[Cloud9...68]

A friend at work recently bought his wife a new Honda Civic automatic. It's EPA city/highway mileage rating is 30/40, respectively. She drives it mostly on the highway, with just a very slight amount of stop & go, and he says she's a very conservative driver. Based on this, the car should easily be getting in the low to mid 30's, but it's averaging about 26, which is just way too low. My friend drives a Corvette C5, and his commute has much more stop-and-go than his wife's, and he is something of a leadfoot, and he's averaging 21!



The Civic has about 600 miles on it, but has shown no improvement since they've had it. He took it to the dealer, where they ran an OBD test, and no codes were thrown. The car doesn't smoke, and drives smoothly, with good power. He tested the odometer by having he and his wife drive the identical routes, and they both showed exactly the same 11.5 miles. There is no gas smell, and I suggested he put it neutral on a level road and see how easy it is to push. He said it pushed very easily, so there's no unusual rolling resistance, and this indicates the tire pressure is also OK.



He posted his problem on a Civic forum, and a couple of people responded that they've seen comparable mileage, but most people seem to be getting in the mid 30s. I was hoping somebody on this forum might have some additional suggestions for him to try. Thanks.

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[TheMirror]

Strange stuff, but driving habits can affect that sort of thing. I have friends that don't drive smoothly, but constantly dip, dip, dip into the throttle. It makes me carsick, and makes their mileage go down.



The best way to troubleshoot this is to top off the tank, then take a 40 mile trip on the freeway using cruise control at @ 70mph. If the mileage is in the high 30s, then its the driver. If the mileage is in the high twenties to 30, then its probably an issue with the car.



Troubleshoot....

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[Cloud9...68]

Thanks. That's the next thing they're going to try. I suspect it's either an indirect sensor issue, an example of which would be the car running slightly hot, causing the computer to richen the mixture, or a sensor, most like the the O2 sensor, that's marginal, but not far enough off to throw a code. I suggested he pull the plugs to check for fouling, but I don't think he's done that yet.

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[flash]

ok - first a verificaton question - the EPA estimate is for an automatic, and not a manual, right? an automatic will generally cost you about 5mpg



then, is she running the recommended octane fuel?



how is the tire pressure? low pressure easily causes loss in mpg



the last time i checked, EPA mileage estimates are at a steady state 55mph - higher speeds result in lower mileage - sorry truckers, the "officer, my truck gets better mileage at 65" argument does not fly - physics are physics - more speed means more fuel

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[Cloud9...68]

The EPA figures are for the automatic, which is what hers is. We have a 2004 Corolla automatic, and we routinely get in the low to mid 30's around town, so it's safe to say a Civic should be in the same ballpark, especially since she drives it mostly highway.



Not sure what octane she's running, but 95% of "normal" (as in non-high performance) cars today recommend 87, so this should should be OK.



I don't know the exact tire pressure, but I suggested he put the car in neutral on a flat road, and see how hard it is to push the car. He tried it, and said it was very easy, which pretty much takes care of tire pressure, binding of some sort in the driveline, gross misalignment, etc.



A real puzzler for now...

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[flash]

hmmm - ok



i wouldn't consider our bmw a high performance car - it's only got 185hp - needs 91 octane though - check the manual to see what her car needs



i would still check the tires - it will roll like that with 20lbs in them - a 10lb drop from correct pressure though can easily cost 4mpg



take a look at the tread wear - see if it's doing anything odd indicating bad alignment

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[TheMirror]

I'd be almost certain that car has an 87 Octane requirement. I believe my mom's accord does, and that car has the V-6 which is no slouch.



I've run 87 in my TSX several times, which has a 91 requirement. It feels a little fuzzy around the edges with the lower octane fuel map, and economy suffers about 10 percent. Less on pure highway driving.



Cheers,

-Mirror

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[Ceenit]

I doubt the engine has been appropriately broken in at 600 miles. There have been similar reports on other 'new cars', mileage tends to get better when you get past the 4k-8k mileage mark. This is also when the initial 'starter/break in' oils and fluids typically get replaced.



I wouldn't get too stressed on mileage being out of whack until after the initial break in period. Lower fuel mileage is very common on brand new engines.

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[flash]

don't know what year that one is, but a 2000 civic si requires premium (freakishly i just read that today in an issue of road and track)

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[Bob Kovacs]

I agree with flash's recommendation to check the tire pressure, which should be in the 32-34 psi range with the tires cold. You should also pop the air filter out to make sure it's clean and that there are no obvious obstructions in the intake system. I've heard of a plastic bag that got sucked into the intake and was half covering the air filter in a new car. Do the obvious and simple stuff before you start looking for more esoteric causes.



I also agree that an engine with 600 miles on it is not yet broken in. It will really take 5k miles or so to consider it broken in.



--Bob

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[flash]

just looked up a 2006 civic - 10.5:1 compression - definitely needs premium in any other car, though the site specs regular - that one i don't understand - i would seriously check the owner's manual on that one



check this out 2007 civic si 22/31:



http://www.autobytel.com/content/shared/ar...cle_id_int/1107

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[TheMirror]

The vast majority of Honda products going way back have been engineered to take 87 Octane. Any Si model with the performance version of VTEC, be it a B16A, K series, or whatever, will have a 91 requirement.



For example, all 2006 Hondas (regardless of engine) except the S2000 and Civic Si have a Regular unleaded requirement. Only those two require Premium.



