:root { --yellow: #F5C400; --yellow-dark: #D4A900; --steel-900: #0D0F12; --steel-800: #141720; --steel-700: #1C2030; --steel-600: #252A3A; --steel-500: #323848; --steel-400: #4A5268; --steel-300: #6B7490; --steel-200: #9AA3BC; --steel-100: #C8CFDF; --steel-50: #EFF1F6; --white: #FFFFFF; --red: #E03A3A; --green: #2ECC71; --r: 4px; --fh: 'Oswald', sans-serif; --fb: 'Inter', sans-serif; } *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; } html { scroll-behavior: smooth; scroll-padding-top: 80px; } body { background: var(--steel-900); color: var(--steel-100); font-family: var(--fb); font-size: 16px; line-height: 1.7; overflow-x: hidden; } .container { max-width: 1140px; margin: 0 auto; padding: 0 24px; } h1, h2, h3, h4 { font-family: var(--fh); font-weight: 700; text-transform: uppercase; letter-spacing: 0.5px; line-height: 1.1; } h1 { font-size: clamp(36px, 6vw, 64px); } h2 { font-size: clamp(24px, 4vw, 38px); } h3 { font-size: clamp(18px, 3vw, 26px); } p { margin-bottom: 1em; color: var(--steel-200); } a { color: var(--yellow); text-decoration: none; } a:hover { opacity: .75; } strong { color: var(--white); font-weight: 600; }
/* Hero */ .hero { background: var(--steel-800); padding: 80px 0 60px; border-bottom: 1px solid var(--steel-600); position: relative; overflow: hidden; } .hero::before { content: ''; position: absolute; inset: 0; background: repeating-linear-gradient(90deg, transparent, transparent 60px, rgba(245,196,0,.025) 60px, rgba(245,196,0,.025) 61px); pointer-events: none; } .hero-grid { display: grid; grid-template-columns: 1fr 360px; gap: 60px; align-items: center; position: relative; } @media (max-width: 768px) { .hero-grid { grid-template-columns: 1fr; } } .eyebrow { font-family: var(--fh); font-size: 13px; letter-spacing: 3px; text-transform: uppercase; color: var(--yellow); margin-bottom: 16px; font-weight: 600; } .hero h1 { color: var(--white); margin-bottom: 12px; } .sub { font-family: var(--fh); font-size: clamp(14px, 2vw, 18px); color: var(--steel-300); letter-spacing: 2px; text-transform: uppercase; margin-bottom: 28px; } .answer-box { background: var(--steel-700); border-left: 5px solid var(--yellow); border-radius: var(--r); padding: 24px 28px; margin-top: 28px; } .answer-box::before { content: 'DIRECT ANSWER'; font-family: var(--fh); font-size: 10px; letter-spacing: 2.5px; color: var(--yellow); font-weight: 700; display: block; margin-bottom: 8px; } .answer-box p { color: var(--steel-50); font-size: 16px; line-height: 1.65; margin: 0; font-weight: 500; }
/* Stats panel */ .stats-panel { background: var(--steel-700); border: 1px solid var(--steel-500); border-top: 3px solid var(--yellow); border-radius: var(--r); padding: 24px 20px; } .stats-panel h4 { font-family: var(--fh); font-size: 13px; letter-spacing: 2px; color: var(--yellow); margin-bottom: 16px; font-weight: 700; } .stat-row { display: flex; justify-content: space-between; align-items: flex-start; padding: 10px 0; border-bottom: 1px solid var(--steel-600); gap: 12px; } .stat-row:last-child { border-bottom: none; } .stat-label { font-size: 12px; color: var(--steel-300); font-weight: 600; text-transform: uppercase; letter-spacing: 0.5px; flex: 1; } .stat-val { font-family: var(--fh); font-size: 15px; color: var(--white); text-align: right; } .stat-val.red { color: var(--red); } .stat-val.green { color: var(--green); }
/* Sections */ .section { padding: 64px 0; } .section + .section { border-top: 1px solid var(--steel-700); } .section-label { display: inline-block; font-family: var(--fh); font-size: 11px; letter-spacing: 2px; text-transform: uppercase; padding: 4px 10px; border-radius: 2px; background: var(--yellow); color: var(--steel-900); margin-bottom: 12px; font-weight: 700; } .section h2 { color: var(--white); margin-bottom: 16px; } .section h3 { color: var(--white); margin-bottom: 14px; margin-top: 36px; } .section h3:first-child { margin-top: 0; }
/* Warn box */ .warn-box { background: rgba(224,58,58,.12); border: 1px solid var(--red); border-left: 5px solid var(--red); border-radius: var(--r); padding: 20px 24px; margin: 28px 0; } .warn-box::before { content: '⚠ WARNING'; font-family: var(--fh); font-size: 11px; letter-spacing: 2px; color: var(--red); font-weight: 700; display: block; margin-bottom: 8px; } .warn-box p { color: var(--steel-100); margin: 0; }
