A Basic Understanding of ZDDP
07-29-2019, 05:16 PM
#1
A Basic Understanding of ZDDP I put this together over the past week and figured I'd post it here since it's nearly impossible to discuss engine oil without bringing up ZDDP. If you have any questions not answered here or need clarification on something, feel free to ask.
Zinc Dialkyl Dithiophosphate
Zinc Dialkyl Dithiophosphate (ZDDP) is a very common additive found in most engine oils. It is a dual purpose additive functioning as both an anti-wear additive and an anti-oxidant. As an anti-wear additive, it chemically forms a film over metal parts that acts as a barrier against metal to metal contact in mixed and boundary lubrication regimes. As an anti-oxidant, it resists oil oxidation, and the protective film protects the metal surfaces from corrosion. Recently, some studies have found that ZDDP can help deter low-speed pre-ignition (LSPI) in turbocharged gasoline direct injected engines. Many tribologists, formulators, certified lubrication specialists, and consumers alike consider ZDDP to be the most important additive in engine oil, and it's easy to see why.
The History of ZDDP
ZDDP was first introduced to engine oils in the early 1940s as an anti-oxidant and extreme pressure additive. It wasn't until a decade later, in the early 1950s, that the anti-wear capabilities of ZDDP gained recognition, and it's been used as the primary anti-wear additive ever since. It was also discovered in the 1950s that the alkyl groups used have an impact on the rate of ZDDP reaction. In the 1990s, it was discovered that ZDDP was harmful to catalytic converters and other emissions equipment which lead to regulations that reduced the maximum amount of phosphorus and sulfur in engine oils. It looked like ZDDP would be phased out completely, but so far, no other anti-wear additive has been found that can match the effectiveness and cost efficiency of ZDDP. Modern oil standards require phosphorus retention testing to ensure minimal amounts of phosphorus find their way into the emissions systems. This has lead to the use of ZDDP additives with a lower volatility, which isn't a bad thing.
Mechanisms of ZDDP
ZDDP is composed of zinc, phosphorus, sulfur, and various alkyl groups. The alkyl groups are often changed to form different types of ZDDP with varying effectiveness on wear protection and oxidation inhibition. There are 3 main types of alkyl groups called primary, secondary, and aryl. Aryl type ZDDP provides the best thermal stability, but has lower wear protection and hydrolytic stability. Secondary type ZDDP has the best wear protection and hydrolytic stability, but is less thermally stable. Primary type ZDDP functions better as an anti-oxidant but is less effective at wear protection. Diesel oils tend to prefer primary type ZDDP to help with oxidation inhibition in the dirtier diesel crankcase and add longevity to the oil's service life. Primary type ZDDP is also less damaging to emissions equipment. Gasoline oils tend to prefer a blend of primary and secondary ZDDP for a balance of oxidation inhibition and wear protection. This is usually in a 30% primary to 70% secondary blend for API/ILSAC oils and some non-ILSAC oils. Dedicated engine break-in and racing oils tend to contain secondary type ZDDP, usually short-chained, for maximum wear protection. Aryl type ZDDP isn't used in engine oils due to it's slow rate of film formation and inconsistent film thickness. Many primary, secondary, and blended primary/secondary types of ZDDP produce a protective film at a moderate rate with good longevity. Certain secondary types of ZDDP produce films much more rapidly, but are quickly depleted under constant high temperature and pressure. This type of ZDDP is great for break-in oils as it promotes the formation of the protective film as fast as possible on fresh engine parts. It's also a good choice for high end racing oils where the oil is changed very often, if not after every race.
ZDDP must be activated in order to start working. It can be activated by temperature, pressure, or rubbing. The temperature activation (aka thermal activation) of ZDDP usually occurs above 150*C (302*F) and is a chemical reaction that occurs slowly even without pressure or rubbing forces present. Pressure activation occurs much like thermal activation but is localized to the areas of the pressure. This is common in rod and main bearings. When ZDDP is activated by rubbing, it reacts much more rapidly, even at temperatures as low as 25*C (77*F). This is where ZDDP shines as an anti-wear additive for flat tappet cams as the face of the flat lifter rubs on the cam lobe. This is also the primary activation on cylinder walls from the rubbing action of piston skirts and rings. Rubbing and pressure between the timing chain and gears also promotes ZDDP activation in this way.
A downside of ZDDP is increased hydrodynamic friction, most notable in the elastohydrodynamic lubrication regime. ZDDP has high boundary friction which is largely dependent on the alkyl structure. However, the largest increase in hydrodynamic friction from ZDDP is due to the ZDDP tribofilm delaying the formation of a hydrodynamic oil film at high entrainment speeds. Secondary type ZDDP has a greater effect on hydrodynamic friction than primary type ZDDP, despite each producing tribofilms of similar thickness.
