Hi!

I know there is a MPG thread, but I wasn't finding anything there that seemed relevant, and I was hoping a few of you who are more knowledgeable might have some ideas that are more specific.

I have a 98 Suburban 2500 with 105,000 miles. No special modifications done on it. I'm only getting about 12 MPG!:( Does someone know what is typical for fuel economy in this vehicle (mostly city driving)?

I know it's winter-time and that affects things (I'm in Anchorage, AK), but I usually park in the garage overnight which stays between 45 - 50 degrees F.

I changed the air filter (and fuel filter if that makes a difference) about three months ago. I add a little Diesel Service Plus with Cetane boost to the fuel (though I don't measure it out, so maybe I don't add quite enough). I can't detect any fuel leaks. I'm a careful driver that is easy on the accelerator and on the brakes. My tires are fully inflated. I had been using WVO (blended) in my tank until it got too cold last October and I've used straight diesel since. Last oil change was also about three months ago. The vehicle seems to run well: engine sounds good and there are no Service Engine warnings.

That's the low down. Any other ideas about what I might check for? Any other maintenance-type issues that can have an effect on the fuel economy?

Thanks in advance for any ideas.

What is your rear end ratio and your tire size?
That's pretty bad mileage, mine had crappy mileage when one thermostat stuck open, took a long time for the engine to warm up and used much more fuel.
Is your converter locking up and is it shifting into overdrive properly?

My truck only gets 12-13mpg in town on a good day during cold weather (2 warm-ups per day). Right now I'm getting 15-16 mpg on highway with my aggressive Mud Tires.

on a 128l fill up im luckey to get 550km at the moment. My over drive dosent kick in till the gadge says im doing about 65km is that right??

i only get about 13mpg in town with 3.42 gears. I know i need injectors and a new timing chain would probably help too with 242k on the originals but also when its cool out my truck never gets up to temp. I think the 'stats might be stuck open. In fact i think most of the time my truck doesnt get up to temp until its been running and driving for a long time. That could be a problem. I dont think anyone ever sees more than 15-16 in town tho.

Wow, you guys have lead feet! hahaha. I got 20 mpg on average with my 6.5. Got 22 mpg with more highway driving, I'm hoping for much better than 22 once I get my new engine built.

i very rarley take myne above 2000rpm thow the engine does have 300000km on it with the factory injectors and glow plugs still in there.

Wow, you guys have lead feet! hahaha. I got 20 mpg on average with my 6.5. Got 22 mpg with more highway driving, I'm hoping for much better than 22 once I get my new engine built.
Not to call you a liar or anything but with a turbomaster (especially set to 12-15psi max) I don't see a 6.5 getting over 20 mpg with 3.73s.

now with a stock vac system I can see it as it lowers the boost pressures while cruising unlike the TurboMaster.

Maybe I drive slower, I always cruise at 80 km/h which is around 49 mph, and 50 km/h in the city which is 31 mph. I keep all my fuel receipts so I can scan them if you like. Most people don't believe me when I tell them I get 26 mpg highway with my carburetor equipped 383 stroker, but I do and plan on hitting 30 mpg highway with it this year.

Maybe I drive slower, I always cruise at 80 km/h which is around 49 mph, and 50 km/h in the city which is 31 mph. I keep all my fuel receipts so I can scan them if you like. Most people don't believe me when I tell them I get 26 mpg highway with my carburetor equipped 383 stroker, but I do and plan on hitting 30 mpg highway with it this year.

Speed has a lot to do with fuel economy. That's how many O/O truckers are still making good money, they're just slowing down. Running at a speed that matches the engine's peak efficency through the proper gearing is also important. For example, truck A with engine X, and gearing M may get peak effiency at 55 MPH running 1500 RPM, while truck B with X, and gearing N may get peak effiecency at 65 MPH running 1500, and Truck C, also with engine X, and with gearing L may be running 1500 at 45 MPH.

What is your rear end ratio and your tire size?
That's pretty bad mileage, mine had crappy mileage when one thermostat stuck open, took a long time for the engine to warm up and used much more fuel.
Is your converter locking up and is it shifting into overdrive properly?

The tires are 245/75/R16 regular All-Season (which is what is recommended). I don't know what the rear end ratio is...how would I find out? It is probably the way it came from the factory. What would be the optimum rear end ratio for city driving and not towing anything.

I guess I'll check the overdrive when I'm driving next.

Sounds like a lot of people aren't getting much better mileage than me, though I'd like to know what the people who are saying they get 20+ are doing. I had thought diesels did significantly better than gasoline engines in fuel economy, and I was expecting better from this rig when I bought it.

