The 10 Best Oil Additives
Updated by · How we research
Ten oil additives compared by job: stabilizers, ceramic, zinc, diesel cleaners and flushes. Lucas Heavy Duty Oil Stabilizer leads for worn, older engines. When users buy our independently chosen editorial selections, we may earn commissions to help fund the Wiki.
A good motor oil already carries its own blend of cleaners, anti-wear zinc and friction reducers, so most healthy engines need nothing extra. Additives earn their place on narrower jobs: quieting a worn motor, protecting a classic flat-tappet cam, freeing sticky diesel injectors or flushing sludge once. This list is for drivers facing one of those problems.
From the manual
- Most engines take 10 to 20 percent of the oil, up to a quart per gallon; Lucas allows more in a worn engine. p. 1
- Manual gearboxes and transfer cases take a 20 to 30 percent mix, differentials 10 to 20 percent. p. 1
- It's made to raise the oil's viscosity at all temperatures, and it blends with synthetic oils as well. p. 1
- For Ford Power Stroke diesels, Lucas suggests its Pure Synthetic stabilizer instead, a quart per oil change. product page
Why Lucas Heavy Duty Oil Stabilizer is our top pick
Our pick is the thick one, and thickness is the point: a worn, high-mileage engine that burns oil is one of the few cases where an oil maker agrees a bottle earns its place.5 Its data sheet lists a viscosity of 112.4 cSt at 100 C, about two and a half times the 44.1 of our runner-up, the Lucas Pure Synthetic Oil Stabilizer.1,3 The sheet credits it with better ring seal, less blow-by and, in a smoking engine, less smoke.1 Those benefits are the maker's claims; the viscosity figures are the sheets' typical lab values.
The two go in the same way, at 10 to 20 percent of the oil or up to a quart per gallon, and both suit manual gearboxes and differentials.1,3 Even the runner-up's own sheet sends a badly whining differential to our pick.3 Being pure petroleum, our pick blends with synthetics, gear oil and automatic transmission fluid.2
The runner-up is the right bottle for a newer engine. Its maker recommends it over our pick for small cars on light oil such as 5W-30 and for Ford Power Stroke diesels,4,2 and pitches it for easier cold-weather cranking.3 If your owner's manual calls for a thin oil, buy the runner-up; our pick is for engines already past that stage.
| Lucas Heavy Duty | Lucas Pure Synthetic | |
|---|---|---|
| Viscosity at 100 C | 112.4 cSt | 44.1 cSt |
| Base | 100% petroleum | Pure synthetic |
| Dose, most engines | 10-20% of the oil | 10-20% of the oil |
| Maker's steer | Worn engines, whining diffs | Thin-oil engines, Power Strokes |
Sources
- Lucas Heavy Duty 1Product data sheet, 2024 (PDF, archived copy), pp. 1, 2 2Product page
- Lucas Pure Synthetic 3Product data sheet, 2024 (PDF), pp. 1, 2
- 4Lucas oil stabilizer FAQ, reseller copy (Good Vibrations Motorsports)
- 5Valvoline: Oil additives vs. full synthetic oil
From the manual
- Same dose as the Heavy Duty: 10 to 20 percent of the engine oil, or up to a quart per gallon. p. 1
- A differential needs no separate limited-slip additive with it, but Lucas sends a badly whining one to the Heavy Duty. p. 1
- Lucas recommends it for cold-weather use, for easier cranking and protection during cold, dry starts. p. 1
- The sheet says being pure synthetic, it won't void warranties; that's the maker's claim, not a warranty term. p. 1
From the manual
- One 300 ml can treats up to 5 liters of oil; Liqui Moly puts the best dose at about 6 percent of the fill. p. 1
- Not for automatic transmissions or for motorcycles with a wet clutch. p. 1
- Pour it in with fresh oil at a change, and keep to the car's normal oil-change interval. p. 1
- Its proof is an outside gear-rig scuffing test: oil with Cera Tec held to load level 9 before damage, the plain oil to level 4. p. 2
From the manual
- Not for 2005 and newer gas engines or 2007 and later diesels: Rislone says current oils carry enough zinc for them. p. 2
- Gas engines from 1996 and older take a full bottle, 1997 to 2004 about half. Don't overfill. p. 2
- It isn't a break-in additive, and it lasts only until the next oil change, so add it at every change. p. 2
- Older diesels take a bottle per 5.5 quarts of oil; motorcycles only without a wet clutch, at 2 ounces a quart. p. 2
From the manual
- Engine oil takes 28 parts oil to 1 part AR9100; transmission oil takes 12 to 1. p. 2
- Oil-analysis reports will show high potassium and boron from it, which Archoil says is normal. p. 1
- It's an ester-based fluid that Archoil says raises the oil's base number, helping it resist acids. pp. 1-2
- Drain a little oil before adding it to a full crankcase; Archoil warns that overfilling can damage the engine. how-to page
Editor's Notes
November 4, 2026, by Ezvid Wiki Editors:
We read the makers' data sheets for both Lucas stabilizers, Liqui Moly's Cera Tec sheet, Rislone's ZDDP FAQ and Archoil's AR9100 tech sheet, added notes from them under those picks, and explained why Lucas Heavy Duty leads. We fixed the Marvel dosing advice, which had borrowed Rislone's model-year chart, noted that Rislone's FAQ rules out 2005 and newer gas engines, and corrected claims about Red Line Break-In, Cera Tec's lab test and Hot Shot's wear figure.
