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

wwillson

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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".
 
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I guess I should be glad my new (to me) 4cyl diesel consumed zero oil screaming along the interstate at 3500+ rpm!
 
Keep in mind that the 3.0L Duramax has an even higher specific power than the 6.6L Duramax, so we shouldn't be surprised that piston temperatures are a problem. 2023 forward the 3.0L has steel pistons, which replace the aluminum pistons. Why? Because steel has a much higher softening and melting point than aluminum. The torque race continues, oil consumption seems to be a given with the 3.0. If everyone had an iDash and kept there EGTs below 1100F for continuous runs, I don't think these 3.0Ls would have an oil consumption problem. Just my opinion.
 
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Keep in mind that the 3.0L Duramax has an even higher specific power than the 6.6L Duramax, so we shouldn't be surprised that piston temperatures are a problem. This year for the 3.0L has steel pistons, which replace the aluminum pistons. Why? Because steel has a much higher softening and melting point than aluminum. The torque race continues, oil consumption seems to be a given with the 3.0. If everyone had an iDash and kept there EGTs below 1100F for continuous runs, I don't think these 3.0Ls would have an oil consumption problem. Just my opinion.

This guy owns the same truck and not a drop of oil used to date:
 
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).
You are correct, this guy's 3.0 hasn't used any oil.

I didn't see you posted another video below the video that shows oil consumption.
 
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".
Do you think dropping down a gear or two to raise RPMs would have helped reduce the high load and thus oil consumption?

As well, dropping his speed from 75 to 60 (facing that 30 MPH headwind) would have helped.

105 down to 90 is a decrease of 1/7.

(6/7)^2 = 36/49 = just under 3/4 of the original wind resistance.
 
Guessing OP was at or nearly at full throttle while driving into the wind so agree that dropping down a cog would have been beneficial. While 1500 rpm isn`t lugging a diesel, under the conditions reported the load was substantial INMHO. Not sure the 3.0 is designed for such.
 
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