How do you deal with late-model vehicles that use excessive amounts of oil between scheduled oil changes/services? More to the point though, what constitutes excessive oil consumption, and what constitutes normal oil consumption as seen from a vehicle manufacturer's perspective? Despite what vehicle manufacturers regard as normal oil consumption rates though, many average car owners claim that there might be something wrong with their new vehicles that consume oil at the rate of 500ml or more of oil per 1000km.
The fact is that in many cases, there is something wrong with low-mileage engines that burn excessive amounts of oil and in this article, we take a closer look at some of the causes of excessive oil consumption, how to diagnose some of them, and what to tell customers who complain about excessive oil consumption on late-model vehicles. Let us start with this question-
Persuading customers that many car manufacturers regard oil consumption of up to and sometimes more than, 500ml of oil per 1000km as normal is not always easy. Moreover, if you are new to the car repair industry it becomes even more difficult because there are many things about engine oil and how / why so many low mileage engines burn excessive amounts of oil that trade schools do not teach.
There are many examples of things that trade schools do not teach, but since limited space precludes a comprehensive critique of trade school curricula, we will focus on why many low-mileage engines burn high volumes of oil. Nonetheless, and while all of what follows might appear as a digression from the main topic of this article, much of what follows not only lays at the heart of many excessive oil consumption issues on low-mileage engines but also provides the starting point from which many excessive oil consumption issues must be approached.
This is especially true of European vehicles that must use oil formulations that comply with ACEA (European Automobile Manufacturers' Association) oil standards and performance levels. The ACEA represents more than a dozen of Europe’s most important and biggest vehicle manufacturers but limited space precludes the inclusion of the actual ACEA oil classification system here. Nonetheless, it is important to mention the fact that since many ECEA-approved engine oil formulations are NOT compatible with API-approved formulations, this resource on ACEA oil standards should be required reading for all.
As far as non-ACEA-approved oil formulations are concerned, however, many, if not most of us older technicians still believe that the presence of the SAE (Society of Automotive Engineers) seal of approval on an oil container is definitive proof of that oil’s suitability for a particular application, but in reality, the SAE seal means nothing in isolation. This is saying a lot, but the fact is that the SAE seal on oil containers is just one requirement for an oil supplier to comply with the rules, regulations, and standards of the Engine Oil Licensing and Certification System (EOLCS), a regulatory body that is overseen and managed by the American Petroleum Institute (API).
The core business of the API is to establish and maintain quality and performance standards for all automotive lubricants and to do this, the API works closely with organisations such as the American Society for Testing and Materials(ASTM),the Society of Automotive Engineers (SAE), and the American Chemistry Council (ACC), to develop and perform rigorous and ongoing physical, chemical, and performance tests to ensure that the characteristics and physical properties of licensed engine oil formulations* supplied by licensed oil suppliers** comply with the technical requirements of engine manufacturers. These include among others, Ford, General Motors, Fiat Chrysler, as well as manufacturers that are members of the Japan Automobile Manufacturers Association, and the Truck and Engine Manufacturers Association.
*The API also maintains a database of unlicensed engine oil formulators and suppliers that use the API logos fraudulently and/or illegally. While most of these suppliers are based in North America, one is based in Vietnam, which goes to show that there is no telling where counterfeit/harmful oil formulations might turn up.
**Note that one of Australia’s leading oil suppliers, the Penrite Oil Company Pty Limited, is a long-standing member (Licence # 3044) of the Engine Oil Licensing and Certification System, and it is therefore both entitled and required to display the API’s registered marks, logos, and seals that look like this-
Image source: American Petroleum Institute
If we are going to understand at least some of the principal causes of excessive oil consumption on low-mileage engines, we need to understand the information the above logo(s) convey, so let us look at what these logos tell us-
API SERVICE SN
This indicates the oil's service category. For instance, all oil formulations that are intended for use in petrol engines are identified/indicated by "S" service categories, while oil formulations that are intended for use in diesel engines are identified /indicated by "C" service categories. Note that the Engine Oil Licensing and Certification System rules actively prohibit the use of more than one service category in this part of the logo.
