Gas Mileage - Page 5
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Page 5 of 6 FirstFirst 1 2 3 4 5 6 LastLast
Results 61 to 75 of 84
Like Tree4Likes
Cadillac STS Forum - 2005 through 2012 Discussion, Gas Mileage in Past Cadillac Vehicle Discussion; How many tanks of fuel for the average? I never base anything on 1 tank of fuel, I prefer no ...
  1. #61
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
    Join Date
    Aug 2004
    Location
    Rockford, IL
    Age
    47
    Posts
    7,490

    Re: Gas Mileage

    How many tanks of fuel for the average? I never base anything on 1 tank of fuel, I prefer no LESS than 6 tanks to determine an average, 18 is preferred.

    Things I have learned over the years of high mileage driving that affect mpg (based on my 94 Fleetwood with LT1 and V4P Tow Package):

    Most affect:
    Ambient Temp (1-1.5 mpg)
    Driving Style (keep speed limited to 65 mph on highway no matter what has big effect)
    2nd gear starts (this also sorta forces easier take offs)
    Cruise control

    Moderate affect:
    87 vs 93 octane. Difference was in city mpg more than highway. Note this is a 10:1 iron headed LT1 that is designed for 87 octane.

    Least affect:
    10% ethanol (0.15 mpg loss over 20 tanks of fuel)
    Mech fan vs Electric fan (no change)
    Weight of oil (15W40 vs 10W30 vs 5W30 vs 0W30) I would expect less impact on mpg with thinner oils in cold temps and more city only driving where the oil never gets fully warmed up.
    Adding Acetone to fuel (did slightly hurt mpg)

    Notes: I would cold start and take off to 30 mph within 1 min in most any weather and within 1 mile was up to 65 mph, and then within 4 miles up to 75 mph. Very consistent on my daily commute (drive was 65 miles each way), combined city/highway with 26 opportunities to stop on the drive. The last 10 miles to work was awful, upwards 60 mph and then stop lights, a real rat race commute in moderate to heavy traffic.

    I have posted my results in the RWD forum with putting my results in MiniTab and analyzing the test runs (see above) and have a much more accurate idea on what works and what doesn't.

    I did testing on E85 as well, my mpg dropped around 15-20% on average, and temp greatly affected mpg on E85. Colder, mpg really falls off. For considering 50% more fuel needed for Stoich, only losing 20% at the time made E85 a bargain, but costs on E85 now are ludicrous and I don't recommend at all. If you aren't saving at LEAST $0.60 a gallon at the pump, it isn't even worth considering. Note, power was up on E85, the higher the compression the more power and less mpg loss.

    Quote Originally Posted by jmildoc View Post
    I switched to 89 octane and my MPG went down 1.6 mpg?!?!?!

  2. #62
    cadillacmike68's Avatar
    cadillacmike68 is offline Cadillac Owners Connoisseur
    Automobile(s): 68 DVC, 96 FLTWD Brg, 09 STS N* Platinum, 11 CTS Premium
    Join Date
    Jan 2005
    Location
    Left the desert - Back in FL
    Age
    53
    Posts
    1,030

    Re: Gas Mileage

    Hey NODIH,

    What was the mpg impact on 93 vs 87 fuel? 0.5 MPG? As you noted, Fleetwoods were designed to run on 87 Octane, and that's what i use most of the time in mine (both the long gone 1995 and the current 1996).

    And everyone, cruise has probably the greatest impact besides keeping it below 65MPH. You simply cannot regulate the fuel / speed like the comperized cruise control can, same as with ABS.

    I got 20.9 avg MPG on 78.9 agv MPH the other night going from Tampa to Orlando. That only holds when you are on the interstate. if my ACC was working correctly it would likely have been higher.

    I'm surpised Hess isn't a top tier fuel. I like their gas and my cars seem to like it as well.

  3. #63
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
    Join Date
    Aug 2004
    Location
    Rockford, IL
    Age
    47
    Posts
    7,490

    Re: Gas Mileage

    In the FW I was getting 19-19.5 city/highway (long stretches of each) and the city mpg seemed to come up around 0.5 to 1 mpg. Not enough to justify the cost of it really. It helps, but not worth it. This was with some PCM tuning on the LT1 too, not stone stock tune.

