lubrication considerations for ships using emerging marine fuels

Diversifying marine fuels introduces impacts from new fuel chemistries on engine lubrication. Biofuels such as FAME (Fatty Acid Methyl Esters) and alcohols like methanol are now available at increasing scale, offering shipowners practical alternatives to conventional marine fuels. However, these fuels present specific characteristics that may influence lubricant performance and the accuracy of used oil analysis. This has implications for engine reliability, maintenance intervals, and lubricant management strategies. 

 
Chevron Marine Lubricants is dedicated to investigating these dynamics through field-based research. At the 31st CIMAC World Congress in 2025, Chevron presented a technical paper summarizing the results of two multi-engine field studies: one focusing on FAME use in four-stroke engines, and the other evaluating methanol’s interaction with lubricants in two-stroke low-speed engines. Together, these findings offer practical insight into lubricant behavior across a more complex fuels market.

Understanding Fuel–Lubricant Interaction

In any internal combustion engine, a degree of interaction between the fuel and lubricating oil is expected. A common example is ‘blow-by’ in the combustion chamber, where compression and oil control rings exhibit a degree of inefficiency in separating combustion matter from the crank case lubricant. Emerging fuels introduce new variables, including different boiling points, polarities, and chemical compositions, which in turn influence the physical and chemical condition of the lubricant in service. 
 
While traditional used oil analysis protocols are well suited to fossil-based marine fuels, Chevron’s research suggests these methods may need to be adapted to reliably capture the effects of newer fuel types. For example, dilution from FAME or methanol may not always be detected using conventional flash point or gas chromatography methods alone.

FAME in Medium-Speed Engines

Chevron’s CIMAC paper details a long-duration field trial using 100% FAME (B100) in three MAN 8L27/38 four-stroke marine engines. The vessels operated for more than 7,000 hours on neat FAME, using Chevron’s HDAX® 9700 lubricant as the baseline formulation throughout. 
 
One consistent observation was a measurable drop in lubricant viscosity during FAME operation, compared to periods when the engines were fueled with marine diesel (MDO) or EN590 ultra-low sulfur diesel. The reduction in viscosity was attributed to the ingress of unburned biodiesel into the oil system as a result of either raw fuel leakage or incomplete combustion. 
 
Used oil analysis techniques including FTIR (Fourier Transform Infrared Spectroscopy) and gas chromatography were used to assess fuel dilution. FTIR analysis showed a clear ester peak consistent with FAME contamination, while adjusted gas chromatography methods allowed for estimation of FAME content in the lubricant. The correlation between increased fuel dilution and viscosity drop was well established across the test period. 
 
Despite these changes in oil condition, engine inspections at end-of-test revealed clean internal components, low levels of wear, and no significant deposit formation. Pistons, ring grooves, cylinder heads and crankcases remained in good condition. Importantly, the white deposits observed on piston crowns during FAME operation were soft and easily removed, and overall component cleanliness was comparable to earlier inspections carried out following distillate fuel operation.

Early Findings for Methanol and Two-Stroke System Oils

The paper also summarizes Chevron’s monitoring of methanol-fueled operations aboard vessels equipped with MAN B&W 6G50ME-C9-LGIM two-stroke engines. Here, the primary focus was not the main oil system, which sees limited interaction with the fuel, but rather the sealing oil used in the methanol injection system. 
 
Over a period of 6,000 engine hours, with approximately 3,500 hours on methanol, Chevron monitored viscosity, TBN, TAN, i-pH and wear metal content in the sealing oil. These properties remained stable and within expected limits, and the methanol content detected via headspace gas chromatography (HS-GC) was low. No significant wear metals or acid formation were observed, and the oil continued to provide appropriate hydraulic and sealing functionality. 
 
A parallel program monitoring cylinder drain oil from methanol operation showed that BN depletion, water content and viscosity remained within acceptable parameters. Port inspections at 8,300 running hours showed that the condition of pistons and cylinder liners remained good, with no adverse effects linked to methanol use.

Interpreting the Results

While Chevron’s findings confirm that both FAME and methanol can be used effectively in marine engines, they also highlight the importance of adapting lubricant monitoring and selection practices. 
 
In the case of FAME, the primary watchpoint is fuel dilution and its effect on oil viscosity — particularly in four-stroke engines where oil is recirculated and exposed to fuel contamination over time. For methanol, the concern is less about oil degradation and more about understanding subtle chemical shifts and ensuring effective sealing system performance. 
 
Used oil analysis plays a central role in identifying and managing these changes. However, the Chevron study makes clear that legacy test methods may not fully capture emerging risks. Adjusted or alternative techniques, such as FTIR for biofuel esters, or HS-GC for methanol, may be necessary for accurate diagnosis and trend monitoring.

Supporting Multi-Fuel Operations

Across both studies, Chevron used HDAX® 9700 as the test lubricant, providing a stable baseline for evaluating the fuel’s effect on oil condition. This formulation is designed for medium-speed four-stroke engines and has been validated for operation with distillates, LNG, and biofuels. In the FAME trial, its performance remained stable despite fluctuating viscosity, and internal engine inspections confirmed effective deposit control and wear protection. 
 
These findings reinforce the value of using lubricants with proven tolerance to varied fuel chemistries, particularly as operators adopt more flexible or transitional fuel strategies. The paper also illustrates how used oil monitoring, when coupled with the right laboratory and onboard analysis tools, can help prevent unplanned downtime and protect engine assets under less familiar operating conditions. 
 
As alternative fuels gain traction in the marine sector, fuel-lubricant compatibility is becoming a more important consideration. Chevron’s ongoing research, which includes real-world engine trials and method refinement, provides actionable insight for shipowners and engineers managing this transition. The results to date are encouraging, but they also underscore the need for vigilance, adaptation, and continuous monitoring as fuel options evolve.