Lubricants Answer Hub: Short Answers to Real Sourcing Questions
Short, sourced answers to the lubricant questions that procurement managers, fleet buyers, and importers ask most often when evaluating supplier TDS documents, placing bulk orders, or writing RFQs for engine oils and related products. Each answer is self-contained and draws only from current, named industry standards. Suppliers who list lubricants on Altonex Global can reference these answers when preparing their technical documentation for buyer review. For the full technical background behind these answers, see the Industrial Lubricants technical guide; for a side-by-side of the two service categories referenced throughout, see API SP vs API SQ; and for the wider sourcing process, see the B2B Buyers Sourcing Guide.
In this guide:
- Does API SQ replace API SP, or can I still order SP-rated engine oil for my fleet?
- If my supplier ships API SQ engine oil, can I use it in vehicles that currently run on API SP or older grades?
- What exactly is HTHS viscosity and why does it appear on the technical datasheet my supplier sent me?
- My supplier offers both a 5W-30 with HTHS 2.9 mPa·s and one with HTHS 3.5 mPa·s — which should I choose for a bulk fleet order?
- What is the difference between an engine oil that "meets the API SQ specification" and one that is "API SQ licensed"? Does it matter for my purchase order?
- What is the relationship between API SQ and ILSAC GF-7? Are they the same specification?
- My supplier's TDS lists Group III base oil. Another supplier offers Group IV (PAO). What is the practical difference for a bulk lubricant order?
- What is sulfated ash and why does API SQ set a maximum limit of 0.9%?
Frequently asked questions
Does API SQ replace API SP, or can I still order SP-rated engine oil for my fleet?
API SQ does not replace API SP. API SP remains a current, valid, and licensable category — available for suppliers to produce and for buyers to order alongside SQ. API SQ was introduced by the American Petroleum Institute on 31 March 2025 as a new top-tier gasoline engine oil category that builds upon and enhances SP. Both categories coexist. If your fleet vehicles specify API SP, your SP inventory remains compliant and mid-contract orders for SP-rated oil do not need to be rewritten. (Source: Chevron Lubricants — Understanding the New API SQ Category, 2025.)
If my supplier ships API SQ engine oil, can I use it in vehicles that currently run on API SP or older grades?
Yes. API SQ is backward compatible with vehicles specifying API SP and ILSAC GF-6. This means a procurement manager sourcing a single SKU for a mixed-age fleet can specify API SQ and cover vehicles that previously ran on SP-rated oil without risk of specification mismatch. When requesting a quote, confirm the supplier's product carries an active API SQ license — not merely a claim that it "meets" SQ. An active license means the product has passed the required performance tests and is registered with the American Petroleum Institute, so you can verify it against the API Engine Oil Database independently. (Source: Chevron Lubricants — Understanding the New API SQ Category, 2025.)
What exactly is HTHS viscosity and why does it appear on the technical datasheet my supplier sent me?
HTHS stands for High Temperature High Shear. It measures an engine oil's apparent viscosity under conditions that simulate highly loaded journal bearings in a fired internal combustion engine: specifically at 150°C with a shear rate of 10⁶ s⁻¹ (one million per second). The result is expressed in mPa·s (millipascal-seconds). It appears on a TDS because it is a mandatory property under SAE J300 and ACEA sequences — standard test methods are ASTM D4683, ASTM D4741, and ASTM D5481. HTHS tells you how thick the oil film remains at the temperatures and loads that actually occur inside a running engine. (Sources: ADDINOL — HTHS Viscosity Definition; SAE J300; ASTM D4683.)
My supplier offers both a 5W-30 with HTHS 2.9 mPa·s and one with HTHS 3.5 mPa·s — which should I choose for a bulk fleet order?
The choice depends on the engine design and the OEM specification your fleet vehicles require. SAE J300 sets a minimum HTHS of 2.9 mPa·s for SAE 5W-30. Both products therefore meet the SAE floor. Under ACEA 2023, oils with HTHS between 2.6 and 2.9 mPa·s are classified as reduced-HTHS fuel-economy grades — the primary class in this band is C5. Note that C7 (a 0W-16 grade) is a distinct ACEA 2023 category with its own HTHS range of 2.3–2.6 mPa·s and should not be grouped with C5. Oils above 3.5 mPa·s are normal-HTHS grades (A3/B4, E4, E7). Higher HTHS provides a stronger oil film on journal bearings under load, which is the preference for heavy-duty or high-temperature duty cycles. Lower HTHS is associated with reduced friction and potential fuel-economy gains, but requires confirmation that the engine is designed to tolerate reduced-HTHS oil. Check your vehicle OEM service manual for the required ACEA class before placing a bulk order. (Sources: SAE J300; ACEA 2023; ADDINOL — HTHS Viscosity Definition.)
