My kid has the 240 now, and came to visit this weekend. This morning, he drove back to Santa Barbara. His mileage report:

From King City to Santa Barbara I did a test. I tried to keep the speedometer precisely at 60 -- but my speedo is fast, so I think it was really about 55mph. Anyway, flat, long stretches, and I made an extreme effort to avoid accelerating or decelerating. It was a test. Empty car, no wind, no a/c, 55mph, and basically no acceleration: back home the car took only 4-point-something gallons. I calculated 43 mpg. I shit you not. In my '88 volvo.
--
David Brick, Santa Cruz CA, 1988 245

I did a similar experiment in my '92 745. Got 34.47 on a 200-mile highway trip. Unloaded anything unnecessary from the car, drove without A/C, and checked tire pressures before I left. Forced myself never to break 65 mph. It can be done!

Thanks for sharing!

Guid
--
Guid ('92 745 257k, '91 940 SE 278k,)

For accuracy's sake you have to record the number of gallons at each fill up and in your case - you will probably have to borrow someone's GPS to figure out the miles travelled. Sounds like you have a flaky speedometer to me but you can verify that by comparing it to what the GPS reads.

I surely didn't expect all this scrutiny :) I'll show my math next time.

Here's the map of the trip, though: not much controversy on the actual distance.

http://tinyurl.com/3mpwrou

HA haha. sorry for the third degree. I feel that as a community of enthusiasts we are all insanely jealous of your mpg! The mpg figure is the most tangible mean of assesing the condition of a twenty+ year old daily driver and should be taken very seriously!!!!

It's fine :) Given the whole discussion, I'm rather skeptical of what I calculated. Undeniably though, the brick is running great, and whatever the verifiable and replicable mpg is, I'll likely be quite pleased.

i commute about 100 miles everyday in my 1985 aw70 240 I drive really slow, sometimes 55 but usually about 62, my car with the a/c gets 22.9 last fill up, iam jealous of your good miles per gallon!

Simply impossible. Redo the experiment and math for proof.

jorrell
--
92 245 315K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

I suspect the odometer reading and gas pump cut-off adjustment more than the math.

It does seem unbelievable. And if it looks like bear shit, and smells like bear shit... so for logic's sake, I agree.

I will do another experiment using the same gas station and posting the math, next time I go somewhere. I tend to avoid long drives.

That could be the case, if so that's great! One problem though is that when you fill up at different pumps, your readings can change. Your fuel tank can hold quite a bit more fuel than what most pumps will allow. It's best to check your fuel economy by filling up at the same pump, same time of day, same temp, etc. to get the most accurate reading. And if your ODO is over-reading it's going to also make it look more "economical" since you're logging more miles than actually travelled.

The best I have gotten yet on my new engine and AW71L lockup trans is 30MPG and that came from cruising at about 65MPH steady on a long trip. I usually cruise at about 60MPH on my short highway trips around here and pull about 28MPG now. I thought I was hitting some kind of sweet spot going a bit faster, but you've got me doubting now. I'll do a slow cruise this weekend and see what I come up with.

Steve

That makes sense; I identified some of those variables but couldn't control for them. As far as I can tell, the speedometer is mis-calibrated but the odometer is accurate.

From the various trips I've taken, the most important variable by far is speed. 55mph seems golden for mileage.

Well, 55MPH was supposed to be the magic number for everybody after the 70's fuel crisis in this country. I think that's why they made all the highway speed limits 55MPH after that.

I also have a Ford Focus DOHC that I always drove at 72MPH and couldn't get over 27MPG. One time I drove it 60MPH (while also overloaded with boxes) and I got about 33MPG. After I adjusted my driving habits to 62MPH, I was consistently getting 36-38MPG on long trips and 34-35MPG on my daily commute to work. I figured that was costing me about 3-4 minutes each trip but was also putting $450 back in my pocket - time well spent!

