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".
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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