Choose the Right Oil: Everything You Need to Know from the Experts at Motul

What is ZDDP and why Does my Engine Need it?

Our first question for Joey: What’s ZDDP, and why does my engine need it? ZDDP stands for zinc dialkyl dithio phosphate, and it’s a high-pressure anti-wear additive. There’s also ZDTP, a slightly different form. Both prevent wear on metal-to-metal interfaces–like those found throughout an engine. If you’ve ever seen oil marketed as containing zinc, it’s one of these two additives that’s being promoted. As Joey explains: “Before the 1930s, oil was just oil, there were no modifiers in it, and you had to deal a lot with issues like wax residue and frequent oil changes. As time wore on, more additives were added to the base oil, like zinc, to help with anti-wear and oil longevity.”

So, if it was introduced in the ‘30s, why is zinc the new buzzword? Joey clarified: “The issue with zinc and high-pressure additives in oil is that they pollute.” He explained that they were mostly phased out of common oils in the ‘70s and ‘80s, as manufacturers scrambled to meet ever-changing emission standards. “There was a lot of confusion during these decades, as the amount of zinc added was going down, but oil companies weren’t necessarily putting the exact numbers out there. Standards were changing just as quickly as the lubrication requirements were, so it was a tumultuous time.” 

In addition to changing emissions requirements, the physical requirements of cars changed, too. Newer engines featured fewer harsh interfaces–moving from solid to roller lifters, for example–and didn’t need the zinc additives as much as they had before. ZDDP is also tough on catalytic converters, another reality of the time period, and a primary reason it was mostly removed from oil.

So oils were updated along with modern cars, but that didn’t change the requirements of older vehicles. If your car isn’t modern, odds are you should be running an oil with more zinc than what you’ll find at the average Jiffy Lube.

Why Does Oil Weight or Viscosity Matter?

Viscosity is a simple concept–it’s the difference between warm and cold maple syrup–but choosing your oil weight isn’t as simple. The biggest factor is your engine’s tolerances, which are specified with a specific weight of oil in mind. Sure, there are other factors, but in general you should run whatever oil weight your owner’s manual recommends. Run a 5W-30 in an engine that requires 20W-50, and you run the risk of thin oil not providing the necessary lubrication or oil pressure. Flip the script and run 20W-50 in an engine that requires 5W-30, and you risk oil-starving tiny passages.

What about using heavier oil in a worn-out engine? That’s just a band-aid, but in certain circumstances it can be a viable way to improve oil pressure in an engine that you’re already planning on rebuilding.

 

What About Modern Oils?

Simply put, the newer the car, the newer the oil standard it will require. You’ll probably kill the catalytic converter on a new Camry if you use an oil with a higher ZDDP content, which is why every manufacturer will recommend a specific oil standard, not just a weight. Most advice in this category boils down to one thing: If in doubt, read the bottle before pouring it in. Every oil will list the standards it meets on the label.

Wondering if that 0W-20 oil will really keep your new car safe? The answer is yes: Though the switch to lighter and lighter oils in recent years is primarily driven by the quest for better fuel economy, manufacturing tolerances have tightened up accordingly. Replacing these light oils with old-school heavyweight oil is a terrible idea.

Does that mean that the reverse is true, and modern oils are bad for a classic car? “Absolutely,” says Joey, “While modern oils still have some level of ZDDP in them for their anti-wear properties, the amount is much, much lower and would certainly shorten the life of your classic engine regardless of how you use the car. Stick with oil grades that were made for your specific car.”

What About Diesel and High-Mileage Oils?

Diesel engine oil is a longstanding silver bullet on automotive forums, so we asked Joey if it was really appropriate for older cars. “Diesel oils are not necessarily a good option for older cars. As newer diesel engines run cleaner than before, you’re going to run into the same problems that you would with oils for gasoline engines. Yes, the viscosity can be higher, but you’re going to run into an oil with more detergents for the diesel engine that your classic car doesn’t need, and less zinc that your car does need.”

And according to Joey, it’s much the same story for high-mileage oils. “They don’t necessarily have more ZDDP additives, but rather more detergents and dispersants, which themselves work as trash bags to help with sludge buildup. So even if you have a higher mileage classic, an SN grade high-mileage oil is not going to have the ZDDP additives your engine needs.”

What’s wrong with detergents and dispersants? They’re necessary in older cars, too, but zinc still takes top priority inside an engine where real estate is precious. Anything in oil that isn’t oil isn’t lubricating, and zinc has a second downside: it’s actually corrosive, meaning it has to be well-managed in the formulation.

Of course, there’s more to classic car oil than zinc: It’s, well, the oil. After all, most of that bottle is oil, which is technically known as base oil.

Put simply, base oil is the raw material that Motul starts with, and Joey is mighty proud of it. “Motul uses the best additives and best base oils imported from France,” says Joey. Why does that matter? He explains this way: “If you start out with Kevlar and work your way up, you’re starting with a strong foundation that can withstand what you’re asking of it. The base must be strong. If instead you start with cotton and work your way up, it will work, but not as well.” Low-quality base oils can break down in an engine, and the results can be catastrophic.

Is it Okay to Run Mineral (Conventional) Oil in my Classic?

Conventional wisdom says that classic cars can’t be switched from traditional mineral oil to synthetic lubricants, so we asked Joey why: “In short, on older, unmodified engines, gaskets can deteriorate, especially cork gaskets, and seals become pretty accustomed to the same basic formula. You also have to keep in mind that any buildup around the seals or gaskets can actually help seal and could easily become dislodged by a synthetic oil’s detergents. They work a little too well in the full synthetics on an old engine that’s hasn’t been rebuilt with newer gaskets.” Fortunately, Motul’s catalog includes a line of mineral-based oils designed for classics.

What’s the use case for that mineral oil? Joey gives an example of an unrestored Porsche 356: “Maybe the owner only takes it out and drives it occasionally. He lives in a pretty nice climate like Southern California so extreme heat would rarely be an issue. For this customer, I’d recommend our 20W-50 classic performance oil which is mineral-based and comes in a vintage-look can. We have a wide-range of mineral oils in the classic line, all with varying levels of detergents, which we state specifically on the can.”

Classic oils have high levels of ZDDP, since flat-tappet lifters and vintage bearings need more high-pressure additives to help lubricate them against metal-on-metal wear.

Not Living in That Perfect So-Cal World?

Motul has a trick up their sleeves: The semi-synthetic. They call their particular line of semi-synthetics Technosynthese®, which they describe as the best of both worlds, offering great performance at a reasonable price. Their most common line of semi-synthetic oils for classic cars is called 4100 Power.

What do semi-synthetics do well? Manage heat, as Joey explained: “Semi-synthetics can take heat better, and will work better in hot climates, or if you might experience any stop-and-go traffic situations where temperatures can climb. And let’s assume that Joe Customer does some racing, as well as taking it on long, spirited drives.” In this situation, the semi-synthetic is the right choice.

What About Synthetic Oils?

Of course, the holy grail of oil will always be full-synthetic products. Motul has multiple synthetic lines, most notably their 8100 line for newer cars, and their 300V line of 100% ester-based full racing oils. 300V is perfect for modified engines that require the most protection but is designed for racing: only for track conditions or off-road use. It’s offered in multiple weights, everything from a 0W-15 qualifying oil all the way to a 20W-60 oil like what’s required in some specialty applications.

What Did we Learn?

There’s more to oil than meets the eye, and Motul offers a huge range of products to meet every need. Click here to learn more about their full product lineup.