Ask an Oil Expert: Industry Specialists Set the Record Straight on Motor Oil for Classic Cars

Illustrations by Sarah Young

Three topics that always prove to be controversial: religion, politics and motor oil.

We can’t help with the first two, but we do know about oil–or, more accurately, we know people who know about motor oil. So we queried their scientific brains on the subject, peppering them with common questions. And the answers flowed.

 

 

Q. My collector car only drives a few hundred miles per year. How often should I change the oil?

  • A. Collector cars typically sit for extended periods and can be subjected to a wide temperature range. Additionally, they’re normally taken for short trips, which don’t allow the engine to reach operating temperature and evaporate accumulated moisture from condensation. For best protection, change the oil in collector cars once a year.

LEN GROOM
Technical product manager
Amsoil

  • A. Unfortunately, engine oil still gets contaminated while sitting in the crankcase in your garage. It collects condensation and debris and should be changed every 12 to 15 months.

MICHAEL TRUEBA
MPT Industries

  • A. For a collector, classic, vintage, legacy or historic street or muscle car, I recommend every 3000 miles or once a year, whichever comes first. It’s always best to change oil prior to any lengthy storage period (weeks to months) so the engine sits with fresh oil in its block. It’s never good to store a vehicle with used oil in the crankcase, as used oil contains harmful internal combustion byproducts, like acids, soot, varnish and moisture.

KENNETH M. TYGER
Director of Technical Services
Penn Grade/PennGrade1 Lubricants

Q. Since modern oils are so much better, do we stick with 20W-50 in our older engines or move to a modern, lighter oil?

  • A. Stick with what the OEM recommends. Your engine was designed to use a specific viscosity of motor oil. An oil that’s too thick or too thin can, for example, fail to adequately fill the clearances between the bearings, leading to wear. While modern oil technology is better, the oil’s viscosity still plays a vital role in protecting your engine.

LEN GROOM
Technical product manager
Amsoil

  • A. It’s always better to use an oil of the same viscosity specified by the engine manufacturer. Unless the engine is being run in an extremely cold climate, continue to use 20W-50 if that is what’s recommended.

MICHAEL TRUEBA
MPT Industries

  • A. The viscosity choice is a matter of bearing clearances and oil temperature. Again, keep the application in focus and not the motor oil. There isn’t a one-size-fits-all chemistry. The application always dictates the chemistry, so the choice of oil should always be made in light of the application.

LAKE SPEED JR. 
Certified lubrication specialist
Driven Racing Oil

  • A. There is no universal answer. It’s important to consider the engine and application as well as to consult the original equipment manufacturer owner’s manual.

Viscosity is a very important parameter of a motor oil. Some modern engine manufacturers recommend 0W-grade motor oil products, even in high-output systems. These engines have been engineered for low-viscosity oils, generally to help deliver either more power or better fuel economy.

An older engine may have specific requirements driving the use of a heavier oil, so it’s important to follow the OEM’s motor oil specifications. For modified or custom engines, the modifications made and the expected use should guide the selection of the engine oil viscosity.

In instances like this, it’s beneficial to understand what the SAE J300 designation specifies for multi-grade engine oils. Take 20W-50, for instance: 20W is the oil’s “winter grade,” with the 20 representing its viscosity under cold operating conditions. The 50 is its “summer grade” and specifies its viscosity under hot operating conditions.

Another example: A 0W-40 and a 10W-40 oil have comparable performance at higher temperatures, but the 0W product would perform much better in cold conditions.

Determining whether you can switch to a different grade of motor oil requires taking a detailed look at your vehicle handbook and consulting any service advisories that your OEM may have issued. If your engine is modified, you should also seek your engineer’s advice and consider your desire to experiment.

ERIC W. KALBERER, PH.D. 
Global product application specialist
Pennzoil

RICHARD DIXON
Technology manager
Pennzoil

Q. Which is better for my original, older engine and why: conventional oil or synthetic? And which one leaks less? And what if that older engine has been recently rebuilt?

  • A. As long as your engine is mechanically sound, a motor oil isn’t going to cause leaks–whether it’s conventional or synthetic. If it’s leak-free and in good shape, use a synthetic oil to provide maximum protection. The same goes for healthy rebuilt engines.

If your engine is older and does leak, the problem could be seals and gaskets that have become brittle or worn. Even if the engine doesn’t leak, those seals could still be in poor condition. Sometimes sludge builds up enough to effectively prevent oil from slipping past deteriorated seals or gaskets. 

Using a high-quality synthetic oil with good detergency can dissolve that sludge and reveal the true condition of the seals, causing leaks. If you suspect your engine falls into this category, we recommend sticking with a conventional oil.