Cheers,

-Mirror

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[TheMirror]

Indeed, the K24 in my Acura TSX took a full 10,000 miles to truly break in. Gives me high hopes for a long, long future.



[quote name='Ceenit' date='Jun 19 2006, 11:57 AM']I doubt the engine has been appropriately broken in at 600 miles.  There have been similar reports on other 'new cars', mileage tends to get better when you get past the 4k-8k mileage mark. 

[right][post="22998"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[flash]

that's what was so confusing - on one page it says regular is required, but when looking at the engine specs, and seeing 10.5:1, the presumption would be requiring premium



i suspect it may be like our engine - it will run on 90, but not as well as on 93 - mileage drops about 1% per octane point - on the civic, going from 93 to 87 that would be 37 versus 40 on the 2006



but, the 2007 spec is only 22/31 anyway

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[Cloud9...68]

Got a new data point. John (my friend) topped up the tank, and then drove it about 60 miles on the highway with the cruise control set most of the way. He says he only had to make one brief stop. The result: 35 mpg. I asked him about his wife's driving style, whether she keeps her foot steady on the gas when driving at a steady speed, and he told me that she actually tends to oscillate the pedal up and down quite a bit, to the point where it is annoying if you're a passenger. So, at this point, my bet is that it's a driving style issue.



The car now has a little over a thousand miles on it. It's interesting to hear opinions on break-in periods. Hopefully, they will see their mileage improve, particularly is she could get some coaching on keeping her foot more steady.



Too lazy to look it up, but I seem to remember that the mileage on the "performance" versions of cars like the Civic (the Si in this case) get considerably poorer mileage than the base models. My friend's wife's is a garden variety model, so it should have no problem getting in the 30s if driven conservatively. And I'd be willing to bet a case on any type of beer that running higher than 87 octane will have zero impact on the mileage or performance of this engine. Several recent studies have been performed on this sort of thing.



Thanks for all the inputs - I knew I could count on this community to shed some light on this issue.

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[flash]

glad it is working out like it should - the only specs i cold find were on the vtech



a new thought too:



if she's a "two footer" this could be part of the problem - also could be explained if she is one of those gas-brake-gas-brake people that never figured out that you can just lift the right foot to slow down



as for octane and mileage, there is a direct correlation between octane, power, and mileage - it's a physical constant, as long as the engine can manage it - higher octane fuel will give you better mileage if the engine makes mixture and timing adjustments accordingly - our car is a prime example of this capability



the difference is 1% per point in octane - a one point raise (i.e. 91 to 92) will reap a 1% gain in horsepower and mileage



this presumes that the engine is tuneable by means of controls such as ours - try it yourself, it really does happen



i have no idea what the honda is capable of managing though

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[TheMirror]

Honda, and to a lesser extent, Toyota, have been very successful in running high compression on their garden variety fours with regular gas. Call it good combustion chamber design, good intake charge turbulence, likely a combination of both. In theory its easier for an engine with a small bore, for example Honda's 1.6L D16, to run higher compression on less octane because the combustion chamber and cylinder size is smaller in general. Less surface area for possible pre-combustion, less distance for flame travel, etc. In our humungous 750cc per cylinder thumpers, It becomes a lot harder. If one of the older Honda 1.5s had cylinder sizes similar to the 968, it would be an inline twin

. Porsche's flat 6 has a very good combustion chamber design, but when you get into bores over 95mm (3.3L and up) on the air cooled engines, you need twin plugs to deal with all of that area.



Not quibbling with the math, flash, in theory its quite true about higher octane giving better mileage in high compression engines. With current Honda motors, methinks they are optimized to run on crappy Regular 87 from the factory and putting 91 in them would give you fractional gains, if any.



The Si is another story though, if it requires 91 from the owner's manual, you will definitely see a hit on mileage with 87.



Cheers,

-Mirror





[quote name='flash' date='Jun 19 2006, 04:34 PM']that's what was so confusing - on one page it says regular is required, but when looking at the engine specs, and seeing 10.5:1, the presumption would be requiring premium



i suspect it may be like our engine - it will run on 90, but not as well as on 93 - mileage drops about 1% per octane point - on the civic, going from 93 to 87 that would be 37 versus 40 on the 2006



but, the 2007 spec is only 22/31 anyway

[right][post="23018"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[TheMirror]

Ah, yes, there we go. Tight Honda engine combined with exaggerated throttle inputs equals poor mileage. Case closed.



It will improve as it loosens up, and mileage will also improve if the dear lady in questions smoothes out the go-pedal.



Best,

-Mirror





[quote name='Cloud9...68' date='Jun 19 2006, 07:26 PM']Got a new data point.  John (my friend) topped up the tank, and then drove it about 60 miles on the highway with the cruise control set most of the way.  He says he only had to make one brief stop.  The result:  35 mpg.  I asked him about his wife's driving style, whether she keeps her foot steady on the gas when driving at a steady speed, and he told me that she actually tends to oscillate the pedal up and down quite a bit, to the point where it is annoying if you're a passenger.  So, at this point, my bet is that it's a driving style issue.



[right][post="23026"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[flash]

nah - no quibbling - i pulled the math out of a book



as i said, it is entirely dependent on the engine management being able to advance the timing and such to utilize the higher energy fuel - our engines can do that to a point (up to about 95 octane) - i have no idea what the honda can do



anyway, sounds like things are really pretty normal on that car, and it is just the driver - i have one here who is somewhat similar - she's not too bad, but has a somewhat irregular throttling technique - i get a good 1-2 mpg average better than ayn does in the denali

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