Thanks

me, my dad, my gpa (3 trucks), and my uncle all get right around 20 with our trucks. most of them are 4:10 except one with 3:73 and they all have 265/75/16's. I get crappy mileage when im on the express way because i like to run with traffic which puts me at like 2300 rpm. if i keep it down right at or below 2000 i get good mileage. I also use manual TC lockup and lock it up whenever i am cruising above like 40.

haha my mileage blows on the highway. When I worked down on LBI I took the highway daily and normally do about 75ish. And with a 4.10 final drive the RPMS are really up there. Of course this was before any mods where done to the truck. Now I'm not working there anymore unfortunatly(damn economy) Mileage has sure gone up for me

if you want to find your gear ratio an easy way is to look in the glovebox. there will be a sticker in there on the inside of the glovebox itself showing a bunch of codes. take a digital pic of it (thats what i did) then go on google and type in chevy RPO codes. there you can also find out what other features your truck is equipped with and GVWR etc etc

I'm getting 15 mpg on the winter blend right know. And still waiting for the summer blend to get in the gas station.

this might sound crazy but i got a standard 6.5 engine execpt for straight pipe and im getting upwards of 600 to 650 km when im doing high way driving and im doing around 110, 120 which i suppose is really good im not sure what my ratio is of my rear end.

Wow, you guys have lead feet! hahaha. I got 20 mpg on average with my 6.5. Got 22 mpg with more highway driving, I'm hoping for much better than 22 once I get my new engine built.

Rarely a led foot here! Dont see over 2000 rpm much. Even at 70mph im under 2000 (barely). But I do have 3.42 gears. Ive seen 22-23 mpg on the highway once and i was going 80mph that trip and it was very hot out. I had no functioning liftpump at the time and the turbo was non fuctional so there wasnt any backpressure from the wastegate. Now i have a turbo master and i get right at 20mpg and no more. Not complaining tho. I do wish it was better, and it will be after i change the 242,000 mile old injectors and timing chain and get rid of the factory restrictive exhaust. Even the way it is now, when diesel was $5 a gallon it was cheaper to drive this burb than it was either of my previous gas burbs and this one has more power, more miles on it and is heavier!

Just curious, how much of a difference do you guys think changing injectors makes? Aside from slightly sub-par mileage my truck runs great so I haven't had the urge to change the injectors. My Tahoe with 3.42 gears gets at best 17-18 mpg on the highway and that is really babying it at 65 mph. Its not really bad mileage just seems a little on the low side for a Tahoe.

My injectors have about 193k on them now, just debating if its worth changing them. Would a timing chain help much either? I thought the computer would compensate if there is a bit of slack in the thing.

Just curious, how much of a difference do you guys think changing injectors makes? Aside from slightly sub-par mileage my truck runs great so I haven't had the urge to change the injectors. My Tahoe with 3.42 gears gets at best 17-18 mpg on the highway and that is really babying it at 65 mph. Its not really bad mileage just seems a little on the low side for a Tahoe.

My injectors have about 193k on them now, just debating if its worth changing them. Would a timing chain help much either? I thought the computer would compensate if there is a bit of slack in the thing.

The computer can variate the fuel injection timing but it cant compensate for valve timing which, with a stretched timing chain would be either late or early (not sure which). The computer cant tell that the chain is stretched or it would warn you when it got worn enough to effect things. So with a stretched chain the injection timing is also altered.

As for the injectors, when they get worn they don't spray very well. Rather they kind of shoot out a stream of fuel instead of a "mist" This is bad in more ways than one. It causes hot spots in the cylinders which can melt pistons and also, the fuel wont burn as well or as fast since its injected as a stream and not a spray. Combine early or late valve timing, injection timing AND a "stream" of fuel instead of a spray and i'd bet the thing runs sluggish compared to what it would run if it was new. I have this problem. My truck seems to run fine, but how much better would it run with new injectors and timing chain, considering the fact that both are 242,000 miles old? Im betting the difference would be pretty significant. I cant see any way that it would NOT run better, start better, get better mileage and have more power too.

18mpg from a tahoe on the hwy really is kinda bad. I make better mileage than that with a loaded burb with the same gear ratio... at a faster speed on top of that.

mine gets 16-17 city and about 21 highway running ~75 mph with a not-so-light foot :confuzeld

This is on a '98 standard cab long bed F code 2wd with stock size tires and 3.73 gears. I just put the diamond eyes exhaust on yesterday so hopefully I will see improvement. Is mine just a freak? those are pretty poor numbers..

300000km on my injectors going to change them at the end of spring when i have some cash.

Just filler her up a couple hours ago. All of the 14.671 miles to the gallon. Cant wait to start burnin summer blend again. YEEPPE.