LEN GROOM
Technical product manager
Amsoil

  • A. In most cases, classic engines that have been using conventional oil for several years should stay with conventional oil. The seals get accustomed to the lubricant, and big changes (like switching from conventional to synthetic) can cause them to leak. For rarely driven cars, the risk is not worth the reward, so just stick with conventional oil. Now, if the engine is getting rebuilt, then you can go with synthetic (and then stay with synthetic) after the breaking-in process.

LAKE SPEED JR. 
Certified lubrication specialist
Driven Racing Oil

Q. Is there anything to these oils aimed at high-mileage and older cars, or this just a marketing gimmick?

  • A. Many high-mileage or vintage-car oils have higher amounts of zinc, which does help decrease wear in older engines. Their additive packages also include the detergents and dispersants needed to help clean and protect your engine, along with seal conditioners and more. Of course, with these products you also have a lot of marketing noise and false promises–as you do in any other segment–but quality high-mileage oils are certainly good for your classic or vintage car.

Remember to be specific and differentiate between oils for high-mileage cars and classic or vintage cars. There are many different high-mileage oils, but a 2009 Audi diesel with 200,000 miles will need a different motor oil than a car from the ’70s.

OLE WAGENBACH
Rowe Motor Oil

  • A. I strongly believe that a legacy stock engine should use an engine oil formulation that was more prevalent in the earlier era–certainly one that is conventional or mineral-based and possesses higher antiwear content. I have never been a fan of running modern-day, full-synthetic engine oils in older engines. Due to their light nature, synthetic oils could exacerbate any leaking, blow-by or oil burning issues. If your engine has been rebuilt and the system is without a catalytic converter, reach for oil laden with antiwear additives.

KENNETH M. TYGER
Director of Technical Services
Penn Grade/PennGrade1 Lubricant
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Q. What is an acceptable max oil temperature?

  • A. Once again, this will depend on the design of the engine. Turbocharged engines usually run much hotter–sometimes 250 to 300 degrees Fahrenheit. Generally, oil should stay in the range of 220 to 260 degrees. Temperatures above that may raise evaporation loss and shear issues.

MICHAEL TRUEBA
MPT Industries

Q. What is this talk about seal-swell additives? What are they, and is it all just marketing speak?

  • A. In the early days of synthetic oils (back when they were polyalphaolefin-based) seal shrinkage was commonplace, which means leaky engines were, too. Today, formulators use additives or ester base stocks to counterbalance seal shrinkage issues, so leaks are no longer a concern.

MICHAEL TRUEBA
MPT Industries

  • A. Seal-swell additives are seal softeners, or conditioners. They can clean seals and swell them slightly by replacing elastomer molecules or nitrile atoms that they’ve lost to wear, oxidation and sludge. In other words, seal-swell additives can help stop and prevent leaks.

LEN GROOM
Technical product manager
Amsoil

 

Q. Once I move to an oil with seal-swell additives, can I go back to an oil without them?

  • A. Technically, yes, but it would not be wise, particularly after the reconditioning of seals.

KENNETH M. TYGER
Director of Technical Services
Penn Grade/PennGrade1 Lubricants

Q. How do I determine exactly what percentage of a semi-synthetic oil is synthetic?

  • A. You can’t. Oil companies maintain that information as proprietary, and the percentage of synthetic base oils in a “semi-synthetic” oil can vary from brand to brand.

However, 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:

  1. 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.
  2. Pour Point: This measures the oil’s fluidity at cold temperatures and refers to the lowest temperature at which it maintains its ability to flow. Lower numbers are likely to indicate a better synthetic base oil.

LEN GROOM
Technical product manager
Amsoil

 

 

Q. How much zinc does my older engine need?

  • A. It depends on the engine’s make, model and vintage as well as its purpose–is it for racing or just the occasional trip around town?

Modern engine oils are formulated to be backward-compatible with older stock gasoline engines. However, plenty of modified older engines are out there with flat tappets and aggressive performance cams. For these souped-up old-timers, a higher-zinc oil (like some racing oils) might be prudent. Defer to OEM recommendations for stock engines and to the engine builder’s recommendations for modified engines.

VALVOLINE TECHNOLOGY TEAM
Compiled by Josh Frederick
OEM technical manager

  • A. I recommend above 1200 ppm if it has a flat-tappet cam and lifters.

MANUEL A. GUTIÉRREZ
Director of marketing
Lucas Oil

Q. A lot of people recommend diesel oils for older gasoline engines. Is this good advice? Why or why not?

  • A. The diesel oil recommendation most likely started when API reduced the amount of zinc in gasoline engine oils. Diesel oils contain higher amounts of zinc, so this is why people use them in gasoline engines.

Another potential factor is the wider viscosity selection of diesel oils. If your classic requires a 15W-40 oil, for example, it’s going to be hard to find a gasoline engine oil in that viscosity.

