GM I6 Diesel Impressions

/ GM I6 Diesel Impressions #1  

lostcause

Veteran Member
Joined
Mar 29, 2010
Messages
1,044
Location
Maine
So, I broke down and bought a new truck last month. I had been internet shopping and pricing on & off for the last year or so, since I had heard about this engine. A little over a month ago I was internet browsing and the Chevy site had an NADA link right on the truck build page, so I looked my current truck up, and the value was a lot higher than I expected. On the way home from work that Saturday I stopped at a local dealership and talked figures to see if those numbers were what I could really get, and they actually went a little better. I digested it all over the weekend and on Monday I checked against another local dealer who was horribly off in comparison, so I went back to the first dealer and pulled the trigger, and picked it up the following night. They didn't even have what I wanted on the lot so they had to go get it from another dealer for me.

4 years ago I had bought a diesel Colorado to replace the 6.0 gas that I had for a decade. I loved that 6.0 truck and it had been bulletproof, but around here there is a fine line where a vehicle still has good value, and where it is a rusty as-is money pit of a trade-in, so it was time to go while the money was still there. I didn't have the need to tow like I had a decade prior, so the diesel Colorado looked like a good fit - good fuel economy to cover a 100 mile a day round trip and still modest truck-like capability. The Colorado was a good vehicle, but after over 20 years in a full size, I really did miss the interior room. When we go away for a day trip we seem to be packed like we're off for a week, and if we go for a week you'd assume we were moving cross-country. Enter the Silverado 1500 Diesel...

On paper this full size was advertising the same 29mpg that my Colorado stated, though I was never able to get over 27-ish, with a 4 year average of 25.4 cumulative, including empty, loaded, plowing, and a little towing, but it was overall mostly just body cargo. The Silverado certainly isn't going to be a towing monster, but it will cover the overall need for me. I sure do enjoy the interior space it has, and the whole package. I have to say the Colorado was more fun to drive - the Silverado is kind of like driving your living room couch - I guess I like to feel all the bumps and cracks in the road, and after the 2500HD followed by the Colorado, it is a lot different ride.

Around Christmas 2018 I had an emissions issue with the Colorado. The biggest issue with a small-market vehicle like that is the knowledge base and part availability. I knew this going in and took the gamble and lost this time. Apparently the entire batch of replacement parts GM had were also faulty, so I was without the truck for 7 weeks while I waited on a slow boat from China (or wherever...). it was all under the emissions warranty, so no major worry. During that time I had a couple nice loaners, including a brand new off the lot 2019 Silverado 1500 5.3. Since I had this truck for an over 2000 mile test drive, I was able to calculate what a new gas engine would do for my driving. I got 18.6mpg for the entire time, but that was only empty trips to and from work. With the price of diesel in comparison to gas here at certain times, diesel is hardly justifiable, so you really have to want it. When I bought the Colorado, diesel was only about 10% higher at local stations, but there have been times where it was 50% higher.

I was talking about the Silverado somewhere back there wasn't I? So anyways, I'm 5 tanks into the little I6 diesel and my calculated average is 28.6mpg cumulative, with a best single tank of 30.8 and a worst of 27.3. the on-board mpg calculator seems to be a half mpg plus on the low side compared to hand calculating the mileage. I'm still not sure if its justifiable to have the diesel, but it's certainly not horrible. The sicker difference between a 5.3 and a diesel is about $2500, so it's not a price killer like when you go the 2500/3500 route and need different transmissions too. I think my favorite thing is the once-a-week fuel ups. I had to fuel up about every 4 days with the Colorado, and the 2500HD would only get me 2.5 days between fuel-ups. With the 24 or 26? gallon tank - I forget, I'm easily able to go at least 600 miles of routine driving before a fill up now.

With any luck I'll be bringing home a new (used) tractor tomorrow too, so I will kill the fuel economy, but for a good reason :D
 
/ GM I6 Diesel Impressions #2  
Sounds like you like your new truck, have you driven the RAM 1500 diesel if so how was the power delivery comparison.
Is yours 4wd if so doyou have the low range in the transfer case and hows it feel to you.
 
