To 6.5 or not to 6.5?

[Big T]

I might offer this guy $4K max due to the dent in rear driver's side panel:
https://sandiego.craigslist.org/nsd/cto/5329562455.html

 

[Big T]

Clean '94 in Eugene, OR for $5K

http://www.autotrader.com/cars-for-sale/vehicledetails.xhtml?zip=92835&endYear=1999&listingType=used&engineCode=8CLDR&listingTypes=used&sellerTypes=p&sellerType=p&mmt=[CHEV[CHEVSUB[]][]]&driveGroup=AWD4WD&fuelTypeGroup=DSL&modelCode1=CHEVSUB&showcaseOwnerId=586852&startYear=1994&makeCode1=CHEV&engineCodes=8CLDR&firstRecord=0&searchRadius=0&listingId=414421385&hideBackLink=true&Log=0

 

[THEFERMANATOR]

Yeah, whenever someone says they are getting 20+ mpg out of their diesel, chances are they are over exaggerating, can't calculate mpg correctly, or are just flat out lying. I've never had any diesel (Duramax, 6.5, 6.2) ever get better than 15 mpg....with the exception of my k2500 suburban. It was getting 18mpg when I got it. I have no idea what I did to make it hate me, but now I'm lucky if I see 15.

I should mention that I tow a lot with my diesels, with the exception to my suburban. And they have all always averaged in the 12-13 mpg, in stock form, in modified form, with stock tires, or with larger tires, they all seem to get around the same mpg regardless.


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I ROUTINELY get OVER 20 MPG out of mine driving on the interstate. I average 21 running 70-75 in my BURB, and the best tank has been 23 so far to date(would have been higher, but trying to keep my foot out of it for that many miles is TOUGH!). And I've personnally tuned SEVERAL DURAMAX trucks that all get 20-21 running down the interstate with stock size tires. So it IS possible. The problem is MOST people tend to not drive with an egg under there foot, which kills MPG, or they do more stop and go than actual true highway driving.

With the budget listed though, I would not be looking at a diesel. Anything in the $3-5K range for a diesel is going to be high milage, or in need of work, and in the long run is going to cost you more in the end.

 

[3500_6.5]

All I'm saying is that I always hear people bragging about how their diesel (6.5, Duramax, powerstroke, whatever they have) get 20-25 mpg all the time, even people claiming they get 25 mpg pulling a trailer. But between me, my dad and my brother, we currently have 4 6.5s and a Duramx and none of them have ever broken the 20 mpg mark. The only time I have ever seen any of them over 20 mpg is my dads Duramax when it shows his "instant" fuel mileage. But it NEVER averages that. My suburban has hit 18 and my dads 92 k2500 regular cab 6.5 generally gets 17-18 mpg. His Duramax averages 15, and all the other diesels average in the 12-15 mpg range. Both of the past Duramax's I've owned also averaged 12-15 mpg. My first 6.5 (regular cab k2500) averaged about 12 most of the time. Now, we use our truck as, well, trucks, and they don't see much highway driving, but do all these people claiming 20+ mpg really do nothing but cruise on the highway for hundreds of miles?? I'm not saying it isn't possible, I guess. I just think that unless you cruise on the highway for all of your driving and do nothing with the truck but use it as your grocery getter, daily commuter to work, and do absolutely nothing with your truck, chances are you are highly unlikely to be getting in the 20 mpg range and to not expect that kind of fuel mileage out of any heavy vehicle. Just me though....


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[Big T]

I'm with 3500_6.5. Have owned 3 K2500 4wd Suburbans with 6.5 and the best mileage has been a little over 17 mpg at 70 mph for the '95 (since wrecked). Same for my son's '94 w/ ATT and 4 position tuner. My '99 the best it gets is a little over 16 mpg and that's with ATT and Heath tune. Towing boats, it drops down to 10 to 12 mpg. All of them have had 4.10 gearing.

 

[WarWagon]

Our 2008 2WD crew cab long bed Duramax would top out at 18MPG. My 2003 Manual trans 5.9 Cummins crew cab long bed 2WD will get 19.5 MPG mixed driving and 16 MPG with the AC on. It goes over 20 MPG Freeway. It gets the same MPG towing as a 6.5 unloaded at 15 MPG. The repairs are costing me more than the fuel savings.

I drive a diesel for other reasons than the economy. Frankly I blow up diesels so a gas engine wouldn't have a chance and historically they didn't do well with belts flying off the engine from extended high RPM, blue TCC clutch areas on ruined converters, oil cooler lines overheated and ruined to leaking, engine oil failures... The terrain here is all grades (7-18%) in extreme high temps so this affects my MPG numbers over the "flat" and cooler east coast.

My 2005 reg cab 2WD Duramax was the same as Patch in town at around 10 MPG.

My 6.5's (4x4 autos) are hard pressed to break 15 MPG no matter what I did to them. #2 diesel vs. #1 Winter blends, LSD, ULSD, Biodiesel all affect MPG. Towing 6.5 best was 11 MPG and worst 7MPG.

The NA 6.2's in 2WD were best remembered on the unaltered Diesel from the 1980's. Many changes reduce the BTU's of diesel since.

