2023 GM Duramax Diesel 3.0L I6 - Test Drive Impression

[HEMIMANN]

Due to all the hubbub going on with Stellantis truck model changes, and issues with Hemi engine design never resolved, I went to see what a GM Duramax Diesel truck was like. I haven't driven a GM truck since I got rid of my oil-pumper 5.3L AFM engine in 2012.

I read up what is going on. GM has made an inline 6 cylinder diesel, 3.0L displacement and offered in half ton trucks, among other vehicle types (not in HD trucks - V8 6.6L diesel continues for them). They released it in LM2 sales code, and this year upgraded it to LZ0 sales code. I tested the new version.

Test vehicle was Chevy 1500 Silverado Crew Cab 4x4 with "standard" bed (6.5 feet long). It also had NHM sales code max trailer option. This is another leaf spring in the rear axle and change from 3.23 gear ratio to 3.73. It has the new 10 speed automatic transmission. Trim was LTZ, similar to Ram Laramie (which I own), one shy from the top trim "High Country", whatever that is, and excluding any Limited releases.

Engine started right up, and is as quiet as a gas motor now. I understand the latest diesel injectors can inject up to 10 fuelings per stroke, compared to the original 5 with the first electronic piezo injectors. Undoubtedly, this accounts for the near silent combustion. Was shocking to me.

Powertrain operation was smooth and quiet - barely perceptible shifts from the 10 speed transmission, near seamless operation. Engine remained quiet under acceleration. Then we get to the handling and ride - steering was phenomenal, no doubt electric rack and pinion. But ride was marginal, not as smooth as my 3/4 ton Ram. Why? Old time rear leaf springs vs. coil and link on Ram.

Interior is still shoddy compared to Ram. Not even close to as nice, and not as comfortable as Ram. Clearly noticeable comfort difference. Tech was fine, all sorts of bells and whistles like everybody else, laid out about as nice as Ram.

And then - the engine overheated on a 77 degree F day after app. 5 miles of easy driving. Sales lady had no idea why, it hadn't been inspected after delivery yet. But for the factory to release a product that overheats requiring dealer intervention? Does that sound normal? Not to me, but maybe I'm just an old fossil now.

Final thoughts - better drivetrain the Ram (sans bizarre overheat), worse comfort and ride than Ram. Pricing now about the same.
My 2017 Laramie 2500 priced app. $52k, 2023 value for consumer price inflation is $68.5k. The problem today's price is consumer wages didn't go up as much as price inflation, and the $52k in 2017 was pricey to begin with. A Chevy HD 2500 with the gas 6.6L V8 costs about the same as the little diesel in the 1500, with half the fuel mileage.

EPA has made a mess of everything.

 

[crash68]

the engine overheated on a 77 degree F day after app. 5 miles of easy driving. Sales lady had no idea why, it hadn't been inspected after delivery yet. But for the factory to release a product that overheats requiring dealer intervention? Does that sound normal?

GM had this issue since the first 3.0L diesel a couple years back, there's been two redesigns since, the latest which you were driving was a major revamp. The original motor used a coolant control valve to get the engine up to temperature quicker something they use in a lot of their engines but it's been problematic with the 3.0L diesel.
All the big construction equipment and now even the Cummins use pilot injections to quiet the combustion cycle. That's one of the nice qualities of the EcoDiesel and Cummins is they're just as quiet towing a load as just driving down the road.

 

[Treburkulosis]

Im just glad GM dumped that 6.5 and its injector pump crap.

 

[HEMIMANN]

GM had this issue since the first 3.0L diesel a couple years back, there's been two redesigns since, the latest which you were driving was a major revamp. The original motor used a coolant control valve to get the engine up to temperature quicker something they use in a lot of their engines but it's been problematic with the 3.0L diesel.
All the big construction equipment and now even the Cummins use pilot injections to quiet the combustion cycle. That's one of the nice qualities of the EcoDiesel and Cummins is they're just as quiet towing a load as just driving down the road.

