6.2 GM Diesel

[jmodge]

Greetings from the other side! I am curious if anyone on the site travels using a 6.2 diesel. If so, what kind of fuel mileage do you get with the camper on? Thanks

 

[Zoomad]

Greetings from the other side! I am curious if anyone on the site travels using a 6.2 diesel. If so, what kind of fuel mileage do you get with the camper on? Thanks

Is your K5 a diesel? I've had a couple crazy thoughts about a 6.2 due to the fuel mileage but I can't get over the problems the 6.2 is well known for. In my case with the lift/tires/gearing and the added weight/drag of the FWC I can only imagine how it would chug along. Sure a Banks sidewinder can perk it up, but not enough. Throw in the terrain I'm used to traveling in (the Rockies) and I'd be getting passed by loaded VW microbuses.

The big block plan is fully in the parts procurement phase, fuel mileage be damned. I need to be able run the speed limit on the passes. As it is, the mileage will probably be on par with the 5.3 I have in there. But the engine won't get whipped like a rented mule when the road goes up in elevation.

 

[jmodge]

I have the original 5.7, I installed vortec heads, low rpm cam, and an electric fan. I bought an '85 K5 with a 6.2 figuring to do a swap strictly for fuel mileage. Since then the price of diesel and gas went opposite direction. I was just wondering if there was anybody carrying a FWC camper with a 6.2, there is a wide range of claimed fuel mileage out there.
Wouldn't want to get caught from behind on a mountain road by a large truck, that's for sure They have a very narrow powerband, damn strong for a couple hundred rpm though, which would work good for us as we putt backroads a lot here. It would be a lot of work and I am leaning toward the idea not being worth it. I like using it more than working on it One of these years I would like to make it out to the FWC gtg out there.
I can't coax quite 13mpg out of my small block

 

[ntsqd]

If you can live with the NA 6.2 I'd drive it as-is.

I couldn't.

I've been semi-sort of on the look-out for a 6.5tD donor for a project vehicle of mine. I think they're a little in over their heads when put in a 3/4t or 1t, but in what essentially is a SuperCab short-bed Early Bronco I think it would work very well. And weigh a lot less than a 6.9L or 7.3 IDI.

 

[jmodge]

If you can live with the NA 6.2 I'd drive it as-is.

I couldn't.

I've been semi-sort of on the look-out for a 6.5tD donor for a project vehicle of mine. I think they're a little in over their heads when put in a 3/4t or 1t, but in what essentially is a SuperCab short-bed Early Bronco I think it would work very well. And weigh a lot less than a 6.9L or 7.3 IDI.

The 6.2 I have is in a rusted untitled k5 that is on a friends hunting property. Runs great and has everything needed for a swap outside of upgrades. Just curious about others experience carrying a FWC with one. So far no real life feedback. If I don't hear something by spring, I guess that tells me not many dinosaurs running those dinosaurs.

 

[Zoomad]

I've collected a serious amount of Blazer FWC camper photos since obtaining mine. One reason to document the differences, reference for my build and looking how else it's been done. I don't think I can recall any of them being powered by a 6.2. It's not to say it can't be done, but I don't remember seeing it.

Just going off of what I've heard talking from other Blazer guys, I've heard 20mpg possible with one in a lifted truck with 35" tires and proper gearing for the tires. So often the gearing really gets overlooked and undergearing one just makes it that much more sluggish. Granted that's not a fair comparison to the load of the FWC and the aero drag, but it's close.

If it's just for running around your home state of MI, it may not be the issue I would have out here in CO. Less altitude and less grades for sure.

I just don't know that the 6.2 is going to net a stellar mileage gain over what the small block is already doing. At least it's not a big enough gain to warrant the change.

At 13mpg with the small block I think you are doing pretty good. Also, even though diesel has come down it will go back up. Since they have to refine it more to get to the ultra-low sulfur standard, the price will always be higher than before. That also brings the point up that the 6.2 was never intended to be run without the sulfur in the fuel. The sulfur is was gave the fuel it's lubricity for the injection pump and injectors. Take that away and run the pump without it and it will fail. Fuel additives can be added to give the lubricity back to the fuel, but it's an every tank scenario that would need to be factored into the fuel costs.

I'm curious about the rest of the setup just to see if there are any areas some gains could be made. Still running a carb or TBI? OD trans? Gearing? Tire size? Depending on what you have there could be some left on the table, probably not monumental gains but every little bit helps.

