Extending maintenance intervals for standby generator sets

by Contributor oltwodogs on ‎03-01-2010 09:22 AM

Kevin Benz

I was reviewing posts on this forum in regards to maintenance intervals, and found the one titled Altering recommended maintenance with low gen set hours by Psheehy interesting. I'd like to hear your thoughts about extending the oil change interval for standby gen sets beyond the typical 12 months time frame.

When extending oil change intervals for standby generator sets, the usual concerns include:
    Condensation / Water
  • When ambient conditions are right, water condenses on the interior surfaces of the engine. This condensation, besides rusting and pitting metal surfaces, will combine with sulfur in the oil to form acid vapors, then corrosive attack occurs.
  • Besides the damage the rusting process creates, the increased iron content can cause abrasive and adhesive damage to other areas of the engine. Condensation combined with oil will create an emulsion, which will plug the oil filter and allow potential bacterial contamination.
  • Engine oil stored in unsealed containers (i.e. engine sump) for a prolonged period of time can absorb moisture from the air. Standby generator sets located in controlled environments will typically experience fewer condensation problems.
    Additive Depletion
  • The acid formed when condensation and sulfur combine is neutralized by part of the oil's additive package, thus depleting it and lowering the oil's ability to protect the engine.
  • This can lead to deposits, sludge formation, lacquering, varnish and carbon build-up, liner bore polishing and ring sticking.
  • Oil will oxidize at a rate directly related to time and temperature.
  • The more oxidized an oil becomes, the less protection it provides to an engine's moving parts.
    Filter Media
  • Filter media will tend to deteriorate from being immersed in oil or fuel for prolonged periods of time.
  • Any water or acid content will speed up this process.
What your thoughts about extending the oil change intervals for standby generator sets?
  • Do you have concerns on extending the oil change interval?
  • Is this widely accepted in the industry today for standby generator sets?
  • What's the value?
  • Do the cost savings of oil outweigh any perceived risks?
  • Are you extending the oil change interval today? If so, how often are you changing the oil?
  • If you're extending the oil change interval currently, do you base this decision on experience, or look to the OEMs to provide you with guidelines to follow?
  • Are any OEMs providing this guidance to your knowledge?
Not knowing the worldwide population of standby generator sets, I did some basic math. If you assumed 80 gallons of oil (average sump) times 100,000 standby generator sets, and extended the oil change interval to every 24 months, that's a reduction of 8 million gallons of waste oil. Do it every 36 months, and that's a reduction of 16 million gallons of waste oil. See where I'm going? Does going “green” influence this decision?

As OEMs continue looking for positive sustainable solutions, I'm very interested in hearing your thoughts. Please post them via the form below.

About the Author: Kevin Benz

by New member supercole
on ‎03-03-2010 07:58 PM

I am sales rep for a company that is one of the leading distributors of anti-corrosion materials.  I worked on a project, for a CAT distributor in the Peoria area,    that addressed some issues raised here.  We came up with a plan that protected both the cavity of the unit, and the internal components of the engine.  With the plan in place you could protect the unit for upwards of two years.  There are a number of products that are available that will reduce the maintenance interval.  Their several people within the company who are aware of such products, such as Dave Haney.   

on ‎03-15-2010 06:44 AM



I am working in a CAt rental store where we provide Caterpillar construction machines and Generaotrs on rent both diesel and gas ranging from 27 - 2450 kVA.One of my job responsibility is to looking after the maintenance related issues sepcially oil change interval so as to minimise the per hour operation cost without putting equipment health to risk.I keep looking for extending oil intervals of my rental generators and construction machines. i dont change oil in my stand by sets irrespective of period either 1 year or more. but yeah as far as filter is concerned, i keep changing the filters after every 6-8 months without changing oils. i strictly follow SOS routine, and eveyr now and then keep performing SOS of my stand by engines. The results are pretty good up till now and my oil related failures has decreased to Zero for last four years every since i have taken the charge. And by doing so, my oil change intervals has increased drastically thus costing me lower cost per hour. CAT SOS program has helped me a great deal in building confidence over equipment's behavior and now even without SOS at times we already predict the expected oil change drain.

on ‎03-15-2010 11:26 AM

I am the PSSR for the Caterpillar Dealer in NW Wisconsin.  I have some customers with 3500 series engines that we have extended the oil drain interval.  Strictly in standby applications, and low annual hours.  If it is an outdoor unit, in a skin tight enclosure that is affected by the ambiant temperature,  we only extend the oil drain to 24 months.  We do change all filters (oil and fuel) at 12 months with an S.O.S. 


