FAQ: Improving Bad Gas Mileage

i pay no1 to look at the Riv...my dad works as a service advisor..where i bought the car also...they all love the car and look at it for free.

as for the driving around city...im literally driving 7-8 miles city...not heavy foot at all.

btw my knowledge on cars in very minimal.

sea foam is a good place to start IMO. especially in a 13yr old car no matter how low of miles it has, you will still have carbon built up on the intake and internals. WOT daily helps keep that away too
if it were me, i would dump 1 can of sea foam in the gas tank mixed with about 4-5 gal. (1/4 tank) of 93 oct. and use another can to do a top end clean through one of the vacuums lines. (look for leaks while doing this too.) if you dont see alot of smoke from the exhaust then you could have a clogged up cat which will also kill mpg, but thats not very common with our cars and with your low miles.
after you run as much of the gas as you can out of that tank, fill her all the way up and see where your mpg sits and get back to us.
good luck!

65 and flat you should be getting better than 14 mpg. Do you let the car warm up? If you let it warm up in your driveway too long you are killing gas milage right there. It only needs a minute unless you wait for full heat... but there's a big chunk of your milage.

How long is your average drive? enough time to compensate for warm-up time?

Do you have a scan tool? I'd be curious to see what the MAF, TP%, IPW LTFT and O2s are at cruise.

Since your dad is service advisor, in my opinion you should be able to arrange to meet one of the mechs after/off hours and connect your Riv to a Tech 2 and take it for a drive pretty much like your normal drive. Loop back to the dealership. When you get back you can look at the log in the Tech 2 and see what the MAF, TP%, and oxy sensors are doing. As well as what the transmission is doing. The tech you ride with has to have an idea of what the sensors *should* be doing. A better idea would be to buy a cheapie laptop computer off ebay or some such, buy an OBD-2 dongle (a cord to connect a computer to your car) from Alex Peper (http://www.carcode.com) and download Alex's Car Code program. It will take a log and show you all the gauges - even some you did not know you had like MAF. It will log MPG as you drive, too, so youcan see which parts of your drive cost you what. Then you can print out a log and talk about it with a tech - or even more fun take the laptop and run the log and watchthe techs eyes light up while watching the virtual dash gauges do their dance.

Back to the earlier comments on this thread - the things they guys are saying about warm ups are spot on, no more than a clock minute - that's right 60 sec - to warm up or else you are killing mileage. Try thinking of it this way - in each minute at about the cold idle RPM you could move at least 1/3 mile. As for me, when I start my Riv (Eleanor), I open the garage door and turn the key. Once the idiot lights go out I check the mirrors and back out of (heated) garage. Back down (50 ft short) driveway, into the street, about a gentle mile to the interstate. By the time I get to the interstate (a couple minutes) the Riv is ready to romp. Sometimes for a little variety I take the lower speed access road next to the interstate. Rural area, so no stop & go. Mileage? On the highway, as good as the Subaru I used to own, 25+ MPG, around 30 for long cruises when I'm not pushing it hard. In the city, mileage is not so good like 13-16 MPG. As far as I can tell, this is normal for the Riv in 30 MPH stop and go city driving. My 5-on-the-floor Subaru got much better city mileage. Think of your Riv ngine as a high-performance engine that's been tweaked and mated to a drivetrain to get reasonable mileage while still delivering spirited performance. If you want Chevy Cobalt mileage you will most likely succeesd if you get a Cobalt...

I have had a couple gas milege problems. One was that the torque converter clutch had become stuck off, had to overhaul tranny to fix that one. Another was the oxy sensors had become less responsive. At the dealer one of the mechs can flash your PCM with an updated map that will compensate to some extent for the lower sensiticity of worn oxy sensors if you don't want to replace them yet. I do not think that's been done to my Riv.

In my opinion you have some good options here. Depending on your dealerships rules for parts, what you *could* do is order them from gmpartsdirect.com (your parts guy will call this "two stepping" them) to come to your house. Install yourself (never too late to learn) or throw them in the trunk when you get 'em for the dealer mechs. When and when the service write (dad) writes up your order he should be able to write "customer expedited parts" on it so you don't have to explain why there's no parts $$$ on the work order, keeps dad out of trouble, and the mech can just list the fair labor for the job & you are done and nobody is hurt or fibbing. For older cars, 'customer expedited parts' is no big deal, the GM folks know that they have cut parts inventory at dealerships to new lows expecially for older models, and I can not see how anybody will want to bust your chops about expediting parts to keep a daily driver on the road.

In closing it sounds like:

1) need to make sure you are caught up on major maintenance like the oxy sensors, fortunately your diagnostic costs should be reasonable;

2) need to think about your behaviors and expectations; it will help to to have a way to actually measure what's going on;

3) need to take a fresh look at costs. I suspect that new drivers underestimate the cost of using a car by a factor of 2 or more at the margin, if only because gas prices have ~tripled over the past few years. I think demoraphics and habits of drivers here could start to look more like Europe; unless we have more exporting jobs (wealth increase for everyone) marginal drivers (and cars) will be fewer.

Albertj

all i gottta do is put sea foam in the gas tank?
and this will make it smoke??
and how the hell do i do vaccuum lines?

on your vacuum cylinder thing ( i forget whats its called , long week , headache) or the big round black thing in front of the firewall in the engine bay theres a 3/4" or so hose thats a vacuum line , i poured it in there but im not sure if the series I has the same vacuum routing.

xxsupergman25xx wrote:

all i gottta do is put sea foam in the gas tank?
and this will make it smoke??
and how the hell do i do vaccuum lines?