Kind of like transmission oil control valve (a.k.a. a thermostat) in the RFE transmission oil cooler line?

I worked for Cummins. The first piezo injectors came out 15+ years ago. They're made by Bosch, btw. They were subject to silt-level filtration because the ceramic injector pintle balls dribble at the slightest scratch. They were lasting only 20,000 miles.

They had up to 5 injections per stroke - pilot, pre-main, main, post-main, cleanup. The Duramax I drove today has up to 10 injections per stroke. So many you can't hear combustion. Surely all the other diesel engine brands are using the same injector.

 

[HEMIMANN]

Im just glad GM dumped that 6.5 and its injector pump crap.

That's kinda like admitting you're glad they don't make flatheads anymore.

 

[ramffml]

I'm surprised at the interior/ride you mentioned, because all the reviews I've watched have it on par with the new rams. Maybe you need to move to the GMC At/4 or the denali to get a better interior, I'm not that familiar with the differences in trim in the GM line up.

Ride and comfort is a double edged sword; ram might drive nicer yet, but the GM will definitey tow heavier loads better so it comes down to what we as individual buyers prioritize more. I think the Ram's air suspension is probably best of both worlds, haven't towed with it though so dunno for sure.

Also surprised at the temp issue but that's not normal and would obviously get fixed by dealer.

Now you should test drive the GM 6.6 2500 with the 10 speed that's probably the more natural upgrade for you from your truck, but not sure if you'd be comfortable with the DI. Haven't seen too many reports of engine issues but it may be too early to tell.

 

[HEMIMANN]

I'm surprised at the interior/ride you mentioned, because all the reviews I've watched have it on par with the new rams. Maybe you need to move to the GMC At/4 or the denali to get a better interior, I'm not that familiar with the differences in trim in the GM line up.

Ride and comfort is a double edged sword; ram might drive nicer yet, but the GM will definitey tow heavier loads better so it comes down to what we as individual buyers prioritize more. I think the Ram's air suspension is probably best of both worlds, haven't towed with it though so dunno for sure.

Also surprised at the temp issue but that's not normal and would obviously get fixed by dealer.

Now you should test drive the GM 6.6 2500 with the 10 speed that's probably the more natural upgrade for you from your truck, but not sure if you'd be comfortable with the DI. Haven't seen too many reports of engine issues but it may be too early to tell.

Thanks for thoughts.

As per Chevy brand, the LTZ interior was their top leather. It sucked compared to Ram. I don't tow as heavy as you guys, so I like the coil spring / lever arm suspension. The ride isn't really a show-stopper for me, but boy, that seating sure was lousy.

Prettery sure crash68 nailed it on the cooling - for whatever reason their rapid warmup thingy isn't letting go after warmup on this particular truck. Shouldn't be an issue, just entertaining on a potential customer test drive.

I didn't bother driving their HD / 6.6. combo. It's the classic chevy small block, iron block for trucks and aluminum head. Has proportionately more torque than Hemi 6.4, almost exactly and at exactly the same rpm. So basically it's the same engine plus a smidge more torque. Big deal. GDI, well, meh - wifey has it in her Mazda, don't know if it yields much fuel savings, but sure as hell soots the oil quick. Very few will bite the bullet and put in dual injectors as required.

I'd imagine GM HD would ride like a dump truck being all leaf springs. The only thing going for it vs. mine is maybe a more reliable transmission (?) and no engine lifter issues. Trade for a less comfy ride and beaucoup payments again. My truck is paid for. Doesn't excite me very much.

 

[crash68]

Kind of like transmission oil control valve (a.k.a. a thermostat) in the RFE transmission oil cooler line?

It's a motorized valve controlled by the ECM. A similar system is used in many of the small GM motors but this one has proved troublesome.

 

[ramffml]

My truck is paid for. Doesn't excite me very much.

Yes this is key; you can do a lot of repairs for an $800 truck payment every month for a few years.