/* Table */ .tw { overflow-x: auto; margin: 24px 0; } table { width: 100%; border-collapse: collapse; font-size: 15px; } thead tr { background: var(--steel-600); border-bottom: 2px solid var(--yellow); } th { font-family: var(--fh); font-weight: 600; text-transform: uppercase; letter-spacing: 0.5px; padding: 14px 16px; text-align: left; color: var(--white); font-size: 13px; } td { padding: 13px 16px; border-bottom: 1px solid var(--steel-600); color: var(--steel-200); vertical-align: middle; } tr:nth-child(even) { background: var(--steel-800); } .badge-yes { display: inline-block; background: rgba(46,204,113,.15); border: 1px solid var(--green); color: var(--green); font-family: var(--fh); font-size: 12px; padding: 2px 10px; border-radius: 2px; letter-spacing: 1px; }
/* Two-col compare */ .compare-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin: 24px 0; } @media (max-width: 600px) { .compare-grid { grid-template-columns: 1fr; } } .compare-card { background: var(--steel-700); border: 1px solid var(--steel-500); border-radius: var(--r); padding: 24px; } .compare-card h4 { font-family: var(--fh); font-size: 16px; color: var(--white); text-transform: uppercase; letter-spacing: 1px; margin-bottom: 12px; } .compare-card ul { list-style: none; padding: 0; margin: 0; } .compare-card li { font-size: 14px; color: var(--steel-200); padding: 6px 0; border-bottom: 1px solid var(--steel-600); display: flex; gap: 8px; } .compare-card li:last-child { border-bottom: none; } .compare-card li::before { content: '→'; color: var(--yellow); font-family: var(--fh); flex-shrink: 0; }
/* Use-case grid */ .use-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin: 24px 0; } @media (max-width: 600px) { .use-grid { grid-template-columns: 1fr; } } .use-card { border-radius: var(--r); padding: 24px; } .use-card.yes { background: rgba(46,204,113,.08); border: 1px solid rgba(46,204,113,.3); } .use-card.no { background: rgba(224,58,58,.08); border: 1px solid rgba(224,58,58,.3); } .use-card h4 { font-family: var(--fh); font-size: 15px; text-transform: uppercase; letter-spacing: 1px; margin-bottom: 12px; } .use-card.yes h4 { color: var(--green); } .use-card.no h4 { color: var(--red); } .use-card ul { list-style: none; padding: 0; margin: 0; } .use-card li { font-size: 14px; color: var(--steel-200); padding: 5px 0; border-bottom: 1px solid var(--steel-600); display: flex; gap: 8px; } .use-card li:last-child { border-bottom: none; } .use-card.yes li::before { content: '✓'; color: var(--green); font-weight: 700; flex-shrink: 0; } .use-card.no li::before { content: '✗'; color: var(--red); font-weight: 700; flex-shrink: 0; }
/* Product CTA */ .product-cta { background: var(--steel-700); border: 1px solid var(--steel-500); border-radius: var(--r); padding: 28px; display: flex; align-items: center; justify-content: space-between; gap: 24px; flex-wrap: wrap; margin: 24px 0; } .product-cta p { margin: 0; color: var(--steel-200); font-size: 15px; } .btn { display: inline-block; background: var(--yellow); color: var(--steel-900); font-family: var(--fh); font-weight: 700; font-size: 14px; letter-spacing: 1px; text-transform: uppercase; padding: 12px 24px; border-radius: var(--r); white-space: nowrap; } .btn:hover { opacity: .85; }
/* FAQ */ .faq-list { margin: 24px 0; } .faq-item { border: 1px solid var(--steel-600); border-radius: var(--r); margin-bottom: 12px; overflow: hidden; } .faq-q { font-family: var(--fh); font-size: 16px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.5px; color: var(--white); padding: 18px 20px; background: var(--steel-700); } .faq-a { padding: 16px 20px; background: var(--steel-800); } .faq-a p { margin: 0; color: var(--steel-200); }
/* Related links */ .related-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 12px; margin-top: 24px; } .related-link { background: var(--steel-700); border: 1px solid var(--steel-500); border-radius: var(--r); padding: 14px 16px; display: block; color: var(--yellow); font-family: var(--fh); font-size: 14px; letter-spacing: 0.5px; text-transform: uppercase; transition: border-color .2s; } .related-link:hover { border-color: var(--yellow); opacity: 1; }
10W-30 Diesel Oil for Semi Trucks
10W-30 CK-4 is approved by most Class 8 OEMs as a secondary viscosity grade for moderate temperature operation. It provides better cold-start flow than 15W-40 without the HTHS reduction of FA-4. Primary use cases: fuel economy optimization on CK-4 engines, cold weather operations, and specific OEM recommendations for highway applications. It is NOT a low-viscosity FA-4 grade — 10W-30 CK-4 maintains the ≥3.5 mPa·s HTHS minimum.
