Beginners Guide to interpreting methane gas engine oil analysis

I often get asked for a crib sheet on how to read a report from customers as well as how to interpret certain types of samples by lab personnel at laboratories all across the world from Australia to Zambia. I recently have had a few questions from people and requests for custom training days on the topic of reading methane gas engine reports so I thought I would put together a short guide on how to read the report.

OEM limits

Many of the gas engine OEMs publish recommended alarm limits for their engines. These are black and white limits but don’t really help you in the grey areas such as several things are close to alarm limits but passing vs one thing borderline failing. It may be the one actually passing the limit is of more concern than the one just failing. So in addition to these guides from OEMs it’s useful to understand how to put these into context to make the most suitable maintenance decision based on these limits.

It is also worth pointing out that there is debate on how they should be used, as the limits are black and white and every lab works on a variation of a traffic light system so at least 3 colours e.g. Green, yellow and red or in labs such as ourselves a 4 code system of green, yellow, orange, red. After all condition monitoring is designed to help so you never get to the red stage so a 2 code system seems difficult to use in a practical sense for condition monitoring and trending etc.

Another thing you may see is hours based limits e.g. 10ppm per 1000 hours etc. These work well to handle oil that’s been in for a very long time to account for normal wear, but I see so badly used for low hours. For instance I have seen labs diagnose a sample with 10 hours of use the oil needs changing based on wear limits. That’s because the limit of say 10ppm per 1000 hours is 0.1ppm for 10 hours. So basically the noise of the icp could give a condemning alarm. Hence I always take a more sensible approach in how I use OEM limits to avoid over flagging based on poor limit setting design concepts.

Despite the clear limitations of OEM limits, it is important to know that as the owner or operator of equipment the OEM will likely expect you to act based on their limits to correct any alarms observed and your warranty may be based on this. So this guide is designed to help you put these into context to best respond to alarms rather than to replace OEM advice which your warranty will depend on.

So now you understand this let’s get onto interpreting your reports. I will base it on the layout of one of our reports but many reports follow a similar format from other labs so you should be able to still use this with those too even if you are not our customer (yet!)

Order of reading

I look at a report starting with the physical tests, condition, wear and wrap up with the additives. However if you are an oil supplier you may want to look at the additives earlier based on what is important to you.

Physical Tests:

  • Viscosity: Measures the oil’s resistance to flow. It is usually measured at 40c and 100c and is expected to stay in grade. All bar 1 product is an SAE 40 in this market, which is a 15w40 so unless you have a really unusual oil grade in use the limits you will be using will be 12.5 to 16.3 for viscosity at 100c.

What to do if flagged.

If viscosity is outside the normal range, consider changing the oil and checking for issues like wrong oil use (low viscosity) or oil degradation and contamination (causing thickening).

Oil Condition Tests:

  • TBN (Total Base Number): Indicates the oil’s capacity to neutralize acids. A decrease to below 50% of the oil’s original TBN suggests that the oil is losing its anti-corrosive properties.
  • TAN (Total Acid Number): Measures the oil’s acidity. An increase of approx 2.0 mg KOH/g above the baseline can indicate oxidation or contamination.
  • Initial pH should be above 4 and also indicates oil degradation when low.
  • Oxidation: A value 20 above the new oil baseline assuming not a very high percentage of carbonyl containing additives could mean the oil is aging and thickening, causing harmful deposits.

What to do if flagged.

If your oil is looking degraded then an oil change or significant top up are the likely next actions you should look at. If the ageing is premature, sample your coolant to assess the condition and check for signs of overheating.


  • Silicon: High levels (above 20 ppm) often mean dust or dirt is infiltrating your engine, which is particularly relevant for engines used in dusty environments. In landfill sites the limits could be as high as 200ppm depending on the gas quality as these often contain siloxanes.
  • Sodium or potassium: A sharp increase or level above 50 ppm can indicate a coolant leak.
  • Chlorine: occasionally found in landfill gas, high chlorine (above 0.1%) can contribute to corrosive wear in the engine.
  • Appearance – visual contaminants such as dirt, water or metal can indicate serious issues or poor sampling technique.

What to do if flagged?

High silicon in landfill gas suggests you need to change your oil and look at gas clean up system conditions. In non landfill check all filter conditions.

Sodium or potassium you should review any recent maintenance works that could have introduced coolant and consider further investigation such as pressure checking the system.

Chlorine present the customer should monitor water content closely to reduce the risk of hydrochloric acid formation. Expect to require more regular oil changes as the oil will degrade quickly in its presence.

Appearance issues you should confirm you flush the sample point correctly and on the next sample flush 3 times as much sample before sampling as usual.

Wear Metals:

You should work to OEM limits but for very low hours consider using a sensible multiple e.g. 10ppm per 1000 hours consider using no less than 5ppm for instance for very low hour samples to avoid over flagging, but please do discuss with your OEM how you plan to use the guidance from them so you maintain in accordance with their recommendations. Equally with all limits also factor in running in wear where you see increased wear during the initial use of the machine when installed or components replaced which is to be expected. These limits are only for if your OEM does not provide limits to work to.

  • Iron: Comes from cylinder liners. An increase over time or level above 30 ppm might indicate a problem.
  • Copper: Originates from bearings, bushings or oil coolers. If the level rises above 50 ppm, it might warrant further investigation. However keep in mind the concept of leaching where additive interactions when a new oil formation reaches copper components can cause values up to 2000ppm for the first few oil changes. Use tin and lead to help differentiate between bearing wear and leaching in these cases.
  • Aluminum: Points towards piston wear. A level above 15 ppm is usually a concern.
  • Other wear metals such as chromium (rings), manganese, nickel and other alloy elements you would normally expect to be less than 15ppm.
  • LubeWear: Our unique LubeWear test identifies larger wear particles, often missed by standard elemental analysis tests. A serious split between the standard element and LubeWear values indicates an abnormal wear process is taking place.

What to do if flagged

If levels are high or increasing, or if LubeWear shows an increase in larger particles, try link the wear to a cause from other findings in the report. For instance high iron liner wear might be caused by a low initial pH in which case an oil change will likely solve. However for unknown causes where the oil is in good condition and free from contamination further inspection or closer monitoring may be required. Discus these with your lab how best to approach.


Calcium and magnesium detergen/dispersant additives and zinc phosphorus antiwear additives – are elements added to the oil to enhance its properties. The specific elements and their acceptable ranges can vary by oil type. Significant deviations could indicate additive depletion. Generally a 50% change from the new oil is considered significant.

What to do if flagged

Additive elements even when spent will still show as present in terms of the element analysis. If additive levels are decreasing rapidly it could suggest a wrong oil, top up, change in formulation or over filtration of the oil. In most cases additives may appear to increase at the end of life as the oil volatilises, thickens and concentrates those additives. This does not mean the oil is performing better. Very large increases in additives also risk the formation of ash / coking problems.


Your oil analysis report is a vital tool for preventative maintenance. Remember, it’s about spotting trends over time, not just individual readings and comparing normal and abnormal wear particle sizes. We’re here to help you understand these patterns so you csn make informed decisions to keep your engine performing at its best. With our gas engine oil analysis service, especially our LubeWear analysis, you can extend the life of your engine, optimise its performance, and reduce costly repairs and downtime.

If you have any questions about oil analysis get in touch using the contact us button below.