WTF does all of that mean?
To summarize, ZDDP reacts to high temperature, high pressure, and high rubbing forces to lay down a protective barrier over parts that reduces wear and protects against corrosion. Some types of ZDDP make better anti-wear additives while others make better anti-oxidants. Some types of ZDDP increase friction more than others. Diesel oils tend to use primary type ZDDP that's less focused on wear protection, gas oils use a blend of primary and secondary alkyl ZDDPs for a balance of wear protection and oxidation inhibition, and break-in and racing oils use a specific type of secondary ZDDP for maximum wear protection where long oil service life and emissions equipment damage isn't a concern.
What about aftermarket ZDDP additives?
In any case, aftermarket ZDDP additives should be avoided if at all possible. Finished engine oils are a carefully balanced formula that takes into consideration how well the additives, base oils, and solubilizers play with one another. Adding a foreign aftermarket additive to that oil will upset that balance. Everything has a trade-off. Additive clash is a big concern if the aftermarket additive and the additives already in the oil are not synergistic. Potentially toxic chemical reactions can occur between opposing additives and can form corrosive acids like sulfuric acid or nitric acid. This is why it's important, if you need an oil with higher amounts of ZDDP, to use an oil that already contains higher amounts of ZDDP, as it will be accounted for in the oil's formula.
So how much ZDDP do I need?
The ideal amount of ZDDP varies from one engine to another. There isn't a one-size-fits-all answer, and ZDDP should never be the only specification considered when choosing an oil. Ideally, you'd want to use the lowest concentration of ZDDP that provides sufficient wear protection. If your engine is showing very little to no wear concerns using an oil with 1000 ppm of zinc, then going to an oil with 1400 ppm will just increase hydrodynamic friction with no benefits. Think of this like rear tires on a drag car. If 275 radial tires can take all of the power you can throw at them, then going to 315 radials will just add weight and slow you down.
Also note that it is possible to have too high of a ZDDP concentration. Concentrations higher than about 1900 ppm zinc can cause corrosive wear and potentially abrasive wear, especially if corrosion inhibitors and detergents aren't increased proportionately. When it comes to ZDDP, and all oil additives for that matter, more is not always better. This also part of that careful balance.
Although stock or stock replacement flat tappet cams can survive with modern API limits on phosphorus, I still prefer to see at least 1000 ppm. It just gives a good safety margin. Most roller cams, especially hydraulic rollers, will be more than happy with the 800 ppm limit. When you start getting into really high spring pressures (>800 lbs) and aggressive solid roller profiles (>.900” lift), then higher concentrations of ZDDP can be beneficial to maintaining a film between the roller and the lobe.
What other additives synergize well with ZDDP?
Many additives work well with ZDDP, but the best pairing is with a friction modifier called tri-nuclear molybdenum dithiocarbamate (MoDTC). This additive is also serves double duty as a friction reducer and anti-oxidant. MoDTC reacts the same way as ZDDP, with temperature, pressure, and rubbing, to form a slick barrier on parts to reduce friction. It synergizes well with ZDDP as it will bond with ZDDP's tribofilm, reducing the friction generated by ZDDP's film, while not hurting ZDDP's effectiveness. You'll often find higher concentrations of MoDTC along with higher concentrations of ZDDP in dedicated racing oils.
Zinc Dialkyl Dithiophosphate
Zinc Dialkyl Dithiophosphate (ZDDP) is a very common additive found in most engine oils. It is a dual purpose additive functioning as both an anti-wear additive and an anti-oxidant. As an anti-wear additive, it chemically forms a film over metal parts that acts as a barrier against metal to metal contact in mixed and boundary lubrication regimes. As an anti-oxidant, it resists oil oxidation, and the protective film protects the metal surfaces from corrosion. Recently, some studies have found that ZDDP can help deter low-speed pre-ignition (LSPI) in turbocharged gasoline direct injected engines. Many tribologists, formulators, certified lubrication specialists, and consumers alike consider ZDDP to be the most important additive in engine oil, and it's easy to see why.
The History of ZDDP
ZDDP was first introduced to engine oils in the early 1940s as an anti-oxidant and extreme pressure additive. It wasn't until a decade later, in the early 1950s, that the anti-wear capabilities of ZDDP gained recognition, and it's been used as the primary anti-wear additive ever since. It was also discovered in the 1950s that the alkyl groups used have an impact on the rate of ZDDP reaction. In the 1990s, it was discovered that ZDDP was harmful to catalytic converters and other emissions equipment which lead to regulations that reduced the maximum amount of phosphorus and sulfur in engine oils. It looked like ZDDP would be phased out completely, but so far, no other anti-wear additive has been found that can match the effectiveness and cost efficiency of ZDDP. Modern oil standards require phosphorus retention testing to ensure minimal amounts of phosphorus find their way into the emissions systems. This has lead to the use of ZDDP additives with a lower volatility, which isn't a bad thing.