October 23, 2026, by Ezvid Wiki Editors:
Lucas Heavy Duty Oil Stabilizer is the new top pick. Most people shopping for an additive have an older engine that burns, leaks or rattles, and a cheap thickener is the honest answer for that. Lucas Pure Synthetic stays for newer engines on thin oil, now in the quart bottle, and Marvel Mystery Oil, Rislone Hy-per Lube ZDDP, Red Line Break-In, BG MOA and Archoil AR9100 stay too.
We dropped Rev-X Stiction Fix, which now costs far more for two small bottles, BestLine Engine Treatment, whose replacement rests on the maker's own friction figures, and the Liqui Moly MoS2 treatment, which can upset wet motorcycle clutches. zMax went too. New picks fill gaps readers ask about: Liqui Moly Cera Tec for wear, Hot Shot's Secret Stiction Eliminator for diesel injectors and Liqui Moly Pro-Line Engine Flush for one-time cleaning.
No lab or magazine has published a test of these bottles that we could check, so we leaned on makers' dosing charts, Rislone's zinc and phosphorus figures, the FTC's warranty guidance and years of enthusiast forum threads, and we treated every wear percentage as a sales claim.
Earlier notes
November 3, 2020, by Brett Dvoretz:
Everybody wants their car to operate smoothly and run well for as long as possible. Despite that, most don't take any preventative steps to ensure that happens. Something as simple and affordable as using one of the oil additives on this list may help prevent expensive fixes down the line, and even extend the service life of the internal components of your engine.
Marvel Mystery MM13R is one of the most versatile options here simply because it works as both an oil additive and a fuel treatment in gasoline engines. Conversely, Rislone ZDDP Supplement is probably the least versatile as it should only be used in older vehicles. In cars and trucks with gasoline systems manufactured before 1997, it can be used at full strength, but it is also suitable for use at half strength in those manufactured before 2005. In diesels, it is suitable for use in vehicles manufactured before 2007. At the opposite end of the spectrum we have Red Line 81403 Break-in, which is intended to be used during the break-in period on new motors.
High-performance engines would do well with Lucas Pure Synthetic Stabilizer, Rev-X Stiction Fix, and BestLine Engine Treatment, all of which are effective at mitigating excess engine heat by reducing friction and increasing the film strength of your engine oil. Both Rev-X Stiction Fix and BestLine Engine Treatment are free of solids and Teflon, too.
While zMax 51-212 may not be well suited to very warm climates or engines that run very hot because of its low flash point, it does a good job of reducing carbon build up, and thereby helping to reduce emissions, making it a good choice for old vehicles that may be having trouble meeting emissions standards testing.