    I use only top tier fuels unless I absolutely can't get to one, then usually BP or Mobil. No off brand unless desperate. I had a BAD experience with Citgo station and bad gas once, won't do that station again.

  4. #64
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
    Automobile(s): 2006 STS4 V8 1SG & 2007 STS V8 1SE
    Join Date
    Jun 2008
    Location
    Cedarburg, WI
    Age
    56
    Posts
    7,230

    Re: Gas Mileage

    Given a price differential of about 5% ($0.20 more for premium @ $4/gal?) it doesn't take much improvement to make it worthwhile. I'm talking 1 MPG!

    As the price goes up, the break-even is even less!

  5. #65
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
    Automobile(s): 05 STS AWD 1SG
    Join Date
    Apr 2009
    Location
    Fishers, Indiana, USA
    Posts
    469
    Quote Originally Posted by jmildoc

    I hope my mpg stays the same with my new wheels. I got the 17's on now
    Someone at a tire shop said today that my gas mileage is also suffering because I have P235/50/18's all way round, and my door jam says I should have different ones in the back. And that I'm hurting the entire drivetrain like this.

  6. #66
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
    Automobile(s): 2006 STS4 V8 1SG & 2007 STS V8 1SE
    Join Date
    Jun 2008
    Location
    Cedarburg, WI
    Age
    56
    Posts
    7,230

    Re: Gas Mileage

    I doubt your hurting anything. That's what I'm running. They ride better & quieter than OEM.

    The OEM front & back are virtually identical circumfrance. Besides, its an open differential with traction control provided F1-style via automatic control over braking.

  7. #67
    ddalder's Avatar
    ddalder is offline Cadillac Owners Connoisseur
    Automobile(s): 2008 STS-4 N* 1SG
    Join Date
    Aug 2008
    Location
    Canada
    Posts
    1,878

    Re: Gas Mileage

    Quote Originally Posted by maiahsdad View Post
    Someone at a tire shop said today that my gas mileage is also suffering because I have P235/50/18's all way round, and my door jam says I should have different ones in the back. And that I'm hurting the entire drivetrain like this.
    I think someone at that tire shop needs to do the math. While it's true GM put different sized tires on the front and rear (keeping in mind this concern was raised because of your AWD), the more important part to this is overall outside diameter. By having P235/50R18's on the back, instead of the OE spec P255/45R18's there is an overall diameter difference of 0.21" or 5.5mm between yours and what's recommended. Honestly, variances in inflation pressures between tires could likely cause just as much or more of a difference. Even having worn tires on the front and new ones on the rear could have just as much of an effect front to rear. Your tires in the rear aren't quite as wide as what OE spec indicates but there's nothing that will cause you any grief. Just make sure you keep all your tires inflated properly.

  8. #68
    cadillacmike68's Avatar
    cadillacmike68 is offline Cadillac Owners Connoisseur
    Automobile(s): 68 DVC, 96 FLTWD Brg, 09 STS N* Platinum, 11 CTS Premium
    Join Date
    Jan 2005
    Location
    Left the desert - Back in FL
    Age
    53
    Posts
    1,030

    Re: Gas Mileage

    Quote Originally Posted by ddalder View Post
    I think someone at that tire shop needs to do the math. While it's true GM put different sized tires on the front and rear (keeping in mind this concern was raised because of your AWD), the more important part to this is overall outside diameter. By having P235/50R18's on the back, instead of the OE spec P255/45R18's there is an overall diameter difference of 0.21" or 5.5mm between yours and what's recommended. Honestly, variances in inflation pressures between tires could likely cause just as much or more of a difference. Even having worn tires on the front and new ones on the rear could have just as much of an effect front to rear. Your tires in the rear aren't quite as wide as what OE spec indicates but there's nothing that will cause you any grief. Just make sure you keep all your tires inflated properly.
    That difference is less than the range of wear on a set of tires! most tires have a "safe" range of 2/32 thru 12/32.

    Plus your tire shop has it backwards. all other things being equal, if you have narrower rear tires, they will have LESS rolling resistance translating into higher MPG.

