Choosing an engine oil for your car isn’t always as simple as referring to the owner’s manual. What if you’re dealing with an unusual situation, or a daily driver that sees autocross use? What if you still have questions (because, we admit, it’s a complicated subject)?
We have answers. More specifically, we know oil experts who have answers. So, we peppered …
Is it okay to run a racing oil in my street car?
Stick with a passenger-car motor oil (PCMO) for a few reasons. First, some racing oils contain increased zinc, which can damage the catalytic converter. Second, racing oils typically have a lower total base number (TBN), which reflects the oil’s ability to neutralize acids from combustion. Oils with a lower TBN require more frequent changes, which wastes time and money in non-competition vehicles. Third, PCMOs are designed with fuel economy in mind–racing oils are not–so they will help you maximize fuel economy and save a little money at the pump.
–Len Groom, Technical Product Manager, Amsoil
Which is worse for my car: the wrong oil or dirty oil? In other words, if I get in a jam, which is the lesser of two evils?
Both scenarios are detrimental to the engine. Dirty, contaminated oil could raise or lower viscosity. The wrong oil may not have the proper additive package necessary for the needs of the given application.
–Kenneth M. Tyger, Director/Technical Services, Penn Grade/PennGrade1 Lubricants
How can I determine exactly what percentage of a semi-synthetic oil is synthetic?
You can’t. Semi-synthetic is a marketing term and not a technical definition.
–Lake Speed Jr., Certified Lubrication Specialist, Driven Racing Oil
You can look for clues to help interpret which oils might be formulated with increased levels of synthetic-base oils. Visit the manufacturer’s website and look at the product data sheet or technical data sheet for its oils. In this document, look for “Typical Physical Characteristics” or “Typical Technical Properties.” This section provides a high-level peek into the base oils used in the formulation. There are two numbers to pay attention to:
Viscosity Index: Oils with a higher number include a better synthetic-base oil that provides more protection to critical components over a wide temperature range by maintaining fluid thickness and the necessary fluid barrier between parts.
Pour Point: This is a measure of the oil’s fluidity at cold temperatures and refers to the lowest temperature at which the oil maintains its ability to flow. Lower numbers are likely to indicate a better synthetic-base oil.
–Len Groom, Technical Product Manager, Amsoil
Does running E85 affect my oil?
Yes, it does. Alcohol (methanol/ethanol) is an excellent degreaser, which makes it more prone to washing oil from the cylinder walls. And as we all know, no lubrication means more wear and corrosion. The air/fuel ratio is richer with E85, and combustion temperatures are lower. Therefore, oil used with E85 needs to have a very strong oil film that can stand up to the wash effect and also have good anti-corrosive additives to protect cylinders, piston rings, etc.
–Stefan Braun, Application Specialist, Liqui Moly
I added forced induction to an engine that was originally naturally aspirated. How do I determine what oil to use?
Look for a high-quality synthetic engine oil that can withstand high temperature operation without thinning, breaking down or evaporating. Check ASTM test results for high temperature/high shear and Noack volatility, which should be available from the oil manufacturer. This oil will offer better protection and performance.
–Michael Trueba, MPT Industries
My BMW manual says to use 10W‑60, but I can’t find it locally. Is there a suitable substitute?
The 10W-60 was specifically designed for that particular engine application. Using another viscosity could void any warranty coverage. The only suitable substitute would be one approved by the manufacturer.
–Kenneth M. Tyger, Director/Technical Services, Penn Grade/PennGrade1 Lubricants
A lot of people recommend diesel oils for older gasoline engines. Do You?
Many people believe the use of diesel engine oil will help an older engine because these oils are formulated for heavy-duty use with extra detergents and anti-wear additives. This assumption is now changing. As modern diesel engine oils change to accommodate the new, cleaner-running diesel engines, the additive packages are changing to accommodate the higher emission standards. The better strategy is to use
the recommended-viscosity oil and add a zinc additive for additional anti-wear protection.
–Michael Trueba, MPT Industries
I’m trying to clean up an older, dirty engine. What oil do you recommend, and what about the aftermarket additives that promise to help?
I’d suggest rebuilding it and properly cleaning it. If some additive or oil cleaned off a dirty engine part, how do you know that piece of dirt won’t cause abrasive wear elsewhere in the engine?
–Lake Speed Jr., Certified Lubrication Specialist, Driven Racing Oil
Can I run a high-zinc oil in my newer engine?
