Khash asked himself 😀 ==> in Engine oil detergents are used to clean surfaces and neutralize acids, why in Turbine oils same chemistry is not used to do the same for acids and varnish on surfaces ?

Khash Answers:

Why Engine-Oil Detergent Chemistry Is Not Simply Used in Turbine Oils

By Khash

The engineer’s question is a good one: if detergents in engine oils clean metal surfaces and neutralize acids, why not use the same chemistry in turbine oils to neutralize acids and clean varnish from turbine surfaces?

The direct answer is: because turbine oils and engine oils are solving different problems under very different operating conditions. The same general idea—keeping surfaces clean, controlling acid formation, and preventing deposits—is absolutely important in turbine oils. But the same high-detergent, high-TBN metallic chemistry used in engine oils is usually not suitable for turbine oil systems, because it can damage the very properties turbine oils must preserve: water separation, air release, foam control, filterability, oxidation stability, cleanliness, and long-term compatibility.

1. Engine oil is designed to hold contamination; turbine oil is designed to reject it

In an internal combustion engine, the lubricant is exposed to combustion byproducts: fuel dilution, soot, nitrogen oxides, sulfur compounds, water, blow-by gases, and high-temperature piston-zone deposits. Engine oil detergents and dispersants are formulated to neutralize acids, keep pistons and ring grooves clean, and hold soot and oxidation products in suspension until the oil is drained. STLE describes engine-oil detergents as additives that neutralize acids formed by combustion and oxidation, provide high-temperature detergency, and help protect against rust, corrosion, deposits, wear, and oxidation. (STLE)

A turbine oil system is different. A gas, steam, or hydro turbine is normally a large circulating oil system with no soot loading and no direct combustion blow-by into the oil. The lubricant may remain in service for many years, and the system depends heavily on water separation, particle removal, air release, low foaming, oxidation resistance, and filterability. Machinery Lubrication notes that turbine oils are R&O oils—rust and oxidation inhibited oils—and that, unlike engine oils, turbine oils are formulated to shed water and allow solids to settle or be removed by filtration; therefore they are generally not additized with high levels of detergents or dispersants. (Machinery Lubrication)

That is the first major difference: engine oils intentionally carry contamination; turbine oils are expected to separate contamination.

2. Engine detergents are usually metallic, alkaline, and surface-active

The classic engine-oil detergent chemistries are calcium or magnesium sulfonates, phenates, and salicylates. Many of them are “overbased,” meaning they carry an alkaline reserve measured as BN or TBN. This reserve neutralizes acids produced by fuel combustion and oil oxidation. STLE explains that overbased detergents provide base reserve, higher BN gives greater acid-neutralizing capability, and typical metallic detergents contain metals such as calcium, magnesium, boron, or sodium. (STLE)

This is very useful in an engine. It is not automatically useful in a turbine. In fact, in a turbine, the same surface-active nature that makes a detergent clean surfaces can create problems. Detergent molecules often have a polar “head” and oil-soluble “tail,” which is why they can attach to metal surfaces, interact with deposits, and form micelles. That same surfactant behavior can also interfere with water separation and emulsify water into oil.

3. Why the same detergent chemistry can be harmful in turbine oils

The most important reason is demulsibility—the ability of oil and water to separate. Steam turbines, hydro turbines, and many plant environments are exposed to water ingress. If a turbine oil emulsifies water, operators lose one of their main defenses against rust, bearing distress, oxidation acceleration, additive depletion, and filter problems.

