TBN 400 — Overbased Calcium Sulfonate Detergent

What Is TBN 400?

TBN 400 is a super overbased synthetic calcium sulfonate — the highest-alkalinity detergent additive in commercial lubricant formulation. The "400" is its total base number (TBN): it packs enough alkaline reserve to neutralize 400 milligrams of KOH per gram of additive.

That's roughly twice the TBN of a standard heavy-duty diesel engine oil concentrated into a single component.

It's used where acid attack is relentless. Marine cylinder oils burning 3.5% sulfur heavy fuel. Turbocharged diesels running extended drains. High-temperature crankcase environments where combustion acids eat through ordinary detergent packages in hours.

A few things to get straight right away:

• TBN 400 is a detergent, not a dispersant. It contains calcium, it produces ash, and it neutralizes acids. Dispersants are ashless, metal-free, and don't neutralize anything — they suspend soot. Different job.
• It's not the same thing as calcium sulfonate grease. Same raw material. Different application. The grease uses the crystalline calcite form. This product uses the amorphous carbonate form — engineered to stay colloidally suspended in liquid oil, not gel up.
• High TBN doesn't mean "better" in every engine. There's a trap here, and we'll get to it.

Don't confuse maximum TBN with the right TBN. The additive can deliver ≥400 mg KOH/g. The finished oil only needs enough alkaline reserve to match the fuel sulfur and drain interval. Over-treating creates deposit problems — we cover every one of them in the trap section below.

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Why TBN 400's Chemistry Matters

Most product pages tell you TBN 400 "neutralizes acids." Fine. But they skip the part that actually matters if you're formulating with it.

Here's the structure nobody talks about.

A TBN 400 molecule isn't a simple salt. It's a reverse micelle — a core of amorphous calcium carbonate (CaCO₃) wrapped in a shell of calcium sulfonate soap molecules, with their hydrocarbon tails pointing outward into the oil. This structure was first systematically described in Rudnick's Lubricant Additives: Chemistry and Applications and has been the standard model for overbased detergent chemistry ever since.

The sulfonate shell is roughly 18–19% of the additive. The carbonate core is the rest.

This means:

1. The acid neutralization comes from the carbonate core. When sulfuric acid from fuel combustion hits the additive, the CaCO₃ reacts, neutralizes it, and the carbonate is consumed.
2. The detergency comes from the sulfonate shell. The sulfonate head groups adsorb onto deposit precursors — soot particles, varnish, sludge — and the hydrocarbon tails keep them suspended in the oil so they don't settle on piston rings or cylinder walls.
3. These two functions run on different chemistry. The sulfonate provides corrosion protection by forming an adsorbed hydrophobic film on iron surfaces. The carbonate provides alkalinity only. If you need both rust protection AND acid neutralization, you can't just load up on TBN 400 and assume both are covered. The sulfonate component caps out at ~19% regardless of how high the TBN goes.

This is why overbased calcium sulfonate with a TBN of 300 can actually provide better corrosion protection than a TBN 400 product — the 300-grade has a higher sulfonate-to-carbonate ratio. Less alkalinity, more surface-active rust inhibitor.

Nobody's product page will tell you that.

The practical implication: if you're formulating a marine cylinder oil that needs both extreme acid neutralization AND saltwater corrosion resistance, TBN 400 handles the acid load beautifully — but you may want to blend it with a medium or neutral calcium sulfonate for the corrosion side. Or pair it with an overbased magnesium sulfonate, which delivers TBN more efficiently per unit of sulfated ash.

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Key Features & Benefits

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Technical Specifications

About the viscosity number. At ≤150 cSt @100°C, TBN 400 is pumpable at ambient temperatures above 20°C. Below that — and this is worth reading carefully — it thickens substantially. More on that in the Storage section.

About the sulfated ash. 38–47% is high. That's the trade-off for the TBN: every gram of alkalinity reserve comes with ash-forming metal content. For marine cylinder oils, this doesn't matter — MCO has no SAPS limit. But if you're using TBN 400 as a TBN booster in a heavy-duty diesel formulation with a 1.0% sulfated ash cap, you need to account for every tenth of a percent.

COA per shipment. Every batch ships with a Certificate of Analysis covering TBN (ASTM D2896), calcium content (ASTM D4951), kinematic viscosity (ASTM D445), flash point (ASTM D92), and density (ASTM D4052). TDS and MSDS available. Third-party inspection on request.

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When High TBN Can Work Against You

See, this is the part the spec sheets don't mention.

