3.0L Duramax - who owns or has driven one

becker87 · March 3, 2020

Just got back from a New Orleans -> Houston drive and tried to do a little MPG calculating/estimating.

From DIC for as long as I could sustain. Please note this is not scientific, just gives a rough idea in real world driving.

Cruise Control set to:
60mph - 32/33mpg
65mph - 29/30mpg
70mph - 25/26mpg
75mph - 22/23mpg
80mph - 20mpg

Crew cab 3.0L 4wd Z71 275/60R20 stock Dueler ATs
Temp: low 70’s, not very windy, “low” humidity considering the territory [emoji38]

I plan on trying to fine tune this as accurate as possible to compare once I get leveled and bigger tires : )

I see very similar numbers with mine at speeds above 75 but seem to get around 25-26 at 65-70. I do have larger and much heavier duratracs on mine though. Thinking of switching back to a lighter tire for summer driving. Even with the heavier tires but with this warmer weather still seeing about 22 mpg in town, granted it's small town driving

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Whipped500 · March 3, 2020

2 hours ago, HondaHawkGT said:

The best way to destroy a modern diesel is to start it up, drive a few miles, and shut it back down. I watched a guy with a Ram 1500 Ecodiesel destroy two engines plus exhaust system doing that. He's drive across town to work every day. If you have a habit of doing short drives like that, diesels with modern emissions systems are not for you.

I agree and understand this but I think 20 miles is plenty fine. This is why my LML has such low miles. I bought it to tow the boat and I only drive it if I know it will get up to operating temp.

I have a LM2 on order and will be using it for a service vehicle. Some days I drive a mile or two to a customer then have multiple ones blocks apart from there...other days I drive 20+ miles before I get to the first one. I'm hoping that the cooling system gets things to temp faster as they describe it to do. If not, it's under warranty.

6sigma · March 3, 2020

1 hour ago, Whipped500 said:

I agree and understand this but I think 20 miles is plenty fine. This is why my LML has such low miles. I bought it to tow the boat and I only drive it if I know it will get up to operating temp.

I have a LM2 on order and will be using it for a service vehicle. Some days I drive a mile or two to a customer then have multiple ones blocks apart from there...other days I drive 20+ miles before I get to the first one. I'm hoping that the cooling system gets things to temp faster as they describe it to do. If not, it's under warranty.

The LM2 seems to be setup to warmup up relatively quickly for a diesel. I've been monitoring various temps with Torque app and it shows the exhaust temps inc DPF get to 400+F pretty fast (5 min maybe). Oil temp seems to get to 180-190 about the same time as the LT1 in my Camaro. Coolant temp takes longer to get hot though but I think that is by design in the active cooling system. It seems LM2 is setup to get emissions equipment up to temp quickly.

Agreed that a lot of short trips are prob not ideal for any diesel though. If you have a lot of short trips I'd make a point to get it out on the highway occasionally to let everything get hot. I had a 2013 VW Passat TDI 2.0 when I had a 100+ mile daily round trip. That TDI was known to have frequent turbo failures, but my car never did and I think it was because everything got fully up to temp with almost no short trips.

tvette1993 · March 3, 2020

4 hours ago, HondaHawkGT said:

The best way to destroy a modern diesel is to start it up, drive a few miles, and shut it back down. I watched a guy with a Ram 1500 Ecodiesel destroy two engines plus exhaust system doing that. He's drive across town to work every day. If you have a habit of doing short drives like that, diesels with modern emissions systems are not for you.

I don't necessarily disagree that this was a factor in older diesel engines, however if this was a legitimate concern for GM, why would they have installed the Autostop feature on the diesels???

If you have a 30 mile city commute, the truck could be turning off and on 20 times in 1 commute...

I tend to believe with the technology in the engines today, run time isn't a big factor.

Duramax3oh · March 3, 2020

5 hours ago, HondaHawkGT said:

The best way to destroy a modern diesel is to start it up, drive a few miles, and shut it back down. I watched a guy with a Ram 1500 Ecodiesel destroy two engines plus exhaust system doing that. He's drive across town to work every day. If you have a habit of doing short drives like that, diesels with modern emissions systems are not for you.

That’s not what I want to hear! I’ve always seen diesel trucks sitting there idling and not turned off at stops some and wondered if the new engines should still do that?

I’m curious about why it’s the case that short trips are bad for the engines.

redwngr · March 3, 2020

3 minutes ago, Duramax3oh said:

That’s not what I want to hear! I’ve always seen diesel trucks sitting there idling and not turned off at stops some and wondered if the new engines should still do that?

I’m curious about why it’s the case that short trips are bad for the engines.

Because water is a byproduct of combustion, and water will condense out of the exhaust stream when the engine and exhaust or not hot enough.

This is true for both gas and diesel engines.

It's not the start and stop that causes the problem -- it's the cold running / not running long enough to get warmed up enough that the moisture can be carried out.

Duramax3oh · March 3, 2020

3 hours ago, becker87 said:

I see very similar numbers with mine at speeds above 75 but seem to get around 25-26 at 65-70. I do have larger and much heavier duratracs on mine though. Thinking of switching back to a lighter tire for summer driving. Even with the heavier tires but with this warmer weather still seeing about 22 mpg in town, granted it's small town driving

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I was pleasantly surprised by the 75-80mph numbers, good to know those do somewhat hold up.

what size Duratracs do you have? I’m looking at adding a level with 275/65R20 which seem to run ~15lbs heavier than stock.

