Advice: Just lost 2 engines pre-100k miles

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Most diesel-engine wear is caused by abrasive soot particles at high loads combined with low RPM. High loads combined with low RPM decrease the minimum oil-film thickness (MOFT), which causes the abrasive soot particles to grind onto sliding metal parts and wear them away.

Advice:

(1) Don't run the shredder when the truck is idling. If you need to do so, install some type of idle-up mechanism so that when the shredder is turned on, the engine automatically runs at higher RPM. That's because the minimum oil-film thickness is inversely proportional to load and directly proportional to RPM. You want to keep the oil film thick, which means you need higher RPM when there is load.

(2) Don't run anything thinner than 15W-40 on these engines, as the oil-film thickness is also proportional to viscosity. Don't run any certification other than API CJ-4, which has excellent soot control. I recommend Mobil Delvac 1300 Super 15W-40.

(3) Soot builds up over oil-change interval. If there is a lot of idling, you should change your oil frequently as soot will also build up during idle. Abrasive soot particles are what damages diesel engines; so, change your oil frequently. If you are idling 10 hours a day, this is equivalent of 500 miles or more of driving. This means you need to change the oil every month or so. Again, don't use anything other than API CJ-4 (excellent soot control) and 15W-40 (thickest oil film among diesel-engine oil viscosities). Once more, my recommendation is Mobil Delvac 1300 Super 15W-40 with an oil-change interval of no longer than about 30 days. You can also use any other major-brand API CJ-4 15W-40 with approximately 30-day oil-change intervals.
 
Always a good thread when Gokhan posts.
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Gokhan, on the matter of higher oil film thickness at higher RPM: is that mainly because the oil pressure is higher, or is there another effect? I'm wondering if an electric oil pump could help by raising oil pressure with load.
 
Originally Posted By: Gokhan
(1) Don't run the shredder when the truck is idling. If you need to do so, install some type of idle-up mechanism so that when the shredder is turned on, the engine automatically runs at higher RPM.

I kinda hinted at that earlier on but didn't get an answer. PTO stuff is really not supposed to be run at idle, and I'm hoping this isn't the case here.
 
Do you have the same driver in each truck or do they rotate?

Fleet vehicles with rotating drivers tend to get ignored. Stick one driver in each truck, and make it their responsibility to promptly report problems. I doubt you have a cooling problem, but if you do, the drivers should notice the temp gauges going up and the warning lights!

Same with fluid checks, every morning they should have to check the fluid levels.

Lastly this is a perfect situation for UOA, start taking samples and doing what the lab recommends.
 
Originally Posted By: d00df00d
Always a good thread when Gokhan posts.
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Gokhan, on the matter of higher oil film thickness at higher RPM: is that mainly because the oil pressure is higher, or is there another effect? I'm wondering if an electric oil pump could help by raising oil pressure with load.

Thanks!

This is a good question. The answer is no, the oil pressure has no effect on minimum oil-film thickness at all. Yes, there is another mechanism that causes the RPM to increase the minimum oil-film thickness.

The only thing the oil pressure does in the engine is to pump the oil through the lubrication system so that it could flow back and forth between various parts. Otherwise, oil pressure doesn't help lubrication in any way.

There are so-called hydrostatic lubrication systems where oil pressure separates rotating parts. However, hydrostatic lubrication systems aren't used in the engine.

The mechanism that provides the minimum oil-film thickness in the engine is the viscous reaction force of the oil. This type of lubrication system is known as hydrodynamic lubrication system. When a moving part moves against the oil, the viscosity of the oil creates a reaction force and pushes back against the oil. The important thing is that the viscous reaction force increases with the speed of the moving part. This is how hydrodynamic lubrication works.

Here is how hydrodynamic lubrication works in more detail. Consider a journal bearing for example. When the engine is stopped (RPM = 0), the journal (shaft) will touch the bearings. Therefore, there will be metal-to-metal contact. The only thing that will protect the engine when you first start it will be the antiwear additives in the oil that coated the bearing surfaces. When you start the engine, oil will be pushed between the shaft and bearings and the viscous reaction force of the oil will separate them entirely, eliminating the metal-to-metal contact.

