Boomer34

I have recently bought a nice '99 2500 Suburban. It only has 100K miles and is in great shape. I had all the fluids replaced when I got it and put on some new Bilstein shocks. Not much else was needed. I have been tracking my gas mpg over the first 1,000 miles I have had it. I made 1 long highway trip and got 10.9 mpg. Since then, I have done mostly city driving and have gotten 9.8, 9.4 and 8.6 mpg on my last 3 tanks.

I am wondering what I can do to improve this. I have done a little research on here and have read about doing the cold air intake, a friend mentioned removing the catalytic converter...I'm not a "car" guy, so don't know much about "under the hood" type work...I did check, and it appears the fuel filter has been replaced recently (Car Fax says it was a couple thousand miles ago, and it's an after market one). My fuel pump does wheeze while the truck is cranked.

I'd do pretty much anything needed to get 2-4 mpg more than I am now. This is going to be our main family car, so it will be driven a lot and we are planning to keep it for the next decade.

Thanks for any insight!

Boomer34

A few of the other things I've read people doing are:
-Electric fans
-Some type of specific tune-up
-Fuel additives

73shark

I would not recommend removing the catalytic converter. However cold air intakes might improve efficiency somewhat, it typically is in the higher RPM range of the engine. My recommendation would be if anything is to replace plugs and wires. Don't forget that you have a heavy 3/4 ton truck and mileage is not ever going to be that great.

SabrToothSqrl

Removing the catalytic converter would be illegal under federal law, and would most likely cause a check engine light, and the vehicle to fail inspection...

Realistically I don't see much you are going to do, to improve this. I assume you need to tow, which is why you bought the 2500. That's an old school 6.0L V8? or is it the even bigger one?
My last boat - I went from a 1990 Carb 460 to TWIN 2001 EFI 350s. At 35 MPH... the 5.7s burn the SAME fuel.
(At 70 MPH all bets are off)... lol

My daily driver is a Tesla, and I rent a F350 when needed (2-3x/year). Between fuel costs, insurance, inspection, registration, etc. etc. I found that renting a truck or 'burban when needed works for me. However if you need it almost daily, that's not going to be an option.

The basics really: Don't 'modify' anything... you are a self stated 'not car guy' and you don't want to open pandora's box.

New air filter. Change the oil, new spark plugs, new spark plug wires. Clean the throttle body (or replace).
Maybe run some Fuel Injector cleaner through it. If you can, replace the fuel pump.
Always run 100% gasoline if you can. E10 or E15 will result in worse MPG. (and if you look at Cost/Mile, I'm not sure E10 was ever a good idea).

You can inflate your tires to the max pressure - which will gain MPG, but you may lose traction and cause an unsafe driving situation. This is AT YOUR OWN RISK. you are giving up traction for MPG.

Most engines use less fuel than you think to start - 7-10 seconds is the break even point. However a 1999 engine was not designed to start/stop 20x a day either... and a starter will cost you more than gas.

Basically you want to get it back to 1999 state, right off the line. Clean things, replace things, but I wouldn't modify anything...
Don't forget other areas too:
Verify none of the brakes are dragging.
Verify you're in 2WD. Not Auto or 4. (unless you need to be).
Verify the alignment. Dragging a tire sideways adds.. well.. drag.

Doug D

Not much you can do. You are pretty much driving a vehicle with the aerodynamics of a brick with a big engine.

What type of tires does it have? All terrains tend to get worse mileage than all seasons.

Keep it in good tune. When was the last spark plug change? New plugs might get you 1-2 mpg.

Removing the catalytic converter is a legal no no. Plus the emissions controls, fuel metering, etc are dependent on the existence of the catalytic converter.

The only additive I know of that actually works is Techron, but it doesn't necessarily result in better fuel mileage.

Some inexpensive things you can do include driving like an egg is under the accelerator. Smooth takeoffs and gentle braking.

Son has a '07 Avalanche with the 5.3L V8. Even after changing the plugs he averages 13 mpg no matter if he is going uphill, downhill, level ground, city or highway.

Hope that helps.

intheburbs

Well, to be honest, in that context, you chose poorly.

The 2500 trucks are completely overbuilt and designed for towing large things. If you wanted a grocery-getter soccer mom vehicle, with respectable mileage, the half-tons are where it's at. You'll notice your GVWR is 8600 lbs. That's because any vehicle with a GVWR of 8600 lbs or higher is not subject to CAFE regulations, so GM had no incentive to do anything to make the truck get better mileage.

There is nothing you can do to improve the mileage that much. Maybe drop in a diesel?

In my experience, tires are probably the biggest factor in changing gas mileage. A soft all-terrain tire will really kill MPGs. Get a highway tire with the highest treadwear rating you can find and that would be your best bet. And keep the tires inflated to max cold PSI. Of course, the downside will be rain/ice/snow performance.

My 2008 2500 is a little better on mileage, but not much. I usually get 12 MPG around town, and if I really try, I might get up to 15 MPG on the highway, but only if I keep it around 65-70, which doesn't happen often.

Look on the bright side - gas is super-cheap right now. I just filled up for $1.87 at Sam's Club in my AO.

Boomer34

Thanks everyone...that is helpful. I knew when I purchased, it was not an economical decision. I have 5 kids, and prefer to drive a tank around, even if it costs more in gas. I was just trying to make the best tasting lemon water I could. I will follow the advice and check some of the easy things, and mostly live with it.

I believe the spark plugs and wires were changed in the last 10K miles, at least that is what the car fax says, and my friend's shop didn't mention them needing to be replaced. How often should I be doing that?

Right now, the tires is 275/65R16, which I think is a little bigger than what was stock. The truck came with Goodyear's on the front tires and Continentals on the back, although they are the same size. But I have noticed that the front tires stick out wider than the back tires...not sure why?

Doug D

If they are copper plugs (check the owner's manual for the OEM recommendation) you should be good for another 20K miles. If they are platinums you are good for another 90K miles. Having said that my '06 Ram 1500 (Hemi) uses copper plugs. Suppose to change them every 30K, but I usually change them every 100K. The gap is noticeably bigger, but installing new plugs only nets 0.5-1.0 mpg difference.

Just purchased a '14 Equinox with the 2.4L engine to replace my wife's Journey that she totaled on black ice. Have yet to check what type of plugs it needs.

73shark

If the wheels are OEM then the only reason I can see the tires would stick out was because they are several sizes wider than the stock tires were.

Boomer34

What's weird is the tires are the same size currently, on the front and back...they are just different brands. But the front tires stick out a touch from the wheel wells, while the back tires are tucked inside.

I did just have the front brake pads replaced, but I would assume the shop put the tires back on properly.