Duramax 3.0L oil consumption while driving with low RPMs and high power output

[DuckRyder]

you can get this is an escalade?

Ive got a friend with an earlier one (i think its a 2019) in a Sierra, i'll have to check in with him on how it is doing...

 

[Bighorn2500]

you can get this is an escalade?

Ive got a friend with an earlier one (i think its a 2019) in a Sierra, i'll have to check in with him on how it is doing...

Yes, you can order it.

I've seen one in a Tahoe High Country with all the bells & whistles, my neighbor works for GM. He brings home different vehicles occasionally, pretty sharp looking SUV.

 

[dbphillips]

Watch at 4:20, he checks the oil twice and both times it's still way over the full mark (GM intentionally ships an extra quart from the factory).

Whaaat? That makes no sense. Most cars/trucks can be damaged by overfilling the oil, or create a fire hazard. But I believe I checked my oil early while familiarizing myself with the truck and it definitely was not overfilled. Sounds like Internet blather to me.

 

[dbphillips]

A friend of mine called me yesterday asking about poor fuel economy in his 3.0L Duramax. His drive was from Kentucky to Denver in 30+ MPH headwinds. He normally gets 29.5 MPG, but one this trip he only got 20.5. He wanted to know if I thought something was wrong with the engine, because it was getting such poor fuel economy. I told him his engine is fine and that bucking such a strong headwind required a lot more power. He is a +3 over driver, so most of the trip the cruise was set at either 73 or 78 MPH. If the headwind averaged 30 MPH, then he effectively was moving through the air mass at an average of 105 MPH. Drag increases as the square of the increase in speed. 105 is 1.4x faster than 75, so we square 1.4 = 96% more drag. That is why he got such poor mileage.

I’m a little confused here. My first assumption is that he is concerned because he drove substantially the same before and after. He wasn’t driving in 30 mph headwinds the whole way. Something is wrong.

If the post about moving away from aluminum pistons is true, then likely it’s fatigue over time, likely exacerbated by the sloppy programming that optimizes fuel economy by minimizing rpm at the expense of cylinder temperature. If that is true. I will be investigating next tow trip. Only GM knows. Hopefully Banks releases a white paper with the Derringer.

Aluminum has no fatigue limit. Not a great material for a quarter million mile engine.

 

[wwillson]

I’m a little confused here. My first assumption is that he is concerned because he drove substantially the same before and after. He wasn’t driving in 30 mph headwinds the whole way. Something is wrong.

The oil consumption happened on the 1000 segment of the mile trip heading west. There were strong headwinds the entire way.

likely exacerbated by the sloppy intentional programming that optimizes fuel economy by minimizing rpm at the expense of cylinder temperature.

I corrected your sentence above

Only GM knows.

GM understand that this engine will use oil when there are high EGTs, read the TSB on oil consumption. GM states more or less that, "if you work it hard, it's going to use oil". A by-product of high specific power and lots of heat.

Aluminum has no fatigue limit. Not a great material for a quarter million mile engine.

Please explain.

 

[dbphillips]

The oil consumption happened on the 1000 segment of the mile trip heading west. There were strong headwinds the entire way.


I corrected your sentence above


GM understand that this engine will use oil when there are high EGTs, read the TSB on oil consumption. GM states more or less that, "if you work it hard, it's going to use oil". A by-product of high specific power and lots of heat.


Please explain.

My use of the word sloppy is assuming that the anecdotal evidence I have read is correct. It would be sloppy to assume lower rpm is automatically more fuel efficient. Someone claimed they dropped their EGT 100+ degrees with no significant change in fuel economy by dropping a gear. Which kind of makes sense if you assume the energy of the fuel went into propelling the truck, rather than generating heat. Next towing trip, I will be playing with gears to verify. But I haven't been able to find the EGT PID someone said was in the GM standard setting in the iDash.

To oversimplify, steel has a fatigue limit at which it will support infinite load cycles, typically half of yield strength. Aluminum doesn't, or is much lower. So aluminum is really a terrible material for high cycle components. There are improvements made with crystal structure, etc, but still risky. What has me more concerned is the typical forged piston material, 4032 aluminum, has a melting point below 1060F, has typical fatigue characteristics and people were citing EGT in the 1300 range. There is ambient air and fuel cycling through, but still kind of concerning. And of course, there is the claim LZ0 has steel pistons, versus aluminum for LM2, which means there is concern enough for GM to spend some money.

2618 vs. 4032 Piston Material Differences

2618 and 4032, the two most prolific piston materials, have a long list of differences that make them best-suited for specific vehicle usage applications.

info.jepistons.com

Exclusive: New 3.0L LZ0 Duramax Diesel fixes long-crank issue, extends belt life - Pickup Truck +SUV Talk

Taking a deep dive into the General Motors LZ0 Duramax Diesel engine with John Barta, Chevrolet assistant engineer for diesel engines.

pickuptrucktalk.com

Aluminum Vs. Steel Diesel Engine Pistons

Just as we debate which truck manufacturer is the best—engineers debate which material is the best. When it comes to diesel pistons, right now it’s hard to tell

www.motortrend.com

And of course, any time a manufacturer goes to so much effort to wordsmith a story my Spidey Sense tingles. I guarantee oil consumption correlates more directly to engine failures than purely high load mileage on the truck.

