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Questions about reliability and mpg of the 6.2 engine

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71K views 31 replies 12 participants last post by  BigMike8504  
#1 ·
Hello,
First post, but ill make it a long one.
im driving an skoda to work and back getting lousy 25mpg having no fun.
sure im getting 38mpg on the highway but thats not where i drive to and from work. pulled a trailer on the highway got 25mpg.

now to the question can i get simular performance around town using a 2wd truck with the 6.2 engine? ofcourse it will need more fuel.. the engine is after all 5-6times the volume of my 1.6 liter skoda.

kinda hard putting together a good picture of the mpg with ppl using big tires, etc.
also the amount of rumors around this older american diesels is huge.
 
#2 ·
I think 25mpg average is doable in a 2wd 1/2 ton 6.2


I get 21-22 from my 91 4x4 burb with 1-ton axles and 35" tires
 
#9 ·
I get 21-22 from my 91 4x4 burb with 1-ton axles and 35" tires
These are pretty good numbers considering all the rotating mass the 6.2 has to get rolling.

Heck if it's possible to get these numbers with a 84 k20 then all the more reason to take the spare motor I have and put it in the k20
 
#3 ·
im driving an skoda to work and back getting lousy 25mpg having no fun.

now to the question can i get simular performance around town using a 2wd truck with the 6.2 engine? .
If you are no higher then 2000 feet above sea level -you can expect this in hilly areas. If you live in a area that is 100% flat, you can add 1 extra MPG. I know because I live in two places. Mountains of New York and flatlands of northern Michigan.

1/2 ton truck with 3.08 axles and over-drive - highway avg. 21 MPG
"around town" avg. 16 MPG

1/2 ton truck with same but no overdrive highway avg. 19 MPG and "around town" avg. 16 MPG.

3/4 ton truck or Suburban with 3.73 axles and no overdrive - - highway avg. 16-17 MPG and "around town" avg. 13 MPG.

I've got an 82 K10 with 3.08 axles and a manual trans with overdrive. Back before low sulfur fuel came out - on rare occaisons -it got 23 MPG on a long flat highway drive. Now with the new diesel -21 MPG is the best I can get.

By the way, one of my favorited small trucks is my Isuzu PUP diesel 4WD mini-truck. Same as a Chevy LUV. Has a 2.2 liter diesel and gets a best of only 28 MPG on the highway. My diesel Chevy Chevette with a 1.8 gets up to 48 MPG but it is NOT a truck and DOES have overdrive.
 
#10 ·
3/4 ton truck or Suburban with 3.73 axles and no overdrive - - highway avg. 16-17 MPG and "around town" avg. 13 MPG.
that is almost exactly what i've been getting with my 3/4 ton suburban with 3.73's and a th350. mixed driving with a mostly going up into the mountains and back highways i would get 16-16.5 consistently. and would also tend to get about 12 around town...

but my shift points were terrible and the tranny refused to stay in 3rd gear if you dropped below 36 mph, and most of the roads are 35mph and the stupid thing would constantly be shifting back and forth. really wanted a manual when that would happen. we will see how this new 700r4 changes things.
 
#4 ·
now to the question can i get simular performance around town using a 2wd truck with the 6.2 engine?

also the amount of rumors around this older american diesels is huge.
You are correct about many "rumours." When it comes to diesels and fuel mileage it gets even worse.

I had a friend who I trusted generally. He bought a brand new 3/4 ton diesel Suburban in 1987. 3/4 ton, 4WD, 3.73 axles and a TH-400 trans. He bragged for many years about the 30 MPG plus he was getting. Well he died and I got it. Guess what? Best ever on on long flat highway trip at 60 MPH got 18 MPG.

Same with another friend who bought one of the first Ford pickups with a 6.9 diesel. He claimed to get 35 MPG. Well I wound up getting that truck also. 4WD, 4.10 axles and a C6 trans. Best mileage was 14 MPG.

Also - watch out for "gallons." In the US, our gallons are smaller then in Canada and Europe. So, MPG ratings can be confusing if someone is using Imperial gallons instead of US.
 
#5 ·
:welcome2:Welcome to Diesel Place....

There are many variables to fuel mileage claims, one being the weight of the right foot.....:D

Used to love "our gallon" for the reason it was larger. Canada has changed over to liters now, takes more calculating.:rolleyes:
 
#6 ·
:welcome2:Welcome to Diesel Place....

There are many variables to fuel mileage claims, one being the weight of the right foot.....:D

Used to love "our gallon" for the reason it was larger. Canada has changed over to liters now, takes more calculating.:rolleyes:
The highway specs I posted were "light foot" in attempts to see how good I could do.

My father-in-law is a retired Ford engineer and was involved in fuel-mileage testing. In many circumstances his tests showed that some "heavy foot drivers" got the same fuel mileage as the "light foot" ones. Especially when it comes to hill climbing. It sounds counter-intuitive but he's not the type to make things up.