April 9, 2019, by Brett Dvoretz:
Extending the life of your engine can be as simple as pouring one of these additives into it. [2026 update: a healthy engine on the oil its maker specifies usually needs no additive; the buyer's guide explains when one helps.] Yet for some reason, many vehicle owners don't bother to do so. If you are one of the few people who know better, you'll find exactly what you are looking for here. Anyone who owns a classic vehicle will be well-served by Rislone Supplement Concentrate, since it contains high levels of zinc. Red Line 81403 Break-in also contains zinc, but not as much as Rislone, so it is just as well-suited to newer and older cars. [2026 update: Red Line's published figures put about 20,500 ppm of zinc in its bottle, a stronger concentrate than Rislone's, and it is sold mainly for engine break-in.] Lucas 10131 Stabilizer is safe to use in gas, diesel, and high-performance engines, so no matter what type of ride you have, you can't go wrong with it. Rev-X Stiction Fix is another option that works well in diesel and gasoline engines. Marvel Mystery MM13R is both a fuel and oil additive, making it extremely versatile, plus it is also very affordable. If you live in a cold climate, Archoil AR9100 Friction Modifier and BG MOA Supplement are smart choices, since they can help cut down on thickening, proving good cold start protection. Whichever formula you choose from this list, your vehicle and wallet will thank you.
Special Honors
Blackstone Laboratories Blackstone Laboratories is an independent lab that analyzes used oil samples you mail in and reports wear metals, fuel or coolant contamination and how much life the oil had left. A test before and after an additive is the only way an owner can see whether it changed anything inside the engine. blackstone-labs.com
Do You Need An Additive At All?
A classic engine with a flat-tappet cam may need extra zinc.
Finished motor oil is already a recipe: base oil plus detergents, dispersants, zinc-based anti-wear compounds, viscosity modifiers and friction modifiers, balanced by the oil maker to meet a standard (Wikipedia: Motor oil). Pouring more chemistry on top can shift that balance, which is why Valvoline, which sells both oil and additives, says most engines on a modern full synthetic need nothing on top (Valvoline). Your owner's manual is the first stop: use the oil grade and change interval it lists, and don't treat any bottle as a reason to stretch that interval (Cadence Petroleum).
Additives make sense when there's a specific problem. An older engine that burns oil or knocks on a cold start may quiet down with a thick stabilizer. A classic engine with a flat-tappet cam may need extra zinc. A diesel with sticky injectors may need a cleaner. Most makers also tell you to add their bottle again at every oil change, since it drains out with the old oil (Marvel Mystery Oil).
Worried about your warranty? The Federal Trade Commission says a warranty stays in effect when you use aftermarket parts, and a dealer must show that the part caused the damage before denying coverage (FTC). That's a reason to keep receipts and oil-change records, not a promise that any additive is harmless.
Match The Bottle To The Job
Stabilizers are thick liquids that raise the oil's viscosity. They can cut smoke, leaks and noise in a worn engine, but a thicker oil isn't what a modern engine with tight clearances and a 0W-20 spec was designed for, so pick a lighter synthetic stabilizer there or skip it.
Friction reducers use ceramic particles, molybdenum compounds or esters to coat metal surfaces. Molybdenum disulfide turns oil black and can make a motorcycle's wet clutch slip, so check the label before using one in a bike that shares engine and clutch oil (Wikipedia: Motor oil).
Zinc boosters add ZDDP, the anti-wear compound older flat-tappet camshafts relied on. Modern oils carry less of it because phosphorus can damage catalytic converters. Rislone, for example, scales its dose by model year, says not to overfill and says its supplement isn't meant for break-in (Rislone). Break-in additives carry heavier doses of the same zinc for a new cam's first miles. Mike Mavrigian, writing MOTOR magazine's Performance Perspectives column for repair technicians in April 2010, advised breaking in a new flat-tappet cam on a dedicated break-in oil or a mineral oil plus a bottle of ZDDP additive, and, for the long haul, either a high-zinc oil or any oil plus "a bottle of ZDDP additive with every oil change" (MOTOR).
Diesel stiction treatments target the oil-driven HEUI injectors in older Ford Power Stroke and Navistar engines, where burnt-oil residue makes the injectors stick on cold mornings (Hot Shot's Secret). Engine flushes are a different tool entirely: they go in just before an oil change and come out with the old oil.
How To Add One Without Causing Trouble
Add the additive at an oil change so you can measure it against fresh oil, and use one at a time so you know what made a difference. Follow the label's dose, which often depends on the engine's age or oil capacity, and never overfill the crankcase: check the dipstick after the bottle goes in, and drain a little if the level sits above the full mark.