Mechanisms of ZDDP
ZDDP is composed of zinc, phosphorus, sulfur, and various alkyl groups. The alkyl groups are often changed to form different types of ZDDP with varying effectiveness on wear protection and oxidation inhibition. There are 3 main types of alkyl groups called primary, secondary, and aryl. Aryl type ZDDP provides the best thermal stability, but has lower wear protection and hydrolytic stability. Secondary type ZDDP has the best wear protection and hydrolytic stability, but is less thermally stable. Primary type ZDDP functions better as an anti-oxidant but is less effective at wear protection. Diesel oils tend to prefer primary type ZDDP to help with oxidation inhibition in the dirtier diesel crankcase and add longevity to the oil's service life. Primary type ZDDP is also less damaging to emissions equipment. Gasoline oils tend to prefer a blend of primary and secondary ZDDP for a balance of oxidation inhibition and wear protection. This is usually in a 30% primary to 70% secondary blend for API/ILSAC oils and some non-ILSAC oils. Dedicated engine break-in and racing oils tend to contain secondary type ZDDP, usually short-chained, for maximum wear protection. Aryl type ZDDP isn't used in engine oils due to it's slow rate of film formation and inconsistent film thickness. Many primary, secondary, and blended primary/secondary types of ZDDP produce a protective film at a moderate rate with good longevity. Certain secondary types of ZDDP produce films much more rapidly, but are quickly depleted under constant high temperature and pressure. This type of ZDDP is great for break-in oils as it promotes the formation of the protective film as fast as possible on fresh engine parts. It's also a good choice for high end racing oils where the oil is changed very often, if not after every race.
ZDDP must be activated in order to start working. It can be activated by temperature, pressure, or rubbing. The temperature activation (aka thermal activation) of ZDDP usually occurs above 150*C (302*F) and is a chemical reaction that occurs slowly even without pressure or rubbing forces present. Pressure activation occurs much like thermal activation but is localized to the areas of the pressure. This is common in rod and main bearings. When ZDDP is activated by rubbing, it reacts much more rapidly, even at temperatures as low as 25*C (77*F). This is where ZDDP shines as an anti-wear additive for flat tappet cams as the face of the flat lifter rubs on the cam lobe. This is also the primary activation on cylinder walls from the rubbing action of piston skirts and rings. Rubbing and pressure between the timing chain and gears also promotes ZDDP activation in this way.
A downside of ZDDP is increased hydrodynamic friction, most notable in the elastohydrodynamic lubrication regime. ZDDP has high boundary friction which is largely dependent on the alkyl structure. However, the largest increase in hydrodynamic friction from ZDDP is due to the ZDDP tribofilm delaying the formation of a hydrodynamic oil film at high entrainment speeds. Secondary type ZDDP has a greater effect on hydrodynamic friction than primary type ZDDP, despite each producing tribofilms of similar thickness.
WTF does all of that mean?
To summarize, ZDDP reacts to high temperature, high pressure, and high rubbing forces to lay down a protective barrier over parts that reduces wear and protects against corrosion. Some types of ZDDP make better anti-wear additives while others make better anti-oxidants. Some types of ZDDP increase friction more than others. Diesel oils tend to use primary type ZDDP that's less focused on wear protection, gas oils use a blend of primary and secondary alkyl ZDDPs for a balance of wear protection and oxidation inhibition, and break-in and racing oils use a specific type of secondary ZDDP for maximum wear protection where long oil service life and emissions equipment damage isn't a concern.
What about aftermarket ZDDP additives?
In any case, aftermarket ZDDP additives should be avoided if at all possible. Finished engine oils are a carefully balanced formula that takes into consideration how well the additives, base oils, and solubilizers play with one another. Adding a foreign aftermarket additive to that oil will upset that balance. Everything has a trade-off. Additive clash is a big concern if the aftermarket additive and the additives already in the oil are not synergistic. Potentially toxic chemical reactions can occur between opposing additives and can form corrosive acids like sulfuric acid or nitric acid. This is why it's important, if you need an oil with higher amounts of ZDDP, to use an oil that already contains higher amounts of ZDDP, as it will be accounted for in the oil's formula.
So how much ZDDP do I need?
