Practical Automotive Maintenance: Oil Replacement Intervals
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Oil Replacement Intervals
07.10
| 00:00 | In this module we're going to cover oil replacement intervals and when we may need to deviate from the OEM service schedule. |
| 00:06 | It's common to see in a service manual that we should change the engine oil and filter approximately every 10, 000 kilometres, depending on the vehicle's environment and how harsh the operation conditions are, with harsher conditions requiring more regular servicing. |
| 00:22 | In some instances, with full synthetic oil, the recommended service intervals might be pushed out as far as 20, 000 kilometres. |
| 00:30 | One reason behind this is that the servicing costs can factor into a consumer's purchasing decision, so if they're comparing two brands of car with comparable sticker prices, but one needs to be serviced twice as often, this could affect the sales. |
| 00:44 | Manufacturers also usually recommend changing the oil every 12 months, regardless of the mileage. |
| 00:50 | This is due to factors like moisture accumulation and oil oxidation that can still occur even if the vehicle isn't driven regularly. |
| 00:58 | While these recommendations may be perfectly acceptable for non-performance petrol engines, let's discuss why this might not be ideal for our application with performance or motorsport focused engines. |
| 01:09 | We already know that oil provides essential lubrication, cooling, cleaning and protection of our drive components, and that oil begins to break down with extreme heat or when contaminants and fluids like fuels are introduced. |
| 01:22 | This can negatively impact the oil viscosity, which can then lead to an oil film that's insufficient to provide proper protection. |
| 01:30 | Another important variable is an oil's regular operating temperature. |
| 01:34 | Repeated extreme temperature use leads to accelerated oxidation and breakdown of the oil, while consistent cold operation may mean the oil doesn't get hot enough to boil off contaminants. |
| 01:46 | Let's look at what happens in some performance application when the oil becomes thinner due to the introduction of fuel contamination or excessively high oil temperatures. |
| 01:56 | Fuel contamination can happen with petroleum fuels, but it typically happens at a much slower rate due to the less overall volume being used compared to alcohol fuels. |
| 02:06 | Regardless of the type though, fuel contamination affects the oil's viscosity and can break down the additives, reducing its ability to do its job. |
| 02:15 | In the previous two modules we touched on the solvent properties of alcohol fuels and the fact that they absorb moisture from the atmosphere. |
| 02:22 | This coupled with alcohol's higher boiling point and higher volume required can accelerate oil dilution. |
| 02:30 | All of these reasons are why it's recommended for cars running alcohol fuels to perform oil changes more frequently. |
| 02:37 | This dilution can be slightly offset though and this is done in a few different ways. |
| 02:41 | Firstly, as our oil temperature increases to operating temperature, it'll be able to boil off some of the water and fuel contamination, which is why it's crucial to be careful when adding oil coolers and thermostats to our vehicles. |
| 02:54 | If the oil cooling system is too efficient and doesn't allow the oil to reach a reasonable operating temperature, we'll lose the ability to boil off some of these fluid contaminants, increasing the oil dilution. |
| 03:06 | Another way to offset this is with a slightly thicker oil or by increasing the oil capacity with extended sumps or oil cooler systems with a larger oil filter, as this increase in volume and thickness will take longer to dilute. |
| 03:20 | Remember though, the thicker viscosity must still be appropriate for our engine clearances as going too extreme with this can harm the engine. |
| 03:28 | If you need a refresher on this, head back to the oil specifications module for more information. |
| 03:33 | Even if we're running an appropriately thicker oil or much larger oil capacity than factory, for high performance alcohol fuelled cars, a guideline of about 5000-7000km between oil changes is typically recommended instead of the usual 10, 000km manufacturer intervals. |
| 03:51 | This is highly dependent on how the car is being used however. |
| 03:55 | Our own SR86 race car for example always gets an oil change after every event, as the oil is the first line of defence and it's a whole lot cheaper and easier to do this than dealing with something going wrong in the engine. |
| 04:09 | This frequent changing keeps the oil viscosity as close to perfect as possible, which is extremely important when working with a high power, high revving and very aggressively driven engine. |
| 04:20 | It's also worth understanding how an oil can thicken over time or start to develop into a sludge. |
| 04:26 | Oil thickening is a complex degradation process that occurs when lubricating oils aren't properly maintained or changed at the recommended intervals. |
| 04:34 | This process involves multiple chemical reactions and environmental factors that transform lubricants into a much thicker substance, which can lead to reduced efficiency, increased wear and potential mechanical failure. |
| 04:47 | This can cause some of our key components and oil passages to become blocked or restricted, which is where we can start to run into some serious problems with engine wear and longevity. |
| 04:56 | You might be wondering if there's any harm in going to the other end of the scale and changing our oil extremely frequently, say every 1, 000km. |
| 05:05 | While this wouldn't have any negative effects on the engine components, there is a point where it becomes a waste of both time and money for non -motorsport applications, as lubricants are usually, able to maintain the correct viscosity, lubrication and cleaning properties well past that. |
| 05:20 | Moving on, unlike engine oil, gear oils typically have a much larger service window. |
| 05:26 | A normal service range for differentials and manual transmissions is about 40-80, 000km, depending on the manufacturer, the materials and the quality of the gear oil used. |
| 05:36 | This larger gap in service intervals is due to several reasons. |
| 05:40 | First of all, these components are typically sealed units and aren't exposed to the same level of contamination as the engine, as obviously no combustion events are happening in sight. |
| 05:50 | The average operating temperature of driveline oils is also lower than engine oils and this leads to less oxidation and breakdown, which when coupled with less contamination, compounds and drastically extends service intervals compared to engine oils. |
| 06:04 | This isn't always the case though and it's worth noting that motorsport applications that see high torque and speed output will most definitely see higher driveline temperatures, therefore, accelerating the oxidation process, requiring a more frequent service interval than recommended by the manufacturer. |
| 06:22 | While contamination is far less likely in these components, it's not impossible. |
| 06:27 | Failed items such as axle seals can allow contaminants like water and dirt from the environment to enter these usually sealed units, which will cause oil breakdown and component wear. |
| 06:37 | Let's summarise what we've covered here before moving on. |
| 06:40 | As engine oil ages, it collects contaminants and thickens, reducing its ability to lubricate bearings, the crankshaft and camshafts. |
| 06:48 | For regular use cases, oil should be replaced every 5-10, 000km or 6-12 months, depending on the conditions, with harsher environments requiring shorter intervals. |
| 06:58 | Alcoholed fuel engines typically need oil changes more frequently, while high performance race engines are serviced after each event. |
