IcemanG17

On the way to the track yesterday I drove 120 miles at a leisurely 70-80mph pace with the headlights up for maybe 90 miles....I got to the gas station and filled up....my mileage was 17.2mpg...which seems LOW for easy cruising at such slow speeds..... Does having the headlights up hurt the mileage that much?

I have noticed that my mileage hasn't been that good....BUT my mileage on the track seemed quite good....I got an hour on the track for under 1/2 a tank (3 20 minute sessions?) then made it home on the same tank that I would guess has used 15 gallons total at 185 miles (including 60 miles on the track)???

If my car has smog problems next week due to high HC then I'll think the O2 sensor is dying causing a rich condition...but sharky sure runs well??

bigmac

I suspect that there is a moderate drag. Chaad told me that he could only do 163mph with lights up in his 88 which should do 171 as per the add in 1987.

dr bob

In the way back when, we determined that mirrors and windshield wipers just mounted on the car cost between 1 and 2 MPG. Roof rack on my Explorer cost almost 2 at freeway cruise speeds. Add skis to that and chew off another 1.5. It wouldn't surprise me if 928 headlights cost 1-2 MPG at 80. I suspect that a flush-fit cover over the retracted lamps would improve 0.5 or better too. Cd on the 928 is less than stellar, although some of that is sacrificed for less lift at speed. I had a 'new' ME working for me who bragged that the drag on his new Miata was so much better than my 'old' Dino Spyder. Had to explain the 'costs' of stability at speeds his Miata would never see.

Premium gas is well over $4 a gallon here this week. I was in NJ last week, where there was crying when regular went too $3.20/gal. K was searching last evening for the lowest cost station to fill her SUV, and found one that was $0.08 less than the one by our house. Saved a whopping $1.70 on the $85 fillup.

Want to save money on gas? Stop driving. So far, none of the people in front of me seem to understand that advice.

9two8

......,$4 dollars a gallon !! here in England we are paying approx £5-50 a gallon,... which is roughly $10 to $11 us dollars,......think your very lucky !!!

hitbyastick

Honestly 9two8. How would that possibly cheer anybody up?
In all seriousness, having lived in Germany and dealing with those gas prices for about two years, I can just say it is different here. In Germany, basically everywhere I ever needed to be was within say ... 5 miles of each other, and I did not live in a major city. Public transportation is also really great throughout europe.

Now fast forward to me moving to California. What a shock! Everything is super far apart. I drive 34 miles one way to work. That was almost unheard of in Germany. Then my school is another 20 minutes by car. Could I take the bus? Actually to get to work with public transportation would take me the better part of a day! Could I move closer to work? Probably but my college would then be about 30 something miles away too.

Don't get me wrong I absolutely feel your pain on the gas prices, and it's just going to get worse.

928SS

it's the shock of it all for us in the US - a 200% increase in fuel prices since our beloved dubya took "control" has put us into an energy fueled inflationary period that has put many sectors into a recession. it'll take a while for us to adapt, readjust everything.

guess my little AX habit is gonna cost more now.... I used to think the $40.00 entry fee and tires were the biggest costs. looks like fuel is going to eclipse them both.

our food bill for 3 has jumped from $500/mo to almost $1000/mo and we haven't started a caviar, lobster and champaign diet by any means.

it's gonna get worse before it gets better.

PorKen

Back when I was 'Cadillac Ken', I found I got about 2 mpg less with the top down on my '76 Eldorado convertible.

13 instead of 15 hwy.


Not mine but it looked like this one. 500ci/8.2L. FWD. All wheel disc brakes.
(D-Jet fuel injection was an option.)

mark kibort

you can ball park this by doing a little test or guess. what do you think the drag is of the lights? say its 5lbs for both of them, then thats near 5hp at near 100mph, and 5ftlbs of torque at 100mph. take the HP of what you think you need at 100mph and get a percentage of the total HP. that would be the drop in efficiency. ball park i know, but i would think at 50hp, and 5hp to drive the lights, thats a 10% loss in fuel economy

There was a test i did many years ago following a Semi truck, that was proved on Myth busters. following a truck, you can get near 20% better fuel economy. Its a range, i know, depending on how close you tailgate. a car length or so, gives some pretty impressive results.

mk

erwalker

In Grand Forks, ND mid-grade is around the $3.50/gallon mark - Here in Winnipeg, Canada (120 miles north of Grand Forks) we are paying $1.30/liter or about $4.92/U.S. gallon - and the gas in Grand Forks is shipped by the tanker full out of Winnipeg! Figure that one out! Almost worthwhile to make the trip across the border to fillup. Maybe if I drop the headlights, I'll save enough gas to make the trip worth it.

Supposedly the difference are taxes that are collected to "maintain" our roads but few Manitoba roads are capable of handling 140 mph in a 928 - ND/MN highways are like glass in comparison.

Just my 2 cents worth!

nosnow

Could it be your last tank of gas was that special CA summer blend which will easily knock 5mpg off?

SteveG

I tried drafting in a mini van and the buffeting was tedious, I mean it was work. There was a lot of wind that day.

ew928

That's it.
I'm calling Porken, Cadillac Ken.

I'm not comfortable drafting tractor trailers too closely. Great for mpg but you cannot see the road conditions. Potholes they just drive over can wipe out 1/2 a 928.

IcemanG17

One other possibility I found out today is a less than ideal wheel bearing or dragging brakes...my drivers side wheel does not spin as freely as the passenger side?? It not that sticky but spins maybe 40% less for the same effort in "spinning" it....which also might be correlated to my odd non existent brake pad wear on the inside brake pad too?

I have noticed a drop in fuel economy over the past year or so.....I thought it was just too much BWAAH..but maybe there is something else adding to it?

mark kibort

I think you need to draft a semi. on a long trip, if fuel economy is a goal, this can be done pretty easily. (only problem, you might have to only drive 65! )

there were substantial gains at 2 car lengths too (based on the controlled tests)

mk

928SS

drafting should do wonders to the paint on the front end too... I wonder if the cost savings would cover a paint job if enough miles are covered...

brian - a ton of stuff affects mileage - tires type/inflation, drive train, a vacume leak, failing accessories, plugs, wires, injectors, etc, etc...

might start w/an engine analysis on a sharktuner or hammer, do an oil analysis (blackstone is pretty good), even a sniffer test might give a clue.

then go through the drive liine/brakes, alignment, change and ck all fluids, etc. even a heavy electrical load can affect mileage, so ck for that too.

should keep you busy for a weekend or two