Technical Electronic oil pressure sender/guage, problem

Ran across "this" (more in depth) zinc-phosphate ZDDP level information. After reading your's and this ZDDP level. It mostly boils down to,,, How much you want to spend. How easy it is to get. (Probably the most important) Your driving habits/requirments. Brand loyality(?).

If you own a cl***ic car or hot rod with a flat-tappet camshaft, choosing the right motor oil can mean the difference between decades of reliable performance and catastrophic engine failure. Since 2004, when the API reduced zinc levels to protect catalytic converters, cl***ic car owners have faced a critical challenge: modern oils don't provide adequate protection for vintage flat-tappet engines.

This guide compares the best high-zinc motor oils available today. As a former Ford truck/automotive engineer and seasoned AMSOIL dealer, I've tested and used many of these products extensively across various engine types and applications.

Motor Oil Zinc Content Chart
Here's the definitive zinc content comparison showing actual ZDDP levels across the top high-zinc motor oils:

Street Performance Oils - Zinc Content Comparison
Brand & Product Zinc (ppm) Phosphorus (ppm) Type
AMSOIL Z-ROD 10W-30 1,400 1,300 Full Synthetic
AMSOIL Z-ROD 20W-50 1,400 1,300 Full Synthetic
Valvoline VR1 20W-50 1,400 1,300 Conventional
Royal Purple HPS 10W-30 ~1,770* ~1,350* Full Synthetic
Royal Purple HPS 20W-50 ~1,770* ~1,350* Full Synthetic
Castrol GTX Cl***ic 20W-50 1,400 Not Specified Conventional
Lucas Hot Rod 20W-50 1,667 Not Specified Conventional
*Royal Purple doesn't specify their zinc or phosphorus ppm levels, these are from real-world testing.

But can high-zinc motor oils truly be compared with another by just strictly looking at zinc & phosphorus levels? We certainly don't think this is the case. Any engine oil is only as effective as it's entire formulation. Below we'll look at how these oils truly stack up against one another.

Top 5 High Zinc Motor Oils Compared
High Zinc Motor Oil Comparison - 20W-50 Viscosity Grade
Oil Specifications AMSOIL Z-ROD Royal Purple HPS Lucas Hot Rod Valvoline VR1 Castrol GTX Cl***ic
Kinematic Viscosity @ 100°C, cSt (ASTM D445)Kinematic Viscosity @ 100°C measures oil thickness at operating temperature. Higher values indicate better high-temperature protection. 19.3 18.06 20.1 20.0 18.0
Kinematic Viscosity @ 40°C, cSt (ASTM D445)Kinematic Viscosity @ 40°C measures oil thickness at ambient temperature. Lower values indicate better cold-start flow. 140.3 122.2 191.3 183.0 163.0
Viscosity Index (ASTM D2270)Viscosity Index measures how oil viscosity changes with temperature. Higher numbers mean more stable viscosity across temperature ranges. 157 164 122 127 123
Cold Crank Simulator, cP @ -15°C (ASTM D5293)CCS measures the oil's ability to flow while cranking an engine at cold temperatures. Lower values indicate easier cold starts. Not Listed 5,027 Not Listed <8,900 8,588
Pour Point, °C (°F) (ASTM D97)Pour Point is the lowest temperature at which oil will flow. Lower values indicate better cold-weather performance. -40 (-40) -45 (-49) Not Listed ≤-24 (≤-11) -27 (-17)
Flash Point, °C (°F) (ASTM D92)Flash Point is the temperature at which oil vapors will ignite when exposed to flame. Higher values indicate better high-temperature stability and lower oil consumption. 254 (490) 224 (436) >204 (>400) Not Listed 210 (410)
NOACK Volatility, % weight loss (ASTM D5800)NOACK Volatility measures oil evaporation at high temperatures. Lower percentages indicate less oil consumption and better high-temperature stability. 4.0 Not Listed Not Listed <15.0 Not Listed
Total Base Number (TBN) (ASTM D2896)TBN measures an oil's ability to neutralize acids formed during combustion. Higher values indicate longer-lasting acid-neutralizing capability. 9.1 9.6 Not Listed 8.3 Not Listed
HT/HS Viscosity @ 150°C, cP (ASTM D5481)High-Temperature/High-Shear Viscosity measures oil film strength under extreme conditions. Higher values indicate better protection under high stress and temperature. 5.2 5.2 Not Listed Not Listed Not Listed
Oil Type Full Synthetic Full Synthetic Conventional Conventional Conventional
1. AMSOIL Z-ROD (Best Overall)
AMSOIL Z-ROD touts the highest flash point (254°C) and the lowest NOACK volatility of the products that provide those specifications, suggesting very good high-temperature stability and low oil consumption. Unlike racing-specific oils requiring frequent changes, Z-ROD supports 5,000-mile service intervals. With their Preferred Customer pricing, you can pickup a quart of AMSOIL Z-ROD 20W-50 for a fraction of the cost of Royal Purple HPS (the most expensive product in our comparison).

Z-ROD is also highly protective during long-term storage. Z-ROD was tested in ASTM D1748-10 (Rust Protection by Metal Preservatives in the Humidity Cabinet) to evaluate rust-preventative properties of oil under high-humidity conditions, similar to those faced by a covered hot rod in a damp garage. The metal coupon treated with AMSOIL Z-Rod showed no signs of rust.