Caltex/Chevron explains this very clearly in its discussion of varnish-removal chemistries: detergent/dispersant formulas can be effective at varnish removal, but they may change fundamental oil characteristics, especially water separability; a detergent can make oil and water bond together and emulsify, making water removal extremely difficult. (me.caltexlubricants.com) Precision Lubrication similarly notes that alkylbenzene sulfonate detergents can remain after flushing and can damage demulsibility at very low concentrations because their polar/non-polar molecular structure helps combine oil and water phases. (Precision Lubrication)

A second issue is filterability and cleanliness philosophy. In engines, dispersants keep soot and oxidation products suspended until drain. In turbine systems, especially with servo valves and last-chance filters, we often want soft contaminants, water, and particles to be removed, not stabilized and carried throughout the system. Varnish contamination is especially dangerous in control circuits because it can plate out on servo-valves and last-chance filters, causing sticking and restricted flow. (Machinery Lubrication)

A third issue is additive balance. Turbine oil formulations are delicate. Power Engineering describes typical turbine oil as approximately 99% base fluid and only about 1% additive, with that small additive package balancing antioxidants, rust and corrosion inhibitors, demulsifiers, defoamants, pour-point depressants, and sometimes antiwear chemistry. (Power Engineering) If we add an engine-style detergent or aftermarket TBN booster, we may improve one narrow parameter while damaging water separation, foam control, air release, oxidation life, seal compatibility, or filter performance.

So the answer is not that detergent chemistry “does not work.” It is that in a turbine oil system, it may work in one direction and fail in several others.

4. Acid control in turbine oil is handled differently

In engine oils, acid neutralization is a central function because combustion continuously introduces acidic species. In turbine oils, the acid problem is normally not combustion acid; it is mainly oxidation acid, often linked to heat, air entrainment, water, catalytic metals, electrostatic discharge, contamination, and additive depletion.

Therefore, turbine oils control acid formation mainly through:

High oxidation-stability base oils, such as high-quality Group II, Group III, GTL, PAO, or other synthetic/advanced base stocks.

Antioxidant systems, commonly phenolic and aminic antioxidants, designed to slow the oxidation chain reaction.

Rust and corrosion inhibitors, which protect metal surfaces from acidic or water-related attack.

Metal passivators, which reduce catalytic effects from copper and other metals.

Demulsifiers, antifoam agents, and air-release control, because water and air accelerate oxidation.

Condition monitoring, especially TAN, RPVOT, RULER, MPC, particle count, water, and demulsibility.

The key difference is this: engine oils often fight acids after they are formed; turbine oils are formulated to prevent acids and varnish precursors from forming in the first place. Once oxidation has progressed far enough to create acids, polar degradation products, sludge, and varnish, the oil is already moving into a failure mode.

5. Varnish is not simply “acid on the surface”

Varnish is often misunderstood. It is not just acid sitting on metal that can be neutralized by adding base. Machinery Lubrication defines varnish as a thin insoluble film on fluid-wetted surfaces in turbine systems, made from oil additives and high-molecular-weight thermo-oxidative breakdown products with limited solubility in the base oil. These compounds are polar and migrate from the oil to metal surfaces over time. (Machinery Lubrication)

That means varnish is usually a solubility, oxidation, temperature, and polarity problem. It forms when degradation products exceed the oil’s ability to keep them dissolved. They often deposit in cooler, low-flow areas such as hydraulic control circuits, servo valves, or last-chance filters. This is why adding a strong alkaline detergent is not a complete answer. Varnish control requires preventing oxidation, controlling soft contaminants, maintaining solvency, managing temperature, removing precursors, and preserving the turbine oil’s separation and filtration properties.

6. Modern turbine oils do include varnish-control chemistry from the start

This is where the engineer’s question becomes very relevant today. Oil companies now recognize that varnish is a major turbine reliability issue, especially in modern high-temperature, cycling gas turbines and combined-cycle plants. As a result, many turbine oils are now formulated from the start with deposit-control, varnish-control, keep-clean, or solvency-enhancing chemistry—but these chemistries are balanced specifically for turbine oil requirements, not copied blindly from engine oil formulations.