 

[jmodge]

31" tires @ 50lb, 3.73 gears, 700r4, vortec heads, flex-a-lite dual fans, tbi w/gm performance intake. I have heard some pretty outrageous claims on mileage for the 6.2, 20mpg sounds doable. I can get about 12.5 babying it on a steady cruise. It is usually a little less.Having the aerodynamics of a block of lead doesn't help
Price of diesel used to be lower than gas, but I don't think we will see that anymore. I heard the nautical shipping industry has been regulated to use a more refined diesel fuel and if true that would change the supply and demand. I worked fleet maintenance for a municipality and up until a couple years ago we ran off road diesel in all our trucks. That could have been out of ignorance, our director had an engineering degree in concrete. Intelligent guy but definately a fish out of water.
Anyway, 19 or 20 mpg is probably not a good enough savings unless I plan on putting megamiles on the truck. Easier on my body to leave it alone too, I just diesels I guess.

 

[Zoomad]

Just comparing your gearing and tire size, in OD you are pulling nearly the same RPM at 65 that I am (1850). I'm running 4.10's with the same trans and 315-75/16 tires which measure out to a little over 34.5". In my case the 5.3 is well under the torque peak and why I'm lacking power on grades unless I carry momentum or pull it out of OD earlier to keep the engine rpm's up.

Your setup is probably building torque a little lower in the RPM band than mine is. With the tire size you run and the gearing it's probably pretty close to ideal. Jumping to 4.10's would bump the cruise RPM to 2000 at 65 mph and might keep the engine closer to it's peak torque which might net a little mileage gain. I know that sounds backwards as going steeper in gearing usually cost fuel economy, but running well below peak torque is requiring the trans to kick down to lower gears anyway to maintain speed if you are pushing a headwind, hill or just trying to pass a slower car in front of you. I just don't think the expense of changing gearing is going to be worth the slight MPG bump. Again, like you said you would have to put megamiles on the truck to justify the expense to get the fuel savings.

I'm a bit of a nerd when it comes to tracking fuel economy on mine. Down to the point of using an app to track it on my phone. For an example here is some of my data over 63 refuelings in 611 days I've spend $2,672.00 in fuel, costing me $4.37 per day to run it at a per mile cost of $0.25. Put into perspective, it's still not cheap but for what I can do and where I can go with it (away from crowds of people at normal RV campsites) the price is totally worth it.

Here's some more nerd worthy data. Since I've been tracking I've poured 997 gallons of fuel down the gullet at a total average 10.72 mpg. Highest mpg I pulled was 23.03 (stock top, no camper), lowest was 5.87 (with camper, winds and heavy right foot) and the last tank was 9.68. Highest I've pulled with the camper was 16 and I honestly have no clue how I pulled it off. It was on the Desert trip last year on our blitz to get to Kingman AZ from southern Colorado in one day.

Point being, these trucks without campers weren't known to be stellar on fuel economy. Add the aerodynamic greatness that is about as good as a barn door or drive in movie screen and the mileage is going to fall. I think at even 12 mpg you are doing pretty good with your terrain. Mine would do better down there for sure. You could be driving a class A motorhome with a V10 ford (all that is out today for gassers) getting 8 mpg in a 38ft coach and relegated to campsites with more class A's, 5th wheels and travel trailers and the scores of people that go with them. Or you are driving one of the coolest little homes on wheels getting out to spots where the masses can only dream of. All the while still spending less on fuel than those people are.

My hope is going to the big block in my case the power is where I need it. This way grades aren't the chore that they are now. If my Buddy's 8.1 K10 with the Phoenix camper can consistently get 13 on the highway with his at 8,000 pounds loaded, I'll probably have an improvement in mileage over what I have now. Not a big one, but better than the average I'm pulling now.

 

[jmodge]

The cam I put in starts power @ 600 rpm with a low torque curve. Trans is switched to hydraulic lockup and cruises pretty good, but cruising range is above the rpm I drive on the highway. But, we are rarely on the highway. I have a fuel log that dates back to early 2014 when I made my changes. I don't know where the older one is, if I had one. It seems I did. Towing with it really drops fuel mileage. But like you say, there is definately something special about it. Took me nearly two years to discover then find one I wanted.something that I could hall wood with, navigate my dump trailer in my narrow lot, 4wd, and fit under an 8' garage door. It fits the bill. In the end I will probably just keep going forward with it the way it is. I may get a tunercat or tunerpro program and fart around with timing curves fueling a bit.
Have you ever considered a 6 liter? Being an LS like your 5.3 would make it a simple swap wouldn't it? They do like to rev more than the conventional big block though.
Next trip I go on I am going to track my mileage by gps instead of the speedo. Hopefully I will feel better not worse. Lol.

I saw quite a few of these rigs while I was looking, as well as after also. I had to quit looking because I kept having the urge to fly out west and grab another. One still sticks in my mind and it was probably 6 years ago! In the Colorado mountains for $1500 with a newer camper than mine Oh well, it's winter, I retired, and I think of making work for myself. Gotta quit that. Think I will load up the K5 and quad and go check my game camera this week.

