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 Unexplained MPG increase

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Mikel
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PostSubject: Unexplained MPG increase   Mon Jun 02, 2014 10:02 pm

Hello,
I've owned two '97 Rivieras and I've never gotten the high MPG numbers other people report. I typically get about 20-22, with a small increase when spring time comes. Both cars did exactly the same.

In the last few weeks my fuel economy has all of the sudden jumped 5MPG over my previous records, four fill-ups in a row. I am obviously thrilled, but rather annoyed that I can't explain it.

The engine has 160K miles, O2 sensors, plugs and wires are 40K miles old. Air filter is a few months old. Other than oil changes, nothing has been done to it in months.

Any ideas? Thanks.
Mikel
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gunmetalRED
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PostSubject: Re: Unexplained MPG increase   Tue Jun 03, 2014 8:07 am

Have you had a look at the engine compartment? I noticed a significant increase suddenly with my first Riv and it turned out my supercharger belt had broken! It ran fine without it, no Check Engine light or anything, but it was sluggish without those extra 45 horses. I missed them so I fixed it. wink

'Course maybe you're finally getting the MPGs the rest of us get too! Have your driving habits changed? The warmer weather helps too. I get about 25-26 MPG on average and I have seen 30 before. (I've also seen 14 in the winter. Ouch.)
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brutusk1
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PostSubject: Re: Unexplained MPG increase   Tue Jun 03, 2014 4:08 pm

My guess is that for some reason you're getting fuel without the "normal" amount of ethanol in it.

Have you changed fueling stations or has your fueling station changed suppliers ? 10% Ethanol in gasoline causes cars to lose (what I've read) 10 - 15% mpg due to the lower energy density in the alcohol.
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deekster_caddy
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PostSubject: Re: Unexplained MPG increase   Tue Jun 03, 2014 4:19 pm

brutusk1 wrote:
My guess is that for some reason you're getting fuel without the "normal" amount of ethanol in it.

Have you changed fueling stations or has your fueling station changed suppliers ? 10% Ethanol in gasoline causes cars to lose (what I've read) 10 - 15% mpg due to the lower energy density in the alcohol.

x2 - have you started using a new gas station?
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AA
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PostSubject: Re: Unexplained MPG increase   Tue Jun 03, 2014 5:35 pm

Has your driving style or route changed at all? A 5 mpg increase is pretty significant - I'd suspect the driver to be more of a factor than the car or the fuel. Another possibility is a mistake in the fuel log, or an inaccurate fuel pump meter. Rule these out just in case.

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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stan
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PostSubject: Re: Unexplained MPG increase   Tue Jun 03, 2014 5:53 pm

use a Tornado?
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High Chaparral
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PostSubject: Re: Unexplained MPG increase   Tue Jun 03, 2014 8:10 pm

Wish there were more non-ethanol stations around my neck of the woods. Seem to be increasingly rare. Found one (internet) that is 20 miles away. Next time I'm traveling that way will have to try a tankful. Pretty sure it has been quite awhile since any of my cars enjoyed the good stuff ............
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Rivillac
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PostSubject: Re: Unexplained MPG increase   Tue Jun 03, 2014 9:20 pm

High Chaparral wrote:
Wish there were more non-ethanol stations around my neck of the woods. Seem to be increasingly rare. Found one (internet) that is 20 miles away. Next time I'm traveling that way will have to try a tankful. Pretty sure it has been quite awhile since any of my cars enjoyed the good stuff ............

A new station here offers it at the same price. Trouble is, it's 87 octane.
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AA
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PostSubject: Re: Unexplained MPG increase   Wed Jun 04, 2014 3:50 pm

stan wrote:
use a Tornado?

___________________laughat

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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http://www.cardomain.com/ride/657082/4
stan
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PostSubject: Re: Unexplained MPG increase   Wed Jun 04, 2014 4:04 pm

I know....hahaha
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IFallsRon
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PostSubject: Re: Unexplained MPG increase   Thu Jun 05, 2014 6:58 am

Spring MPG increase is pretty normal for me on all vehicles likely due to warmup and different blends.
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rivi95era
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PostSubject: Re: Unexplained MPG increase   Thu Jun 05, 2014 8:40 am

Hey guys this may be a little off topic but I found that lucas makes and ethanol type cleaner for the fuel system. My 97 was quivering at idle and had really poor fuel mileage. Somewhere around 15 mpg or so. Well I was hesitant at first cause nobody could tell me if it was any good but I gotta say after one bottle (not even run through the system completely) has smoothed out my idle and increased my mpg to around 22. Its green so as not to be mistaken for the regular lucas injector cleaner. We have two different gas stations in town that offer premium ethanol free fuel but thats a little too high for my blood, granted my lawn mower gets it, lol ride
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brutusk1
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PostSubject: Re: Unexplained MPG increase   Thu Jun 05, 2014 2:30 pm

rivi95era wrote:
My 97 was quivering at idle and had really poor fuel mileage. Somewhere around 15 mpg or so.ride


That sounds like the effect of dirty injectors and that the "Ethanol Cleaner" is pretty much the same thing as injector cleaner. But it sounds like it worked.

I've got some rebuilt injectors I'm planning to install, but I may try some of that Lucas Ethanol cleaner myself to see if it improves my mpg a bit.
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IFallsRon
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PostSubject: Re: Unexplained MPG increase   Thu Jun 05, 2014 8:07 pm

You'll want to replace fuel filter. My guy says they're a fail center.
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rivi95era
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PostSubject: Re: Unexplained MPG increase   Fri Jun 06, 2014 2:30 pm

brutusk1 wrote:

rivi95era wrote:
My 97 was quivering at idle and had really poor fuel mileage. Somewhere around 15 mpg or so.ride



That sounds like the effect of dirty injectors and that the "Ethanol Cleaner" is pretty much the same thing as injector cleaner. But it sounds like it worked.

I've got some rebuilt injectors I'm planning to install, but I may try some of that Lucas Ethanol cleaner myself to see if it improves my mpg a bit.

I think there may be a little more to it than just an injector cleaner. Ethanol leaves deposits all over the engine. From the fuel pump all the way to the catalytic converter. So I am thinking that it may even be a more potent formula. We have some commercial grade lucas here at the shop and its thicker than what you buy at the auto parts store. Even with the commercial stuff it didn't correct the problem. I could be wrong but this is my theory.
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albertj
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PostSubject: gas mileage   Sun Jun 08, 2014 10:26 pm

Mikel wrote:
Hello,
I've owned two '97 Rivieras and I've never gotten the high MPG numbers other people report. I typically get about 20-22, with a small increase when spring time comes. Both cars did exactly the same.

In the last few weeks my fuel economy has all of the sudden jumped 5MPG over my previous records, four fill-ups in a row. I am obviously thrilled, but rather annoyed that I can't explain it.

The engine has 160K miles, O2 sensors, plugs and wires are 40K miles old. Air filter is a few months old. Other than oil changes, nothing has been done to it in months.

Any ideas? Thanks.
Mikel

might be switch to summer blend gas, or a gas formula change

might be the SC isn't engaged for some reason

might be that tailwind off the ocean or some of that downhill both ways action

might be CT is about to close the interstates again and your car's getting its last licks in

did you switch to synthetic oil?

Albertj
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