By the way -my 85 Ford with a 6.9 diesel never, ever got better then 14 MPG. Then on one long trip in the UP of Michigan, I drove all day on flat roads at 50 MPH. I really thought I'd see a huge improvement. Well? I got 14 MPG and was pretty disappointed - but the 6,9 IS a big engine.

There are still places in Canada selling by the Imperial gallon instead of litres. Canadian law states that litre prices have to be posted everywhere but using gallons is optional. I filled up my truck recently by gallons in Canada up near Lac Nipissing in Ontario. Did the same at Saute Ste. Marie. I pay attention since whenever in Canada, I go nuts with a calculator trying to convert the US-Canadian exchange rate, and litres or Imperial gallons per kilometer - to US gallons per Statute mile. No longer a problem though since I've been banned from Canada.

There has been some upset with US car dealers near the border because Canadian car dealers often post fuel mileage specs by gallons that are much better then the same cars in the US. That got some people thinking that US cars sold in Canada were somehow better.
 
#7 ·
My K5 (pre lift and tires)With a C-code 6.2/700r4 with 3.42 gears was able to see anywhere from 17-25MPG in a mix of city and highway. Now it gets no better than 16MPG but is still nice for a lifted truck.

It isn't as spectacular as most will claim, but I still think that is quite high for a truck. Even my 4.3L V6 was harder on fuel, but could also run circles around the diesel unloaded.
 
#8 · (Edited)
So what stuff should i go looking for to get the best fuelmilage? and still not make it way to lazy 0-60.

well 16mpg is a killer on the wallet here in Sweden.. a gallon costs around $8-10 here.
i love these big trucks but being a delivery truck driver dont give me the $ to drive them if its down to 16mpg over 20mpg is doable.. 16mpg and my wife will beat me ;)

btw i need a truck older then 30years.. since then its tax free.. no $700 each year:)
and the older American trucks sing better to my heart..

btw my Skoda is an Octavia with 1.6 gas engine;) im feeling like an old sensible family father and i just cant have that! i wanna be young and stupid till i need to grow up:p
 
#11 ·
I love my Jimmy its been reliable and decent on fule HOWEVER it took me a couple of months to realise the speedomiter was off 5mph so i had to recalculate what i thought was incredible fule milage

Just watch out for trucks that have been severly tampered with i belive my good milage to be from maintence and keeping it allmost stock
 
#18 ·
I love my Jimmy its been reliable and decent on fule HOWEVER it took me a couple of months to realise the speedomiter was off 5mph so i had to recalculate what i thought was incredible fule milage
/QUOTE]

I had the same problem with my 1991 Dodge W250 with a diesel Cummins. for years I thought it was getting 21 MPG on highway runs. Then when I got a hand-held GPS, it said my speed of off. Found out the factory speedo-gearbox was wrong and "lied" to me. I put in the correct gearbox and now only get 18 MPG. Still OK for a heavy 4WD, extended cab truck, but I felt better when I thought it got 21 MPG. The "incorrect" gearbox was factory isntalled when new, so I wonder how many others were wrong?
 
#13 ·
Yea mine will downshift at the slightist hill if its a big hill it will downshift into 2nd Idk how they use to ride with the stock tires maby it wouldnt do it as much
 
#14 ·
A 6.2L, TH700, 2wd with a 3.08 rear end can do about 21 to 22mpg highway in factory configuration.
To get 25mpg like me it will take a few mods to get there.

With my new engine on its first tank I got over 21mpg, that was loaded down with tools and parts, with a 24 foot lader on top while pulling my little utility trailer.

I am looking forward to seeing what it can do unencombered with the engine properly broken in with the right injector pump timing.
 
#17 ·
A 6.2L, TH700, 2wd with a 3.08 rear end can do about 21 to 22mpg highway in factory configuration.
To get 25mpg like me it will take a few mods to get there.
There was a fuel-mileage contest back maybe 10 years ago for 6.2 diesels. It was held out in Arizona as I recall. Many modified rigs entered. The winner got 24.5 MPG in a 1/2 ton, two-wheel drive truck with small-chamber heads. All the winners -2-3 and 4th place also ran small chamber heads.
My unmodifed 82 K10 has gotten near 24 MPG, so I call that pretty good.

But now? Gas here today is $3.65 and diesel is $4.30. A newer gas truck can get 21 MPG. So, no big gain with the diesels anymore - at least for simple cruising. When towing . . . still a big difference.

I have an 8000 lb. 6.2 diesel Blazer camper that gets 16 MPG and it has a lot of mods. The original camper setup used a gas-engine SB 400 and a TH-350 trans and got 12 MPG. With the price difference between gas and diesel - I sometimes wonder if building this diesel rig was worth the bother.
 
