What's Your Fuel Economy for Your Vert(s)?

[Rick]

Just curious what everyone else is getting MPG wise for their convertibles.

 

My 1994 3.1L seemed to average a little of 20 mpg per tank, mainly city driving.

 

However, my 1995 BARELY squeezes out 200miles on a 15gallon tank, which isn't even 14mpg. I have driven it like a granny and once or twice got around 220-240 but mostly its around 200 miles on a tank. Its got the 3.4L engine, but its not doing what is considered standard. I noticed during winter the tire psi was only at 20 so i moved that up to 42. We'll see if that makes much of a difference.

[jake91]

my 94 dohc vert got 17 city if i beat it and 18 city if i was nice. average tank was 19mpg 75% city. strait highway at 80 it got about 26mpg, and one time i got 30mpg but that was a 100 mile trip (60 miles were downhill) at 90mph.

 

just for kicks though i figured my mileage after doing 7 passes at the track it only got 2mpg there lol

Edited February 19, 2012 by jake91

[Rick]

my 94 dohc vert got 17 city if i beat it and 18 city if i was nice. average tank was 19mpg 75% city. strait highway at 80 it got about 26mpg, and one time i got 30mpg but that was a 100 mile trip (60 miles were downhill) at 90mph.

 

just for kicks though i figured my mileage after doing 7 passes at the track it only got 2mpg there lol

 

Hmm..ill remember that.

 

No more max out runs lol. Hmm maybe thats why this tanks so shitty...wanted to see what max was on the car and never even got to it but gps said max speed of 124 but it was still pulling. (on a empty highway of course)

 

I just figure because im taking it up to chicago this spring break to work on it at my gpas shop hopefully and might turn it into a vacation for a week and one plan me and a few friends have is a total of 1500 miles lol. The 3.1L definitely treated me better mpg wise lol

[94 olds vert]

I'll get around 16-17 mpg city and I have a 3.4. On the highway going 65 mph I've gotten 29-30 mpgs.

[oldmangrimes]

With my 95 3100 with 138k, I get about 20mpg, with about 70% city driving, with no WOT or hypermiling, with studless snow tires and winter gas. I get about 23 mpg in the summer with a higher mix of freeway driving and better gas and tires, but I've don't have a DIC (wow that looks awkward:lol:) and I've never done a really long freeway trip to see the max mpg. As the price of gas keeps climbing, I will be lighter on the throttle and drive less.

 

Does anybody know how much mpg is affected by dropping the top in a convertible?

[GOT2B GM]

FWIW, the automatic LQ1 cars were rated for 17 city, 26 highway.

 

Edited February 20, 2012 by GOT2B GM

[94 olds vert]

Does anybody know how much mpg is affected by dropping the top in a convertible?

 

I'm not sure. I've tried to tell a difference with my DIS in the instant fuel economy gauge, but I really don't know for sure.

[95cutlass]

My cutlass averages on city roads 14-16, I have never really done better on my cutlass. Mine never really sees the highways either so I don't know my highway mpg.

[Galaxie500XL]

My 1995 LQ1 convertible is driven daily to and from work, about 50/50 highway, and surface streets. Over the past two years, I've been averaging between 19.2 and 19.9 MPG. Recently, I had to replace the ICM (cracked), found a ICM and fresh coils from a 3400 Intrigue. Since then, I'm averaging just under 21 MPG.

Edited February 20, 2012 by Galaxie500XL

[Galaxie500XL]

Been thinking about your '95's gas mileage, and have a few thoughts...

 

The 60-degree V-6 runs exceptionally smoothly, due to the even-fire design--makes it VERY easy to overlook a slight miss, because even then, it's pretty smooth.

 

When I first bought my '95, I got similar mileage as you did, and found that even though the engine seemed to run smoothly, the ignition wires were a disaster. Two of the wires had separated electrical connectors STILL ATTACHED to the plugs, but no obvious misfiring. Replacing the plugs and wires made an immediate improvement, but mileage was still around 17...

 

The oxygen sensor turned to be the culprit. As O2 sensors age, they tend to get lazy, and begin reporting the mixture is leaner than it actually is, the ECM then enriches the mixture, trying to correct a nonexistent "lean" condition. In my experience, this begins to become a factor long BEFORE you'll ever see a "check engine" light.

 

A less common issue, but I've seen it a couple of times, is a bad knock sensor. The valvetrain is a pretty busy place in a DOHC engine, and I have seen that valvetrain noise get interpreted as "knock" by the sensor, which immediately dials back ignition advance to correct the knock. This kills both power, and fuel mileage. The only way you'll find that problem is with a scantool that will allow you to see the data coming from the sensor. An occasional "count" isn't unusual, but if the sensor is consistently showing frequent knock, even at idle, check the knock sensor, and associated wiring.

[pshojo]

My 1995 CS with 3.4l, I get 15-16 MPG if its mostly in town. If mostly Highway, i pretty consistantly get 24MPG if mostly highway.

[Rick]

Been thinking about your '95's gas mileage, and have a few thoughts...

 

The 60-degree V-6 runs exceptionally smoothly, due to the even-fire design--makes it VERY easy to overlook a slight miss, because even then, it's pretty smooth.