 

[HEMIMANN]

Yes this is key; you can do a lot of repairs for an $800 truck payment every month for a few years.

Except to find a rebuilt transmission no longer in production that didn't have enough service spare parts made for it.

Yeah?

Maybe a guy could wedge in a ZF8, I dunno - I didn't keep up with you guys on all that stuff. That would be pretty cool, though. Hell, I'd take a rebuilt 66RFE if mine hatches, but there aren't any. ATS said they'd rebuild mine, but for how much longer. Plus my truck would be out of service.

So, this is basically my point.

Edit: thanks to all you guys, I did all the good stuff to try to save the thing - deleted trans oil cooler thermostat, don't drive O.D. hauling anything, only use tow mode shifting when hauling, turn MDS off when hauling (take out torque hammer going in and out of MDS), got 2 gallons Red Line C+ATF and a synthetic control filter in the sump.

Not much else to do except rebuild (PCM is tuned, don't want a do-over with a new VB).

 

[Treburkulosis]

That's kinda like admitting you're glad they don't make flatheads anymore.

Hey the one I had for work was a flatbed and a stick lol. It barely had enough power to tow a trailer and a forklift.

 

[20IndyRam]

Final thoughts - better drivetrain the Ram (sans bizarre overheat), worse comfort and ride than Ram. Pricing now about the same.
My 2017 Laramie 2500 priced app. $52k, 2023 value for consumer price inflation is $68.5k. The problem today's price is consumer wages didn't go up as much as price inflation, and the $52k in 2017 was pricey to begin with. A Chevy HD 2500 with the gas 6.6L V8 costs about the same as the little diesel in the 1500, with half the fuel mileage.

EPA has made a mess of everything.

Curious why you thought the GM 3.0 inline was better than the Gen 3 RAM Eco? I've driven both (2020) and chose the Ram. I did like the exhaust brake on the GM.

Aside from that, the Ram had better power/torque/fuel economy, much better fit finish, and a much better ride. In short, I haven't had an issue in 44K miles and am very pleased with the Ram.

Most of the Diesels are now plagued by the Bosch CP4 recall. The Eco's seem to be fairing well with their lift pumps and low high pressure pump demands (I have used Hotshots ETD since new). GM has a track record of not using lift pumps on the previous Duramax diesels. That was reported to increase the likelihood of CP4 pump failures. Not sure if they took the same approach on the 3.0L inline, or whether it makes a difference on the smaller engine.

Still happy with the Ram.

 

[HEMIMANN]

Hey the one I had for work was a flatbed and a stick lol. It barely had enough power to tow a trailer and a forklift.

I drove an old Ford F700 gasser for a Landscaping Service in college. Don't know what the motor was in it, but for a ton and a half truck loaded with topsoil black dirt, it was a real mutt. So much so it had a split real axle. You had to have it in granny gears just to get it going. Boy, people didn't like being stuck behind me when I was loaded!

 

[HEMIMANN]

Curious why you thought the GM 3.0 inline was better than the Gen 3 RAM Eco? I've driven both (2020) and chose the Ram. I did like the exhaust brake on the GM.

Aside from that, the Ram had better power/torque/fuel economy, much better fit finish, and a much better ride. In short, I haven't had an issue in 44K miles and am very pleased with the Ram.

Most of the Diesels are now plagued by the Bosch CP4 recall. The Eco's seem to be fairing well with their lift pumps and low high pressure pump demands (I have used Hotshots ETD since new). GM has a track record of not using lift pumps on the previous Duramax diesels. That was reported to increase the likelihood of CP4 pump failures. Not sure if they took the same approach on the 3.0L inline, or whether it makes a difference on the smaller engine.

Still happy with the Ram.

ED is underdesigned - marginal crank and bearings. Many failures Gen 1, Gen 2 they tried to half-a$$ upgrade it, mandated higher viscosity engine oil to try to save it. Best read up on all the failures on these engines.

