Straight 6 vs 305 TBI Fuel Mileage

[chevymotocross]

I got a new job, traveling pretty far, and I go through a tank of gas a week in my 87 r10 short bed. It has a 305 tbi, 700r4, 3.08 gears, and I'm only getting 13mpg. Mods include true dual exhaust, k&n filter, new fuel filter. It's mainly city driving. I have an opportunity to get a very clean 1976 c10 long bed with a 250 straight 6 auto for $1000. I wasn't really wanting to get a 2nd truck, I was looking into a small car for commuting, but since it's a square body with a 6, it caught my eye. Will a truck like this get any better mileage than a 305 TBI for city driving? Or, is it worth just getting a car.

[Pyrotechnic]

The sixes don't get better mileage unless you give them overdrive and do a bunch of work to them. They were mostly designed to be cheap, simple, and reliable. For $1000, I would still buy the truck for a backup vehicle.

Your current truck should be getting better mileage than that. How fresh is the oxygen sensor ? That's important for fuel economy while cruising. Done an ignition tune up ? Set the timing ?

Second, the 3.08 gears will kill mileage in the city because they lug the motor around town. I don't know what GM what thinking, but 3.42's or 3.73's would be a much better gear. 3.08's are the WRONG gear for a vehicle with overdrive running 28"+ tall tires.

[chevymotocross]

After looking at old posts around here, about I-6 economy, they really aren't any better than the 8 cyl. It still is a nice truck though, and it would be nice to have a lwb.

As for my current truck, I only drive around in D. I only use OD when I know I will be on the highway for a long distance. If I use OD around town, it constantly shifts in and out of OD. Seems to cruise better in D instead of it lugging. O2 sensors I am unsure of. When I bought the truck, it had new true dual exhaust, manifolds back, with new cats. Wouldn't a dirty O2 sensor throw a code, triggering the SES light?

I haven't done an ignition tune up since I bought the truck last year. Main reason, I want to replace the leaky valve seals first. If I were to put new plugs in, they would probably become dirty quickly since the valve seals cause the truck to smoke on startup.

I'm running 265/75/15 tires. I will be dropping down to a 255/70/15 or maybe even a 255/60/15 since I plan on lowering it. I am betting the big tires I have on there now are hurting mileage.

[CLASSIC87']

IMO... spending the $1000 plus insurance and tags... your not going to be saving anything in gas. If your looking to save gas... buy a 4cyl Honda (late 80's early 90's). They are cheap and still get 30+mpg. Also with the oil per barrel going down... gas will continue to go down as well so you may just want to keep driving your truck and save the $1000+.

[chevymotocross]

Originally Posted by CLASSIC87'

IMO... spending the $1000 plus insurance and tags... your not going to be saving anything in gas. If your looking to save gas... buy a 4cyl Honda (late 80's early 90's). They are cheap and still get 30+mpg. Also with the oil per barrel going down... gas will continue to go down as well so you may just want to keep driving your truck and save the $1000+.

Funny you say that, that is exactly what I am looking for... a 90-93 accord. That truck actually sold. It was a sweet truck no doubt, but it looks like those 250 6's barely reach the 15 mpg mark. It appears if I get my 305 tbi in better running efficiency, it should actually exceed what an old 250 can achieve.

[Pyrotechnic]

A bad O2 sensor will throw a code. An old one won't give the computer a truthful reading of the fuel/air ratio and the computer has no idea anything is wrong.

The fact that you are driving around in 3rd gear and the transmission can't stay in overdrive is a sure sign that the motor is below it's power band. The only solution here is to install more desirable rear end gears. Smaller tires will help a little bit, but still not as much as changing the gears would.

[gchemist]

Put on a tonneau cover. Even in the city it will help.

[PhilaTruck]

You should get 15 or so in city driving. You're not too far from that now. But the thing that makes the most difference in city is how you drive it. Take it easy for a tank or two and I think you'll be surprised. That OD tanny is great for highway, you should be around 20 with a TBI, but you gotta granny the gas pedal. I used to get 15-20+ with my 305/700R4.

[79blazer]

smaller lighter narrower tires would defiantly help. Inflate them a little extra, then you should be able to use overdrive more. Coast 1/4 mile before you have to stop. A slight advance in the timing should help too.

[Captkaos]

My 87 R10 with a 305/700R4 and 2.76 gears gets 17mpg for city driving and 22.8mpg for highway. This was averaging about 60-65mpg. Yours is WAY off.

A 6 won't get any better than your current truck, a diesel will though.

If you are after huge economy gains, get a 4 cylinder.

[Hoods69BadBowTie]

Yea a straight 6 aint going to help out at all. Your current setup should be getting better then that with your T.B.I. I would check into a 4cyl. car for good gas mileage just my opinion.

[chevymotocross]

Thanks guys, it definetly is a bit sluggish and I guess that contributes to my bad mpg. All I have done was change the oil and filter every 3,000 miles, and put a new EGR valve. Should I wait on new plugs and wires after I put new valve seals in? I don't want the new plugs to become oil fouled.