2021 Duramax L5P oil consumption cause and solution

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I started with Mobil Delvac ESP 5w40 but doing UOAs it was shearing. To fix this I switched to 15w40. If it’s 0F or colder I drive the wife’s van. She’s a [email protected] and is adamant that she’s not going anywhere if it’s that cold 🤣

I also don’t mind the price of the 15w40 🤷‍♂️

Just w$0.02
15W-40s are a much better oil.
 

JHZR2

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More RPM = more airflow through the engine. That results in more cooling for the same amount of power/work needed to be done.

Where is the EOT being taken from? I’d suspect it is much hotter someplace else.
 

wwillson

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More RPM = more airflow through the engine. That results in more cooling for the same amount of power/work needed to be done.
Plus less work done per combustion event, because you have more of them/minute to do the same amount of work. Less work, less fuel, and less heat per combustion event.
 
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I started with Mobil Delvac ESP 5w40 but doing UOAs it was shearing. To fix this I switched to 15w40. If it’s 0F or colder I drive the wife’s van. She’s a [email protected] and is adamant that she’s not going anywhere if it’s that cold 🤣

I also don’t mind the price of the 15w40 🤷‍♂️

Just w$0.02
Do you have that oil analysis posted anywhere here? I ran some Delvac 5W40 way back in 2008 for a test and wasn't impressed. I was actually very surprised. After 3000 miles or so you lost about 5 psi of oil pressure (this would have been an LBZ Duramax). I used the pail up and never got it again. But, I happily run Delo 5w40 and have an extensive history of it holding up quite well in Duramax engines with no shear issues. Gotta think Mobil and Chevron would be similar quality oils no?
 

wwillson

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@wwillson , any chance you could repeat the experiment on the next tow and look at EGT as well as EGT5 at the same time?
I have lots of pictures of all temp sensors from the manifold all the way back to the SCR exit during regen, but no pictures non-regen. However, I can tell you that when pulling and not in regen the EGT5 temp is rarely over 550°F. During regen EGT5 temp is usually > 1000°F.

2232B567-40E3-4E38-B8AF-5C71B30CF69A.jpeg
 
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Ya, I was curious about EGT 5 when towing in 10th vs 9th vs 8th gear sorta thing.....to see you you lowered the EGT reading what it did to post DPF temps is all.

550F on EGT 5 when towing is very interesting.....my guess is you know how to drive for fuel mileage! I get that when I'm not towing.
 
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Do you have that oil analysis posted anywhere here? I ran some Delvac 5W40 way back in 2008 for a test and wasn't impressed. I was actually very surprised. After 3000 miles or so you lost about 5 psi of oil pressure (this would have been an LBZ Duramax). I used the pail up and never got it again. But, I happily run Delo 5w40 and have an extensive history of it holding up quite well in Duramax engines with no shear issues. Gotta think Mobil and Chevron would be similar quality oils no?

I believe I have posted them on here. My phone doesn’t seem to like the search. It will be under my user name and for my 2012 Cummins Ram.

Just my $0.02
 
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Going against the grain here. I suspect it has naught to do with the piston or crown, but the Turbo and it’s seals. The lower (number) the gear, the less influence the turbo has for the same load. Try it out and you’ll see. Your turbo is the culprit.

Your pistons are able to handle a lot of heat. You aren’t the first one to run those temps. I’m sure you’re equally surprised when it regens and see the egt’s.

If it were mine, I’d bring it in for a looksy.

All the best
 

wwillson

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The lower (number) the gear, the less influence the turbo has for the same load.
When you say "influence", do you mean less boost? The boost when pulling at 1,880 RPMs vs 1,400 RPMs is virtually the same at 10 PSI. The peak boost you'll see at 1,880 RPMs is about 27.5 PSI and the peak boost at 1,400RPMs is about 24 PSI.

I’m sure you’re equally surprised when it regens and see the egt’s.
No, actually not surprised. The fuel used to heat the exhaust flow is injected into the flow after the turbo, so a regen does not affect the EGTs in the engine or turbo.

Your pistons are able to handle a lot of heat.
Yes, but not 1,200°F EGT all day long. The temperature in the piston bowl at ignition may be as high at 3000°F-4000°F.