On a temperature controled indoor unit or a unit in a temperature controled walk-in encloser, we have extended the oil drain to 36 months.   Again, changing all filters (oil and fuel) with an S.O.S. at 12 and 24 months. 


Many customers are satisfied with a site inspection at 18 and 30 months and an S.O.S.  If anything, our technician and myself, get more face time with the customer this way, and any service reccomendations (batteries, belts, hoses) can be monitored.  This gives the customer peace of mind, and the ability to focus on their business, and not their generator set.


Jim Gorecki

FABCO Caterpillar

by New member pumpprincess
on ‎03-15-2010 12:18 PM

What are your thoughts on prelubing gensets?

by Regular Contributor
on ‎03-15-2010 12:28 PM

I've been going around with  Cat on this for years....Changeing  the oil ever year with 20 hrs on the engine?? Crazy waste of money. Particulary on a unit inside a powerplant.  Keep the Jacket water at 125 degrees, have an aggressive oil monitoring program (we do every quater) and monitor delta P across the filters.  Now this is on 3516's and bigger in a  wind foloowing/standby/peak shaveing operation don't know what you on little emerg only units...

by Contributor wlj1943
on ‎03-15-2010 01:10 PM

I want to reinforce Plantpro's  position. Most of issues and questions raised about oil change intervals, acid buildup, additive depletion and moisture in standby generator sets can be accurately measured if the owners perform a regular oil sampling and have a formal analysis regimen, as do most power plants.


This is what I advise my clients to do, and I do myself in all my personal and business equipment and vehicles.  The advent of quality (in Canada and the US anyway) independent third party laboratories that can perform this work for under $20 per sample is a quantum change that is now available to even an individual. Oil analysis takes most of the guesswork out of what is occurring  inside any internal combustion engine.   If the standby generator application is critical, usually the oil and coolant temperatures are kept reasonably warm to facilitate starting.  This means that  often the temperature environment of the installation location is such that ambient moisture is unlikely to condense inside the engine, and hopefully the engine is exercised periodically UNDER LOAD long enough for all operating temperatures to stabilize; so valid oil samples can be taken.


When all the above condition are met, I would suspect that at least a two year or possibly longer interval would be possible, depending on what the oil analysis results indicate.


That said, like the ads say, oil is cheaper than engines, and I have never see any IC engine damaged by too frequent an oil change. Cat's position, although conservative, is probably well supported by the fact the engines in standby duty are often times neglected and not located in the best of environmental conditions and locations (think rental units), and Cat cannot insure the controls, attention and professional maintenance practices will always be present for this class of equipment. 


by New member kalmick
on ‎03-15-2010 06:25 PM

I have recently left Cummins based in Western Australia and have had this discussion many times,mainly clients with multiple large standby sets .

Clients find it difficult to understand the need to throw away 1000's of litres of oil on a constant basis when their machines have done minimal hours,have block heaters fitted ,have performed monthly startups and load-tests and maintained a vigilant oil sampling process.

I myself have questioned both the rationality and morality of this seemingly widespread practice.


Call me a cynic but is it to do with most engine / powergen companys also being heavily involved in filter and oil sales ??????

by Visitor Allentp
on ‎03-15-2010 08:11 PM

A very interesting story line. On many occasions I have expressed a position about standby generator sets. If they are "mission critical" units that must run when the outside world is experiencing major problems, the gen set must be the absolute best we (Caterpillar) can offer, and must be kept in top condition. With that said, it would seem that I may be against extending maintenance intervals. Not so.


