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Fuel mileage results - as promised several weeks ago.
Well, OK, this is not a scientific test. But I think it's more sound than some of the "I get about x mpg" statements I've heard on occasion.
I wanted to test for any difference in mpg when using 87, 89, and 93 octane gas. Why? Commuting about 160 mi. total every workday, I spend a bit of money on gas. And, I think, it puts me in a position to measure fuel economy.
Basic informtation:
'89 Volvo 245, 4-cyl, non-Turbo, auto tranny
Tires: 195-75-14 on steel wheels, cold pressure about 34-35 psi.
No roof rack, no roof holes (less air drag)
15W-40 dino oil. (Soon switching to 10W-30 dino)
My plan was to drive a week or more on each octane rating, noting the miles from my trip odometer and gas consumption from the fuel pump at every fill-up. I did my best to keep everything else the same, changing only the octane. I was mostly successful at being consistent. Details after the numbers below.
87 octane - 1716.1 mi. - 69.4 gal - 24.7 mpg
89 octane - 1666.6 mi. - 64.2 gal - 25.95 mpg
93 octane - 1160.8 mi. - 46.2 gal - 25.1 mpg
I used 87 octane gas first, then 93 (after several days driving in between to get all the lower-octane fuel out of the tank), and lastly 89, again after a few days changeover period.
I drove the same route most every day: 98% highway on the way to work, and about 80% highway coming home. I did continue the test on weekends, but they included no extremes of heavy city drives or long highway trips.
After running the 87 octane test, I removed the heated-air damper from the air intake box. This caused no change to intake air temperature as the metal hose to the exhaust manifold was removed some time ago. My intent was to eliminate any restriction to the air path in the box. As most of my driving is highway, at fairly steady speeds, I don't think this affected fuel economy one way or the other.
About 400 miles into the 1666-mi. run of 89 octane, I did a tuneup - new plugs (Bosch Platinum), Bosch cap and rotor. I just couldn't stand to let it go any longer; the previous tuneup (same parts selected) was 30K miles ago in September '04. I'm sure that this improved the results of the 89 octane test. Shoulda done this before I started!!
Why lower mpgs with the 93 octane than with 89??
Two contributing factors:
1) I did the tuneup during the early stages of the 89-octane test, after the 93.
2) Having 93 octane tempts the driver. The car definitely ran stronger than on the previous 87 octane, so I think I did use a heavier "foot" during that test. You pay for that at the fuel pump.
What are the effects of higher/lower octanes? One mechanic explained to me that the knock sensor causes the computer to retard the timing when it detects knock. I used to adjust timing with a dwell tach while manually turning the distributor (not on Volvos). You could easily hear the rpm's drop as you retarded the timing. I think that anything that retards timing will reduce power AND fuel economy at that moment, assuming all other things being equal. Anyway, with 87 octane, if you step hard on the pedal, relatively little happens. With 89 or higher octane, the engine rewards you better when you step on the pedal. That's what my backside reports, anyway.
Some of you must be wondering why I've been using 15W-40 oil. Several of the best local Volvo gurus told me to use it year 'round, quite a few years ago. It's served us well, "Sophie" is now nearly up to 400K miles, but mostly retired. Needs a water pump and the new owner hasn't the money, but that's another story. I read (and recommend) a detailed discussion of motor oil at htp://www.lincolnsonline.com/article105.html
which has convinced me to try a thinner oil with a slightly narrower viscosity range.
If there's any discussion on this, and if anyone seems to care, I might post my calculating spreadsheets where you can see them. Excel files.
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I thought it was interesting your mileage was very close to mine. What I wondered, was if the higher octane's price difference, usually about a dime around here, was offset by the economy. I was surprised after doing a quick calculation to find that some of the folks reported on the TV news to be visiting our area for 15-cent cheaper fuel were actually saving money on an average 15-gal. fillup, even driving 30 miles to do so. Well marginally anyway, not to include time, and cost of operating.
There's a routine I stick to at the gas pump-- I try to set an example for my kids and so forth, but they go their own way: I pop the hood, start the pump, then check the oil, coolant and look things over while the pump is running. When I hear it stop, I close the hood, put the nozzle back on the pump, complete the transaction and reset the trip odometer. No extra clicks or top-offs. I write the odometer readings on the receipt. Always.
I would pull the slips out of my wallet and put the numbers into a spreadsheet, but I fell out of that habit a few years ago. However, in '02 I posted this chart at the tail end of a year's fillups of 87 octane into my 84 B23F auto sedan - most of it under 55 commuting.
The trend was gradual improvement, but the largest effect seemed to be the "winter mix" fuel. Some of the highway trips would blip the curve upward briefly, but over 118 fillings, it all gets pretty smooth within a few tenths of a mile-per-gallon.
--
Art Benstein near Baltimore
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Nice work!
I can't detect the dates on the chart as shown - is the dip in mpg during the winter months? I got about 21-22 mpg avg in New England this past year, with 4 snow tires and 15-40 oil. Next winter, 10-30!