/ GM I6 Diesel Impressions #3  
/ GM I6 Diesel Impressions #4  
I've casually been looking for the scheduled maintenance of the GM I6 diesel but have yet to find it. Curious on oil change intervals and fuel filters versus costs. Dealers around me have been closed since the outbreak and still are.

Six in a row makes it go.
 
/ GM I6 Diesel Impressions #5  
Lots of You-Tube videos on the L-6 Silverado(Fast Lane Trucks),great reviews.I am kind of interested myself but don't really "need" a new truck.Only one I have seen on the lot was $55K sticker.The ten speed auto is a huge plus.I have always bought the 5.3 and have had very good luck with them.
 
/ GM I6 Diesel Impressions #6  
If i ever need a new truck, the 1500 I-6 Duramax will get a hard look. My 17 1500 5.3 is all I need at the moment.
 
/ GM I6 Diesel Impressions
  • Thread Starter
#7  
I didn't try the Dodge or Ford. They all looked pretty close on paper as far as performance and economy stats go. I've had GM trucks for quite a few years now and I've never been unhappy enough about something to change. If one brand had something that was a game changer I might look, but usually what one has, the others have soon after. A big portion of the brand loyalty is the fact that I've got a GM card that has paid me back some really nice discounts on the last few I have bought. I'm probably more loyal to my wallet than GM, but I haven't had a new GM that I disliked either.

The first two oil changes are free, which is going to be a good thing. When I had the Colorado that used a new oil spec (Dexos-2) that was difficult to find and was pricey. None of the big box auto parts chains could even order anything that met the spec. A local Napa got me the Mobil-1 version for about $10 a quart when I bought it by the 6 pack, which was what it needed for a change. This one uses another new spec (Dexos-D) which I haven't found (aside from GM) other than one specific Mobil oil that I can't find any listings of for sale. Hopefully by the time my third change hits I have a source. The fuel filter looks to be the same part number as for the 6.6 now. I haven't kept up on that engine, but I guess they must have moved the fender well filter to a frame rail cartridge.

This truck had a sticker of just over 53k. It was exactly the option build I wanted, with nothing more or less that I had to pay for that I didn't want. It's old school loaded - power windows, locks, tilt, cruise, xm, and a bunch of others that I'm not naming. I gotta admit that keyless start and heated steering wheel are a couple creature comforts that I really love here in the northeast now. it's a long way in options from a 70k High Country, but I can't think of any option that I didn't have that I'm longing for. Steps, bedliner, mudflaps and floor mats are easy add-ins.

As far as 5.3V8 gas vs 3.0I6 diesel, the 5.3 wins in the towing rating by a few thousand pounds if I remember. I think the diesel is rated for 9200 or 9300, and I think the 5.3 is like 11500 to 13500 or something like that, depending on the build. I look at it from a driveability point of view - I mostly drive back roads, 45-60mph, and this diesel and the Colorado both have shined in this setting for me. Today I brought home a new-to-me tractor, with a 250 mile round trip, mostly on I95/I295. I'm pretty sure the 7k trailer was fully loaded to the max capacity, and the tow was perfect, and the new truck did great. The 10 speed did exercise itself on the interstate, especially with speed changes while towing 7k at 60+ mph, but it was always running in the 1400-2000 rpm range. The last 25 miles of the trip home is two lane back roads and it really did great there. It just seemed to idle along at speed while hardly ever shifting, except in the bigger hills and corners. I guarantee a 5.3 would cycle the gears and go to much higher revs in the hills and corners to maintain speed. At the same time, the 5.3 would likely handle the high speed towing as well or better than the little diesel. There's been a lot of great innovations with transmissions and turbos over the last decade, but I think when it comes to towing, the old adage of "no replacement for displacement" still has some validity. One month, 2700 miles in, with one good tow behind me and I wouldn't do anything different.
 
