[Zak99b5]

I just bought a 2010 Z71 Suburban with 123k miles. 3.08 rear end, six-speed tranny, and AFM.

We drove from Albany to Syracuse (150 miles each way) for my son's college visit.

We started out with a completely full tank from completely empty (it took just about 31 gallons), and I reset the trip odometer and average MPGs (was at 15.7).

There's a good upward elevation change going to Syracuse, we had an oblique headwind, and it was in the lower 20s. According to the computer, we got right around 15 MPGs on the way out.

I did not reset the computer, and when we got home the figure had risen to 16.2 mpg. We did hit about 5 miles of stop and go traffic. Gas gauge read half a tank when we got home.

I was expecting to get better mileage than this. My 01 with 205k, 4 speed, and no AFM gets the same.

The new truck has Firesrone Destination A/Ts; could this account for some of the difference? My old truck has Michelin x-radial LTs.

Anything else I need to look into? Thanks.

 

[RayVoy]

300 miles, 31 gals, that's less than 10 mpg!

You didn't say which engine you have,

Extra weight in the truck, extra rolling resistance, mechanical/electrical condition are all factors.

Smooth tires with extra air
New plugs (if originals)
New front O2 sensors
Top tier gas
Synthetic fluids

Not trying to run it in, we travel 90 from Boston to Buffalo (and return of course) quiet a bit and I get just under 20. I know it's a longer distance to average; but it's all up hill going west (that's why I include return). But point is, it's achievable if our engines are the same.

 

[xPosTech]

I don't think the fuel gauge is linear. At least mine isn't. After 7 years I haven't figured out exactly how the instant and average mpg is calculated. My 01 Eldorado uses the fuel level to calculate mileage displayed by the DIC. It also seems to do a calculation on engine start. Most times if I park on an incline the car might lose 2-4 mpg between a shutdown and restart. I'm sure this is caused by the fuel level sender reading less whenever the car is parked inclined (nose in the air). As far as I know it doesn't use a flow meter for consumption.

The truck does use a flow meter. At least I think it does. I can display fuel rate used per hour, per min, fuel level (from PCM), fuel pressure, fuel rail pressure, fuel used/trip, and fuel remaining. These values are displayed via Torque Pro from PIDs on the Canbus. TP also has a scaling factor I can adjust to match the displayed average mpg (in TP) to measured mpg using mileage and gallons used from the pump every fillup. I don't hand calculate and adjust the mileage at every fillup; maybe every 10th fillup or so.

Parking the truck on an incline doesn't change mpg values on the DIC or in TP. So in the intervening 9 years between the Eldorado and the truck the mileage data has gotten more accurate and more sophisticated.

Ted

 

[xPosTech]

And one other thing. I have every reciept from every time I've bought gas. Have any of you ever seen one of the news stories about a station having bad gas and damaging X number of vehicles? The only way to protect yourself if you happen to get a tank of bad fuel is to have a reciept proving you got the bad fuel from so and so at whatever time. I guess with credit cards you could get a transaction statement but can you do that the same day you got the bad fuel?

If you used cash and got bad gas without a reciept you're SOL. Depending on the vehicle you could be out hundreds if not thousands of dollars. Yes I've heard of the tanker filling the diesel tank with gas. After flooding lots of stations pump your tank with water.

I used to use the pay at the pump with a card but since I got burned a couple of times from skimmers the Visa I use for gas will no longer approve paying at the pump. That's one of the dangers living in the boondocks. The only thing I mind about that is having to walk inside usually twice. My stenosis and COPD make that a hassle but I do it to get the reciept.

Ted

 

[Zak99b5]

Sorry if I️ caused any confusion. I️ put 31 gallons in it before the trip, so we stared out with a full load of fuel (and its weight).

It read about 1/2 full when we got back.

I️ have the 5.3, same as in my old burb. I️ drive 70-75 mph, with a pretty light foot. No cruise control.

The ‘01 has new plugs and synth motor and diff oils.

The ‘10 just came from the used car lot, so I️ think he plugs are original and the oil, while fresh, is conventional, I’d bet. Guessing factory fill on the diffs and transfer case.

 

[Zak99b5]

Oh and it was just 5 people, no gear to speak of. I️ got mpgs in the 16.x with 6 people and our luggage for two weeks, some on the roof rack, last summer in the ‘01.

 

[RayVoy]

We always make that trip with 2, I know 3 extra people would hurt my mileage, how much, no idea. We

 

[xPosTech]

You can't depend on the gas gauge to determine fuel used or fuel left in the tank. I'm pretty sure there is more than 16 gallons in it when it reads half full. The only real way to tell how much you used on the trip is to fill up when you get back (at the same pump if possible). Even doing that you might be a half gallon or more off. That's why long term mpg figures are the most accurate. Short term doesn't account for minor speed differences or headwinds, etc.

GM fuel senders (like their speedometers) have always had a built-in non-linear weighting that shows slightly less than the actual amount of fuel. Just like the speeedometer reading slightly faster so they won't get sued if you get a ticket there's a little gas left so it's less likely to run out of gas. That has always led new owners to try to find the exact needle position when it runs out.

Driving style has much more impact on the mileage than many drivers suspect. When driving with the cruise control turned off I can get up to two more mpg. I live in hilly country so the CC is at a disadvantage. Allowing the truck to slow a bit going up a hill and making it up on the downhill side can stretch your mileage.

Ted

 

[blackburb]

ALL full size 1/2 ton trucks get 15mpg no matter how old, new, what engine, axle ratio, etc. It's just one of those immutable laws of nature. Give or take...