Yes, you can, but should you? No, you should not! High zinc in a new engine will damage the catalytic converter and possibly other emission-related equipment installed on the car. Zinc is no longer necessary due to the fact that it has been replaced with better, more up-to-date additives.
– Stefan Braun, Application Specialist, Liqui Moly
There are high-zinc, true-synthetic oils that have very low evaporation loss numbers and do not create excessive tailpipe emissions. These are the only exceptions to avoiding high-zinc oil in sensitive emissions systems. Running an oil with higher evaporation loss numbers and higher levels of zinc will eventually lead to emissions systems and catalytic converter problems.
–Michael Trueba, MPT Industries
Which oil additives do you recommend and why?
Never use an additive. Just use the right oil.
–Lake Speed Jr., Certified Lubrication Specialist, Driven Racing Oil
We don’t recommend aftermarket oil additives. Engine oils are designed with a fine balance of base oils and additives to work holistically to provide optimal protection and performance. A properly formulated oil for the intended application doesn’t require aftermarket additives to provide good protection. In fact, adding aftermarket additives can disrupt the oil formulation and reduce protection.
– Len Groom, Technical Product Manager, Amsoil
When comparing oils, what numbers on the technical data sheet matter?
It depends on the application and operating conditions. A driver who experiences subzero cold will be more interested in the oil’s pour point than someone living in the South. Drivers of hot-running turbocharged vehicles will be more interested in the oil’s Noack volatility (a measure of high-temperature performance) than your average motorist. In the end, all of the oil’s typical technical properties are important to its overall performance. Focus on using a high-quality synthetic motor oil designed for your specific application and you’ll be fine.
–Len Groom, Technical Product Manager, Amsoil
You can’t really compare how an oil actually works just by comparing numbers on data sheets. Here’s a good example:
Two oils might have a viscosity index of 150. The first oil might be a conventional-based oil with a base VI of 120. The addition of VI improver additives brings the finished oil’s VI up to 150.
On the other hand, a base oil blend with a VI of 150 does not need any VI improver additives. Both oils look the same on the data sheet in regards to the VI, but the second oil will be more shear stable. Again, it’s important to avoid the temptation of thinking “more is better.” Be careful not to get caught up comparing numbers before you’ve defined the application. Remember, the application dictates the chemistry, not the other way around.
–Lake Speed Jr., Certified Lubrication Specialist, Driven Racing Oil
How does direct injection affect oil change intervals?
DI engines can create a variety of problems that relate to oil quality. Leaner combustion raises combustion temperatures, and higher temps can cause oil to evaporate. The vapors this creates will “stick” to intake valves and build up carbon deposits. It will also create more vapors for the PCV system to take care of, and this may eventually cause “clogging.” Any time there’s excess oil evaporation, the oil will thicken and this will affect its ability to lubricate. An oil with a low Noack volatility number is necessary to counteract these higher temperatures.
There’s also the fact that a high-pressure pump is driven by a cam lobe that may wear down if not protected by the oil. These pumps put a tremendous load on the lobe. Once a pump is worn, it will produce less pressure, which in turn will cause driveability issues.
Low-speed pre-ignition (LSPI) is another problem caused by elevated temperatures combined with high volatility. If the oil evaporates into the combustion chamber, it can ignite. Since oil is a very low-octane fuel, it will self-ignite and cause knock or pinging, which we all know can damage the engine.
So in the case of a DI engine, it’s more important to use the proper high-quality, low-volatility engine oil than it is to change it often. Don’t get me wrong, changing the oil more often may help, but if a low-quality oil is used, the damage may be done very quickly due to LSPI.
–Stefan Braun, Application Specialist, Liqui Moly
While DI technology facilitates greater power and efficiency in engines, these gains can be accompanied by a number of unintended consequences:
1. The high cylinder temperatures and pressures found in turbocharged DI engines can lead to low-speed pre-ignition (LSPI) and catastrophic piston damage. This condition is exacerbated by detergent chemistries that have been used in engine oils for many years. Last year, a new API category supplement (SN Plus) was hurriedly established to identify oils that provide enhanced protection against LSPI.
2. The byproducts of DI combustion include unburned hydrocarbon particles–abrasive, sootlike particles–in diesel engines. As these particles make their way into the oil, wear accelerates at key interfaces, like the timing chain pins. The presence of these particles in DI engines is a limiting factor in oil drain intervals.