/ GM I6 Diesel Impressions #8  
Congrats on the new truck and tractor. Thanks for the reviews. I will be looking at something smaller than a 2500HD for road trips before long. Also remember the TBN rule, no pictures, it didn't happen. :)
 
/ GM I6 Diesel Impressions
  • Thread Starter
#9  
60821653204__57C9E416-DBD0-41AE-AC2F-DD94C4FF2A38.JPGfirst big storm
 
/ GM I6 Diesel Impressions
  • Thread Starter
#10  
IMG_0973.JPGfirst tow home, and sitting beside the 770 until i clean it up and put it up for sale...

And I downloaded the app, and we're not getting along well when it comes to posting pictures from my phone, as you can tell.
 

Attachments

  • IMG_0976.JPG
    IMG_0976.JPG
    587.6 KB · Views: 385
/ GM I6 Diesel Impressions #11  
Yikes ! Was this the storm from this past week ? We were lucky to have rain only down here. That picture shows it to be a heavy wet snow. BTW is your new 1500 black on black?
 
/ GM I6 Diesel Impressions #12  
Thanks for the write up, my 2012 Silverado 1500 has around 145k on it. Starting to look a little
 
/ GM I6 Diesel Impressions #13  
I was talking about the Silverado somewhere back there wasn't I? So anyways, I'm 5 tanks into the little I6 diesel and my calculated average is 28.6mpg cumulative, with a best single tank of 30.8 and a worst of 27.3. the on-board mpg calculator seems to be a half mpg plus on the low side compared to hand calculating the mileage. I'm still not sure if its justifiable to have the diesel, but it's certainly not horrible. The sicker difference between a 5.3 and a diesel is about $2500, so it's not a price killer like when you go the 2500/3500 route and need different transmissions too. I think my favorite thing is the once-a-week fuel ups. I had to fuel up about every 4 days with the Colorado, and the 2500HD would only get me 2.5 days between fuel-ups. With the 24 or 26? gallon tank - I forget, I'm easily able to go at least 600 miles of routine driving before a fill up now.

I have been thinking about updating my 2014 Sierra 1500 to a 2020 model since the incentives are pretty strong. Have the 5.3L engine now and it's been good, gives me 19-22mpg regularly. Am considering all the engines, and the new I6 diesel is appealing. Thing is, the cost of diesel fuel is enough higher than gas in this area that it kills any fuel efficiency $$ benefit to the diesel engine. So not sure what I'll do. I want to test drive that engine though, and the 6.2L too.
 
/ GM I6 Diesel Impressions #14  
I have been thinking about updating my 2014 Sierra 1500 to a 2020 model since the incentives are pretty strong. Have the 5.3L engine now and it's been good, gives me 19-22mpg regularly. Am considering all the engines, and the new I6 diesel is appealing. Thing is, the cost of diesel fuel is enough higher than gas in this area that it kills any fuel efficiency $$ benefit to the diesel engine. So not sure what I'll do. I want to test drive that engine though, and the 6.2L too.

I haven't driven the Chevy 6 yet but I do have the RAM V6 diesel, will the mileage ever pay for the cost differential, NO..
That said the smooth low end torque delivery of the diesel reminds me of the way the old big blocks would pull at low rpm.
My max torque is around 1600 rpm and that little motor just pulls nice and smooth, no fuss, no muss, no screaming rpm which is what I like.
Is it the motor for everyone, nope. Does it have some turbo lag when cold, yep. I still enjoy the way the motor just pulls unloaded or even over loaded.
 
/ GM I6 Diesel Impressions #15  
I have been thinking about updating my 2014 Sierra 1500 to a 2020 model since the incentives are pretty strong. Have the 5.3L engine now and it's been good, gives me 19-22mpg regularly. Am considering all the engines, and the new I6 diesel is appealing. Thing is, the cost of diesel fuel is enough higher than gas in this area that it kills any fuel efficiency $$ benefit to the diesel engine. So not sure what I'll do. I want to test drive that engine though, and the 6.2L too.