 

[THEFERMANATOR]

I have averaged an HONEST hand calculated 18mpg with mixxed driving out of my burb with a duramax in it. Last trip towing our 32 travel trailer averaged 13 over the whole trip with alot of back road driving mixxed in. When I had my 6.5l in my burb with 4.10 gears, I got 17-18 running 68, but if I bumped to 70 it dropped to 15.

 

[Big T]

I have averaged an HONEST hand calculated 18mpg with mixxed driving out of my burb with a duramax in it. Last trip towing our 32 travel trailer averaged 13 over the whole trip with alot of back road driving mixxed in. When I had my 6.5l in my burb with 4.10 gears, I got 17-18 running 68, but if I bumped to 70 it dropped to 15.

Your 6.5 experience is the same as our '95 6.5: 17 to 18 mpg.

I have no experience with the Duramax. Can only dream about one in the Burb.

 

[jrsavoie]

I ROUTINELY get OVER 20 MPG out of mine driving on the interstate. I average 21 running 70-75 in my BURB, and the best tank has been 23 so far to date(would have been higher, but trying to keep my foot out of it for that many miles is TOUGH!). And I've personnally tuned SEVERAL DURAMAX trucks that all get 20-21 running down the interstate with stock size tires. So it IS possible. The problem is MOST people tend to not drive with an egg under there foot, which kills MPG, or they do more stop and go than actual true highway driving.

With the budget listed though, I would not be looking at a diesel. Anything in the $3-5K range for a diesel is going to be high milage, or in need of work, and in the long run is going to cost you more in the end.

Especially when I always figure on putting 2 to $3000 in extras after I buy it. It would be a very rare find if one had the bypass filter, engine oil cooler lines, new wiring harness, Fluidamper, 97 or newer air filter box and Amsoil front to back

 

[Will L.]

In the fuel company fleet, we had to track mileage in all the vehicles, including the 6.5 trucks. It was all over the place.

We did have some 1/2 ton trucks get the magic 25. Only a few out of a couple hundred. Mostly hi way, and the use of cruise control is massive. If you own anything without cruise control, you are not allowed to complain about mileage Imo.

The driver has THE MOST to do with it. We had 2 drivers that would switch trucks by a wacky schedule, and the difference was obvious. So much so that their boss hired a p.i. to try busting on guy for stealing fuel. One guy accelarated slow and coasted before stops, and the other guy thought his last name was Andretti.

Driving our 01 suburban 6.0- my wife got 15.1 mpg and I got 12.7.

The last part is the fuel change barely mentioned by a couple people like WW. This is huge! Most modern ulsd has 25% less btu than real diesel. Why the power and mpg loss? Physics. I ran some plastic-synthetic fuel in my hummer. Yeah. Big difference.

I will disagree directly with WW and others on n/a getting better mpg than turbo. Every conversion I have seen did better mpg adding turbo- even crappy gm-x.

No set up getting any descent mpg had ANY smoke,(even very dirty tailpipe). Smoke is fuel. If you see a tiny puff and don't think much of it, go light some diesel on fire and see how much it takes to make a puff.

 

[FellowTraveler]

Fuel economy has gone down since they changed the diesel. When I first got our 98 Suburban, I averaged 18 mpg pulling a camper home from Pennsylvania.

I'm using 2 stroke in my fuel and notice a change for the worse if I put too much in tanks....

 

[JayTheCPA]

All I'm saying is that I always hear people bragging about how their diesel (6.5, Duramax, powerstroke, whatever they have) get 20-25 mpg all the time, . . .

Ahhhh . . . Seeing as we are opening up the scope to *all* light truck class diesels . . . My other rig has 3.73's, 4WD, a ZF, highway tires, direct injection, and gets 19 - 20 around town, 21 - 22 highway, and 14 - 18 towing our 'smaller' 32' 5500# RV. Got 10% less mileage when I briefly ran all terrain tires (which was one of the reasons I sold them to a friend and put HT's back on). Also, only modifications I did to it were the air intake and replacement of dyno lubes with synthetic; other than that it is still bare bones stock.

A buddy gets low 20's highway in her mid 2000's Cummins and do not recall whether she did any mods.

I'm with 3500_6.5. Have owned 3 K2500 4wd Suburbans with 6.5 and the best mileage has been a little over 17 mpg at 70 mph for the '95 (since wrecked). . . . All of them have had 4.10 gearing.

The driver has THE MOST to do with it. We had 2 drivers that would switch trucks by a wacky schedule, and the difference was obvious. . . . One guy accelarated slow and coasted before stops, and the other guy thought his last name was Andretti.

Driving our 01 suburban 6.0- my wife got 15.1 mpg and I got 12.7.

And therein lies the real story So in reality, there are many factors that go into mileage where it is not just the motor. Also, all of the same factors will drag down mileage in a gasser.

 

[Big T]

Ahhhh . . . Seeing as we are opening up the scope to *all* light truck class diesels . . . My other rig has 3.73's, 4WD, a ZF, highway tires, direct injection, and gets 19 - 20 around town, 21 - 22 highway, and 14 - 18 towing our 'smaller' 32' 5500# RV. Got 10% less mileage when I briefly ran all terrain tires (which was one of the reasons I sold them to a friend and put HT's back on). Also, only modifications I did to it were the air intake and replacement of dyno lubes with synthetic; other than that it is still bare bones stock.

