. In this video I have teamed up with Progressive, and we are talking about what happens if you forget to change your oil on time. Now, if your question is "Is it okay if I forget to change my oil on time?" the answer is no. The end. Very simple. However, this is Engineering Explained, and we can do a little bit better than that. So if your question is "How bad will it be for my engine if I forget to change the oil on time?" well, suddenly that's a much more complicated question with a much more complicated answer, and that's what we're going to get into in this video.
One of the most important properties of an oil is its viscosity rating. If you take a look at a bottle of oil, it may say something like 5W30, and that number is giving you its viscosity rating. The 5W is indicating the viscosity rating when the oil is cold, the W standing for winter, and then the 30 is indicating that oil's viscosity when it is hot. Generally speaking, the viscosity of that oil will remain the same throughout the useful life of that oil, but as that oil is used, it oxidizes. That oxidation occurs because of the heat, the oxygen, the pressure, and the environment that this oil is within. As that oxidation occurs within the oil, eventually its viscosity starts to increase. There are multiple reasons for that increase in viscosity. Part of it is the oxidation, and part of it is that the volatile components within that oil, the lighter components that cause it to be a bit more thin, start to burn off. Also, as time goes on, you start to include and increase the number of contaminants within that oil. All of that results in the viscosity eventually starting to go up as you have that oil within your engine for longer and longer.
How long does that take? That's unknown. It's going to depend on the oil that you're using and the engine that you're using. But at a certain point, as you start to hit the point of the curve where the viscosity starts to really go upwards, that's where you're going to start to run into danger, because you're not going to have proper flow within your engine. Without proper oil flow within the engine, you're not going to have proper protection, and you're going to start to increase wear.
Another thing we need to consider is oil consumption within an engine. All engines will burn oil. In preparation for this video, one of the things that I did was start closely monitoring the oil consumption within my own car, and to my surprise, and I was happy to find out, the oil consumption was actually pretty low. I changed the oil about every 6,000 miles, and the oil level was still within the range where it should fall during those 6,000 miles. Now, the car only has 20,000 miles on it, so it's still a relatively new engine, and you wouldn't expect to see too much oil consumption. As engines age, they tend to increase the amount of oil that they start to consume.
So why do engines consume oil? There are three major sources for that oil getting into the combustion chamber and then burning off. The first one is the valve guide. As your intake valve is moving up and down, you have oil lubricating that interaction, and that oil can leak down into your intake and eventually work its way into the engine, where it is burned in the combustion chamber. You also have a positive crankcase ventilation system. Within your engine, you build up high pressure beneath your pistons, and that high pressure needs somewhere to go. There's a ventilation system which allows that high pressure to be routed back to your intake. Some of the oil mist that forms within your crankcase can then be routed back into your intake, and as a result, you can burn that oil mist within your engine. Finally, you use oil to lubricate the cylinder walls with that piston-cylinder interaction, so that is a third location where oil will be interacting with the combustion chamber and thus burning off.
So what is the danger of burning off oil? Obviously, our worst case scenario is we just burn off literally all of it, so there's no oil remaining and our engine has no lubricant. As a result, it gets way too hot, a ton of wear is going to occur because you're going to have metal-on-metal interaction, and it's going to lead to catastrophic failure. That's of course the worst case scenario. What's more likely to actually happen, if you're just a little bit late getting to your oil change, is that you're going to have less overall oil within the engine. This poses a problem, because as you have less and less oil in the engine, the remaining oil is going to have to work even harder to protect your engine. Because there's less of it overall, it's going to start to oxidize faster, and as a result you're going to see more negative effects occurring more rapidly as that oil level decreases.
Also, if the oil starts burning off but you leave behind contaminants, the percentage of contaminants, especially dangerous metal contaminants which could be wear from the engine, is going to increase within that oil, which can lead to additional wear. So it starts to spiral out of control, and that's where you start to see these curves right here, where all of a sudden that oil is now oxidizing significantly quicker, it's getting significantly thicker, and the contaminants are increasing rapidly within it.
Now, motor oils are actually really complicated, and they include all kinds of different additives which are important for your engine's health. This is not a complete list of all the additives you can expect to find in an oil, but we are going to touch on some of the major ones here. We're going to work through different additives, talk about what they are, what they are used for within the oil, and then what the consequence is of using that oil for far too long without changing it on time.
The first one is antioxidants. Oxidation is the primary cause of oil degradation, so antioxidants are super important in reducing the rate of oxidation. The consequence of waiting too long is that this oil starts to break down more and more, losing its effectiveness, and you have an increase in wear within your engine.