Nice optimization. As another benefit, I find the slow lane way more serene. If the trip is measured in pain, and pain/time is relevant, than slow trips with low pain/hour can end up being overall less painful.

Yes, very true!!! A long trip in the right lane is so much more relaxing! When you cruise over 70MPH, you're constantly having to change lanes and pass guys like us :) High stress & you arrive at your destination tired and pissed off. Also, you have to constantly adjust your speed up and down when doing that. I'm glad I've disciplined my lead foot.

That's me to a tee. I plant my Volvo butt in the right lane, put the cruise control at 55 MPH and watch everyone else pass me by while I relax and enjoy the ride...and the mileage. One time while interstate driving, my 1984 244 with 300,000+ miles got 33 MPG.

It averages in the upper 20s in mixed driving during the summer, and in the mid 20s in the winter. Unfortunately it needs premium fuel, otherwise it would ping like crazy, so there's not much of a cost-savings for me. But I'm happy knowing that it's an efficient little machine.
--
Mike F - 1984 244 DL - 316,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15

Actually, if you think about it, these are the best days to be buying premium fuel (in terms of cost to value). Usually, it's 10 cents more per gallon for 89 octane and then another 10 cents more for 91 octane (around here at least). It's always been a 10c jump to go to the next higher grade, even when 87 octane was going for $1.12/gal. So look at it this way:

early 1990's gas prices:
- $1.12 for 87oct
- $1.22 for 89oct (costs 8.9% more than 87oct)
- $1.32 for 91oct (costs 17.8% more than 87oct)

today's gas prices:
- $3.64 for 87oct
- $3.74 for 89oct (costs 2.7% more than 87oct)
- $3.84 for 91oct (costs 5.5% more than 87oct)

Many times you'll get better economy on the higher octane stuff too. So in the early 90's, it was harder to justify buying better gas just to get a better fuel burn rate, but today it can easily pay for itself.

Steve

I never thought of it as a percentage comparison to the relatively higher overall cost of fuel compared to yesteryear.

I always thought that premium fuel burns more efficiently than regular, but I've seen discussions all over the Interweb - including on this site if memory serves - that premium fuel is a complete waste of money. And people who feel that way are quite passionate about it. But if that were the case, why is it still being sold? It must have some benefit or else the refineries wouldn't waste their time and money making it. All I know is both my 240 and my wife's old Corolla run much better on premium, so I'm sticking with it. I may start putting it in my old 142 as well and see if it's fuel economy improves.
--
Mike F - 1984 244 DL - 316,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15

Higher octane is a waste of money when you're talking about an engine that is tuned for low octane - an extreme case of this would be a lawnmower (low compression & retarded timing). Generally, most cars are tuned for 87oct but I don't think the fuel pumps deliver 87oct all the time. Your knock sensor adjusts for this and retards timing on the fly so you don't know any differently. The only way you will know this is happening is if you're measuring fuel economy every time you fill up. That's why you have noticed it - because you've been diligent about checking! Some cars have higher compression and advanced ignition and REQUIRE higher octane. My mom has a Lincoln LS 6-cyl that requires 89oct minimum but the manual says you can use 87oct. She usually fills up with 87oct and she gets 15MPG. She refuses to spend a penny more to even try using the higher octane stuff. She will probably get at least 20% better economy if she can bring herself to invest 5% more up front at the pump

Higher octane is a pretty hard sell these days for most people whose cars don't require it. Most cars will tolerate 87oct without bad behavior. Now it used to be that some carburetted cars would buck and kick and knock and diesel every time you punished them with cheap gas. Owners of these cars saw the instant rewards of using better gas so they went to the big name gas stations and bought the higher octane stuff. I'm guessing that's why the percent difference was higher in those days - because of greater demand by the general public.

So here's my mom's Lincoln as an example:

Let's say it gets 15mpg on 87oct, but it gets 18mpg on 91oct. To go a distance of 270mi, it will take:
- 18gal of 87oct priced at $3.60/gal = $64.80
OR
- 15gal of 91oct priced at $3.80/gal = $57.00

Actually, I just looked in my 1990 240 owner's manual and it DOES recommend using 91oct, but minimum allowable is 87oct. Wow! I thought it was 87oct!!!