What is the difference between an engine oil that "meets the API SQ specification" and one that is "API SQ licensed"? Does it matter for my purchase order?
It matters. "Meets API SQ" is a self-declared claim by the formulator or blender — it has not been independently audited or registered with the American Petroleum Institute. "API SQ licensed" means the product has passed the required performance tests and the manufacturer holds a current license from API under the API 1509 licensing program, confirmed by appearance on the API Engine Oil Database. For a B2B purchase order, specifying "API SQ licensed" in your RFQ forces the supplier to provide a traceable license number and enables you to verify the product independently. A "meets spec" claim carries no such accountability and cannot be independently verified by the buyer.
What is the relationship between API SQ and ILSAC GF-7? Are they the same specification?
API SQ and ILSAC GF-7 are closely aligned but not identical. They were developed concurrently and share the same core performance objectives — enhanced fuel economy, LSPI protection for turbocharged engines, superior engine cleanliness, and extended timing chain wear protection. The practical difference for procurement is scope: API SQ covers additional ultra-low viscosity grades, specifically SAE 0W-8 and SAE 0W-12, which fall outside the GF-7 scope. If your fleet vehicles require one of those ultra-low viscosity grades, the relevant specification to cite in your RFQ is API SQ, not GF-7. For standard grades covered by both, either designation identifies a product at the current top tier. (Source: Chevron Lubricants — Understanding the New API SQ Category, 2025.)
My supplier's TDS lists Group III base oil. Another supplier offers Group IV (PAO). What is the practical difference for a bulk lubricant order?
Under API 1509, Group III base oil is produced by severe hydrocracking of crude-oil-derived feedstocks. It must have saturates ≥ 90%, sulfur ≤ 0.03%, and viscosity index ≥ 120. Despite its high viscosity index, it remains crude-derived. Group IV base oil consists exclusively of polyalphaolefins (PAOs), which are chemically synthesized — not refined from crude oil — using feedstocks such as alpha-olefins. Both Group III and Group IV achieve a viscosity index ≥ 120. For most commercial fleet applications, a well-formulated Group III product meets OEM requirements at lower unit cost. Group IV is typically specified where the OEM explicitly requires a fully synthetic PAO base, or where the application demands the tighter molecular uniformity that synthesis provides. Confirm the required base-oil group in your OEM specification before committing to a bulk order. (Source: Machinery Lubrication — Base Oil Groups; API 1509.)
What is sulfated ash and why does API SQ set a maximum limit of 0.9%?
Sulfated ash is the non-combustible residue that remains when an engine oil is burned and the resulting ash is treated with sulfuric acid. It originates primarily from the metallic additive components in the oil — principally calcium and magnesium detergents and zinc-based anti-wear agents. API SQ sets a maximum sulfated ash limit of 0.9% by weight. The rationale is engine hardware protection: modern gasoline engines increasingly use gasoline particulate filters (GPFs) to meet emissions regulations. High sulfated ash content accelerates GPF clogging, reducing filtration efficiency and potentially triggering engine fault codes or requiring premature filter replacement. Keeping sulfated ash at or below 0.9% helps protect GPF service life. When evaluating a supplier's TDS, confirm the reported sulfated ash value and the test method used — typically ASTM D874. (Source: Chevron Lubricants — Understanding the New API SQ Category, 2025.)
Sources: American Petroleum Institute — API 1509 (Engine Oil Licensing and Certification System, current edition); Chevron Lubricants — Understanding the New API SQ Category, 2025; SAE International — SAE J300 (Engine Oil Viscosity Classification, current edition); ACEA — ACEA 2023 European Oil Sequences; ADDINOL Lube Oil — HTHS Viscosity Definition (technical reference); ASTM International — ASTM D4683, ASTM D4741, ASTM D5481 (HTHS test methods); ASTM D874 (Sulfated Ash test method); Machinery Lubrication — Base Oil Groups reference (API 1509 classification). Last reviewed 26 Jun 2026.