My thoughts also;fuel is higher,DEF purchases,higher cost of oil changes;potential cold weather problems.I like what I read about the L6 but for me the 5.3 makes more sense.The diesel has to get 25 mpg to break even on fuel alone.
 
/ GM I6 Diesel Impressions
  • Thread Starter
#16  
Yikes ! Was this the storm from this past week ? We were lucky to have rain only down here. That picture shows it to be a heavy wet snow. BTW is your new 1500 black on black?

That storm was April 10. We got a foot of really wet and heavy snow. I haven't seen as much tree damage since the 98 ice storm. We always lose pine limbs in winter, but since the hardwoods have dropped their leaves they don't usually take as much damage, but this storm took out a lot of big hardwoods.

The truck is black with black interior, but not full blackout. I have chrome on the mirrors, grille & bumper, and silver painted wheels. My Colorado was a midnight edition full black on black. This was a function of what the dealer could easily get in a swap, and I'm good with the color & trim options. Most of the time I'm more than content to concede a little on some of the fine details. When I got this I had to rush to pick it up after they got it in because they weren't sure whether they were going to be allowed to be open the next day.


Lou said it best - these aren't for everyone. It's not likely that you can justify something like this down to the last penny, but the driveability factor is there in these small diesels. I took my Colorado diesel to Florida last year and going through the hills in Pennsylvania it was like being on an uphill slalom course. I had the cruise control set and the truck was just off idle going up and around everyone as they were using all the revs and gears they had. You have to learn how to drive one though. it's not just mat it and go. Gas engines generally have a constant uphill power curve, but these diesels can be over revved and you will be out of the torque curve at that point. When the fuel prices stabilize I have no clue where it will land, but since I had the ability to do a 5.3 test on an identical 2019 truck last winter I knew I was going to see 18.6mpg gas, so I'm getting a full 10mpg better, or more than 50% better economy. Right now with diesel at just a little better than $2 a gallon near me, it's pretty nice. Course, with gas at $1.40, that would be equally good too.
 
/ GM I6 Diesel Impressions #18  
I'm still considering this engine in a new Sierra, and took a look at historical fuel costs for gas and diesel since 2010, and the effective MPG. Came up with this chart:

attachment.php


The chart shows the equivalent gas MPG of a diesel rated for 26mpg (that is the highway spec for the GM I6 in a 4x4 crew cab Sierra).

When gas prices are cheap, like they are now, 26mpg from diesel is the same as 18mpg from gas. The current batch of V8 gas engines from GMC easily beat that number. On the average though, the diesel ranges between an effective 21-25mpg, so on average it's going to be better than the gas engines. When fuel costs get high, the diesel gets into the 25-28mpg range, which is way better than the gas engines can do.

For reference, here are the historical costs of gas and diesel that went into this calculation:

attachment.php


cost.png

Picture1.png
 
/ GM I6 Diesel Impressions #19  
Any perceived loss of money, due to increased fuel costs, DEF costs, etc., is more than easily made up by the amount of Torque you getting with the diesel. Have had a bunch of gassers and diesels, I'd take a diesel any day, the only application of where the diesel just didn't feel right was with a side by side, that has to be a gasser.
 
/ GM I6 Diesel Impressions #20  
Any perceived loss of money, due to increased fuel costs, DEF costs, etc., is more than easily made up by the amount of Torque you getting with the diesel. Have had a bunch of gassers and diesels, I'd take a diesel any day, the only application of where the diesel just didn't feel right was with a side by side, that has to be a gasser.

Yes, that low end pull is unbeatable. I like diesels.
I look at me buying a diesel in a pickup about like the person that gets the biggest v8 for once a year use.
Or a one ton for once a year use instead of a half ton for year round use, I just like it better and I'll pay a bit more if need be for it.
 
 
Top