How Texaco GST Advantage oils tackle one of the turbine industry's most costly lubrication problems: Varnish

Varnish deposits are a leading cause of turbine downtime, contributing to filter plugging, valve sticking, and bearing failures
Texaco GST Advantage EP and RO are formulated with advanced ashless antioxidant chemistry and premium base oils to minimise varnish formation
GST Advantage EP delivers an RPVOT (Rotating Pressure Vessel Oxidation Test/ ASTM D2272) life of around 2,200 minutes — roughly three times the industry minimum
Both grades are fully backwards compatible with existing GST series oils, making conversion straightforward.

Why Varnish Forms

Varnish deposits are an almost universal problem in industrial lubrication systems. Over time, oil oxidation and thermal degradation produce insoluble by-products that migrate out of the oil and adhere to metal surfaces, forming varnish. These deposits insulate metal surfaces and initiate a vicious cycle of rising temperatures and further oil breakdown, leading to filter plugging, valve sticking, bearing failures, and heat exchanger fouling.

The operational stakes are significant. According to an article in Machinery Lubrication, around 20 percent of power-plant forced outages are turbine-related, and 19 percent of those involve lubricating oil system issues. For operators, a single stuck servo valve can mean unplanned downtime measured in hours or days, with potentially significant associated costs.

GST Advantage EP and RO

Texaco's GST Advantage EP and GST Advantage RO high-performance oils are formulated specifically to help combat varnish formation and extend oil life in modern turbines running under severe conditions and high temperatures.

The two grades serve distinct applications:

GST Advantage EP contains an ashless anti-wear package suited to geared or heavy-duty turbine systems where extreme pressure performance is required.
GST Advantage RO is a non-EP formulation designed for turbines where silver bearings or OEM requirements prohibit EP additives.

Both grades are fully miscible with the previous GST series and most common turbine oils, making conversion in existing units straightforward with no flushing complications (flushing may be recommended based on the condition of the current oil).

How GST Advantage Responds to the Varnish Challenge

Oxidation stability

GST Advantage EP achieves an RPVOT life of approximately 2,200 minutes, roughly three times the industry minimum requirement of 750 minutes. This oxidation resistance aims to achieve longer drain intervals and fewer oil conditioning interventions.

Varnish Deposit Control

Both EP and RO grades use advanced antioxidant chemistry (ashless type) and premium base oils to help minimise sludge and varnish formation. In high-temperature ASTM ageing tests* at 150°C, GST Advantage formulations remained bright and clear with minimal insolubles, producing significantly fewer varnish precursors and helping to keep systems cleaner over the long term.

EP Performance for Geared Turbines

GST Advantage EP achieves an FZG gear test** result of Stage 10, comfortably above the AGMA minimum of Stage 9 for geared turbines. This means the oil provides a meaningful margin of load-carrying capacity beyond the minimum threshold. This is relevant for operators running geared turbines under high loads or elevated temperatures, where scuffing risk is a concern.

Operational and Maintenance Benefits
By resisting oxidation and deposit formation, GST Advantage oils help to extend drain intervals and reduce varnish-related downtime. More stable viscosity and acid numbers over time mean less frequent oil polishing or sweetening. The oils also aim to deliver strong rust and corrosion protection, strong water separability, and reliable foam control.

Critically, fewer varnish deposits mean fewer stuck valves, fewer unplanned trips, and lower overall maintenance costs, helping to keep turbines running reliably between scheduled service intervals. Both grades meet key OEM specifications and have been extensively tested in geared and non-geared turbines under severe operating conditions.

To find out whether GST Advantage EP or RO is the right fit for your turbines, speak to a Texaco lubrication specialist or visit the Texaco Lubricants website.

*ASTM ageing tests in lubricants use high temperatures, oxygen/air pressure, and metal catalysts to simulate long-term, in-service degradation in a laboratory setting.

**The FZG test is a standard laboratory method using a four-square gear machine to evaluate a lubricant's scuffing load-carrying capacity under high-sliding, high-load, and elevated temperature conditions. Results are expressed as load stages, with higher stages indicating greater load-carrying ability.