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Read our primer articles on High Mileage Oil, Synthetic Oil and Kinematic Viscosity

I work for the water/ waste water utility in Anchorage Alaska. We have numerous stationary generators and pump engines.We used to have oil analisis done on a yearly basis but but have quit doing this as the results did not seem to be of any benefit.I geuess the main problem is we did not understand information we got back.We have a natural gas powered Waukesha with approx 50,000 hours. Management decided the cost for an oil change on this unit was exsesive at 37 gallons per change so changes would only be done when analisis showed to be necessary. Engine run conditions are ideal and long life should be expected. We are using A chevron oil for natural gas engines.As the oil approached 3000 hours, oil consumption was increasing but anailsis said oil was fine. At 4000 hours oil consumption was very hi but analisis still said oil was good. Management was considering engine for overhaul. I took this unit under my care and changed the oil. Consumption went way down and with changes done now on 1000 hour interval the engine is clean, happy and oil usage nill! I do not understand how the test could say oil was fine and yet the engine was deteriorating rapidly. I would have thought with over 4000 hours on the oil something would be turning up in the test. Am I missing something here???
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Hmm oil analysis not showing anything out of the ordinary, but high consuption. Obviously the first thought is that your oil is thinning out of grade or there is a volitility problem of some sort.

Without actually seeing the oil reports, this is a random guess work...but, I wonder if you had reports that would show viscosity at 40 and 100 C? Did it change over the interval?

Since the consuption problem was stopped by frequent oil changes, it seems unlikely, valve guide seal leaks are the typically cause for high oil burning that doesn't raise any red flags on oil analysis (in my experence).
There are two components in this problem. One the Engine and other the oil.

1. Waukesha is a well known brand (possibly the best in Gas engines) used widely on Rigs, Drilling, Power Plant etc. No doubt you would have taken some advice from the OEM on the above problem.

2. The second factor is the lube oil. Mobil possibly the undiputed leader in lubricating Gas engines. Castrol has the NG (Natural Gas series) but not not used widely, except possibly with a variant in France.

3. The extension of life of lube oil in an engine, whatever the application, will depend on 5 major factors and indicative discard or drain periods to be used as a thumb-rule (according to Wartsila - with HFO as fuel) are as follows:

a) Viscosity of oil - Discard level + 45% change in original Viscosity at 40 Deg C. or - 25% decrease in KV 40 compared to original viscosity.

b) TBN - Discard at 50 depletion compared to original TBN.

c)Water - Discard at 0.3% Max by volume
d)Insolubles - Discard at 2.0% wt %
e)Flash Point - Min 170 deg (PMCC)
approx 190 deg (COC)

Have the oil tested by you reached these limits?

Hussam Adeni
Don't forget when your are extending the drain intervals, you still need to change the oil filters at the recommended oem interval. The waukeshaws I deal with, some natural gas, some digester gas, we do oil analysis at at the recommended drain intervals, change the filters, and go online to get the lab results. Over 3,000 hours on digester gas and 10,000 hrs+ on natural gas.
For Natural Gas Engines,FTIR Oxidation,Nitration
and Wear Elements analysis are essential for effective condition monitoring.Usually elevated oxi,Nit causes bearing corrosion. Oil change
intervals can be optimized based on wear analysis and FTIR analysis methods.

Due to the intense heat produced by compressing
natural gas,oil molecules gets volatalised
leaving behind sludge and varnish deposits.
Synthetic oils is the best choice for high load
and contineuous operation.

If mineral type oil is used,Consider flushing
procedures and or removal of sludge and varnish
techniques in order to ensure longevity of your


TBN has nothing to do with oil consumption problem.Infact it is the TBN additives(metallic detergents and dispersants)forms harmful deposits in combustion chamber and piston groove
and land areas.Over a period of time these deposits grows,impairs heat transfer,restrict ring movement,leads to bore polishing,excess wear.To address this issue OEM's recommends oil with less sulfated ash around 0.5% max.

TBN keeps sludge and fine solid deposits in
dispersed state.Sludge and varnish deposits forms due to base oil deterioration.Using sour
gas increases acidity,results in corrosion.

Prevention is better than cure.Use best quality
of base oil and fuel.

Each engine is different and the maintenance of the engine changes the results. We run Chevron HDAX Low Ash in dozens of Waukesha engines, although most have sump capacities around 100 gallons. Consumption is reduced significantly over Group I oils, and We've got several that look excellent (2 to 3% oxidation or nitration with 4 0r 5 ppm of iron, etc.) after 3,000 hours. But we normally don't push them beyond that. But getting there requires the right fuel-air ration and the right operating temperatures.
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