Doses come in different shapes. Rislone's chart shrinks with the engine's age, from a full bottle for gas engines from 1996 and older to about half for 1997 to 2004 (Rislone). Marvel has you swap about a fifth of the oil for its bottle (Marvel Mystery Oil). Hot Shot's Secret calls for 4 ounces per quart of oil on the first treatment and every fourth change after, and 2 ounces at the changes in between (Hot Shot's Secret).
With a flush, follow the clock. Pour it into warm oil, idle the engine for the time on the label, then drain and refill right away, with a new filter. Don't drive on it. Take the old oil and filter to an auto parts store or recycling center rather than the trash, and wear gloves: some labels, including Marvel's, carry a California Prop 65 warning.
How we researched this
We compared 18 oil additives across stabilizers, friction reducers, zinc boosters, diesel stiction cleaners and flushes, and kept 10. For five of them we read the maker's own documents: Lucas's 2024 data sheets for the Heavy Duty and Pure Synthetic stabilizers, Liqui Moly's Cera Tec technical information, Rislone's Hy-per Lube ZDDP FAQ and Archoil's AR9100 tech sheet; for the other five, the dosing directions came from the makers' and their distributors' sites, and every wear or friction figure is treated as the maker's claim. The FTC's warranty guidance and a MOTOR magazine column on zinc and flat-tappet cams shaped the guide, and Blackstone Laboratories' advice on additives and oil analysis backs our note on testing used oil. The CPSC recall database lists nothing for any of the ten brands, and Health Canada's lists recalls of other brands' treatments, such as Sea Foam and STA-BIL, but none for these.
Sources (23)
- Wikipedia: Motor oil
- FTC: Auto warranties and auto service contracts
- Rislone: Hy-per Lube Zinc ZDDP Supplement
- Hot Shot's Secret: The science behind Stiction Eliminator
- Marvel Mystery Oil: Original
- Cadence Petroleum: 6 Best Oil Additives
- CPSC SaferProducts.gov
- Lucas: Heavy Duty Oil Stabilizer product data sheet (PDF, archived copy)
- Lucas: Pure Synthetic Oil Stabilizer product data sheet (PDF)
- Lucas: Heavy Duty Oil Stabilizer
- Liqui Moly: Cera Tec technical information (PDF)
- Liqui Moly: Pro-Line Engine Flush
- Rislone: Hy-per Lube ZDDP Supplement FAQ, P/N 4405 (PDF)
- Archoil: AR9100 product tech sheet (PDF)
- Archoil: How to treat your engine with AR9100
- Marvel Mystery Oil: Automobile directions
- Marvel Mystery Oil: FAQs
- Red Line: Engine Oil Break-In Additive
- BG Middle East: Advanced Formula MOA data
- Valvoline: Oil additives vs. full synthetic oil
- MOTOR magazine: Performance Perspectives, April 2010 (PDF)
- Blackstone Laboratories: Which oil is best?
- Health Canada: Recalls and safety alerts
Frequently asked questions
Do oil additives work?
For narrow jobs, often yes: a thick stabilizer can quiet and slow oil burning in a worn engine, zinc helps older flat-tappet cams, and stiction cleaners can free sticky diesel injectors. For a healthy engine on the right oil, there's little to gain. Wear-reduction percentages on labels are the makers' own claims.
Will an oil additive void my car's warranty?
Not by itself. The FTC says a warranty stays in effect when you use aftermarket or recycled parts, and the maker or dealer has to prove a part caused the damage before refusing coverage. Its guidance speaks of parts, not fluids, so follow the oil grade and change interval in your owner's manual and keep your records.
Can a zinc additive hurt my catalytic converter?
It can. Phosphorus from ZDDP can shorten a converter's life, which is why modern oils limit it. Zinc boosters are meant for older engines; ask the maker before adding one to a late-model daily driver.
Can I mix two oil additives?
It's better not to. Marvel says its oil can share a crankcase with other additives as long as you keep to its dose, but Valvoline warns that layering extra chemistry can upset the balance an oil was built around, and stacking bottles makes it hard to tell what helped. Use one at a time, at the labeled dose.
Is diesel exhaust fluid an oil additive?
No. Diesel exhaust fluid, or DEF, is a urea solution that goes into its own tank and is sprayed into the exhaust to cut emissions. It never touches the engine oil, and it should never go in the crankcase or the fuel tank.
