It’s completely normal for a 20–30-year-old car to consume oil between service intervals as friction has taken its toll on moving internal components over time. We wouldn’t expect newer vehicles to consume as much oil, but that’s exactly what appears to be happening according to Consumer Reports and other media outlets. Over the last few decades automotive manufacturing technology has improved in parallel with the evolution of computing. With these improvements we now have the ability to engineer engine parts to much tighter tolerances, and precision machine them to reduce friction between moving parts within the engine. Along with the tighter tolerances have come better lubricants with much lower weights– As an example, 0W-40 full synthetic is now a common lubricant weight and viscosity for many turbocharged applications. With these important industry changes we’d expect that today’s vehicles would be much less prone to oil consumption, but it’s becoming clear that that’s just not the case. About 8 years ago some new car owners started to complain about certain brands and models consuming excessive amounts of oil. Consumer Reports got wind of the issue and published their first story on excessive oil consumption in 2014. Back then they said that excessive oil consumption was considered to be a rare occurrence. Fast forward to 2021 and we’re hearing about it again, but this time the scope has broadened significantly, and we now know more about why this is happening.
Oil Guzzling Brands to Be Wary Of
At first it was thought that there were only a few makes and models affected – Subaru, BMW and Audi would commonly come up in discussion. These were newer cars when the problems were reported– not 100,000-mile, muffler dragging clunkers. Beware of Subaru Foresters, Outbacks, Imprezas, XV Crosstreks and anything else with a boxer engine up to the SJ models between 2014 and 2018. In 2016 Subaru settled a class-action lawsuit over the issue and subsequently made changes to their engines to remedy the problem. Still, a quick look at any Subaru forum will reveal that late model owners remain concerned about excessive consumption. Subaru is certainly not alone, other brands such as BMW, Audi, General Motors and Toyota have been the subjects of other class-action lawsuits and extended their warranties to cover the problem. A current class-action lawsuit against GM alleges that generation IV Vortec 5300 engines are prone to excessive oil consumption due to defect. The suit accuses General Motors of fraudulent concealment, breach of warranty and unjust enrichment.
Why Are Modern Engines Consuming So Much Oil?
There are a few reasons why these newer engines are consuming so much oil and they can all be traced to engine design changes that have been made to meet EPA standards driven by climate fears. To meet these requirements automakers have attempted to accomplish two goals: Reduce fuel consumption and improve combustion efficiency. They’ve been successful in achieving these goals with a few different approaches, all of which come with the increased risk of oil consumption. Some oil consumption over a 5,000-mile change interval is completely normal. Furthermore, the level of consumption can be driven by a variety of environmental factors and driving habits. ½ quart between oil changes is no big deal, but in many cases oil in the pan is dropping to dangerous levels well before service is due. Some automakers have brushed this off as no big deal. BMW for example, has said that some of their engines can consume up to 1 quart of oil for every 750-1000 miles driven and that it’s normal. That’s extraordinary when you consider that on the flipside, they are also recommending 7500-mile oil change intervals for many models. So, between oil changes at 7500-mile intervals they’re expecting some drivers to add multiple quarts of oil? That’s some pretty bad math if you ask us.
1. Internal Friction Reduction
This is something that drivers don’t really recognize. It’s not something they can see or feel, but it’s a part of every revolution that the engine’s cam makes when the driver presses the accelerator. Friction is drag. Friction reduces efficiency any way you apply it in physics. For this reason, automakers have long attempted to reduce friction within engines by dialing back tension on internal parts such as valve guides and piston rings. While it’s great that these measures reduce fuel consumption, saving drivers money on fuel while simultaneously minimizing environmental impact, they do open the door for increased oil consumption.
2. Gasoline Direct Injection Improves Combustion Efficiency
There are a couple of ways that automotive engineers have improved combustion efficiency in modern engines. The first is through direct injection, otherwise known as GDI (Gasoline Direct Injection). As of 2019 most of the world’s largest automakers included GDI engines in 75% of their vehicles and adoption throughout the market has grown at a rate of about 11% per year. In an engine that uses GDI for fuel injection air is drawn into the combustion chamber from the intake where it is then compressed. Next fuel is sprayed directly into the combustion chamber and ignited by the spark from the spark plug. All of these actions are timed by the engine management computer for a much more efficient combustion process compared with port injection. While more efficient than older forms such as port injection, it comes with a major drawback– intake valves develop carbon deposit buildup. This happens because unlike with port injection the fuel doesn’t flow over the valves and wash away the carbon. This contributes to the oil consumption problem because the carbon deposits can flake off of the valves and wear the piston rings, which of course will allow oil to escape and burn.
3. Turbochargers Improve Combustion Efficiency
Over the last few years automakers have really ramped up the use of turbochargers for almost every application. Naturally aspirated 4, 5, and 6-cylinder engines have become a rarity in 2021. The reason is once again the pursuit of improved combustion efficiency to improve fuel economy. Unfortunately, there are a whole slew of reasons why turbocharged applications are prone to oil consumption and they usually come down to unfavorable operating conditions for the turbo. For one, they tend to lose oil through the PCV (Positive Crankcase Ventilation) system where it then is found in the intake piping and intercooler. Although some oil loss in this way is normal, the amount can vary depending on driving habits and climate.
The more dangerous oil consumption issues with turbocharged vehicles lie with the turbo seals and oil return lines, which commonly fail. If the oil return line is compromised in any way, such as a kink, blockage or carbonization, oil pressure in the turbo increases and then it gets by the seals at each end of the turbo impeller. If this happens the oil either enters the intake system and is eventually sucked into the combustion chamber and burned, or it exits the seal on the turbine side and is blown out or burned off in the exhaust. Either way, the level of oil consumption here can be significant. The seals can also be damaged due to excessive EGT (exhaust gas temperatures) on the turbine side of the turbo. Part of the problem here is that many people are new to turbo technology and might not know the dos and don’ts when it comes to shutting their cars down after use. Repeated hot shutdowns, meaning the turbo is still hot from the buildup of EGTs, lead to carbon deposits in the coke in the center housing and damage to the seals.
What This Means for Extended Oil Drain Intervals
There’s been much discussion over the last few years about how far oil drain intervals have been stretched. Recommendations by manufacturer vary wildly– usually falling anywhere from 5,000 to 10,000 miles or more. That’s a far cry from the 3,000-mile intervals that drivers had gotten used to. Naturally, it’s been a concern for the quick lube industry because many believe that less frequent oil changes would translate to less revenue. While there may be some truth to the basic math that’s involved there, there are certainly plenty of ways for them to grow their businesses with other maintenance products. However, considering what we’ve seen with modern engines and their tendency to consume oil, drivers may not actually get to capitalize on extended drain intervals in the ways that many thought possible. If you’re to believe what BMW is saying, 1 qt of oil per 1,000 miles means that the oil level could get dangerously low before the next scheduled oil change. In light of these revelations, it would be wise for professional installers to have candid conversations with customers about the potential for excessive oil consumption depending on the vehicle they drive and their driving habits. If the response is that most of their driving consists of quick around town trips, they should seriously consider cutting the manufacturer’s recommended drain interval in half.