So, now, you really need to understand this part: The shaft will not be entirely centered in the bearings and it will wobble when it rotates. The point where the shaft is closest to the bearings while it wobbles is where the minimum oil-film thickness occurs. If you increase the RPM, wobbling will become smaller because there will be more viscous reaction force on the shaft. Therefore, when you increase the RPM, the minimum oil-film thickness will increase. If you increase the load in the engine, wobbling will obviously become larger as the load forces the shaft. Therefore, load will decrease the minimum oil-film thickness. If you increase the HTHS (high-temperature, high-shear) viscosity of the oil, viscous reaction force by the oil will get stronger, making the wobbling smaller, which will increase the minimum oil-film thickness.

Backup_200507_lubapp-shaft_motion.jpg


So, in summary:

Larger HTHS viscosity: Less wobbling, larger minimum oil-film thickness
Larger load: More wobbling, smaller minimum oil-film thickness
Lower RPM: More wobbling, smaller minimum oil-film thickness

Note that cylinders and rings also work in a similar way.

Now, why is a smaller minimum oil-film thickness is bad? Because that makes it easier for the abrasive soot particles or other dirt to grind against sliding parts and wear them out. In fact, if the minimum oil-film thickness gets too small, there will be metal-to-metal contact at one point.

The most wear in an engine will occur when you're lugging the engine (large load and low RPM combined) and the oil is thin and sooty. This will result in a very small minimum oil-film thickness and the abrasive soot particles will be larger than the minimum oil-film thickness, grinding against the rotating or sliding metal parts. So, keep the RPM high when there is load on the engine; choose an HTHS viscosity thick enough for your engine (HTHS viscosity of 15W-40 oils should usually suffice for most diesel engines in most conditions), and use a CJ-4 oil (which is efficient in dispersing soot) and change it frequently enough for your operating conditions.
 
Thanks for the thorough and informative post! This is one of those rare occasions when BITOG really lives up to its promise. :]
 
Originally Posted By: d00df00d
Always a good thread when Gokhan posts.
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+1, for sure.

Gokhan, that's probably the best tutorial on hydrodynamic lubrication I've read. Makes it so even I can understand now...
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Originally Posted By: Gokhan
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Thanks for the informative post. We are doing a UOA on every single truck and we are going to adjust our schedules accordingly.

Curious to your thoughts on oil bypass filtration and/or synthetic oil? We were considering testing it out, but given our high level of PTO time and city driving, I am wondering if just changing the oil a lot more often would be more ideal.
 
Bypass filtration extends the life of the oil, but the question is whether the cost of the filtration rig is more than covered by the savings in oil, filter, and downtime. Your engine maker may have info.

Synthetic oil will live longer due to its slower rate of oxidation, and it also thins less when very hot. If oil contamination is the end factor for your oil...soot, fuel dilution, etc., the syn offers no benefit. After you get a few analysis reports, you might try one rig with syn, continue analysis, and see how the numbers work out in your service. You can always switch back to conventional oil.
 
Originally Posted By: shredguy
Originally Posted By: Gokhan
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Thanks for the informative post. We are doing a UOA on every single truck and we are going to adjust our schedules accordingly.

Curious to your thoughts on oil bypass filtration and/or synthetic oil? We were considering testing it out, but given our high level of PTO time and city driving, I am wondering if just changing the oil a lot more often would be more ideal.

My main concern was the RPM of the engine when the shredder is being used at idle. So, what's the idle RPM when the shredder is being used? It should be close to the cruising RPM if the shredder takes a lot of power. If this is not the case, you should take your trucks to a truck shop and install some adjustable idle-up device that turns on when you turn on the shredder. You can then adjust and increase and your idle-up RPM so that the engine is not lugged (run at load at low RPM) by the shredder during idle.
 
Before oil analysis and emissions requirements there were guidelines established by Cummins to determine oil change intervals.
Mileage, and for stationary/industrial applications hours of operation and/or the amount of fuel consumed based on engine crankcase oil capacity.
Do you know how many gallons of fuel you use between oil changes?


Ducati996
 
Originally Posted By: javacontour
Yes, the more I think of this, there could be other causes, such as overheating. What about insufficient cooling at idle? Low coolant level?

Did they do any other work such as replace the radiator, etc?

Originally Posted By: zzyzzx
You had to rebuild an engine due to a blown head gasket???
Sounds like it might be operator error to me.
Is there more to this?


While the trucks are idling for an extended period of time, I would pop the hood a little just tp have a vent effect for letting heat escape. Hopefull you have better luck in the future!
 
Fyi. Deleting emissions parts is a federal crime. So if they are gone and he gets pulled into a roadside check hes going to see huge fines. The engine running the shreder will also be checked.
 
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