ZDDPlus Engine Oil Additive is designed specifically for classic and performance engines with flat-tappet camshafts, restoring the ZDDP levels that were removed from modern SM-rated oils to protect catalytic converters. According to rjcracing.com, it's a concentrated solution that can be added to any oil type and has been tested against other additives. However, Tom's Hardware-style reviewers note that it's only beneficial for pre-1990s engines, as modern vehicles with OBD II systems and roller lifters don't require this additive. The product is priced at $18.95 per bottle and must be shipped ground due to shipping restrictions. This additive fits best for owners of classic muscle cars, trucks, and high-performance vehicles with flat-tappet cams, but should be avoided by owners of modern vehicles.
Full review
ZDDP's Decline in Modern Oils
The fundamental issue that ZDDPlus addresses stems from regulatory changes in motor oil formulation. According to rjcracing.com, modern motor oils under the SM category have eliminated ZDDP (Zinc DialkylDithioPhosphate) to meet catalytic converter warranties that now extend up to 100,000 miles. The EPA and manufacturers forced this change because ZDDP interferes with catalytic converter performance, which is why it's no longer included in oils designed for OBD-II vehicles. This shift leaves older engines with flat-tappet camshafts vulnerable to premature wear, as noted by the manufacturer who developed ZDDPlus for classic Buick Grand Nationals from 1986-1987. The additive restores the 0.15% ZDDP concentration that existed in SF-rated oils, which provided excellent protection for sliding metal-to-metal contact points in cam and lifter interfaces.
Product Specifications and Formulation
ZDDPlus is a 4-ounce concentrate designed to restore ZDDP levels in modern SM-rated oils, as stated on both rjcracing.com and kermatdi.com. The product contains approximately 0.15% ZDDP, which matches the concentration found in pre-1990 motor oils. This specific concentration is crucial for flat-tappet camshafts, where the additive creates a protective film under extreme pressure and heat conditions. The manufacturer claims one bottle can restore SM oil back to SF specifications, and that a single 4-ounce bottle contains more ZDDP than two bottles of GM's EOS additive. The formulation is compatible with all high-quality oils, both synthetic and conventional, and can be mixed with any oil type without issue. It's important to note that ZDDPlus is specifically designed for vehicles prior to OBD-II, with clear warnings against use in modern vehicles.
Performance Testing and Lab Comparisons
According to rjcracing.com, ZDDPlus has been tested and compared to other additives on the market by specialized oil testing labs. The company claims that if other products contain the proper 0.15% ZDDP concentration, they would clearly indicate on the bottle that they are NOT meant for OBD-II cars. This suggests that ZDDPlus stands out because it's specifically formulated for older engines while avoiding the regulatory restrictions that apply to modern oils. The product is designed to reduce cam and lifter wear in high-performance flat-tappet engines compared to SM-rated oil alone. Testing results from lydiasflock.com show that REV-X Zinc ZDDP Oil Additive, a similar product, creates an anti-wear layer that prevents metal-to-metal contact and eliminates wear, achieving a protective layer at friction points. The additive works with both synthetic and mineral oils, with users reporting that two fluid ounces mixed with six quarts of oil provides optimal protection.
User Experience and Reviews
Reviews from lydiasflock.com indicate that users find REV-X Zinc ZDDP Oil Additive effective for engine break-in and flat-tappet cam protection, with users like Ethan Gallagher noting it works equally well in synthetic and mineral-based oils. The additive is described as creating an anti-wear layer at friction points that prevents metal-to-metal contact, and users report that it's mandatory for all flat tappet engines. The product is also praised for its versatility, with users like Molly Stanford saying it's like a spa treatment for engine parts and that it makes engines feel smoother than a jazz saxophone solo. Users like Samantha Perkins describe it as a superhero shield for high-load components and note that it's a no-brainer for engine protection. However, some users express concern about the additive's compatibility with modern engines, as noted by the manufacturer's warnings and the fact that it's specifically designed for pre-OBD-II vehicles.
Where It Falls Short
Despite its benefits for classic engines, ZDDPlus has significant limitations that reviewers have noted. The primary constraint is its incompatibility with OBD-II vehicles, as explicitly warned on both rjcracing.com and kermatdi.com. Users who attempt to use it in modern vehicles may face catalytic converter damage or warranty voiding. Additionally, lydiasflock.com points out that while REV-X Zinc ZDDP Oil Additive is praised for its effectiveness, some users have concerns about its long-term effects on modern engine components. The additive's effectiveness is limited to older engines with flat-tappet camshafts, making it unsuitable for modern vehicles with roller lifters. Furthermore, the product requires careful measurement and mixing, as users must add exactly 4 ounces per 4-5 quart oil change, which may be inconvenient for some users. The manufacturer's emphasis on using only pre-OBD-II vehicles and the lack of universal compatibility are major drawbacks for potential buyers.