SAE 5W-20 /SAE 20W-50
These indicate the viscosity grade(s) of oil, which we are all familiar with.
RESOURCE CONSERVING / ENERGY CONSERVING
These designations typically apply only to oil formulations that are intended for use in petrol engines. Using oils with these designations may result in reduced fuel consumption, but note that a reduction is not guaranteed.
SN PLUS
While this particular logo indicates an oil formulation that is intended for use in petrol engines, this part of the logo may sometimes also include a “C” (diesel) service category. This is to allow licensed oil suppliers to market oil formulations that meet the technical requirements of both diesel and petrol applications. Note that in such cases, the “C” service category will always precede the “S” service category.
Service Symbol containing “CI-4 PlUS”
While this designation is not shown on this example of the API logo, “CI-4 PLUS” identifies diesel oil formations that are designed to provide improved protection against viscosity fluctuations caused by soot formation in some diesel engines. Note that oil formulations that display the CJ-4 service category meet all the requirements of the CI-4 PLUS standard, and therefore, CJ-4 and CI-4 PLUS oil formulations can be considered identical. Note though that to comply with Engine Oil Licensing and Certification System rules, the CJ-4 or CI-4 PLUS identifier must appear in the lower half of the so-called “API doughnut”.
Depending on your point of view, you may have found the above either utterly fascinating, or excruciatingly boring, but there is no denying the fact that modern engines are, for the most part, built around specific oil formulations and as a result, failing to comply with vehicle manufacturer’s recommendations regarding suitable engine oil is among-
Having said that though, it must be stated that there are also other major causes of excessive oil consumption on low-mileage engines that neither our customers as car owners, nor we as technicians have any control over. Note though that it is not the intention of this article to denigrate any vehicle manufacturer in any way; it is, however, the intention of this article to provide Australian mechanics and technicians with at least some insights into why some vehicles exhibit excessive oil consumption rates.
Foremost among these other causes is poor engine design, followed closely by engine designs that place extreme demands on even the most advanced oil formulations. In the latter case, the combination of ever-increasing compression ratios and combustion temperatures, high boost pressures on forced induction engines, smaller and lighter pistons fitted with under-designed rings, and poor fuel quality sometimes exceeds even the most advanced synthetic oil formulations’ capacity to provide adequate lubrication under all operating conditions.
Excessive oil consumption due to poor engine designs dates back to at least 2006, and after a good deal of prodding, Toyota released a TSB late in 2011 that inter alia, stated the following-
“Some 2006 – 2011 model year vehicles equipped with the 2AZ-FE engine may exhibit engine oil consumption. The piston assembly has been changed to minimize oil consumption.” And that “P030# (cylinder # misfire detected) DTC may also be set as a result of oil consumption.”
Another good example involves a series of General Motors engines. In this case, GM released TSB 0-06-01-008F in 2012 that addressed excessive oil consumption issues dating back to 2007. While the remedy prescribed in this TSB fixed the issue in many cases, the issue persisted in some other GM engines, and most notably in the 3.6L V6 engine used in a wide variety of GM and related products.
Although there are many other examples we could list here, none of them absolves us as technicians and mechanics of our responsibility to only use engine oil formulations that are recommended by vehicle manufacturers for specific applications. This writer would like to believe that all professional technicians always adhere to these requirements and recommendations, but from a consumer’s perspective price is often the sole criterion upon which many people base purchasing decisions, including the decision to buy the best engine oil they can afford, as opposed to buying the best engine oil that is available or recommended for their specific vehicles.
Vehicle maintenance/servicing is often very low on many car owners' lists of priorities, and especially on vehicles that are not covered by a warranty or some sort of third-party maintenance plan. Moreover, since many people choose to do their vehicle servicing on a DIY basis in tough economic times, it is hardly surprising that many vehicles, and particularly vehicles that are known to burn oil, begin to burn excessive amounts of oil long before others that are maintained professionally or to a high standard.