Steve

The b230f was, as far as I know, always tuned for 91 octane, thus the recommendation of using that grade fuel in the manual. My own vehicle gets 2-3 more miles per gallon with premium than with 87. SO:

Let's say I pay $3.50 per gallon for 87 octane, and 91 octane is a quarter more, so $3.75 per gallon. I get an average of 20mpg around town with 87 octane, and about 23mpg with 91.

87 octane: $3.50 per gallon / 20mpg = $0.175 per mile.
91 octane: $3.75 per gallon / 23mpg = $0.163 per mile.

(BTW, using these numbers, 91 octane would have to cost more than $0.50 greater than 87 oct. before you would no longer see a monetary benefit)

Meaning that 91 octane is saving me money. Further, premium gas usually contains more detergent additives to clean off the ol' valves. Which is why some gas companies claim that using their premium gas will clean up your engine and improve mileage - it may not, but it will certainly help keep things cleaner and prevent performance from deteriorating due to buildup.

Just my $0.02 (which I saved on gas).

"Actually, I just looked in my 1990 240 owner's manual and it DOES recommend using 91oct, but minimum allowable is 87oct. Wow! I thought it was 87oct!!!"

Which calculation method? Makes a 2-3 pt difference if I remember correctly between RON and (R+M)/2.

Mike

I was referring to the (R+M)/2 method... that's pretty much the standard in the U.S.

Right, but every mid-70's and later Euro car, until they focused on developing their cars for the US market, quotes RON in their manuals and they makes a passing reference to "pump octane" or (R+M)/2. I do not know when Volvo changed, but their '86 manual does this. This is often what causes the discussions/arguments.

Either way, as our cars age the resistance to knock can change for a number of reasons often making the higher octane fuel produce better fuel economy due to less intrusion by the knock sensor related ignition timing adjustments.

As an example, my commute is the same every week and consumes about 10 gal of fuel. Over eight weeks of testing various fuels, that car gets exactly the same mileage plus or minus about .5 mpg.

Ont he highway I may find different results but I rarely drive this car beyond the commute.

Mike

As I thought...from an 1986 owners manual online:

"Octane Rating
Volvo engines require unleaded gasoline with an (R+M)/2 octane rating (also called the Anti Knock Index, or AKI) of 87 or higher. This is generally equivalent to a Research Octane Number (RON) of 91 or higher."

US pumps are rated in (R+M)/2...European pumps are rated in RON.

Mike

15 MPG?! With today's technology, there's no reason why any passenger vehicle should get less than 20 MPG. My tank uses almost 30-year-old technology and gets better mileage than that, even with with over 300,000 miles on the clock.
--
Mike F - 1984 244 DL - 316,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15

Yeah, mom's Lincoln only makes it 15 miles on one gallon of 87oct. For that kind of waste, it should have been a V8 but it's only the 6cyl. Now this is a car that has probably never run 91oct, has never been over 45mph, and has only 23k miles on it after 11yrs. So that all probably explains a lot. But, it runs smooth and has lots of power (thank God for electronic fuel injection).

I can recall one 1985 Dodge van (w/318ci V8 and 727) we had when I was working at an aircraft overhaul facility that we used exclusively to transport panels to our offload shop across the street. This was in 1999, so the thing was 14y/o and it had just under 6000 miles on the ODO. It was carburetted and it absolutely would not get out of its own way. We couldn't even get it fast enough to get out of 2nd gear when we did try to drive it down the street! Now THAT is carboned up! :) Kind of makes me wonder if it made it to 12k miles & if someone decided to make up a 10,000 mile "high mileage" badge for it.

Steve

That's me. I could have also mentioned I pumped the tires to the recommended 36 and keep the car in excellent running shape.