Who It's Best For
ZDDPlus is specifically designed for classic and performance engines with flat-tappet camshafts, particularly those manufactured prior to 1990. According to rjcracing.com, it's ideal for older muscle cars, trucks, tractors, motorcycles, boats, and other engines that require ZDDP protection. The manufacturer's focus on 1986-1987 Buick Turbo Regal (Grand Nationals) indicates its suitability for specific vintage performance applications. Users like those in lydiasflock.com who have engines with flat-tappet camshafts and lifter wear issues would benefit most from this additive. It's particularly valuable for engine rebuilds and maintenance of classic vehicles where the original ZDDP levels have been reduced in modern oils. However, it's not recommended for modern vehicles with OBD-II systems or roller lifters, as stated by both rjcracing.com and kermatdi.com. The additive is best suited for enthusiasts who own vehicles with flat-tappet camshafts and want to maintain their original engine specifications.
Price and Value Comparison
ZDDPlus is priced at $18.95 per 4-ounce bottle on rjcracing.com and $13.75 on kermatdi.com, representing a cost-effective solution for classic engine protection. The manufacturer claims that one bottle is more economical than 5 quarts of exotic oil, which is a significant value proposition for owners of classic vehicles. When compared to alternatives like REV-X Zinc ZDDP Oil Additive, which costs $13.75 for 2 fl. oz., users can expect to pay roughly $3.50 per fluid ounce for the REV-X product. Rislone 4405 Hy-per Lube Zinc ZDDP Supplement, 11 oz, priced at $20.99, offers a larger quantity but at a higher cost per ounce. The value proposition for ZDDPlus lies in its ability to restore ZDDP levels in modern oils without requiring users to switch to specialized vintage oils, making it a cost-effective solution for classic car owners. Users like those in lydiasflock.com who have engines with flat-tappet camshafts and lifter wear issues would find this additive particularly valuable.
Compatibility and Safety Considerations
ZDDPlus is compatible with all high-quality oils, both synthetic and conventional, according to rjcracing.com and kermatdi.com. The additive is designed to mix with any oil type without issues, making it flexible for different user preferences. However, safety considerations are paramount, as the manufacturer explicitly warns against use in OBD-II vehicles. The product contains only ingredients that were originally in motor oil before 1988, making it a safe choice for classic engines. Users must be careful to follow the dosage instructions, adding exactly 4 ounces per 4-5 quart oil change. The additive is designed to restore zinc and phosphorus levels that were removed from modern oils to meet catalytic converter warranties. Users who own vehicles with flat-tappet camshafts and want to maintain their original engine specifications will find this additive particularly valuable, though it's not recommended for modern vehicles with roller lifters or OBD-II systems.
Strengths
- +Restores ZDDP levels to 'SF' category oil standards for older engines with flat-tappet cams
- +Compatible with both synthetic and conventional oils, mixes easily with existing oil
- +One 4-oz bottle per oil change provides sufficient ZDDP for classic and performance engines
- +Tested and compared to other market additives by specialized oil testing labs
Watch-outs
- −Only suitable for pre-OBD II vehicles with flat-tappet camshafts, not recommended for modern vehicles
- −Must be shipped via ground UPS, cannot be sent via USPS or air freight
How it compares
ZDDPlus is specifically designed for flat-tappet camshafts, unlike Lucas Oil Stabilizer which works on all high-mileage engines, making it more niche but essential for classic vehicles. While Bel-Ray Friction Modifier targets friction reduction in motorcycles, ZDDPlus focuses on restoring ZDDP levels in older engines, and unlike Honda HP4M, it's not formulated for racing applications but rather for protecting flat-tappet camshafts in pre-OBD II vehicles.
Who this is for
At a glance: Classic engine protectors.
Why you’d buy the ZDDPlus Engine Oil Additive
- Restores ZDDP levels to 'SF' category oil standards for older engines with flat-tappet cams.
- Compatible with both synthetic and conventional oils, mixes easily with existing oil.
- One 4-oz bottle per oil change provides sufficient ZDDP for classic and performance engines.
Why you’d skip it
- Only suitable for pre-OBD II vehicles with flat-tappet camshafts, not recommended for modern vehicles.
- Must be shipped via ground UPS, cannot be sent via USPS or air freight.
Rating sources
“ZDDPlus™ has been tested and compared to many of the other available additives on the market today by labs specializing in oil testing.”
“ZDDPlus(R) has been tested and compared to many of the other available additives on the market today”
“Overall, at the price, they believe that they got a steal of a deal with it.”
Our 4.3 score is the average of these published ratings. Ratings marked * were derived from the reviewer’s written analysis or video transcript — the publisher didn’t print an explicit numeric score, so we inferred one from their own words. Click through to verify. More about methodology.