 

[wwillson]

My use of the word sloppy is assuming that the anecdotal evidence I have read is correct. It would be sloppy to assume lower rpm is automatically more fuel efficient.

I believe when the GM engineers developed the software that controls the engine they had many requirements, including fuel economy and quiet operation. At low RPMs you can barely hear the 3.0L or the 6.6L diesels, but drop a couple gears, like I do, and you can definitely hear them. I choose to trade off quiet operation (10th gear) for lower EGTs (8th gear), evidently the GM engineers did not accepts this trade off, but they do publish and accept that oil consumption is the norm while towing, driving fast, etc. The fuel economy will be slightly less, because of increased friction from increased engine RPMs, very slightly. The ECM is programmed exactly as GM wanted it.

Someone claimed they dropped their EGT 100+ degrees with no significant change in fuel economy by dropping a gear.

Lowering a gear or two and increasing RPMs to lower EGTs is common with line-haul trucks. It physics, the more power strokes you have over a duration of time with the load steady, the EGTs will be lower.

To oversimplify, steel has a fatigue limit at which it will support infinite load cycles, typically half of yield strength. Aluminum doesn't, or is much lower. So aluminum is really a terrible material for high cycle components. There are improvements made with crystal structure, etc, but still risky. What has me more concerned is the typical forged piston material, 4032 aluminum, has a melting point below 1060F, has typical fatigue characteristics and people were citing EGT in the 1300 range. There is ambient air and fuel cycling through, but still kind of concerning. And of course, there is the claim LZ0 has steel pistons, versus aluminum for LM2, which means there is concern enough for GM to spend some money.

Thanks - I didn't know aluminum has these characteristics.

I don't hear of high mileage factory power Duramax engines with piston failures. But we do see increased aluminum in oil samples from engines that work hard and have aluminum pistons. Keep in mind that the 1300+ EGT doesn't mean the pistons are 1300 degrees. They would be melted blobs if they got that hot. Oil squirters, squirt oil into the piston oil gallery that goes in one side of the piston crown and out the other. The circulating oil removes a large amount of heat. I think the 6.6L Duramax pumps over 10 gallons/minute through the oil squirters.

I guarantee oil consumption correlates more directly to engine failures than purely high load mileage on the truck.

I disagree. I've written about the torque race and my opinion is that oil consumption can be highly correlated to the high heat in these high specific power engines.

 

[dbphillips]

I believe when the GM engineers developed the software that controls the engine they had many requirements, including fuel economy and quiet operation. At low RPMs you can barely hear the 3.0L or the 6.6L diesels, but drop a couple gears, like I do, and you can definitely hear them. I choose to trade off quiet operation (10th gear) for lower EGTs (8th gear), evidently the GM engineers did not accepts this trade off, but they do publish and accept that oil consumption is the norm while towing, driving fast, etc. The fuel economy will be slightly less, because of increased friction from increased engine RPMs, very slightly. The ECM is programmed exactly as GM wanted it.


Lowering a gear or two and increasing RPMs to lower EGTs is common with line-haul trucks. It physics, the more power strokes you have over a duration of time with the load steady, the EGTs will be lower.


Thanks - I didn't know aluminum has these characteristics.

I don't hear of high mileage factory power Duramax engines with piston failures. But we do see increased aluminum in oil samples from engines that work hard and have aluminum pistons. Keep in mind that the 1300+ EGT doesn't mean the pistons are 1300 degrees. They would be melted blobs if they got that hot. Oil squirters, squirt oil into the piston oil gallery that goes in one side of the piston crown and out the other. The circulating oil removes a large amount of heat. I think the 6.6L Duramax pumps over 10 gallons/minute through the oil squirters.


I disagree. I've written about the torque race and my opinion is that oil consumption can be highly correlated to the high heat in these high specific power engines.

Let me rewrite that:

I guarantee engine failures correlate more directly to oil consumption than to purely high load mileage on the truck.

No doubt it's exactly how they intended. Doesn't mean they are doing the right thing. They sell a tow package, so they should either manage EGT in tow mode or use steel pistons, which they seem to be doing for LZ0. Really pisses me off. I thought after 2 years in Silverado, I was safe getting the LM2 Tahoe. I suspect this is why Silverado gets it first. Guess I'll ask Banks if they are going to address.

 

[wwillson]

I guarantee engine failures correlate more directly to oil consumption than to purely high load mileage on the truck.

I guess that's probably true and it would be fun to show that with data. I'll bet we could show oil consumption has a very high correlation with the amount of fuel consumed/distance (work). Are the unmodified engines that consume oil and do lots of work the engines that fail? Or, the high percentage of engines that fail the ones that are chipped and the owner can't leave the go-fast switch alone?

No doubt it's exactly how they intended. Doesn't mean they are doing the right thing. They sell a tow package, so they should either manage EGT in tow mode or use steel pistons, which they seem to be doing for LZ0. Really pisses me off. I thought after 2 years in Silverado, I was safe getting the LM2 Tahoe. I suspect this is why Silverado gets it first. Guess I'll ask Banks if they are going to address.