¹Based upon in-house testing of AMSOIL Z-ROD 10W-40 and a leading compe***or obtained on 7/25/2019 in ASTM D1748-10.

For it's effectiveness and overall value, AMSOIL Z-ROD is the best overall high-zinc motor oil in our opinion and is a great choice for daily-driven cl***ics, performance street cars and hot rods that experience extended storage periods.

2. Royal Purple HPS (Best Premium Full Synthetic)
Royal Purple's HPS 20W-50 boasts some impressive specifications, but for it's premium price point (over $18 per quart), it better! With the highest viscosity index, TBN, and lowest Cold Crank Simulator spec and pour point of all the oils we've compared, Royal Purple HPS shines through as having the best viscosity stability across temperature ranges, longer-lasting acid-neutralizing capabilities and superior cold-weather protection.

If you want to pay the most for the most premium quality full synthetic high-zinc motor oil, Royal Purple HPS is your best bet.

3. Valvoline VR1 (Best Budget Option)
Valvoline VR1 conventional just barely nudges out Castrol GTX Cl***ic as one of the best conventional high zinc motor oils, with a decent viscosity index of 127 and a TBN of 8.3 which is nearly on par with the full synthetics in our comparison. VR1 is one of the cheapest high-zinc motor oil products we've compared. For these reasons, Valvoline VR1 is the best budget option for those wanting high-zinc oil protection at the lowest cost.

4. Castrol GTX Cl***ic
Castrol reintroduced their authentic 1980s API SJ formulation specifically for cl***ic cars. Contains 1,400 ppm zinc—adequate for flat-tappet protection under normal service. Available at Walmart and select auto parts stores. Standard 3,000-5,000 mile intervals.

5. Lucas Hot Rod & Cl***ic
Contains the highest zinc content available in a conventional street oil. Standout feature: marine-grade corrosion protection for vehicles stored seasonally or driven infrequently. Race fuel compatible. While ultra-high zinc provides maximum cam protection, it's higher than necessary for most applications.

Important Warnings

• High-zinc oils WILL damage catalytic converters. Only use in pre-emissions vehicles or where catalytic converters have been removed.
• Break-in oils must be changed after 500-1,000 miles. Ultra-high zinc causes bearing damage if used long-term.
• Racing oils require frequent changes. Designed for compe***ion use, not extended street intervals.
• Modern roller cam engines don't need high zinc. Using high-zinc oils provides no benefit and harms emissions equipment.

How Much Zinc Does Your Engine Need?
1,200-1,600 ppm (Street Flat-Tappet Engines)
This range protects flat-tappet camshafts under normal street driving. All the street oils in our comparison fall within this proven range. This is what you need for cl***ic cars, hot rods, and vintage V8s.

1,800-2,400 ppm (Break-In & Racing Only)
Ultra-high zinc for initial engine break-in or racing applications. Must be changed within 500-1,000 miles. Prolonged use causes bearing damage.

Under 1,000 ppm (Modern Roller Cams)
Current API SP specification oils. Adequate for roller lifter engines but insufficient for flat-tappet protection. Don't use these in cl***ic engines.

Warning: Engines with catalytic converters should NOT use high-zinc oils, as phosphorus will gradually poison the catalyst. Most flat-tappet engines predate catalytic converters, making this less of a concern for cl***ic cars.

Why Diesel Oils No Longer Work for Cl***ic Cars
The Forum Advice is Outdated
If you've spent time on cl***ic car forums, you've likely seen recommendations to "just run Rotella T6" or another diesel oil in your flat-tappet engine. This advice is dangerously outdated.

What Changed?
Pre-2007 (API CI-4+ specification):

• Shell Rotella, Chevron Delo, Mobil Delvac contained 1,200-1,400 ppm zinc
• Adequate protection for flat-tappet camshafts
• Forum recommendations were valid

2007 (API CJ-4 specification):

• EPA emissions standards forced reformulation
• Zinc reduced to ~1,000-1,100 ppm
• Marginal for flat-tappet protection

2017-Present (API CK-4 specification):

• Further reduced to 800-900 ppm zinc
• Insufficient for flat-tappet protection
• Formulated for diesel particulate filter (DPF) compatibility, not cl***ic engines

How to Identify Old Stock
If you find old bottles of diesel oil, check the API service donut on the back label:

• CI-4 or CI-4+: May contain adequate zinc (1,200+ ppm) — verify manufacture date
• CJ-4: Marginal zinc levels (1,000-1,100 ppm)
• CK-4 or FA-4: Modern formulation — inadequate for flat-tappet engines

Most diesel oil on shelves today is CK-4 specification. The bottles that worked for cl***ic cars 15-20 years ago simply don't exist in current formulations.

Final Recommendations
For most street-driven cl***ics with flat-tappet cams, AMSOIL Z-ROD offers the best overall value. The fully synthetic base provides superior temperature stability, 5,000-mile service intervals reduce maintenance frequency, and adequate zinc levels protect without excessive bearing wear risks.

Budget-conscious owners get excellent protection from Valvoline VR1 conventional at accessible prices. Modified engines benefit from Royal Purple HPS with LSPI protection.

The key is matching oil characteristics to your specific application: engine design, driving patterns, storage conditions, and maintenance intervals all factor into the optimal choice.

Ready to protect your cl***ic? Shop AMSOIL Z-ROD oils and take advantage of Preferred Customer pricing for up to 25% savings