I find it interesting that the price differences between octanes sold seems to always be just about 10 cents/gallon.
As price of gas goes up, we consumers become more concerned about cost and might buy the less expensive octane.
However, as a percentage of the total cost of fuel, the cost of the increased octane is going down as the price per gallon goes up. At somewhat over $2/gallon here now, the extra dime for 89 octane is less than 5%, and the extra dime (usually) for 92/93 octane is even more of a bargain per increase in octane, since it's a jump of 3 or 4 points.
My wife asked immediately if I'd calculated whether the extra cost was worth it. I haven't gotten to that yet, primarily because I need more testing with the new plugs, and with 10-30 oil to get apples-to-apples results. But I do know tghat I don't like driving on 87 octane any more. It's a much better car on 89!
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Around here, many gas stations have a 10 cent difference between 87 and 89 AKI gas, and the 91 is another 12-20 cents per gallon more.
--
alex
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Good to read all your comments - thanks!
I expect to keep documenting my results.
Won't post every day, of course.
I definitely need to retest all octanes with the recent tuneup and "new" 10W-30 dino oil.
Am considering switching over to standard Bosch plugs based on posts I saw here.
It definitely feels better driving with anything but 87 octane, that's for certain.
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Thanks for the information! Interested in seeing the new mpg #s particularly for 87 octane, post tune-up, etc. Suggest perhaps, a shorter retest would be statistically valid, say 500-1000 miles or so per octane with no changes during actual testing period.
Thanks again
--
dnvolvo '89 765T 200K - '91 245 100K
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Just had to chime in on this one.
I get better performance from 89 than 87, but nothing I can notice when I jump from 89 to 93, except the cost. My mileage is affected by tune-up more than anything else, tuning things up has made the difference between 25 and 29 on an M47 wagon.
Spark plugs... I've tried Bosch Copper, NGK Copper, and Bosch Platinum. My personal favorite is NGK Copper and I keep around a slightly used set of Bosch Copper as back-ups. I'm glad to hear someone has had success with the Platinums, my experience with them has been inconsistent.
FWIW-My opinions on my own car don't come from any controlled study, just the information I get over time from my ears and the seat of my pants, very much subject to my own personality. Talk about inconsistent :)
--
Jim - '92 Red 245 191K, and sometimes an '85 245 275K
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The oil stuff is a total crock - keep doing what you're doing.
Car don't care, and you shouldn't either.
A 240 needs to have *oil* in it - clean and new matters, but it doesn't matter what it is, what bottle it came in, how much you paid for it, what the commercial says, what your neighbour says, what I or anyone else says.
Bottom line - it won't affect mileage - that's a prediction. If it would, you'd already know about it and we'd all be doing it.
--
Stef (81 245 B21A SU M46 3.91) 325000km my volvo pages
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Easy, there.
Early results from 10-30 indicate a n improvement in mpgs.
But that's from just one fillup, about 150 mi.
Details when I have more data.
The logic to the thinner oil is that the pump system has to work harder to pump the thicker stuff. Also, a narrower viscosity spread means more actual oil and less additives (they create the viscosity spread), so you end up with more/better lubrication. 15-40 spread = 25, 10-30 spread = 20.
The only viscosity that counts over the long haul distance is the higher number, effective at operating temp. The lower # is only "active" during startup/warmup, where admittedly it can be critical.
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lubrication will be adequate anyway, but are we talking lubrication or fuel consumption?
New oil does the best job of lubricating; fuel economy difference won't be noticeable with any kind of engine oil, everything else being the same.
Oil thickness is very unlikely to be the single variable you control.
--
Stef (81 245 B21A SU M46 3.91) 325000km my volvo pages
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You wrote "Oil thickness is very unlikely to be the single variable you control"
and I think you're probably right on that.
We'll see what mpgs I come up with after a week or so on the thinner oil.
My thinking is that over a week's time, most changes in driving style, traffic load, mood, weather, whatever, should probably average themselves out pretty well. We could discuss till after the cows come home how precise this all is, and we know it's not very precise, but I'm going to see what I come up with.
If I can make one or two choices in what I put into the car that are just a little bit smarter or more economical than what I've been doing, I might be able to save $5 or $10 over the week, and that would be a good thing!
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Thanks for the post.
I do 50km a day, highway at 80km/hr (I always take it easy), and looked at 94/87 octane results.
Car is a little more powerful with the 94, but mileage is essentially the same, around 9L/100km or about 27 mpg. I'm happy with that on a 3500 pound steel tank (including me and a chrome roof rack).
I had attributed better mileage to the 94 octane, but it was other fiddling with the car factors (carb setting, carb oil, timing, points, plugs, pcv) that improved things.
--
Stef (81 245 B21A SU M46 3.91) 325000km my volvo pages
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This is a very good study and a wise use of time in transit.(In the Charlotte, NC area some of these folks read novels propped up on the steering wheel at 70+.) I switched all of mine to mid-grade fuel a while back and noticed a difference in mileage. My change was to get the benefit of a couple of degrees advance in spark without too much pinging. I am curious about the speed that you drive on the highway or the engine rpms for the majority of the ride.
