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).