We also have anti-wear additives. For example, zinc can be used to do this, and these zinc additives help react with rough surfaces to create a sacrificial barrier and to help smooth out that surface, so that you reduce the friction there and reduce the amount of wear. Over time, as you start to use up that zinc and remove those sacrificial barriers, it loses its effectiveness, and of course you're going to have more wear. If you have something preventing wear and it goes away or is no longer as effective, you have more wear.
Detergents are very important for preventing corrosion within the engine and helping to prevent sludge from building up. Over time, as that sludge starts to build up and your detergents start to lose their effectiveness, that sludge can get into passageways and reduce oil flow within those passageways. If you reduce oil flow through those passageways, you're getting less oil through them, you're getting less protection, you're increasing friction, and you are increasing wear. This can also lead to excessive carbon deposits starting to form within your engine, since the detergents are helping to prevent carbon deposits.
We have dispersants, and dispersants are really cool. They surround deposit precursors, attach themselves to them, and suspend that deposit precursor within the oil. It just circulates within the engine. Perhaps the filter will be able to filter it out, and if not, it just continues to circulate within that engine, but it doesn't attach to anything and form a harmful carbon deposit. These dispersants help to suspend that deposit, and in doing so, you don't have those deposits forming within your engine. Of course, the longer you wait, the more these deposit precursors are going to be held within your engine. If you don't change it out, you've got all those deposits floating around in your oil, just waiting to attach to something, and you're never actually removing them from your engine. It's actually a good thing to see that dark oil coming out, because it means you're taking out all of those contaminants when you change the oil. However, you don't want those contaminants in there forever, so you need to change your oil on time.
Viscosity modifiers are also a very interesting additive. These can be used to allow for multi-grade oils. For example, if you look at a graph of viscosity versus temperature, with viscosity on the vertical axis and temperature on the horizontal axis, low temperature is over here, high temperature is over here, very thick fluids are up top, and low-thickness fluids are down at the bottom. If you look at different grades of oil, say an SAE 30, which is thicker than an SAE 5, both of these oils will decrease in viscosity as you heat them up. However, if you add viscosity modifiers to an SAE 5, you can change its characteristics. At low temperatures it will remain the same, and it'll remain an SAE 5 rated viscosity oil. However, as you get to higher temperatures, these viscosity modifiers start to expand, and as they expand, they thicken that oil, so it acts more like an SAE 30 oil at higher temperatures. If these break down, you will notice a decrease in the viscosity of the oil once it's at operating temperature. You may see initially a drop in the oil's viscosity as you start running it within your engine, because those viscosity modifiers, as they expand, are susceptible to being sheared, split into different parts, and then you have a decrease in viscosity because those viscosity modifiers are no longer effective. Ultimately, oxidation is going to play a stronger role and your viscosity is going to increase, but you may see an initial dip as a result of these viscosity modifiers being worn out.
Motor oils can also contain pour point depressants, and these are really important for improving low-temperature flow. If you live in a cold area, it's important to have these pour point depressants to make sure that you have plenty of flow on startup. During startup, it's a critical time to make sure the oil is flowing within the engine to avoid too much wear. If these pour point depressants start to wear out, your oil is too thick at startup and you don't have proper flow within the engine. In that critical moment, when you need that oil circulating within the engine on startup and the engine is cold, you're going to have excessive wear occurring, because you can't get that thick fluid to flow within the engine.
Finally, we get to foam inhibitors. If you look within the crankcase of your engine, you've got the crankshaft rotating around, and it's splashing the oil all over the place. In splashing that oil, it can create foam and start to create bubbles. Foam inhibitors work to reduce the air and oil bubble surface tension, so those bubbles pop very easily and you don't create foam within the engine. If these are no longer useful, the oil will foam up, which reduces your oil pressure, and it can cause cavitation, where you have sloshing of the oil, which means you won't have protection. Without that protection, it can lead to additional wear.
Going back to our original question: how do we know if we waited too long to change our oil, and whether we did any damage? Thankfully, there are labs out there where you can submit a sample of your oil. You take some of the oil from your engine and submit it to a lab, and they will analyze it based on its viscosity and by looking at metals within the oil. They can tell you where your oil stands. Maybe it was way too long and you did some damage to components of your engine, or maybe you were fine, and everything was within the normal specification of an engine oil. If you're really curious, say you went 5,000 miles over your interval and want to know whether you actually caused damage, you can take a sample of your oil, send it to these third-party labs for testing, and they will tell you what has changed in your oil and whether it was okay or not.
Huge thank you to Progressive for sponsoring the video, and thank you all so much for watching. If you have any questions or comments, feel free to leave those below.