Kindest Regards,
--
Will Dallas, www.willdallas.us, www.willdallas.org, www.willdallas.com 86 245 DL 205K miles, 93 940 250K miles, 88 765 GLE 149K miles, 86 244 DL 200K Miles, 88 744T 200K miles
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some of these folks read novels propped up on the steering wheel at 70+.)
I love a good novel while on the turnpikes. However, for me, it must be on cassettes.
--
Art Benstein near Baltimore
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You mention that you use Bosch platinums. Not recommended on this board (high internal resistances?).
--
1980 245 Canadian B21A with SU carb and M46 trans
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Boy, quite a sub-thread got launched here.
What I don't know about spark plugs would fill several books, I'm sure.
I've read nothing on the design intent of the platinum plugs from Bosch or anyone else till what I read here in this thread.
I figured the Bosch had platinum to function as in the catalytic converters, to "combust" additional fuel content not usually burned in the cylinder. This should also help keep the plug from fouling.
I'm not a believer in super-extended intervals between tuneups. This time it simply got away from me. I think that driving about 45-50K yearly, I'll probably change them 2X yearly, with one change just before winter sets in.
I'll have to do some research on plugs!
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" You mention that you use Bosch platinums. Not recommended on this board"
Sorry Trev,
But IMO, that is one of several myths frequently propagated here, supported occasionally by vague references to "Volvo says...", but never backed up with the specific TSB number or text.
They have worked fine for me from K-jet to LH 2.4 cars.
Possibly there is a valid concern with the later electronics (from another forum) that was misapplied to our cars.
In my opinion, the Bosch Platinums (single electrode) are especially good on 240s that don't get serviced as often as they should, based on experience with four family cars.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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I have used Bosch plugs since 1968. I've tried many different brands,
but always came back to Bosch. When the Platinums became available,
I switched and never returned. No re-gapping, last forever. What else
could you ask for.
--
-Cool Volvo- 1982 240 4 Spd OD w/ 227K, 1989 240 5 Spd w/ 214K. Used to own 1966 122, 1968 144, 1970 145, 1972 144, 1980 245
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Bruce,
That bad rap started with Volvo Turbos, which do indeed foul Bosch Plat's fairly quickly, especially ones that have been ahh . . . shall we say "enhanced" even if they are tuned/running properly in other respects. This I know from experience ;-) Over time it seems to have spread to include all Volvos which I have not found to be true, again in my experience YMMV.
--
Dave Shannon
Spring Valley, California
'67 1800s
'73 1800ES
'88-240
my pages
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While they may be okay in the non-turbo applications, that doesn't justify their use. NGK copper plugs (BPR6ES for me turbo) are cheap (I paid $1.89/ea), and work quite well.
I fail to see the benefits of a long lasting plug, especially in a motor with an aluminum head. Leaving the plugs in for extended periods of time just encourages the plugs to be more stubborn on their removal.
I'll take my NGKs and change them every few years, thanks.
--
alex
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Once again calling on opinion, I feel they're crap - based on the fact that I've had one Volvo & 2 VWs that, when I got them, idled poorly, accelerated poorly, and generally acted as though they had bad plug wires. Upon further investigation it turned out they all had the single-electrode Bosch Platinums, and when replaced with standard plugs they ran fine. And to test the theory further I bought a new set for my B21F, and threw them out about 500km later when the same symptoms returned. Arguably there are other factors at work here, perhaps marginal ignition components that still work OK with the regular plugs but can't handle the platinums, but whatever the reason in 4 out of 4 cases they didn't work for me and regular plugs did.
-Chris
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina
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Thanks for this post - it's one of the few gas mileage stories I've seen that I'd say has meaningful numbers. That's because you covered a LOT of miles, with consistent driving style.
The mid-test tune up kinda throws an apples/oranges factor in there. The first two tests were within about 0.5MPG of each other, which is probably within the repeatability envelope of this kind of test. The 93-octane just might have given that difference, but at today's prices, it's not an economic proposition. (~10% costlier fuel for 2% better mileage). The tuneup could easily have given you the additional mile-per-gal. that the final stage showed.
It would be interesting - since you're doing the commute anyway - to go back to the 87-octane and see what mileage results.
Thanks again for an interesting post!
--
Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, 94-944 B230FD; grocery-getter Dodge minivan, hobbycar 77 MGB, and a few old motorcycles)
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Thats a great evaluation! Another good one might be a manual transmission vs. automatic.
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Thanks for the good word!
I'll let you know about std. tranny mpg's right after I swap out the tranny - - -
just kidding!
Manual-tranny folks definitely seem to get better mpg's, usually reporting in the high 20's for real-world driving. I seem to recall seeing reports of about 30 mpg for highway-only with std. tranny.
Re. std./auto tranny, my thought is that you have to compare the savings over about 200K miles vs. the cost of the clutch job. Assume fluid changes only for the auto tranny; they seem to last forever.
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