So what does all of this mean for you, a professional technician that always follows manufacturers' recommendations concerning engine oil? It simply means that whether or not a dealership honours an engine warranty is entirely contingent upon a), whether or not the engine failed while running on the correct and recommended oil, and b), that the secondary symptoms of poor engine design could lead you down a rabbit hole when a customer’s vehicle exhibits various driveability issues in conjunction with excessive oil consumption, which begs this question-
The primary symptom of poor engine design is excessive oil consumption, but you may see other symptoms that result from poor/inadequate/incomplete/ testing during the vehicles’ development phase. You may also see multiple warning lights and stored trouble codes and this is where it can get tricky, because it is not always easy to distinguish between cause (excessive oil consumption) and effect (several secondary symptoms as a result of excessive oil consumption). Let us look at two examples-
The above are the principal secondary symptoms of excessive oil consumption on many GM products that use the 3.6L V6 engine. Apart from excessive oil consumption, this engine suffers damage to timing chains, sprockets, and chain guides that result in miscorrelations between the crankshaft and the camshafts. Although there is no empirical information on why timing chains and sprockets wear out on these engines, it appears that poor materials selection and/or a combination of inadequate testing and unsuitable oil might be partly responsible.
It is perhaps worth noting that GM has changed its recommended oil for these engines from a semi-synthetic blend to a fully synthetic formulation with a replacement interval of only 8 000 kilometres. Note also that GM has stated that oil consumption of up to one litre/per 3 000 kilometres is normal for a 3.6L engine- even if it runs with fully synthetic oil.
Whatever the cause though, dealerships will usually replace damaged timing components under warranty conditions, but only under strictly enforced conditions. We need not delve into those conditions here, but suffice it to say that a dealership will not do this major job based solely on the say-so of an independent workshop. GM has strict protocols in place, one of which is to perform laboratory tests on the oil in the engine. The best thing you can do for your customer is to explain the manufacturer's protocols as best you can, and maybe to talk to the dealership on his/her behalf. However, whether or not that is always appropriate is not for this writer to say.
All of the above is common on German oil-burners, and particularly on BMW models/engines. The cause most commonly involves poor crankcase ventilation due to carbon deposits in the PCV system, and while replacement of the entire engine vacuum/PCV system will usually cure the driveability issues, it does not cure the underlying mechanical design problems that cause excessive amounts of oil to be drawn into the PCV system.
The best way to diagnose the PCV system on BMW models is to test the engine vacuum with a manometer that is connected to a suitably modified oil filler cap. While engine vacuum values vary somewhat between models and engines, the recommended deviation from stated/specified values should not exceed 5mB in either direction. BMW engines, and particularly BMW petrol engines are very sensitive to engine vacuum issues and even a slight blockage or leak in the PCV system can influence the engine vacuum enough to produce severe driveability problems.
Note though that BMW considers oil consumption of around 500ml per 1 000km as normal on most of their engines, and as a result, BMW dealerships will perform a series of tests on engines with higher than “normal” oil consumption rates to determine actual oil consumption rates before they will repair an engine under warranty conditions.
The same is true for other manufacturers, including among others, Honda, VW, Audi, and Mercedes, which means that you have to keep your wits about you when you perform oil services on the majority of new vehicles, which brings us to this-
The lubrication requirements of modern engines are more demanding than ever before, and if we are to avoid making mistakes, we all need to learn as much about lubrication technology in general, and engine lubrication in particular, as we can. The days are long gone when the most important thing we needed to worry about were viscosity grades; not that viscosity grades are no longer important, but the fact is that modern engines require oil formulations that are engineered to possess very specific physical characteristics and chemical properties that go far beyond mere viscosity grades.
In today's repair environment it is no longer enough to just check and adjust oil levels on every car we work on. It is also necessary to check for TSB's that may announce new recommendations concerning changes to oil formulations, oil change intervals, "acceptable" oil consumption rates, and oil consumption test procedures. Oil service has become a minefield, so be sure to protect yourself by a), always following manufacturer's recommended oil change procedures, and b), by only using oil and oil filters obtained from a reputable supplier.