 

[Zak99b5]

I can live with that, blackburb.

You don't buy a Suburban for the MPGs lol.

It's just the advertised 20ish highway MPGs that has me wondering.

 

[blackburb]

I think it has something to do with trying to push a giant brick thru the air

 

[squatchy]

ALL full size 1/2 ton trucks get 15mpg no matter how old, new, what engine, axle ratio, etc. It's just one of those immutable laws of nature. Give or take...

Then whys my dads crew cab 4x4 Sierra get 20?

 

[bazar01]

I average 18-19mpg on my 2001 with the 5.3 and 2WD.
19-20 on my 2011 Silverado 4WD with 5.3L.

 

[RayVoy]

It's just the advertised 20ish highway MPGs that has me wondering.

I experimented with mine ('09) one time, it was a 90 mile drive and we were not in a hurry, combo of up and down hills and some flat country.
I drove with the intent of getting good mileage, no heavy foot, easy gas, easy braking (if there was any), never over 55 unless I was coasting downhill, etc.
Net result was 24 mpg, that's how they get the advertised mileage numbers.

I was a painful drive, I just don't drive at that speed; but, I proved something to myself.

 

[xPosTech]

My results were similar to yours, Ray. I live in a hilly rural area. When I bought the truck in 2010 I quickly realized that the cruise control wasn't going to win any mileage rewards. I can get 2 - 4 mpg above the CC driving the 2 lane country roads without much effort. I can get a couple of miles above that when I work at it. And when driving aggressively in a hurry I drop to 16 - 18. I think the window sticker mileage figures are very achievable if you keep your foot out of it.

And if I drove like a cop it would probably drop to around 10 - 12 mpg.

Ted

 

[JackE]

Once upon a time when I bought my wife's hybrid, I asked around about the advertised 47 mpg. The sales guy said he was actually achieving 366 mpg in his, but he plugged it in morning and night and never took it on the freeway. 8 months after buying he was still on his first tank of gas. It's all in how you manipulate the conditions. He told me that MPG ratings listed on vehicles are achieved under the most strict and stringent conditions. Everything is perfect on test day, right down to the barometric pressure, humidity level, temperature, wind speed, vehicle speed, elevation change (there is none) That is how the manufacturers achieve the numbers that the average consumer never will. I have over 100K on my hybrid in 3 years. I have been on 2k mile trips where I have gotten as high as the advertised 47, and as low as 38. I have had a few 35 mile trips home that I averaged 62, and the same trip that has been as low as 36. I even had one 12 mile trip, mostly down hill in elevation, that I got 79.6 mpg. Headwind, season, idiot drivers, daytime, night time, it all plays into mileage. Your best average should be taken over a longer period of time and mileage, a few months and several thousand miles, to give you your true average. My best calculations on the hybrid over thousands of miles is 39.6. Ford adjusted their sticker average down to 42 about 6 months after I bought the car and gave me an $800 'I'm Sorry" check. If I take it easy and drive like an old man, I can keep the running average up around 44, but that's no fun! The 7.4L Burb is another story. No matter what I do, fully loaded or completely empty, towing or not, I can't get any better than 14, and usually no worse than 12. It's the nature of the beast, and I love it!

 

[xPosTech]

Your burb reminds me of my 68 Goat I had in the late 60s - early 70s. No matter what I did I got 8 miles per gallon. Easy cruising on the interstate I got 8 mpg. Hook up the Tahiti ski boat and hammer down and I got 8 mpg.

The kicker is I traded in a 63 VW that got 27 mpg. Was it worth it? You bet!!

Ted

 

[blackburb]

As long as everyone is throwing their mpg in, here goes - My 8.1 on the stock, skinny, 300psi tires hit 14 on the highway. Put wider, softer all-terrains on and that dropped to 12ish. Towing my 6000lb trailer, about 8.5. With my 94 5.7 best was 16.75, typical around 15. Towing the same camper, 9-10. Buddy has 05 5.3 Burb gets best 17-17.5. He previously had 00 5.3 Tahoe, best 16.5.

An attentive driver can always best cruise control by being proactive - cruise is reactive. Skinny, summer tread tires with lots of air will make a bigger difference than just about any other single factor (not including driving style and assuming equal state of tune). Synthetic gear oil can help especially in 4x4 or lots of cold weather.

 

[Zak99b5]

OK--I refilled the truck yesterday. DIC said 15.7 mpg average, 28 gallons used, 441.1 miles traveled.

The pump said I put 29 gallons in (at the first click; i always stop there), which gives me an average of 15.2 mpg.

Driving to Rochester and back on Wednesday. I'll see what my mpgs are then.

 

[Zach Smith]

My results were similar to yours, Ray. I live in a hilly rural area. When I bought the truck in 2010 I quickly realized that the cruise control wasn't going to win any mileage rewards. I can get 2 - 4 mpg above the CC driving the 2 lane country roads without much effort. I can get a couple of miles above that when I work at it. And when driving aggressively in a hurry I drop to 16 - 18. I think the window sticker mileage figures are very achievable if you keep your foot out of it.

And if I drove like a cop it would probably drop to around 10 - 12 mpg.

Ted

I did this...to prove a point to my wife....we made two full trips around the lake (one way then back with essentially no traffic on road) I let cruise handle the first trip, at the speed limit and I handled the second... A bit more aggressively... (Not like a pissed off teenager, just an average relaxed drive for me) what do you know...I got the prize . Of course sometimes its better to be happy than right lol