If the Cat generator set remains sufficiently isolated from the damaging effects of large temperature and humidity swings (and most critical gen sets are kept snug and warm in their own rooms or tight enclosures), and they remain well sealed from blowing sand or airborne corrosives (tight air cleaners and exhaust systems will help here), I see no reason for not extending the maintenance interval to a new comfort level.


But, I also believe a tool must be employed to determine just how far a particular gen set can go - SOS.  A critical generator set will likely be following a regimen of routine test runs - hopefully running at 20-30% load to properly warm up the engine and generator. Those scheduled exercises potentially give the wary service provider an opportunity to collect an oil sample from a runnable engine, and a chance to take a quick look at all the systems associated with the gen set. SOS is a valuable tool. Why not make that tool tell us when the engine's lifeblood is in need of a change?


Some important technology advances should also help us make a decision about increased maintenance intervals. I feel that lubricants are better than ever. The engines have less "blow by" than in the past, so the engine oil is potentially polluted less when it does run. In general, fuels are cleaner and Caterpillar engines burn that fuel more efficiently (cleaner) than in the past. Sealing systems have evolved to better isolate the internal components from the outside conditions.


Of course, all the other routine maintenance schedules must still be followed to properly maintain the cooling system, fuel system, generator, etc.


By the way... I am concerned about the comment "Filter media will tend to deteriorate from being immersed in oil or fuel for prolonged periods of time". I do agree with the comment, and I can only assume that the Cat filter experts go along with the proposed increase?

by Super Contributor
on ‎03-15-2010 10:53 PM

Like so many things in our industry this is an evolution.  Modern engines in good environmental conditions using quality lubricants are excellent candidates for extended drain intervals.  Oil sampling, properly done, is an excellent indicator of oil condition if the sampling is properly done and the correct test carried out.


As pointed out above, a current production engines, at Tier 2 of 3 emissions levels, tight ring packs, low blowby rates, high pressure fuel injection systems, using ultra low sulpher diesel fuel and today's excellent lube oil packages, probably has a great chance of going 2, 3 even 4 years if properly managed.


How about trying the same thing with an old D399, using #2 diesel and a CD straight weight oil?  Add weekly no load test runs, and maybe an annual run at some load, and if you didn't change the oil every year you would know about it.


How about a question no one has raised yet?  Say the end user is a data center with 3 or 4 large standby units under a dealer managed maintenance contract.  The dealer has worked out a good program like FABCO above, actively working to provide good value to the end user, make less of a negative impact on the environment, and be proactive.  At the end of year 3, just before the scheduled lube oil change, a major engine failure occurs.  While the root cause may not be attributed to the extended interval, what happens when the insurer raises the question, "were the engines maintained per manufactuer's specifications?"  When the question gets asked to the local CAT factory rep, he'll flip open the O&M Guide, and if the recommended PM was not carried out per the manual, who is on the hook?  The customer has a unit down, possibly affecting his production or operation, had paid a premium price for ongoing maintenance, and isn't likely willing to foot the bill.  CAT, what will they do?  Will they stand by the dealers decision to extend oil drain intervals beyond the published guidelines?  This isn't strickly a technical issue. Many users of standby engine generators do so becuase they have to, mandated by regulatory or insurance agencies.  If the units are in a mission critical system, even if the extending of drain intervals makes perfectly good technical sense, is it a good decision?


If industry groups, like EMA amd EGSA, along with the manufacturers would develop clear guidelines and programs to manage extended drain intervals, then the would likely become more of a reality.


How about fluid filters?  The technology has only slightly improved over the years.  Yes the micron size is smaller, and their overall efficiency has improved, but has their ability to have a longer "wet life" been documented, tested and approved?  When I started doing training many years ago, there was a guideline published by one of the filter manufacturers that dictated no filter should be wet more than one year.  Is there a new guidline based on modern filter construction techniques and materials?  I just recently did a failure analysis on a small standby unit at a military base with a damaged crankshaft.  The root cause was a collapsed lube oil filter, breaking apart and getting filter media into the oil passages.  The engine was 5 years old, had the original factory painted spin on oil filter, and the original lube oil.  Whe I asked the maintenance tech why the oil and filter hadn't been changed, he said the engine only had 90 hours on it and it didn't call for an oil and filter change until 125 hours.  This particular unit is still down, and a nasty lawsuit is brewing.  The packager is long gone, the engine manufacturer says the information provided to the end user was incomplete, and the  military operates enough mechanical equipment to know better.