 

[ntsqd]

Used to own a '91 Sub 1500 TBI 5.7L (tired, but not used up), 700R4, 8 lug front conversion & a rear 14bff (w/ Detroit), 3.73's with about 3" of lift, and 285/75R16's

I don't check mileage as a rule. Usually spot check it on random occasions. One trip that required heavy right foot to meet someone elses timeline, and she was late getting out of the gate, saw about an 80 mph average and a very, very surprisingly 16 mpg. Checked it 6 ways from Sunday and still got the same results. More normally it was 12-13. I concluded that 80 put it at the RPM where the engine ran enough more efficient that it more than offset the increase in drag from the higher ground speed.

Re-gearing was not in the cards for that vehicle, so I lived with it.

I've driven an NA diesel just far enough to know that I never what to do that again. Turbo-diesels only for me.

 

[jmodge]

I bought an 8600 gvw tbi in Detroit for a work vehicle once. It had 4.10's and a TBI, State of Mich fleet vehicle, I filled before leaving. 170 miles home and I forced 17 gallons into it. Ran AC and cruise part of the time. Great truck, when I replaced it I bought a 2 door '99 Tahoe and drove it home from Florida, also a State fleet vehicle. Still have it, 16mpg for mixed driving with it. The aerodynamics and engine controls are quite a bit advanced on those from the previous straight axle models.

True on the power range of the 6.2, Way more torque off idle than the 350 though. I drove it about 7 miles to the property and it ran very strong. But I do remember delivering parts in the early '80's and there was a dually with a 6.2, The only two things I could pass were time and gas. There was no leaving the right lane. 1800 seems to be the sweet spot that is spoken about with a cruising range of 1700 to 2100. Too bad I can't drive that thing around for a while.

You guys might have points about gear ratios though, I have boogied down the freeway faster than usual with the FWC and still managed over 12.

 

[Zoomad]

A 5.3 was what I had, it was free. Had I been able to go with the 6.0 I would have. But having more cubes is always better. Yeah it is still rev happy than a big block but it would do the job just fine.

As far as the swap goes, it's pretty close to a bolt in. You need swap brackets to adapt the LS engine mounts to the stock engine mounts. Next up is the harness and engine control module, Many places sell them ready to run, saving the hassle of pairing down the factory harness and getting the tune done. You do need to switch out the fuel pump with a higher pressure unit. Tilden sells complete packages, engine, harness, and Ecm.

Keeping your 700r4 is possible if you go with an earlier LS with the cable throttle. With the cable throttle you can use the LS tv cable kit from bow tie over drives. Or move to a 4L60 so it could be run by the LS engine module. Since the 4L60 is the electric version of the 700 it's the same length so no driveshaft mods are required.

It's not always the cheaper way to go, even less if you pay a shop to have it done. If you were closer I'd sell you my complete setup that would drop in pretty quickly.

 

[jmodge]

When did the LS go to DBW? Friend of mine has one along with an ecu, don't know what year. I think aerodynamics play the biggest role in mpg on our trucks though, not a whole lot to be done there. I did not pay attention to your engine swap, did you make your own control harness?

I made a couple hotfoot runs home from the U.P. where I had sustained speeds of 73 to 76mph and points where I buried the 85 mph speedo. I was surprised to matched my peak mpg, I attributed it to small sample error. But your theory on operating under the power curve has some merit.
My rear diff could use a rebuild, howls on decel, and they make an 8.5" 3.90 gear. I am going to contemplate that one because I plan to do that anyway.

 

[jmodge]

as a side note on GM 6liters, we had some in service trucks. Had the opportunity to see one with heads off. They have a long stroke and very tall runners in the heads, must be what gives them the wide power band. Is the 5.3 head constructed the same way?

 

[Zoomad]

When did the LS go to DBW? Friend of mine has one along with an ecu, don't know what year. I think aerodynamics play the biggest role in mpg on our trucks though, not a whole lot to be done there. I did not pay attention to your engine swap, did you make your own control harness?

I made a couple hotfoot runs home from the U.P. where I had sustained speeds of 73 to 76mph and points where I buried the 85 mph speedo. I was surprised to matched my peak mpg, I attributed it to small sample error. But your theory on operating under the power curve has some merit.
My rear diff could use a rebuild, howls on decel, and they make an 8.5" 3.90 gear. I am going to contemplate that one because I plan to do that anyway.

So I did something fairly unique for the harnes and ecm. I used a harness and mefi4 Eco from Howell. The mefi4 controller is the exact same unit used in the two gm ramjet crate engines. It works quite well, but support for it is nearly non existent. My buddy originally used it on his 8.1 swap to his K10. He ended up going back to Howell for another harness using a factory controller. I'm not sure it could even be bought anymore. So for the upcoming big block swap I'm going to Howell for the harness and controller. The money spent is well worth it.