For example, Mobil states that Mobil DTE 932 GT uses selected base oils and a proprietary additive system for long oil life and “keep clean” performance, and that it is specifically formulated for GE Frame turbines where varnish control is most needed. Mobil also states that the base oil and additive combination is designed to limit varnish formation in the hydraulic system. (Mobil)

TotalEnergies describes PRESLIA EVO 46 as a next-generation turbine oil specially designed to reduce varnish and deposit formation, with superior varnish resistance to prevent deposit buildup on critical components such as servo valves and bearings. (TotalEnergies Lubricants Catalogue)

Caltex/Chevron describes GST Advantage RO with VARTECH Technology as a turbine oil formulated with advanced chemistry to improve oxidation stability, reduce oil degradation, and extend oil life by limiting harmful precursors that can lead to varnish formation. (Caltex Singapore)

So yes: today’s oil companies are already formulating turbine oils with chemistry intended to address varnish, deposits, oxidation, and acid formation from the beginning. The difference is that the chemistry must be turbine-compatible. It must control varnish while still preserving demulsibility, air release, foam control, oxidation life, seal compatibility, and OEM approval.

7. “Cleaning” a turbine system is not the same as cleaning an engine

In an engine, detergent action helps keep piston deposits from forming and keeps contaminants suspended until drain. In a turbine, aggressive cleaning can be risky. If varnish is rapidly stripped from surfaces without proper removal strategy, it may move into servo valves, filters, bearings, or control components. If the cleaning chemistry remains in the oil, it may reduce water separation or consume antioxidants.

That is why varnish remediation is usually handled through a controlled method: dedicated varnish-removal systems, electrostatic separation, ion-exchange or resin technologies, depth filtration, balanced-charge agglomeration, controlled chemical cleaning before a planned oil change, or conversion to a varnish-resistant oil after cleaning. Caltex notes that varnish-removal options include solvents, detergents/dispersants, synthetic solvency enhancers, and filtration technologies, but also warns that each approach has tradeoffs such as seal compatibility, flash-point reduction, water separability loss, antioxidant depletion, or removal of beneficial additives. (me.caltexlubricants.com)

This is why I would not recommend adding an engine-oil detergent, TBN booster, or aftermarket dispersant to an in-service turbine oil unless the OEM, lubricant supplier, and a competent oil-analysis program have approved it. Turbine oil chemistry is not a place for casual top-treating.

8. The practical answer to the engineer

The correct reply is:

Engine-oil detergents are not used in turbine oils at the same treat rate or in the same way because turbine oils must separate water, release air, resist foam, remain highly filterable, and stay in service for many years. Engine-style metallic detergent chemistry can neutralize acids and clean surfaces, but it can also emulsify water, interfere with rust inhibitors and antioxidants, alter filterability, increase ash/metals, and disturb the carefully balanced turbine oil additive system.

At the same time, it would be wrong to say turbine oils have no chemistry for acids and varnish. They do. Modern turbine oils are formulated with antioxidants, corrosion inhibitors, metal passivators, demulsifiers, antifoam systems, antiwear additives where required, and increasingly varnish-control or keep-clean chemistry. The best modern turbine oils are not simply “plain mineral oils”; they are carefully balanced formulations designed to control oxidation, acid formation, sludge, and varnish while still meeting the critical turbine-oil properties.

Final conclusion

The same objective exists in both oils: clean surfaces, protect metal, control acids, and prevent deposits.

But the same chemistry cannot always be used.

In engine oils, detergents and dispersants are used aggressively because the oil must handle combustion contamination and is replaced relatively often. In turbine oils, the lubricant must remain clean, dry, air-free, filterable, and oxidation-stable for long service periods. A turbine oil does not need a high-TBN engine-oil detergent package; it needs a balanced, turbine-specific additive system.

Today, oil companies are indeed formulating turbine oils from the start with varnish-control and deposit-control technologies. That is the right direction. But the chemistry must be engineered into the formulation from day one, tested for turbine performance, and supported by oil analysis—not added randomly as an engine-oil detergent after varnish appears.