When I worked for a dealer, we had a number of successful cases of extended oil drain intervals, programs very similar to FABCO's as described above.  After one very nasty and expensive experience we went back to "by the book".  Maybe it's time for the book to change?


Nice topic, hope it opens some more discussion, and maybe leads to some real changes.

by New member CptMicro
on ‎03-17-2010 09:07 AM

Moisture / condesation can be reduced by using crankcase heating at regular intervals.  This has been used in commercial HVAC for decades. PH testing can help in quatifying when heating intervals need to occur and when the oil needs to be changed.

by New member Roktgr
on ‎03-17-2010 11:18 AM

I recently looked at this same issue with our two smaller standby emergency power generators for our hospital.   We switched the gen-sets over to fully pure synthetic oil and I am anticipating on getting 3 years on the oils before they will need to be changed.  Figuring payback in -3 years.  We have also switched to oil analysis as several have mentioned above to verify the quality of the oil.  Filters are still changed as specified in the OEM manuals however.  I would think the issue of filter breakdown would be fixed by using a high grade of filter that contains a synthetic element not a paper element, I don't have anything to back that up however.

by Contributor oltwodogs
‎03-18-2010 09:13 AM - edited ‎03-19-2010 02:31 PM

I've been reviewing all the comments, and am intrigued with all the interest. In regards to the question from AllenTP - In 2008, Caterpillar did review an extended oil drain program for standby gensets with the Caterpillar fluids and filtration experts. It was determined that the filter media will tend to deteriorate from being immersed in oil or fuel for prolonged periods of time. Of course, any water or acid content contained in the oil will speed up this process. Whether a paper media or synthetic based element is being used in an extended oil drain program, it is always recommended to replace the oil and fuel filters at a maximum of one year.


Is there a sweet spot or pay back based on the sump capacity? Consider the cost of diesel engine oil today. Assume your paying $10.50 per gallon, and using the 80 gallon sump capacity average I referenced above. The potential cost savings to the end user is $1680.00 per genset over the course of 3 years if you were to extend the oil change interval from every 12 months to every 36 months. This excludes the cost to remove the waste oil which can average $.50 per gallon.


Now I'm curious. What are you paying for quality diesel engine oil and waste oil removal today?


Is there a particular sump capacity for standby gensets that it just doesn't make sense to administer an extended oil drain program on? Where do you see the sweet spot being to pay you back?


Great discussions. Keep those comments coming!

on ‎03-25-2010 04:35 AM

In the UK in the Cat Power and Energy field we basically replace filtration annualy and oil sample every six months with a lube change every three years. We try and take into account the environmental issues with disposing of used oil and the cost to the end user can blow our contracts out of the water in what is a very competetive environment.

The biggest issue we currently come up agauinst is fuel sampling, stand-by applications may have in excess of 100,000lt of diesel in underground storeage.

This can lead to microbiotic activity in the fuel that will destroy and engine in a short amount of time, the problem is getting samples from the lower regions of bulk storeage vessel.

Our analysis lab in the UK has vast amounts of data which all departments use to our and customers advantage with the best advice for their product at the best value. 

by Dan Foster
on ‎05-24-2015 08:19 PM

If the decision to change the interval didn't harm the genset's life in any way, and would save money, why not? "Going green" would be a convenient byproduct. <a href="http://www.dfcmechanical.com">Chicago Home Generators</a>

<a href="http://www.chicagogenerator.com">Chicago Commercial Generators</a>


by anil sharma
on ‎06-02-2017 04:09 AM

we need to replace D-399 engine with the cat 3516. please let me know the deffrince between the d-399 vs cat-3516 relibalty and ecnomacily.






by David Walter
on ‎09-12-2017 01:45 PM

I just purchased a vessel with twin D399's. What lube oil do you recommend using?

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