Grade Specifications
~11–12 cSt
≥3.5 mPa·s
−22°F / −30°C
CK-4 (not FA-4)
Extreme heat (100°F+)
10W-30 vs 15W-40: What Actually Differs
Both grades are CK-4. Both maintain ≥3.5 mPa·s HTHS — the critical film strength under load is the same. The difference is kinematic viscosity at 100°C: 10W-30 runs slightly thinner at operating temperature. This gives a small fuel economy benefit without the HTHS reduction that makes FA-4 engine-specific.
10W-30 CK-4
- Kinematic viscosity: ~11–12 cSt at 100°C
- HTHS: ≥3.5 mPa·s (full CK-4 spec)
- Cold start: −30°C (full synthetic)
- Small fuel economy advantage over 15W-40
- Approved for highway operation by major OEMs
- Not preferred in extreme heat (100°F+ ambient)
15W-40 CK-4
- Kinematic viscosity: ~15–17 cSt at 100°C
- HTHS: ≥3.5 mPa·s (identical minimum)
- Cold start: −15°C minimum for conventional
- Industry default for Class 8 fleets
- Preferred in hot ambient and vocational use
- Covers more situations — simplifies fleet inventory
10W-30 vs FA-4 5W-30: Critical Distinction
10W-30 CK-4 and FA-4 5W-30 are completely different products in different API categories:
10W-30 CK-4
- HTHS ≥3.5 mPa·s — full film strength
- Approved for all CK-4 engines
- Backward compatible
- Safe for mixed fleets
FA-4 5W-30
- HTHS 2.9–3.2 mPa·s — reduced by design
- ONLY for specific GHG17 engines
- Not backward compatible
- Not safe in pre-2017 engines
Do not confuse 10W-30 CK-4 with FA-4 5W-30. They are different API categories with different HTHS viscosity requirements. 10W-30 CK-4 is broadly compatible with all CK-4 approved engines. FA-4 is only for approved GHG17 engines and will cause bearing damage in pre-2017 platforms.
OEM Approvals for 10W-30 CK-4
Most Class 8 OEMs approve 10W-30 CK-4 as an alternative to 15W-40 for highway operation. The HTHS viscosity requirement is identical — the OEM is approving a thinner kinematic viscosity for the fuel economy benefit, not compromising film strength.
| Engine | OEM Spec | 10W-30 CK-4 Approved? |
|---|---|---|
| Cummins X15 | CES 20086 | YES |
| Detroit DD15 GHG17 | DFS 93K222 | YES |
| Volvo D13 | VDS-4.5 | YES |
| Mack MP8 | EOS-4.5 | YES |
| PACCAR MX-13 | CK-4 | YES |
Always verify against your engine serial number and current OEM service documentation. Approval lists are updated with model year changes.
When to Use 10W-30 — and When to Stick with 15W-40
Use 10W-30 When:
- Highway fleets seeking fuel economy improvement over 15W-40
- Cold climate operations where better cold-start flow matters
- OEM service documentation specifically recommends 10W-30
- Modern GHG17 engines where FA-4 is not approved (Cummins, PACCAR)
Stick with 15W-40 When:
- Hot ambient operations — desert Southwest, summer haul
- Older engines with looser bearing tolerances
- High-load vocational applications
- Simplifying fleet inventory (15W-40 covers more situations)
AMSOIL 10W-30 CK-4 Products
AMSOIL’s primary heavy-duty diesel lineup is built around 15W-40 — the Signature Series Max-Duty DME and Heavy-Duty ADP. For 10W-30 CK-4 specifically, check the AMSOIL diesel engine oil category for current available products.
AMSOIL Diesel Engine Oil Category — Full CK-4 lineup including 10W-30 options where available.
10W-30 Diesel Oil — Common Questions
Yes — most Class 8 OEMs approve 10W-30 CK-4 as an alternative to 15W-40. HTHS viscosity is identical (≥3.5 mPa·s), so film protection under load is the same. Cold start protection is marginally better than 15W-40.
Kinematic viscosity at operating temperature — 10W-30 runs slightly thinner at 100°C (~11–12 cSt vs ~15–17 cSt for 15W-40). HTHS is the same minimum (≥3.5 mPa·s) in both CK-4 grades. 15W-40 is preferred in hot ambient conditions and older engines with looser tolerances.
No. 10W-30 CK-4 and FA-4 5W-30 are different API categories. 10W-30 CK-4 maintains full HTHS ≥3.5 mPa·s and is approved for all CK-4 engines. FA-4 5W-30 has reduced HTHS (2.9–3.2 mPa·s) and is approved only for specific GHG17 engines. They are not interchangeable — running FA-4 in the wrong engine causes bearing damage.
AMSOIL’s primary heavy-duty diesel lineup is 15W-40 — Signature Series Max-Duty (DME) and Heavy-Duty (ADP). For 10W-30 CK-4, check the AMSOIL diesel engine oil category for available products in that viscosity grade.