Please read this, all you need to know about using Seafoam: https://rivperformance.editboard.com/care-maintenance-f8/write-up-seafoam-to-restore-lost-horsepower-t123.htm?highlight=seafoam

have you verified to see if you have a vacuum leak? have whoever checks your car plug a vac gauge on it.

also, you may want to check for a plugged cat.

I have been getting less - about 5 less per gallon in the past couple of months. Even been going slower - from 68 to about 63 to try and improve it. Only let the tach get up to 2.5 at the very most when speeding up. Is it the methanol?They just switched to reformulated gas here. It pretty much freefalls after 1/2 a tank but that was normal before. Am not getting much past 360 on a tank and used to be able to get to 400. Anyone else notice a diff.?

How new is your O2 sensor? Changed fuel and air filters recently?

AA wrote:

How new is your O2 sensor? Changed fuel and air filters recently?

along with other maint items like plugs, pcv, and top clean?

so many things can effect your mileage. tire pressure, amount of weight in the car, gas used (E90 is at most pumps now), headwinds, if the a/c is used, ambient temp, elevation, etc...

I know reformulated gas gives worse mileage but I don't remember by how much.

Albertj

i was wondering, does winter destroy gas mileage in itself, or could i need new o2 sensors? i used to get 20 and now im at like 18 and sometimes even 17

Dang it AA, just when I've typed out a reply and hit SEND, you go and move Mike's post!! (And I lose the reply)

97rivsc wrote:

i was wondering, does winter destroy gas mileage in itself, or could i need new o2 sensors? i used to get 20 and now im at like 18 and sometimes even 17

Yes Mike, cold winter driving conditions will reduce your mileage. A colder engine is less efficient, and you likely allow some idle time to warm up from a cold start? 17-18 is not abnormal compared to usually getting 20.

It is possible to get decent mileage in the winter, but most people let their cars idle more when it's very cold - including the warm-up period when you start up the car. Idling when not rolling kills economy. On average, cars could get 15% better MPG if they where not idling when they stopped.

Try driving your car immediately as you warm it up. Try to keep revs under 3k RPM until engine is up to operating temp.

Remove snow and ice from the windows before you start the car.

When you are stopped at the ATM or fast food window, stop your engine if you think you won't be moving for more than 20 secs.

I'm currently averaging 19.9 MPG.

My MPG's have steadily dropped from low 20's in mixed driving, down to 19-18-17... and my last tank was only 14mpg.

There are a lot of factors fighting economy in cold weather, especially when it gets really cold in the far northern states. Bearing grease and engine oils are thicker when cold, and it takes longer for the engine to warm up and move into closed loop mode. Wet and icy roads increase resistance to the tires. All of these things add up, but the extra idling is the chief cause of lowered efficiency during the colder months.

I agree, extra idling time is the biggest factor for my reduced mileage. I've NOT idled to warm up until my last tank or 2, when we have had consistent temps of 15-20 below zero. If it's zero or warmer, I start it up, and drive easy right away.

ok thx aaron, i was just hopin it wasnt something else

now that summer is here, i decided to see what kind of mileage i can actually get on an all highway trip.
i left out this morning from orlando headed up to jax at 4:30am.(miss traffic and heat)
topped off the tank,set cruise control to 75 and had the sun roof up, a/c off.

filled up again exactly 151 miles later and topped it off with 6.49 gals. that just over 23mpg. i'm a little disappointed. i only hit the gas one time from 60-120, the rest of the time i almost never touched the gas or brakes. 99% flat florida roads.
i know the one WOT run hurt me some, and if i did 60mph i would have seen better mpg, but i was expecting at least 27/28 on this trip.
i think i'm going to get a new 02 sensor when i get some more money. and scan to see i'm running too rich.
brand new plugs, new fuel filter,good oil,clean K&N, plenty of flow mods, lowered car, not a lot of weight in the car(one big suitcase). am i missing something?

i also plan on manually cleaning my injectors sometime since they have 150k on them. but i run them hard so i dont expect much crude built up in them.

i feel dumb for posting up trying to help others diagnose their low mpg issue, but now i cant figure out my own :/

Matt

That doesn't surprise me, sounds about on par. Try 70 next time. I can get 27 with the cruise set at 70. Gas milage drops exponentially as you speed up from there. 75 nets me 23-24 mpg. 80 gives me closer to 20.

Injectors can get really bad at that mileage, even if you clean and do WOT runs regularly. I noticed a big improvement in power and response after installing rebuilt injectors. Probably improved economy, but no proof of this. Injector duty at low RPM probably isn't too intensive, so maybe won't matter much for mileage.

Try a trip at 60-65 mph and see what you get - no WOT runs. Try to do very little braking on the trip.

I agree with Derek, once you head above 70, you pay an mpg price. My van will do 28mpg at 70, but at 75 it drops to 24/25 at best. I can guarantee you the EPA did not rate these cars at 75mph in their tests.

I have a 95 It's been getting pretty poor gas mileage lately. like 13 or 14 in town. I replaced all the coil packs. and last year i replaced the plugs and wires. it has 121,000 miles on it. its a 1995 S/C.