Bosch CP4 recall is on the bigger engines. Smaller engines have Denso, Stanadyne, or other reliable pumps. CP4 pump is cost-reduced CP3, has nothing to do with lift head. It is a cheap pump underdesigned for its purpose. Well documented by this point. It was all about maximum moola for Bosch - charge the same price for a cheapo.

 

[Treburkulosis]

I drove an old Ford F700 gasser for a Landscaping Service in college. Don't know what the motor was in it, but for a ton and a half truck loaded with topsoil black dirt, it was a real mutt. So much so it had a split real axle. You had to have it in granny gears just to get it going. Boy, people didn't like being stuck behind me when I was loaded!

Sounds like the 90 Kodiak I drove for almost 20 years. Dang tough truck, but it was so slow.

 

[HEMIMANN]

I take it nobody active here has bought or tried one these other than moi?

 

[ramffml]

I take it nobody active here has bought or tried one these other than moi?

I've driven the older 2.7, 5.3, and the older 3.0 from GM. I wouldn't get the 5.3 over my truck because why, less power in a v8. Loved the 3.0, and the 2.7 was very surprising; haven't driven the new variants which both make significantly more torque.

Back then the interior was quite bad, not sure the year I tested, 2019 + 2020 in the diesel probably.

I do like the new gms, but purchasing one for me at this point would be a side step and completely pointless considering what I want from a truck and how my truck is currently running. The diesel is very attractive to me, but horribly expensive given the entry trim level and I'd never make that deal work financially. But if I cracked up my truck? Yeah I'd be heading to the GM dealer for sure to take another look.

 

[Travelin Ram]

I test drove one last year while truck shopping. I was impressed.

I’ve talked with owners and they seem well satisfied and reported mileage around high 20’s to 30.

Now that GM offers the diesel in a ZR2 I may give them another look. I’d probably be driving a ZR2 now if the Chevy dealer hadn’t tried playing the usual games rather than being straight with me.

 

[20IndyRam]

Bosch CP4 recall is on the bigger engines. Smaller engines have Denso, Stanadyne, or other reliable pumps.

Wrong - the CP4-2 is used on larger engines. The CP4-1 is used on smaller. I currently have a recall for my 2020 EcoDiesel with the CP4-1 pump. The F150 3.0L Diesel also uses the CP4-1

CP4 pump is cost-reduced CP3, has nothing to do with lift head. It is a cheap pump underdesigned for its purpose. Well documented by this point. It was all about maximum moola for Bosch - charge the same price for a cheapo.

Wrong again - The CP4 is a higher pressure version of the CP3. It is less expensive, lighter, and more efficient. It's main failure mode is cavitation and lack of lubricity. This is why the lack of a lift pump (higher differential pressure) ABSOLUTELY contributes to the failures. As you said -WELL DOCUMENTED BY THIS POINT. Adding lubricant to our low sulfur fuels makes these pumps last. I'll let the lawyers figure out if that's worthy of a class action suit.

ED is underdesigned - marginal crank and bearings. Many failures Gen 1, Gen 2 they tried to half-a$$ upgrade it, mandated higher viscosity engine oil to try to save it. Best read up on all the failures on these engines.

I read up on the Gen3 ED before I bought it. You should do the same. There were failures on the Gen 1 and 2. Gen 3 has been very good. Unfortunately, they are discontinuing (I would have bought another).

On the flip side, you are pinning your homes and dreams on a Gen1 3.0L Duramax where you don't like the ride quality or Fit/Finish. Sorry, but I wouldn't buy a Gen 1 anything (including Toyota) particularly if I didn't care for the rest of the vehicle.

For your edification - here's the TSB list for the Silverado 1500 with the small diesel. Interesting that the have some related to "excessive fuel contamination" and "fuel additives". Doesn't sound anything like a high pressure pump concern - or does it?

Silverado 1500 3.0L Diesel TSB

 

[Travelin Ram]

It sure would be nice to read about the topic at the top.

GM isn’t selling ED. Neither is RAM.