 

When I first bought my '95, I got similar mileage as you did, and found that even though the engine seemed to run smoothly, the ignition wires were a disaster. Two of the wires had separated electrical connectors STILL ATTACHED to the plugs, but no obvious misfiring. Replacing the plugs and wires made an immediate improvement, but mileage was still around 17...

 

The oxygen sensor turned to be the culprit. As O2 sensors age, they tend to get lazy, and begin reporting the mixture is leaner than it actually is, the ECM then enriches the mixture, trying to correct a nonexistent "lean" condition. In my experience, this begins to become a factor long BEFORE you'll ever see a "check engine" light.

 

A less common issue, but I've seen it a couple of times, is a bad knock sensor. The valvetrain is a pretty busy place in a DOHC engine, and I have seen that valvetrain noise get interpreted as "knock" by the sensor, which immediately dials back ignition advance to correct the knock. This kills both power, and fuel mileage. The only way you'll find that problem is with a scantool that will allow you to see the data coming from the sensor. An occasional "count" isn't unusual, but if the sensor is consistently showing frequent knock, even at idle, check the knock sensor, and associated wiring.

 

I have to replace all of my plugs, already have a set..just need to get around to it. I have the same issue you had with the electrical connectors on the plug attached to the spark plug.

 

Part of my issue is with overdrive...sometimes it works greatly and ill hit fourth gear in no time even at 30 mph, other times it wont shift out of 3rd at 80mph. The original issue was a melted vacuum line that touched the exhaust manifold, but that has since been fixed.

 

Right now I am at 92mi right below 3/4 of a tank. I increased my tire psi to roughly 42/tire and watch it weakly to make sure it isnt affected by temperature. Last tank I got to 240 when low fuel lit up, I usually fill up a FULL tank at 200mi, 210 if I was lucky. That was a 15.x gallon fill up. Last tank I had a gallon and a half left, hit 240mi. So 240/14gallons=17.15mpg aprox with mostly city miles. I am driving the thing like a granny, well today I had a little fun with it being my birthday but it shouldn't affect it too much.

 

I am much happier now averaging 17-18mpg mainly city compared to the usual 13.5mpg. This tank should be exceptionally well with 50/50 being highway and city, after all im at 92miles with about 3/4 of a tank left. Should be easily able to hit 250miles on the tank.

[bender01]

My 91 gets 17. Ive thought about making it my commuter since my truck gets 16!

[Brock]

My 95 3.4L has never made it to 20MPG. Average usually is 14 / 15 mpg, always been that way, no has 28,000 on it bought it new.

[1988PhantomFE3]

My wife use to drive our vert in and around town, she always managed to stretch out the full tank farther than I did. I thought it was because I was a little lead footed, but turns out that had nothing to do with it. One day she pointed out to me that I had the shifter in overdrive, and I said so what? She told me that she never puts it in overdrive unless she's on the freeway. I didn't think much of it, but I decided to do what she was doing, and I ended up getting better gas milage in town too! I don't know if the drivetrain work a little harder in overdrive around the city streets or what, but since I followed her advice, we definately get better mileage.

 

And as far as top down mileage, it drains the tank quicker when we're on the freeway with the top down opposed to it shut.

 

we average about 17 mpg city, 26 mpg highway

[RobertISaar]

driving in 3rd with the TCC locked compared to driving in 4th with the TCC unlocked is a HUGE difference in fuel economy.

[AL]

Really? As in 3rd with TCC locked is a much higher fuel economy?

[RobertISaar]

yeah. think of it this way: in 3rd with the TCC locked, you are VERY close to the transmission efficiency of a manual transmission in it's drive (1:1) gear without any clutch slip. since the torque converter isn't slipping(or at least not very much), you take out one of the largest power drains associated with the automatic transmission.

[Penglii]

Then what's the point of the overdrive gear?

[RobertISaar]

for more RPM drop, which will USUALLY result in better fuel economy(rare, but there are instances where lower RPMs would be a bad thing).

 

also, TCC locked in 4th = roughly the same benefit as TCC locked in 3rd. just at lower RPMs for less noise/vibration/etc.

[Penglii]

Gotcha, that makes sense.

[94 olds vert]

I've been driving mine pretty hard in the city lately. I averaged 14.7 for my last tank. I haven't had it out on the E-way once.

[Luke94vert]

My 94 DOHC Vert with top down 99% of the time have been averaging 21.9 mpg.

 

Got 26.2 with the top down cruise set at 74 mph on the interstate. I thought that was pretty damn good. considering the trip back with the top up and averaging 80 mph i got 27.1 mpg.

[Rick]

for more RPM drop, which will USUALLY result in better fuel economy(rare, but there are instances where lower RPMs would be a bad thing).

 

also, TCC locked in 4th = roughly the same benefit as TCC locked in 3rd. just at lower RPMs for less noise/vibration/etc.

 

So...basically when I drive I should lock the shifter in the "3" spot instead of "D"? Im averaging also still 14-16mpg.

[94 olds vert]

In 3rd the rpms are going to be slightly higher than in D. I just checked mine and I'm getting about 17.6mpgs.

Edited June 21, 2012 by 94 olds vert