Diesel-specific engine oils are designed to help remove the soot and other byproducts of running diesel fuel–a greater amount than gasoline produces. Therefore, diesel oils usually contain a higher concentration of certain detergents to clean the internals better. Usually this is a good thing. However, the detergents can be so effective that they remove part of the oil film from the cylinder walls, and that can mean quicker wear.

There are other reasons why people use diesel oils in gasoline engines, but none of them are, in my opinion, valid. Modern, high-quality gasoline engine oils are much better at protecting the engine than any diesel oil will ever be.

STEFAN BRAUN
Application specialist
Liqui Moly

  • A. That diesel recommendation comes from the days when diesel oils contained more ZDDP than gasoline engine oils. Today’s API CK-4 diesel spec allows oils to be the same ZDDP level as a gasoline car oil, so the “advantage” of diesel oils has been eliminated.

LAKE SPEED JR. 
Certified lubrication specialist
Driven Racing Oil

Q. What oil should I use when breaking in a rebuilt engine?

  • A. We would defer to the engine builder’s recommendation on this.

VALVOLINE TECHNOLOGY TEAM
Compiled by Josh Frederick
OEM technical manager

 

Q. What makes racing oils so special, and when do I need them?

  • A. A properly formulated racing oil is designed specifically to deliver the benefits racing engines need, such as improved extreme-heat resistance; maximum friction reduction for optimum power; and increased film strength to protect bearings in powerful, high-torque engines.

Passenger car motor oils, on the other hand, are designed with fuel economy and longer oil life in mind–benefits racing vehicles don’t need since their oil is changed frequently. Use an oil designed specifically for racing in competition vehicles.

LEN GROOM
Technical product manager
Amsoil

Q. Is it okay to run a racing oil in my street car?

  • A. Using a racing oil in a street car is not a great choice unless you perform very frequent oil changes. Racing oils don’t contain the same amounts of detergents, dispersant, or other ingredients that are needed for longer oil change intervals. Keeping the engine internals clean equals less wear, so an oil needs to clear away byproducts and suspend them long enough that they reach the oil filter and get trapped. Racing oils often contain high zinc levels, and that zinc will damage exhaust emissions equipment that can be costly to replace.

STEFAN BRAUN
Application specialist
Liqui Moly

Q. What oil do you recommend for an air-cooled Porsche?

  • A. A combination of 20W-50 for cars up to 1960s, then 10W-60 till the last 993 models.

TECHNICAL DEPARTMENT
Millers Oil

  • A. Many air-cooled Porsches should run on 20W-50 engine oils. For some of the later models, Porsche recommends 5W-40 or 10W-40. Once again, it’s always best to follow the factory guidelines unless there are special circumstances, such as a very cold climate or racing applications.

MICHAEL TRUEBA
MPT Industries

Q. Can I run a high-zinc oil in my newer engine?

  • A. Yes, you can, but should you? No, you should not!

High zinc in a new engine will damage the catalytic converter and possibly other emissions-related equipment installed on the car. Zinc is no longer necessary because it has been replaced with better, more up-to-date additives.

STEFAN BRAUN
Application specialist
Liqui Moly

Q. Do you recommend using a zinc additive in older engines?

  • A. 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 jamming an extra piece in a puzzle that’s already complete. This change in harmony can have a negative effect on the performance of the oil, not to mention change its identity.

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’re using the wrong oil.

KENNETH M. TYGER
Director of Technical Services Penn Grade
PennGrade1
Lubricants

  • A. We never recommend using aftermarket oil additives. Engine oils are designed with a fine balance of base oils and additives designed 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

  • A. No! If your oil needs an additive to properly protect your engine, then you need a different oil.

LAKE SPEED JR. 
Certified lubrication specialist
Driven Racing Oil

 

Q. When comparing oils, what numbers on the technical data sheet matter?

  • A. Look for the total base number (TBN), which indicates the oil’s ability to minimize contaminants; the Noack volatility, a measure of evaporation loss; and the high-temperature, high-shear (HTHS) viscosity, which is the oil’s ability to withstand breaking down under high heat.

MICHAEL TRUEBA
MPT Industries

Q. With regular driving, how often should modern, synthetic oils be changed?

  • A. The oil drain interval (ODI) is largely dependent on how and where the application is used. With that said, my rule of thumb is to drain every 3000 miles if the engine oil is conventional or mineral-based; every 3000 to 5000 miles if it’s a synthetic blend; and every 5000 to 7500 miles for a full synthetic. Synthetic oils do afford better volatility and longevity than their conventional counterparts.

Still, I would much rather change the oil long before I should than extend a drain interval just because I can.

KENNETH M. TYGER
Director of Technical Services
Penn Grade/PennGrade1 Lubricants

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