We are in 100% agreement.

I believe Dodge has already addressed this the Cummins equipped trucks. My cousin as a new 3500 with 100,000 lb/ft (joking) torque, I think it's 1,050. He called me after pulling his 5th wheel several hundred miles and complained that the trans won't stay in 6th gear when pulling. Dodge and Cummins seem to have their engineering departments wired together. Shift into 5th and keep the EGTs down to a sane level. He doesn't like running down the road at 2,100 RPMs and Dodge/Cummins doesn't like high EGTs.

I have no idea about Ford's programming in the 6.7L.

 

[dbphillips]

I guess that's probably true and it would be fun to show that with data. I'll bet we could show oil consumption has a very high correlation with the amount of fuel consumed/distance (work). Are the unmodified engines that consume oil and do lots of work the engines that fail? Or, the high percentage of engines that fail the ones that are chipped and the owner can't leave the go-fast switch alone?


We are in 100% agreement.

I believe Dodge has already addressed this the Cummins equipped trucks. My cousin as a new 3500 with 100,000 lb/ft (joking) torque, I think it's 1,050. He called me after pulling his 5th wheel several hundred miles and complained that the trans won't stay in 6th gear when pulling. Dodge and Cummins seem to have their engineering departments wired together. Shift into 5th and keep the EGTs down to a sane level. He doesn't like running down the road at 2,100 RPMs and Dodge/Cummins doesn't like high EGTs.

I have no idea about Ford's programming in the 6.7L.

The ironic thing is we have more gears, so dropping it one has far less impact. But they don't make the most of it. smh

 

[xspeedy]

Interesting news, but apparently you can no longer have the LZ0 with the max tow trailering package (NTH). I wonder if GM is seeing these problems with higher loads on the engine.

https://gmauthority.com/blog/2023/03/2023-chevy-silverado-unavailable-to-order-with-duramax-diesel-and-nht-trailering-package-together/

 

[dbphillips]

Interesting news, but apparently you can no longer have the LZ0 with the max tow trailering package (NTH). I wonder if GM is seeing these problems with higher loads on the engine.

Not sure what this is about, but I would bet 300# isn't the make or break point for the Babymax. I bet it's somewhere around GCW being double GVW.

 

[dbphillips]

Banks says they don't mess with gears, but they do watch EGT. Maybe they will add a recommended "L" setting to the iDash display.

 

[dbphillips]

Interesting. On a long tow trip and pretty much only seeing EGT over 1000 during regen, and that was unloaded. Either there is a lot of variation, or there has been a software update since the posting.

After the last tow trip in February, I got an oil consumption test set up. I saw half a quart down (assuming traditional one quart between dipstick marks) a week before the dealer performed the follow up, but they claimed it was full... Gonna start recording my oil checks...

 

[loneryder]

Who makes the 3.0 Duramax?

 

[panthermike]

Who makes the 3.0 Duramax?

In-house IIRC

 

[FastLane]

It’s an interesting engine in my eyes. I would be curious if the oil was at full when your friend left on his trip.

 

[RedVic]

A friend of mine called me yesterday asking about poor fuel economy in his 3.0L Duramax. His drive was from Kentucky to Denver in 30+ MPH headwinds. He normally gets 29.5 MPG, but one this trip he only got 20.5. He wanted to know if I thought something was wrong with the engine, because it was getting such poor fuel economy. I told him his engine is fine and that bucking such a strong headwind required a lot more power. He is a +3 over driver, so most of the trip the cruise was set at either 73 or 78 MPH. If the headwind averaged 30 MPH, then he effectively was moving through the air mass at an average of 105 MPH. Drag increases as the square of the increase in speed. 105 is 1.4x faster than 75, so we square 1.4 = 96% more drag. That is why he got such poor mileage.

I had a few questions for him.
"What gear did you drive in?" - answer "10th the whole way".
"What is the engine RPMs in 10th at 75 MPH?" - answer "I believe around 1500".
"Did is use any oil?" - answer "It has never used any oil".
"Did you check the level when you got home?" - answer "No, but I'll go out and look in a bit".

He called me back about 30 minutes later and found the oil level down 1 quart. He was irritated.

1000 miles with the engine running at high load and low RPMs and oil consumption. Sounds familiar to what I found with my 6.6L Duramax.

I wish he had an iDash to monitor his EGTs.

My opinion is the oil consumption is from high piston temps because the engine is churning along at low RPMs and high power output.

He is going to ask the dealer, but I told him he will get a song and dance that this is "acceptable".

You don't add the mph of the headwind to the mph of the vehicle, people make the same mistakes with head on collisions, they think two vehicles each traveling 50 MPH equals an impact of 100 mph, that is not even close to correct. There are formulas to calculate this kind of stuff.

 

[wwillson]

You don't add the mph of the headwind to the mph of the vehicle,

Reread what I wrote. I didn’t just add the headwind to the vehicle speed to calculate wind resistance.

 

[wwillson]

It’s an interesting engine in my eyes. I would be curious if the oil was at full when your friend left on his trip.

Yes, the level was on the full mark.