Here's the link to my build. There's a lot in there.
https://ck5.com/forums/threads/91-k5-camper-coming-soon-vortec-454-fun.322351/

As far as the gearing idea goes, I'd just make the jum to 4.10's if you are going to make a change. It's a more common ratio and a little more gear will help with the power and keeping the engine (either what you have or LS) in its torque curve.

as a side note on GM 6liters, we had some in service trucks. Had the opportunity to see one with heads off. They have a long stroke and very tall runners in the heads, must be what gives them the wide power band. Is the 5.3 head constructed the same way?

5.3's and 6.0's actually look identical on he outside. Heads have the same setup.

 

[ntsqd]

The whole LS family's controls are a quantum leap beyond the TBI's controls. Though they work very good for what they are, TBI's were pretty stupid the day they were born.
Factor in that the LSx engines are all (?) under square (more stroke than bore) and you get a far more efficient engine. If you're not in the year range where (I'm told) GM had to late inject a little fuel to keep the cat hot for emissions reasons, with a subsequent mpg loss, then that these engines could pull down some mpg numbers a good bit beyond that of the best tuned SBC is not a surprise, it is expected.

 

[Zoomad]

Missed answering the question on when the LS went DBW. The real answer is it depends. Car LS engines (5.7) in he vette and camaros were always DBW. Truck LS engines had DBC when they came out in '99. The DBW trucks started transitioning in around '04 I think.

There are schools of thought for both systems. I won't go into the debate here, but there is a very solid reason why I use cable and my buddy with two 8.1L powered squares runs cable on his. That's purely the simplicity of it. If a cable breaks we can Jerry rig our way back to civilization and fix it pretty quickly. If you loose an electrical component on a DBW you are dead in the water where ever the truck is. That's on the street a block from home or 50-100 miles off pavement like we like to do. Bringing spares of the throttle pedal and throttle body would help, but a wiring issue could be a culprit too. It is not with its downsides though. Idle tuning is a little tougher to do as the IAC (idle air control motor) does not have as much ability to change idle speed as just cracking the whole throttle like they do with DBW. With an auto it's not as big of an issue, but a manual can do odd things when the clutch pedal is on the floor.

That's not to say DBW is bad at all though. The technology has been out since '97 in the vette and improvements made many times along the way for sure. Working at the dealer and at workhorse and gm as long as I have I don't see failures daily. Gm did have some issues on '07 and later truck engines where a sensor inside the throttle body failed and had had an extensive bulletin on replacing the sensor that we did on many trucks. We just don't see a lot of repairs on them otherwise. But even knowing that I'll run a cable on mine for the one less thing to fail idea. As far as LS swaps go I'm well in the minority on that idea too.

One other thing I stated before, if you intend on keeping the 700r4, you have to stay with cable. Otherwise you have no way to hookup the tv cable for the trans. If you do you'll get peppered by other swappers why not go with the 4L60e. I did. The reason was simple, I didn't have a 4L60e to use and buying one and possibly having to rebuild it was more cost than th bow tie tv cable kit.

 

[jmodge]

Yeah, hard to beat technology when it comes to results of power and FE. But, I was raised in the age of simplicity and still cling to much of it. Familiar with the TV cable and the results of not having it tight enough, learned that lesson years ago. Had to fab a mount when I put the vortec heads on, as well as my cruise control which operates via the throttle lever as well.

The truck is loaded with about every option available at the time and it all works, I am unlikely to deviate from that since it is quite dependable, and for me that is important. I do have other toys to romp on

Will pay close attention to the rpms, power range, and any possible future tire size change to determine a gear change since I am going to dig in there anyway. Thanks.

 

[Zoomad]

The TBI system you have is stone simple and reliable. I'd run it as is, with the possibility of bumping the gearing up. If anything you can collect the parts needed to do the swap later.

 

[jmodge]

Geared down I believe you mean, but yeah, I like the TBI. very reliable. I saw someone rigged up something to stream data on one, about a 4 second delay, but it was there. I think it was an offshoot of a tunerpro system. That was the only downside to OBDI, not being able to read live data. I grew up with point systems and HEI so I have tuned and troubleshooted before computors came out. Well versed in the small block Chevy and it's habits as well as what tweaks do what.

As far as swapping, not likely, but if I went through the expense and effort it would be the 6.2 diesel with a small amount of boost at 2100 rpm. But at 60 years old and other things to do, it would be a waste of my time I believe. This truck will take me where I want to go when I want to do it. I think I will save my money for gas. Always nice to hear someone else's opinions to bring things into perspective though, thanks. Happy Camping, who knows, maybe we will run across each other some day. My buddy with the hunting property has an ex neighbor out in Colorado that invited him up Elk hunting a year ago or so. Might be in my future. I think it is up by four mile park, something like that.