Guess I could live with about 25mpg Highway figures at typical speeds but getting up to the 30’s is so incredibly satisfying!!

ETA - From an earlier comment... yes I-10 is a very very flat drive. Highest elevation we get is on the overpasses

Edited March 3, 2020 by Duramax3oh

jaslon · March 3, 2020

6 hours ago, HondaHawkGT said:

The best way to destroy a modern diesel is to start it up, drive a few miles, and shut it back down. I watched a guy with a Ram 1500 Ecodiesel destroy two engines plus exhaust system doing that. He's drive across town to work every day. If you have a habit of doing short drives like that, diesels with modern emissions systems are not for you.

I do not think a 22 mile drive is a short drive, unless you think it is for a diesel engine.

HondaHawkGT · March 3, 2020

14 minutes ago, jaslon said:

I do not think a 22 mile drive is a short drive, unless you think it is for a diesel engine.

Nope not saying it is. Just wanted to throw that in there just in case he or anyone else thinking about getting a truck with this engine does a lot of short trips.

HondaHawkGT · March 3, 2020

1 hour ago, tvette1993 said:

I don't necessarily disagree that this was a factor in older diesel engines, however if this was a legitimate concern for GM, why would they have installed the Autostop feature on the diesels???

If you have a 30 mile city commute, the truck could be turning off and on 20 times in 1 commute...

I tend to believe with the technology in the engines today, run time isn't a big factor.

The autostop shutting off the engine for 30 or 60 seconds isn't the same as hopping in a cold truck and driving for 5 minutes, getting to the destination, and letting it sit 8+ hours. Doing that 5 or 6 days a week, the exhaust system never gets hot enough to keep the exhaust system cleaned out. The Ecodiesel guy was constantly going into regen because 90% of his driving consisted of in-town strolls and short trips.

The autostop feature shouldn't be on this engine IMO, but most guys won't own the truck long enough for the consequences of letting the engine turn off and on like that. GM knows that too (as do all vehicle manufacturers forced to use autostop these days).

HondaHawkGT · March 3, 2020

4 hours ago, Whipped500 said:

I agree and understand this but I think 20 miles is plenty fine. This is why my LML has such low miles. I bought it to tow the boat and I only drive it if I know it will get up to operating temp.

I have a LM2 on order and will be using it for a service vehicle. Some days I drive a mile or two to a customer then have multiple ones blocks apart from there...other days I drive 20+ miles before I get to the first one. I'm hoping that the cooling system gets things to temp faster as they describe it to do. If not, it's under warranty.

Yeah 20 mile trips are fine. I mainly meant it as a cautionary thing for anyone considering the LM2 and are kind unsure about it. Some people do a ton of short trips in these newer diesels and end up with a ton of problems because they don't understand just how bad it is for the expensive filters on these things.

redwngr · March 3, 2020

Autostop doesn't work til the engine is warmed up.

Therefore, not a factor with the cold start/short trip issue.

OTOH, ecodiesel had so many problems they stopped selling them.

Hopefully for the RAM fans a similar level of issues doesn't occur this time around.

newdude · March 3, 2020

3 hours ago, Duramax3oh said:

That’s not what I want to hear! I’ve always seen diesel trucks sitting there idling and not turned off at stops some and wondered if the new engines should still do that?

I’m curious about why it’s the case that short trips are bad for the engines.

Short trips are bad for modern diesels especially. Higher regen frequency, less chance for the DPF to burn properly due to low exhaust heat/temps present. It can load up a filter for the worse if the DPF can't burn itself clean correctly. Also, can load up the emissions sensors and foul them out prematurely.

My 2016 Colorado diesel did great. I'd let it idle in the winter to warm up sure, but my drive to work is 16 miles one way, 85% highway. Plenty of time to get everything happy.

Edited March 3, 2020 by newdude

becker87 · March 3, 2020

I was pleasantly surprised by the 75-80mph numbers, good to know those do somewhat hold up.

what size Duratracs do you have? I’m looking at adding a level with 275/65R20 which seem to run ~15lbs heavier than stock.

Guess I could live with about 25mpg Highway figures at typical speeds but getting up to the 30’s is so incredibly satisfying!!

ETA - From an earlier comment... yes I-10 is a very very flat drive. Highest elevation we get is on the overpasses [emoji38]

I am running 275/70/18 10 ply. Think they were a 33.1 inch tire. I have a two inch level with two inch rear blocks as well

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j-ten-ner · March 4, 2020

6 hours ago, HondaHawkGT said:

...

The autostop feature shouldn't be on this engine IMO, but most guys won't own the truck long enough for the consequences of letting the engine turn off and on like that. GM knows that too (as do all vehicle manufacturers forced to use autostop these days).

I wouldn't mind the autostop feature if there was an integrated starter/generator, like in some Mercedes models.

No starter as we know it anymore.

And it can be used for a little boost for acceleration. Pretty much like the RAM E-torque system. Just better

so long

j-ten-ner

EDIT: ...but first I'd like to see self levelling headlights in our trucks......or maybe both...lol

Edited March 4, 2020 by j-ten-ner