Aluminum piston alloy begins to soften around 800°F and begins to melt at 1,200°F. I'm not saying the pistons are approaching 1,200°F with an EGT in the manifold of 1,200°F, because they aren't. My guess is the piston crowns are around 600°F and the upper cylinder walls are 475°F, that's hot! A bit of the oil being sprayed on the pistons and cylinder walls will evaporate and there will be a loss of oil, which is what I experienced. Pull in 8th gear with manifold EGTs of 900°F and the consumption goes to zero.

Your turbo is the culprit.
I'm willing to listen, but you'll have to explain why you think the oil loss is from the turbo.
 
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Going against the grain here. I suspect it has naught to do with the piston or crown, but the Turbo and it’s seals. The lower (number) the gear, the less influence the turbo has for the same load. Try it out and you’ll see. Your turbo is the culprit.

Your pistons are able to handle a lot of heat. You aren’t the first one to run those temps. I’m sure you’re equally surprised when it regens and see the egt’s.

If it were mine, I’d bring it in for a looksy.

All the best

This post really shows how little you actually know about what you’re talking about.
 
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I'm wondering if you can get a read on engine oil temps, are they much higher when towing and if so, would an engine oil cooler be benificial? I'm not at all familiar with these engines for all I know they could already have one. I do know that on some gas inboard boats a heavy boat with a single engine may have an engine oil cooler as standard equipment to keep the oil from overheating under sustained high loads (in a boat, the engine is under load all the time, pushing water out of the way with a single speed transmission). Boats with oil coolers can run a lighter viscosity oil like a 10/30 or 10/40 but with no oil cooler those oils would shear down and you'd see very low oil pressure at idle after coming off plane. Engines without oil coolers usually run a 25/40, or 25/50 oil, or a straight 40.
 

wwillson

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I'm wondering if you can get a read on engine oil temps, are they much higher when towing and if so, would an engine oil cooler be benificial?
The Duramax has an engine oil cooler and the 2020+ L5P has a larger cooler than in the past. I watch the coolant and oil temps on the main screen I monitor, so I'm very familiar. The engine oil temp, when pulling, runs between 200°F and 210°F with virtually no excursions from that range and the absolute highest engine oil temperature I've ever seen is 212°F.
 
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This post really shows how little you actually know about what you’re talking about.
We’ll see tomorrow if that’s the case. While your at it, maybe you can educate the rest of us how %Load, %Throttle Position, and %PSI, and #Gear interact with each other as pertains to this case. Can you do that? The former three are ECU readouts on modern OBD2’s. The latter can be extrapolated by the dash or selector.

As for the OP, there are so many variables that are unknown that led to his conclusion.

Lest we here not forget the function of a Turbo and it’s cooling/lubrication. Read up
 

dnewton3

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- correlation does not prove causation, folks
- the reality is in the result itself ... using a lower gear during towing makes for lower oil consumption
We can theorize about WHY this happens, but it does not change the fact that it happens.
It was true with my old LBZ Dmax also; no regens in that 2006 model.
 
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To keep in simple The engine is much closer to its peak efficiency at the elevated RPM. It cannot move enough air below 1500 RPM to keep a lean fuel/air ratio (as far as diesels go). At the higher RPM, because the engine is closer to its peak efficiency/torque range, it can move enough air to keep EGTs lower (engine does not have to work as hard, thus smaller throttle input) also keeping the aluminum pistons further away from the melting point of the metal. Sustained EGTs at 1250* or higher for long periods WILL damage the pistons. I’ve seen it many times. This doesn’t apply to just the duramax but every diesel engine fitted with aluminum pistons.

The turbo does not have aluminum bearings or bushings. The increase in oil consumption and elevated aluminum in UOA is not from the turbo.

For the latest design 6.7L PSD they replaced the aluminum pistons with a steel piston that is much shorter.
 
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comparison of the 2 6.7L pistons.

What’s cool is that you can drop a complete 2020+ balanced rotating assembly into any year 6.7L block. Obviously you will need to hone block to fit pistons. Piston to cylinder wall clearances are different due to the different expansion rates of aluminum and steel.
2394D16D-B115-4B88-BA77-5340E70B12FC.jpg
2DC9E08C-74A4-4CE9-8AD3-192FF98BEEA4.jpg
 
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