More alkalinity sounds like more protection. In most cases it is. But not always. There are at least three situations where loading up on TBN 400 can cause problems, and formulators learn these the expensive way.

1. The VLSFO Over-Alkalinity Problem

Since IMO 2020 (MARPOL Annex VI) capped marine fuel sulfur at 0.5%, a lot of operators switched from 3.5% S HFO to VLSFO — but kept using the same BN 70 cylinder oil.

That was a mistake. Here's why.

When you feed BN 70 cylinder oil into an engine burning 0.5% S fuel, most of the alkaline reserve goes unused. The excess unreacted calcium sulfonate doesn't just sit there harmlessly. It reacts with sulfate ash deposits from other sources — residual HFO traces, additive ash from system oil carryover — and forms hard calcium carboxylate deposits on the liner surface.

These deposits abrade the liner. MAN Energy Solutions and WinGD both issued service letters recommending BN 40–70 for VLSFO operations, specifically warning against using BN 70–100 oils with low-sulfur fuel. The deposit mechanism is real, and it's been documented in service.

Fuel sulfur to cylinder oil TBN — field data from crosshead engine service:

Fuel Sulfur	Required Cylinder Oil TBN
0.5%	5 mg KOH/g
0.5–1.0%	5–10 mg KOH/g
1.0–1.5%	10–20 mg KOH/g
1.5–2.5%	20–40 mg KOH/g
2.5–3.5%	40–70 mg KOH/g
>3.5%	70–100 mg KOH/g

The formula behind the table: TBN = 0.35 × X × S × B / L, where X = 0.15 for large marine engines, S = fuel sulfur %, B = hourly fuel consumption (kg/h), L = hourly cylinder oil consumption (kg/h).

The point: TBN 400 is the tool. But the target TBN for the finished oil depends on the fuel. Match them. Don't over-treat just because the additive can deliver it.

2. The Ash Budget Conflict

A CK-4 heavy-duty diesel oil has a 1.0% sulfated ash limit. Every gram of TBN 400 you add contributes roughly 0.38–0.47 grams of sulfated ash. If you're using TBN 400 as a TBN booster in an HDEO formulation, the ash budget runs out fast.

This isn't a problem in marine cylinder oils — MCO has no SAPS limit. But if you're cross-applying TBN 400 into a road-going diesel formulation with DPF compatibility requirements, watch the ash contribution. Once the ash cap is hit, the remaining TBN has to come from ashless sources — dispersants, not detergents.

3. Calcium-ZDDP Competition

In formulations that contain both overbased calcium sulfonate and ZDDP (zinc dialkyldithiophosphate), the calcium ions can compete with zinc for surface activity on ferrous metal.

ZDDP works by thermally decomposing to form a sacrificial phosphate film on cam lobes and valve train components. Calcium doesn't form that film, but it adsorbs strongly to the same surfaces. At high calcium-to-zinc ratios, the ZDDP antiwear film formation is partially suppressed.

This matters in trunk piston engine oils (TPEO) and HDEO formulations where both detergents and ZDDP are present. Marine cylinder oils typically don't contain ZDDP, so the issue doesn't apply there. But if you're using TBN 400 as a treatment in a ZDDP-containing formulation, test the Ca:Zn ratio.

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Compatibility with Other Additives

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Applications & Treat Rates

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Packaging, Storage & Handling

About cold-weather handling. TBN 400 is a viscous liquid at ambient temperature. Below 20°C, viscosity increases sharply — by 15°C the product approaches a semi-paste consistency.

If you're receiving drums in winter or storing in an unheated warehouse, budget 24–48 hours for drum heating before use. Electric drum heaters or a heated storage room at 60–80°C will bring the product back to pumpable viscosity. Do not use open flame. The viscosity returns to normal once the product is warmed — no permanent change to the additive chemistry.

This isn't a quality defect. It's physical chemistry. The high colloidal CaCO₃ loading that gives TBN 400 its alkalinity also makes it more viscous at low temperatures than lower-TBN grades like medium-base calcium sulfonate. The same factor that delivers the performance creates the handling requirement.

For bulk ISO tank deliveries, specify tanks with heating coils. Maintain ≥60°C throughout storage and discharge.

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Frequently Asked Questions

What is TBN 400?

TBN 400 is a super overbased synthetic calcium sulfonate detergent additive for lubricating oils. It has a Total Base Number of ≥400 mg KOH/g — the highest in the commercial calcium sulfonate range — and serves as the primary alkaline reserve in marine cylinder oils, heavy-duty diesel engine oils, and industrial lubricants operating under severe acid-generating conditions.

