Low-hour engine oil reuse

[Bribyk]

Does anyone have experience with reusing engine oil? We load test our engines after overhauls but do not like to ship them full. I am looking into filtering, testing and then reusing the oil used during the QA tests as some of the engines require a large amount of oil and there is a large potential savings if it can be reused. There is also a larger expense potential if it not done correctly.

The proposed system would filter (10 microns?) the used oil as it is returned to a storage tank. Samples would be tested as required (every reuse?) and the oil would be re-filtered using a separate filter set as it is pumped back in to another test engine. They are natural gas engines so the oil will be relatively free from contaminants other than dirt and metal particles from rebuild and break-in.

 

[patprimmer]

It will also contain blow by from combustion products including acids and water, and it will suffer some oxidation.

The metals are easily removed by filtering, and provided the filter is fine enough, the oil will have an infinite life in this regard.

You need to determine end of life by analysing to determine acidity and change of viscosity.

Regards

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[romke]

pat is right.

if you filter the oil, it can be used for quite a long time.

as a filter i would suggest the separator/centrifugal type mounted in such a way that the oil is continuously filtered in bypass (you need an electric pump to circulate the oil through the filter). in the long run this is cheaper then standard type oil filters with replacable elements, they also not only remove wear particles regardless of size but also soot and other combustion byproducts that may get into the oil.

with this setup the oil may be used for a very long time - the time to change it is when either the anti-oxidant or the anti-wear additives have been used up. usually both are based on Zn and S.

there is no easy way though to determine whether the oil is still good enough or not. standard spectrometric analysis will show the amount of Zn, but does not differentiate between "fresh" additives and breakdown products that result from the consumption of the anti-oxidant. a method that is capable of differentiating between fresh additive and break down products is the infra red analysis of the oil. i advise you to talk with your oil supplier to see whether they can do a suitable test and establish the basevalue to monitor the oxidation proces. a third party lab should also be capable doing this, but they will also need a fresh sample of the oil to establish the basevalue.

when you use a centrifugal filter you will hardly see any change in viscosity, because all the thickening components are likely to be filtered out. measuring acidity in my view is not a suitable method to determine oxidation in heavily additified engine oils, the method is more geared towards the changes that occur in industrial oils containing far less additives.

i have used the above described method in an engine overhaul plant and the oil life they got out of it was more then 5 years!

the monitoring of the depletion of the antiwear/antioxidant however is crucial: when you let it go down too far you will experience a lot of premature waer on camshafts and other components in the valvetrain.

 

[Bribyk]

Thanks, romke. It is good to know that this has been successfully implemented before in this exact application. I didn't expect a possible five-year life though! I will look into suitable centrifugal filtering systems. We intend to get baseline oil analysis to compare the interval inspections to. An electric pump will be used to drain/fill the engines as well as prelube them before start-up and can easily be setup to recirculate the oil through the filters.

 

[Bribyk]

Did you have to heat the oil storage tanks to use the centrifugal filtration? Our supplier advised me that the oil had to be at 80-100 degC (175-210 degF) for their filter to work effectively with SAE 40 oil.

We would prefer not to have to install the centrifugal filter into each engine's oil system because the sizes and capacities vary greatly. I would also like to stay away from tank/line heaters for cost and safety reasons.

 

[romke]

the setup i was talking about was using a SAE 10W-30 oil, so the viscosity was quite a bit lower then you intend to use. that viscosity was chosen because it combined easy startup, sufficient oil flow and load carrying capacity for the overhauled engines to be tested and run in (European type gasoline engines), and the viscosity was in fact lower then what the equipment required in the engines in actual service. no preheating was necessary, both for lubrication and filtering.

the non-standard lower viscosity was chosen on purpose to increase the oil flow through the engines and so assist in cooling of the inner surfaces of the engine that had to run in (liners, piston rings, bearings).

in your situation you might also consider using a lower viscosity oil (SAE 30, or 10W-30) for the same reasons. of course those oils are lower in viscosity but when running in that is an advantage - not a disadvantage. when the engines are in actual service with continuous high load the SAE 40 engine oil might prove the better choice because under those circumstances less wear migth occur. during the running in period however higher wear is what you actually want and the better heat carrying capacity that results from the increased oil flow actually helps to protect the parts that have to run in.

 

[Bribyk]

I will have to check with our oil supplier and manufacturer recommendations but we may be able to use 10W-40 or 15W-40 oil so that the centrifugal filters are more effective at lower oil temps. And I will look into the improved break-in characteristics of a lower viscosity as per your recommendations, romke.

 

[evelrod]

Does anyone have experience with reusing engine oil?

Well, Pat will probably shoot me but, I have been reusing my run in oil from race engines (usually Castrol 20w-50) in my Dodge 6BT since it was new...it's well above 200,000 miles these days (the Odo broke at 186k several years ago so I cannot be accurate). It still gets 21+ mpg and makes oil changes, ~7500 miles, without adding additional oil!

Race filters can be as much as 100 microns and the Wix filter on the Cummins is much less. Perhaps 40, but I can get a Donaldson at 10 microns should the mood strike me.

Rod

 

[patprimmer]

Rod

I always find something older and less valuable or less critical to reuse my break in oil in.

I like to let it settle for a month or two then decant, but a really fine or centrifugal filter would also be good.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

Pat, I just put in new Pauter billet rods and JE pistons in the Mini last week (after 21 race weekends on the stock rods)---EVERYTHING I own is "older and less valuable or less critical" than either of my race cars!!!!!!!!

Rod

PS: There is also the not-so-obvious trade off...Bought two toy Pom puppies to keep the piece!