#20 ·
I think its hard to find a 6.2 truck (rare) But try finding a 350 truck with the stock motor All the C/L adds allways brag "rebuilt motor" even the 87 4.3 i got had a rebuilt AC DELCO motor put in at 60k:confused: Yea you COULD blame the owner ive seen people tweek and dittle gas engines to death either trying to get more power better MPG's or because they think theyr fixing a problem

My point is that new f150 that claims 20mpg lets see in 15 years what it will get for milage after everything is worn out I KNOW my truck is getting old not much will change It wont have a computer running error codes telling me a $300 sensor is bad
 
#23 ·
A J-code 6.2L in good state of tune, should tow as good or better than any SBC from its era. I am confident that it will get better mileage in every instance as well.
 
#24 ·
Better fuel mileage with a 6.2 for sure. But a 350 gasser will easily outpull a J-code 6.2. So will a 400.

A C-code 6.2 has the same horsepower and torque as a 305 gasser. A J-code slightly more.

My 78 G van with a 350 gasser and 2 barrel carb pulled much better then my 87 J- code diesel Suburban. Big difference on hills. But pulling a 5000 lb. trailer the van got 8 MPG and the diesel Suburban got 12 MPG. My Dodge-Cummins does the same and gets 14-15 MPG.


GM 379 (6.2) diesel - 130 HP @ 3600 RPM and 240 lbs. TQ @ 2000 RPM, 3.98" bore and 3.8" stroke


GM 6.2 J-code - 148 HP @ 3600 RPM and 248 TQ @ 2000 RPM
GM 305 gas - 150 HP @ 3800 RPM and 248 lbs. TQ @ 2400 RPM, 3.7" bore and 3.48" stroke

GM 350 gas - 165 HP @ 3800 RPM and 275 lbs. TQ @ 1600 RPM, 4" bore and 3.5" stroke
 
#27 ·
Well you are welcome in MY Canada :beerchug:

In my experience with my K5 it is all around town, no highway stuff. So my little K5 has diesel torque to motivate a load to move. I had much better experience towing with my K5 than the TBI 350 Burb we had at work. My truck is older and has more miles too.

This is my experience towing heavy loads with my K5. I don't haul long distances or anything. Heaviest I've hauled was a fully loaded bobcat and bobcat trailer, around town while I went around snow blowing driveways (snowblower attachment is badass) and it could haul it, but the chassis and suspension were definitely arguing with it LOL
 
#28 · (Edited)
It's a 2 way street. A guy I worked with rented a condo in Orlando or whatever, packed up his family and was on his way to Disneyland for March break. Got to the border and was denied entry for an assult charge (bar fight) when he was 18 or 19. No problems with vacations in Mexico or the dominican but the US doesn't want him. Oh well.


To the original question. My truck has th400 and 4.1 gears. I get a consisten 18mpg (american gallons) using #2 diesel. In the winter it's down to 16mpg (this is all averaged over the course of each year. Self employed so I keep my fuel receipts and keep track of the miles on the truck). I always have at least a few hundred pounds in the bed. Not a lot but definitly not empty. I also frequently have 1500lbs or more in the bed. In the past I've had 2 305s, both TBI. I got 12mpg with NP833 and unknown gearing (although I was young and heavy with my foot) and 13 maybe 14mpg with th375 and unknown gearing (both were 1/2 tons with 5 lug wheels so I'm sure they weren't geared as low as my current truck) I once got 10L/100km (24mpg) with my current truck driving on almost flat land doing 80km/hr (50mph) There was no wind and only 2 stop signs on the trip. I couldn't drive like that all the time however.
If MPG is your main focus then you can get close to 25mpg with a 6.2 but probaly not much over 20mpg averaged out.
 
#29 ·
well comparing numbers to the more modern 4bt or 6bt cummins engines its not that bad mpg on the 6.2D considering its a generation older then the cummins.

so well the truth comes down to that ill be lucky if i get it to run over 20-22mpg
but well thats still what i hoped to hear.. now its just the hard way to find a good object..
Chevys are not that common here and i rather wait to find a good object instead of getting fooled like my old diesel project that turned down to be a "lets paint over the rust" kind of car.
 
#30 ·
well comparing numbers to the more modern 4bt or 6bt cummins engines its not that bad mpg on the 6.2D considering its a generation older then the cummins.
The "B" series Cummins came out a year so earlier then the 6.2 diesel came out - around 1980. It's not about generations. More about what these engines were built for. 6.2 is a lght-duty, short-stroke engine never intended for HD use. Cummins is long stroke heavy-block engine and was always intended for truck and tractor use.

6.2 uses the Ricardo Comet precombustion chamber system for an indirect-injection system. Cummins uses direct-injection as do many other diesel engines from the 1960s and older. John Deere went to DI around 1965. Ford had DI diesel engines in the 50s. Perkins DIs since early 60s, at least.
 
#32 ·
My truck is 4x4 C Code engine 3.73 gears with a TH700 OD with lockup converter on 31 inch tires. She gets a honest 18 all around average in complete stock form. I did get 24.4 on a 70 mile highway pull at 60 MPH in the heat of summer. I do not get in a hurry and just sortta chug along. Hope this helps, Mike