Unlike lower-TBN sulfonates (TBN 30–300), the 400-grade carries the maximum possible colloidal calcium carbonate loading. This gives it roughly 2.5× the acid-neutralizing capacity per unit weight of a TBN 150 detergent. The trade-off is higher viscosity and higher sulfated ash contribution.

What does TBN stand for?

Total Base Number. It's a measure of the alkaline reserve in a lubricant or additive, expressed as milligrams of potassium hydroxide (KOH) equivalent per gram of sample, measured by potentiometric titration per ASTM D2896. One mg KOH/g is the amount of alkalinity equivalent to 1 milligram of KOH in 1 gram of sample. A TBN of 400 means the additive can neutralize the same amount of acid as 400 mg of KOH per gram.

Is a higher TBN always better?

No. Higher TBN provides longer acid-neutralizing life, which is why marine cylinder oils running on high-sulfur fuel use BN 70–100. But over-treating creates its own problems. If you put BN 70 cylinder oil into an engine burning 0.5% sulfur VLSFO, the excess alkalinity can react with sulfate ash to form hard calcium deposits on the cylinder liner. MAN and WinGD recommend BN 40–70 for VLSFO — not higher. In road-going diesel engines with DPF systems, high TBN means high sulfated ash, which clogs the filter. The TBN 400 additive gives you the flexibility to target any BN from 5 to 100 by adjusting treat rate. The finished oil's BN is what matters — not the additive's maximum capability.

What happens when TBN is too high for the fuel?

Three things, none of them good:

First, unused alkalinity reacts with sulfate ash residues in the oil to form hard, abrasive calcium carboxylate deposits — particularly on cylinder liners in two-stroke crosshead engines. These deposits score the liner surface.

Second, excess calcium competes with ZDDP antiwear chemistry on ferrous metal surfaces. At high Ca:Zn ratios, the ZDDP film formation is partially suppressed, and valve train wear increases.

Third, in formulations with a sulfated ash limit (API CK-4 caps at 1.0%), high TBN makes the ash budget impossible to close. Every gram of TBN 400 carries roughly 0.4 grams of sulfated ash. The rule: use enough TBN to neutralize the expected acid load over the oil drain interval. No more.

What is a good TBN number for engine oil?

Passenger car gasoline (API SP): fresh oil TBN typically 6–10. Light-duty diesel (ACEA C3): TBN 6–9, constrained by low-ash requirements. Heavy-duty diesel (API CK-4, ACEA E9): TBN 8–12, 1.0% sulfated ash cap. Marine TPEO on residual fuel: BN 20–40. Marine cylinder oil on HFO (3.5% S, pre-IMO 2020): BN 70–100. Marine cylinder oil on VLSFO (0.5% S, current): BN 40–70. A BN 70 cylinder oil reaches that target with roughly 15–17 wt% TBN 400 in SAE 50 base oil.

What's the difference between calcium sulfonate and overbased calcium sulfonate?

Neutral calcium sulfonate is the stoichiometric calcium salt of an alkylbenzene sulfonic acid — one calcium ion per two sulfonate acid molecules. TBN ≤30. Function: almost entirely rust inhibition via sulfonate head group adsorption on metal surfaces.

Overbased calcium sulfonate is produced by reacting the neutral sulfonate with excess Ca(OH)₂ and CO₂. The CO₂ reacts to form colloidal CaCO₃ particles, encapsulated by the calcium sulfonate soap into reverse micelles. Result: same sulfonate rust protection shell, plus a CaCO₃ core delivering 400+ mg KOH/g of acid-neutralizing alkalinity. TBN 400 represents the maximum commercially viable overbasing level.

How should I store and handle TBN 400?

Store in a dry, ventilated warehouse at ≤50°C long-term, ≤65°C short-term. Keep drums sealed — the product is hygroscopic. The critical note: TBN 400 thickens below 20°C, approaching semi-paste below 15°C. Budget 24–48 hours of drum heating at 60–80°C before pumping in cold weather. Use electric drum heaters, never open flame. Shelf life: 24 months in original unopened packaging. For bulk ISO tanks, specify heating coils and maintain ≥60°C.

What's the minimum order quantity?

One 200 kg iron drum. Larger quantities available in 1,000 kg IBC totes and ISO tanks. Standard lead time: 7 days. Ships from Jinzhou, China — production capacity 2,000 metric tons per month. For technical inquiries, sample requests, or bulk pricing: sales@chemost.com.

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Last updated: May 13, 2026