The ideal amount of ZDDP varies from one engine to another. There isn't a one-size-fits-all answer, and ZDDP should never be the only specification considered when choosing an oil. Ideally, you'd want to use the lowest concentration of ZDDP that provides sufficient wear protection. If your engine is showing very little to no wear concerns using an oil with 1000 ppm of zinc, then going to an oil with 1400 ppm will just increase hydrodynamic friction with no benefits. Think of this like rear tires on a drag car. If 275 radial tires can take all of the power you can throw at them, then going to 315 radials will just add weight and slow you down.
Also note that it is possible to have too high of a ZDDP concentration. Concentrations higher than about 1900 ppm zinc can cause corrosive wear and potentially abrasive wear, especially if corrosion inhibitors and detergents aren't increased proportionately. When it comes to ZDDP, and all oil additives for that matter, more is not always better. This also part of that careful balance.
Although stock or stock replacement flat tappet cams can survive with modern API limits on phosphorus, I still prefer to see at least 1000 ppm. It just gives a good safety margin. Most roller cams, especially hydraulic rollers, will be more than happy with the 800 ppm limit. When you start getting into really high spring pressures (>800 lbs) and aggressive solid roller profiles (>.900” lift), then higher concentrations of ZDDP can be beneficial to maintaining a film between the roller and the lobe.
What other additives synergize well with ZDDP?
Many additives work well with ZDDP, but the best pairing is with a friction modifier called tri-nuclear molybdenum dithiocarbamate (MoDTC). This additive is also serves double duty as a friction reducer and anti-oxidant. MoDTC reacts the same way as ZDDP, with temperature, pressure, and rubbing, to form a slick barrier on parts to reduce friction. It synergizes well with ZDDP as it will bond with ZDDP's tribofilm, reducing the friction generated by ZDDP's film, while not hurting ZDDP's effectiveness. You'll often find higher concentrations of MoDTC along with higher concentrations of ZDDP in dedicated racing oils.
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99 Black Bird T/A (09-14-2022), B52bombardier1 (09-05-2022), DualQuadDave (02-08-2024), G Atsma (09-05-2022), streetperf (01-19-2020)
07-29-2019, 08:34 PM
#2
ModSquad
iTrader: (6)
Great write up sir. Appreciate your contributions to the site.
The following users liked this post:
Polyalphaolefin (07-29-2019)
07-30-2019, 01:00 AM
#3
Thanks for the write-up!
If you have the time and inclination, I'd also love to hear about what additives oil vendors have begun to use instead of ZDDP, since the API specs seems to be reducing the allowable amounts of ZDDP over time.
Especially in premium oils, where there's room in the budget for more expensive alternatives.
If you have the time and inclination, I'd also love to hear about what additives oil vendors have begun to use instead of ZDDP, since the API specs seems to be reducing the allowable amounts of ZDDP over time.
Especially in premium oils, where there's room in the budget for more expensive alternatives.
07-30-2019, 03:43 AM
#4
Thanks for the write-up!
If you have the time and inclination, I'd also love to hear about what additives oil vendors have begun to use instead of ZDDP, since the API specs seems to be reducing the allowable amounts of ZDDP over time.
Especially in premium oils, where there's room in the budget for more expensive alternatives.
If you have the time and inclination, I'd also love to hear about what additives oil vendors have begun to use instead of ZDDP, since the API specs seems to be reducing the allowable amounts of ZDDP over time.
Especially in premium oils, where there's room in the budget for more expensive alternatives.
Ceramic anti-wear additives have good anti-wear capabilities, but are tied to the same flaws as other solid particle additives. They have a tendency to fall out of suspension, and are also prone ashy deposits that can cause sticking and coking issues around the rings and pistons.
The types of ZDDP we see today aren't the same as 30 years ago. The environmental hysteria over it has caused a major push in research to make the additive more efficient, more reactive, and less volatile. We now have nearly 200 different types of ZDDP out there.
08-21-2020, 06:01 PM
#6
ModSquad
iTrader: (6)
Putting this one in stickyville...
The following users liked this post:
G Atsma (08-21-2020)
08-21-2020, 06:44 PM
#7
TECH Senior Member
Trending Topics
09-05-2022, 05:43 PM
#8
For those looking for a more in-depth explanation of ZDDP... https://www.sciencedirect.com/scienc...01679X19303214
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G Atsma (09-05-2022)
05-24-2023, 01:13 PM
#9
TECH Apprentice
"We now have nearly 200 different types of ZDDP out there.":
this is imo the most important to take home. probably 30 different zink-phoshorus compounds get currently used.
(the ubiquious question, how much "zink" do i need is like asking how much do i have to drink to get wasted. it depends on what you are drinking.)
this is imo the most important to take home. probably 30 different zink-phoshorus compounds get currently used.
(the ubiquious question, how much "zink" do i need is like asking how much do i have to drink to get wasted. it depends on what you are drinking.)
The following users liked this post:
G Atsma (05-24-2023)