3. Port fuel injectors continuously spray fuel on the intake valves, and this has a cleaning effect. But injectors inside the cylinder do not spray fuel on the intake valves and therefore do not yield the same cleaning effect. With the first generation of DI engines, we observed heavy deposits forming on intake valves. In many cases, these deposits were significant enough to hamper air flow. Our research suggests that these deposits can be exacerbated by using low-quality engine oil or by over-extending drain intervals.
–Valvoline Technology Team, compiled by Josh Frederick, OEM Technical Manager
My valvetrain is noisy. What oil or additive will quiet this?
Engine oils are a very precise balance of additive components and base oil(s) that work in harmony to provide the desired lubrication. The introduction of any type of additional additive disrupts this formulation synergy–like adding an extra piece to a puzzle that is already complete. This change in harmony can have a negative effect on the performance of the oil, not to mention change its identity. All the desired characteristics an end user requires should be contained within the original oil. Bottom line: Additional aftermarket additives are not needed. Frankly, if an end user relies on an additive to change some aspect of their oil’s performance, then they are utilizing the wrong oil.
–Kenneth M. Tyger, Director/Technical Services, Penn Grade/PennGrade1 Lubricants
How do I know which manufacturer is using a high-quality base oil stock?
No oil manufacturer will answer this question sufficiently; however, the ASTM Noack volatility and HTHS tests give the answer away. The better the test results, the higher the quality of the base stocks.
–Michael Trueba, MPT Industries
A quick glance at the oil’s viscosity index (VI) should provide a good clue as to the quality of the base stock. The higher an oil’s VI, the more it stays in grade and the less the viscosity will change over a given temperature range. Higher-quality base oils will afford much higher VIs.
–Kenneth M. Tyger, Director/Technical Services, Penn Grade/PennGrade1 Lubricants
If I autocross once per month, how often should I change my oil?
If you’re using your daily driver at an autocross event once a month, I wouldn’t change the way I replace the oil. Once you’re using a car that’s been tuned and/or has an engine that’s been modified, I’d start looking at replacing the oil much more frequently. Depending on the level of modifications involved, replace the oil once a month or every 1500 to 2000 miles. Once you have money invested in modifications of your car, changing the oil is cheap.
–Stefan Braun, Application Specialist, Liqui Moly
Change it once a month because if you haven’t been using a competition oil, the regular oil may be damaged, oxidized, over-fueled or dirty.
–courtesy Millers Oils
Many newer cars require 0-weight oil. Is that too light for track work?
One of the most common misconceptions with thinner multi-viscosity oils is that they might be too thin to provide adequate lubrication in a high-performance engine at high temperature. The numbers that make up a multi-viscosity rating tell a different story. The first number is the viscosity when the engine is cold. The lower the number, the thinner the oil and the easier it flows. The second number is the viscosity when the oil reaches operating temperature. Consequently, once the oil is hot, a 0W-40 oil flows and lubricates the same as a straight 40-weight oil. This transformation occurs thanks to the rubberlike “viscosity improvers” that are blended with the base oil to give it its multi-faceted personality. For higher-temperature applications (such as endurance racing in hot climates), a heavier multi-viscosity oil is usually recommended.
–Ole Wagenbach, Rowe USA
During regular driving, how often should modern, synthetic oils be changed?
Every engine treats oil differently. Therefore, we always defer to the OEM’s recommendation for oil drain interval. Often OEMs provide intervals for more than one duty cycle (e.g. “Normal” and “Severe”). We always recommend owners review these recommendations carefully, as it can be surprising how many of us fall into the “Severe” category during the course of our daily commutes. We know of no OEM that recommends a different oil change interval for synthetic oils.
–Valvoline Technology Team, compiled by Josh Frederick, OEM Technical Manager
Oil drain interval (ODI) is largely dependent on (and greatly influenced by) how and where an application is used. With that said, my rule of thumb is to drain every 3000 miles if the engine oil is conventional/mineral-based; 3000 to 5000 miles if it’s a synthetic blend; and 5000 to 7500 miles for full synthetics. Again, I would much rather change the oil long before I should than extend a drain interval just because I can. Synthetic oils do withstand greater volatility and will last longer than their conventional counterparts.
–Kenneth M. Tyger, Director/Technical Services, Penn Grade/PennGrade1 Lubricants