A buddy gets low 20's highway in her mid 2000's Cummins and do not recall whether she did any mods.






And therein lies the real story So in reality, there are many factors that go into mileage where it is not just the motor. Also, all of the same factors will drag down mileage in a gasser.

Nice try, but when you're measuring across 500 to 600 drives with one acceleration to get up to hwy speed, the driver element is off the table. 16 mpg in the '99 and 17 mpg in '95 and I'm sticking with that.

 

[3500_6.5]

I would like to think I am pretty easy on my vehicles. I tow 90% of the time with my truck, so I don't expect it to do very well. But it's probably 95% normal driving with my suburban and 5% (or less) towing. And considering I consistently got 24-26 mpg out of my Corvette when I was in my mid 20s and consistently got low 20s out of my Z28 just this last summer, and not to mention all the other high performance cars I've driven over the years that have all done very well on fuel mileage, I would imagine my driving of my suburban would also give me similarly "good" mileage for the vehicle.


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[THEFERMANATOR]

I'll add, the WORST MPG I got was running B-20. Power sufferred NOTICEABLY towing our 32' HOLIDAY RAMBLER, but the tail pipe sure was clean. Even on my big tune it would barely puff smoke out the tail pipe, but the power was terrible. It did make the engine nice and quiet though, sounded like one of dem dare new fancy LML's it was so quiet.

 

[Will L.]

I'm using 2 stroke in my fuel and notice a change for the worse if I put too much in tanks....

Exactly. The btu in 2stroke is low and has a very low flashpoint. When you add it to the fuel you are degrading the fuel. The reason to add it is it extends the life of ip & injectors enough to save "X" amount of $. As long as "X" is greater than the cost of buying it, and the reduction in mpg, you do it.

When it is not a noticeable savings, you don't. Which is why my suburban never got any of the maintanence, only what was required. Now I'm going to sell it for $2,000 less than a comparable maintained one. WAY MORE than $2,000 saved in the 13 years Ive owned it. Fuel mileage is a factor to consider, but if you put in $1,000 a year of goodies and goo to do it, you have to drive the miles to pay for it. Maybe fill in for WarWagon while he's on vacation or something to justify it.

 

[WarWagon]

The NA MPG was specific to the OBS 6.2's 1/2 tons 2WD vs. our 6.2 NA 1988 4x4 1/2 ton Suburban back when this stuff was "New" in the 80's. The lighter rigs esp 2wd reg cab pickups was known to be over 20 MPG back in the day. The 1988 1/2T 4x4 NA burb would get 18 MPG. My 1995 4x4 3/4T turbo wouldn't break 15.

The 1988 ate so many glow plugs, controllers, batteries and starters that it would have been cheaper to own a 454. No one had a diagram for the "new" 1988 glow plug system missing the shorted heads hot switch on the rear passenger head. Then and the loose controller capacitor that chattered the GP relay on kick out burned some GP's in half. It had fuel leaks in it's later life causing hard starting. Front auto hubs, shift fork in transfer case and constant rear seal leak on t case... When the trans quit holding TCC lockup we traded it for a 1994 454 3/4 ton. Gutless 454 that year was... It would idle at 45 MPH due to a tight converter and warm up RPM.

 

[WarWagon]

Exactly. The btu in 2stroke is low and has a very low flashpoint. When you add it to the fuel you are degrading the fuel. The reason to add it is it extends the life of ip & injectors enough to save "X" amount of $. As long as "X" is greater than the cost of buying it, and the reduction in mpg, you do it.

When it is not a noticeable savings, you don't. Which is why my suburban never got any of the maintanence, only what was required. Now I'm going to sell it for $2,000 less than a comparable maintained one. WAY MORE than $2,000 saved in the 13 years Ive owned it. Fuel mileage is a factor to consider, but if you put in $1,000 a year of goodies and goo to do it, you have to drive the miles to pay for it. Maybe fill in for WarWagon while he's on vacation or something to justify it.

I'll answer this shortly as I use 2 stroke in patch and suspect bad injectors in 30K miles - again...

 

[FellowTraveler]

Exactly. The btu in 2stroke is low and has a very low flashpoint. When you add it to the fuel you are degrading the fuel. The reason to add it is it extends the life of ip & injectors enough to save "X" amount of $. As long as "X" is greater than the cost of buying it, and the reduction in mpg, you do it.

Yes, the longevity of IP and injectors is the only reason I use it and my Burb is a keeper. I learned log ago not to invest big into any vehicle I will not keep........

 

[3500_6.5]

Just filled up and checked my mileage on my Suburban. 13.13mpg. I hauled about 2500lbs a total of roughly 15 miles of the 440 miles I drove it. The rest was unloaded driving with a good bit more highway driving than normal.

This does not take into consideration the larger tires (285s vs the stock 245s), but even if it was off by 50 miles (which it isn't), that would only give me a little over 14.5 mpg.


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