  9. #69
    CadillacSevilleSTS is offline Cadillac Owners Fanatic
    Automobile(s): 2000 Seville STS
    Join Date
    Jul 2011
    Posts
    217

    Re: Gas Mileage

    Quote Originally Posted by cadillacmike68 View Post
    That difference is less than the range of wear on a set of tires! most tires have a "safe" range of 2/32 thru 12/32.

    Plus your tire shop has it backwards. all other things being equal, if you have narrower rear tires, they will have LESS rolling resistance translating into higher MPG.
    Actually, the width of a tire has little effect on rolling resistance. The main factor in rolling resistance is loss of energy due to deformation of the tire. In fact, in many cases wider tires can have less rolling resistance because they have less flex in the sidewall. Wikipedia has a great article on this subject.
    http://en.wikipedia.org/wiki/Rolling...ibute_in_tires

    ----------

    Interestingly, tires with less tread life will generally result in higher MPG as long as they aren't so bald as they are able to consistently slip and lose traction. It also again comes down to less tread results in less deformation of the tire.

  10. #70
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
    Automobile(s): 05 STS AWD 1SG
    Join Date
    Apr 2009
    Location
    Fishers, Indiana, USA
    Posts
    469
    Well, got 250 miles out of this tank.

  11. #71
    C&C's Avatar
    C&C
    C&C is offline Cadillac Owners Connoisseur
    Automobile(s): Cadillac STS (2011)
    Join Date
    Feb 2008
    Location
    Mount Pleasant, SC
    Age
    63
    Posts
    1,570

    Re: Gas Mileage

    Quote Originally Posted by maiahsdad View Post
    Well, got 250 miles out of this tank.
    So, how many gallons did you need to fill-up; that's the whole equation.

  12. #72
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
    Automobile(s): 05 STS AWD 1SG
    Join Date
    Apr 2009
    Location
    Fishers, Indiana, USA
    Posts
    469
    Quote Originally Posted by C&C
    So, how many gallons did you need to fill-up; that's the whole equation.
    15,4

  13. #73
    malatu's Avatar
    malatu is offline Cadillac Owners Connoisseur
    Automobile(s): 2006 STS 3.6 AWD
    Join Date
    Dec 2005
    Posts
    1,005

    Re: Gas Mileage

    Quote Originally Posted by maiahsdad View Post
    15,4
    Ok then, so then:

    250 miles divided by 15.4 gallons is 16.2 miles per gallon.

    or another way of writing it is:

    250 mi/15.4 gal = 16.2 mi/gal

    Miles per tank really doesn't say anything, comparatively speaking.
    mckellyb and mckellyb like this.

  14. #74
    jmildoc's Avatar
    jmildoc is offline Cadillac Owners Fanatic
    Automobile(s): 01 Deville
    Join Date
    Jan 2012
    Location
    Indiana
    Posts
    138
    I get better MPG on regular than I do plus or super.

  15. #75
    mckellyb is offline Cadillac Owners Enthusiast
    Automobile(s): 2005 STS N*, 1SF, 123K mi.
    Join Date
    Apr 2011
    Location
    Fort Worth
    Posts
    537

    Re: Gas Mileage

    I experimented with several tanks of 87 vs. 93. No difference in performance or MPG I could detect. I didn't expect to feel a difference in performance. Anything less than 10% on a car of this power, isn't going to be felt by anyone other than maybe a professional test driver.

    My MPG varies little, because my drive varies little. The car is used almost exclusively for commuting, and my commute could not be any less variable.

    Per calculations based on the trip odo and pump gallons...the DIC reads both high and has variance...I get 21.2-21.5. The difference could be oneparticularly bad day of traffic or I stomped on it a couple of times, letting that Northstar wail. Well, occasionally, I'll be lucky and catch a few lights in a row green.

    Tire width plays a part in MPG, as does, believe it or not, tread patterns. On these cars, you're never going to see a difference of 20mm in width. That's less than an inch per tire. Meh.

    Now, if you put 155/85/16's on it, you might see MPG go up one or two, but you'd hate yourself for trying it out.

    One thing people can do to increase MPG is to look ahead. Yes, I'm yelling.

    Watch for traffic changes, lights with an old green or turning yellow/already read, et cetera. Most people can increase their MPG a solid 20% just by backing off, and not always having one pedal in use. The car and associated wear items last longer, passengers have a smoother ride, and you spend less money.
    malatu and malatu like this.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting