Mileage for a mechanical 6.5 Suburban 2500.

[DickWells]

Been a long while since I've paid any attention to my fuel mileage with the Burb, especially, unladen. Around here, we most often have a single axle utility trailer behind us, with anywhere from a couple-hunred to 1500+ lbs on it. ~40 miles, round-trip is average. Been seeing right around 15 mpg. I've considered that as pretty good, since we are in 1st gear most of the time, out and back in, on the two-mile Goat Path, pluss, city driving in either Show Low, Taylor, Snowflake; sometimes, all three.

Well, during our trip to Phoenix and back, I had the chance to fill it up on level ground, let the nozzle click off 3 times with the same insertion. The result was 17.73 mpg. That was for close to 400 miles, with (probably) something near 1.25 hours of city driving in Phoenix and avg 60 mph of fairly mountainous driving. Is that what others who are driving mechanically pumped 6.5's experience?

[DieselDavy]

With all of the "city" driving you did, it seems about right to me.
d

[Robyn]

Those numbers are right in the ball park with Suburbans we have had.
Best we ever saw with our 1994 6.5 (DS4 PUMP) was 18 mpg

[DickWells]

Thanks, Robyn and DD.
The old gal was a delight, for the whole trip to Phoenix and back. Had a bit of sinking "pit of the stomach", when we got stopped in traffic and the AC started blowing warm air. Thought I was gonna need to go and buy a kit. But, soon as the rpms got over a thousand, we had cold air. Happened several times, that afternoon. I have a kit, here at home,and will be hooking on and checking the AC out, but it worked well, ever since we left Phoenix. Well, the temp was 114 F in that fair city and I'll wager that we weren't the only people there with low output at low rpms.
I wouldn't live down there for any amount of money.

It's a rare day that there isn't a traffic fatality, or murder in that area. It isn't at all rare, to have both, on the morning news. Right now, there are high heat warnings and many hiking trails are closed. Camelback has been closed for days, but there have been chopper recuse done, two days in a row, for people out there hiking against the orders. I wonder if there are fines aplied? Those choppers and crews don't run cost-free.

[arveetek]

My electronic 6.5L in my 2 door Tahoe averages 16-17 mpg. Best tank ever was 19.5 mpg.

I have family born and raised here in SW Missouri. They moved to Phoenix for several years. After my cousin and his son witnessed a murder during daylight hours on the street, they decided it was time to move back to Missouri!

Casey

[Robyn]

Dick
At those high ambient temps the R134 AC systems can tend to be a little tough to keep super cold air at low RPM

You may well need to "Top up" the refrigerant charge a bit.
With the charge a tad on the low side it can result in less than optimal liquid refrigerant coming through the orifice tube into the evaporator...

The old R12 systems were far more forgiving and could produce colder air into the cab ....

R134 is sketchy at best.......With all systems at spec, they are decent....But once the charge drops off a little (All automotive AC systems leak) A small amount, but over a year or so they will lose enough to effect the performance....AND 114 F will seriously tax any system, even one in top shape....

Glad your system did the job for you....

[arveetek]

Dick
At those high ambient temps the R134 AC systems can tend to be a little tough to keep super cold air at low RPM

This past winter, I completely replaced the A/C system on my Tahoe: new compressor, hoses, evaporator, condenser, you name it! I also replaced all the blend doors in the HVAC dash system. I can tell you without a doubt that my A/C system works better now than it ever has in the past 20 years I've owned it! It cools down the interior just fine on the hottest of days now, even at idle. It was quite a chore, but I'm sure glad I went through all the work!

The blend doors were shot; all the rubber around the edges had cracked and come off, so a ton of air was leaking past the doors, causing all kinds of issues. I also had developed a slow refrigerant leak I couldn't pinpoint, so I decided to just replace everything. I'm so glad I did.

Casey

[Robyn]

The compressor, hoses and condenser are pretty simple.
Getting at the HVAC system under the dash is just such a pain.

The design on these could be made so much simpler so the control doors, evaporator and heater core as well as the control motors were easy to replace.
MOSTLY ...A simple access panel that could be accessed after removing the glove box and from under the dash .
Even an easily removable lower dash panel piece to allow full access of the HVAC box would be sweet.

The lame servo motors to run the blend and function controls YUCK
The two cable systems are virtually bomb proof. Square body GM
Some vacuum controls were pretty decent as well
Once the servos and all the electronics are added.....PFFFFFFFFT
The miserable amount of work to access these parts is just poor engineering...... Nothing more....

Like having to pull the cab off to change a turbo charger......Start by----- "Remove rear bumper" you know its gonna get ugly..

Replacing in tank fuel pumps....An easily removable panel would be soooooo simple.
And after several years of rust and crud....Getting thew tank out is nasty.

A panel in the floor/bed or????and the task is a few minutes instead of a lengthy fight...

[More Power]

Been a long while since I've paid any attention to my fuel mileage with the Burb, especially, unladen. Around here, we most often have a single axle utility trailer behind us, with anywhere from a couple-hunred to 1500+ lbs on it. ~40 miles, round-trip is average. Been seeing right around 15 mpg. I've considered that as pretty good, since we are in 1st gear most of the time, out and back in, on the two-mile Goat Path, pluss, city driving in either Show Low, Taylor, Snowflake; sometimes, all three.

Well, during our trip to Phoenix and back, I had the chance to fill it up on level ground, let the nozzle click off 3 times with the same insertion. The result was 17.73 mpg. That was for close to 400 miles, with (probably) something near 1.25 hours of city driving in Phoenix and avg 60 mph of fairly mountainous driving. Is that what others who are driving mechanically pumped 6.5's experience?

The 1982 6.2L GMC K1500 I owned in the 1990s was equipped with a Banks turbo, 3.42 gearing and a TH700R4. The engine had been freshly rebuilt along with a new DB2 fuel injection pump and injectors, and it would deliver 24-25-mpg at 65 mph. I've often wondered why the electronic 6.5 couldn't produce numbers like that, and more recently thought about converting Sarah's Blazer to a DB2-4911 and install a Holset turbo to see if mpg could be improved. Her Blazer has 3.73 gears and a 4L80-E. I've heard that the 700R4 (slightly taller OD) does more to help fuel economy than does a 4L80. The 700R4 can me setup to operate without any electric/electronics, so the conversion would be somewhat easier.

[DickWells]

Can't say that I've ever been sorry that I went mechanical (4911) all things considered. But, IIRC, there were times, before the change, that I got above 20 mpg. I rather enjoy (usually) all the simpler aspects about "running" the old gal. Not too surprisingly, that little toggle that runs the cold start advance, can be a little frustrating. It's easy to forget that I haven't flipped it back down (off) and I'll be 2 miles from home when I notice! Funny thing is, I've found that, even in warm weather, I get more instantaneous starts, by flipping it on, even after five minutes of being shut down. Did it today, 3 times. Get in, turn the key, flip the CSA switch, go to "start" and it's almost a matter of just "bumping" the starter. Varoom. Seems like one revolution, - - ' usually. Gotta wonder if, sometimes, the right cylinder, or two, aren't positioned right at shut-down, to fire within that partial revolution, and I'll have to hold the key for something like: "chucka- chuck- chucka- varoom. Anyway, it's all part of the 6.5 mechanical experience, which gives me a nice feeling, every time I feel that torque in a hill..
Oh. I learned, quite a while ago, that, even at 70 degree, of a morning, failing to use the CSA, will result in copious clouds of white. Learning just how much throttle to use is important, too. Warm mornings, mean no throttle to start and to tip it in, lightly, up to 800-900 rpm, from 6- 700, idle. Hardly a puff of white. Gets below freezing and I have to open the throttle to the ~1100 rpm range, which means more smoke. Guess wrong, and it fires up at 1400 , or so, means that you don't want it parked with the exhaust facing the front door!