my 96 civic mpg is down, any idea why?

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brianmanahan

brianmanahan

Lifer
Sep 2, 2006
24,638
6,016
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i used to get like 35-36 mpg average like 5 years ago, but now i cant get any more than 31-32 if i baby the thing. has 260k miles on it. can anyone think of anything that might explain the drop in mpg, or is it maybe just because its old and getting worn out? i dont really drive all that different now than i did then. same type of tires.
 
dfanatic86

dfanatic86

Member
Jul 2, 2012
91
0
0
maybe a tune up. spark plugs, wires, cap&rotor and fuel filter. also maintaing proper tire psi help a little bit. gl
 
brianmanahan

brianmanahan

Lifer
Sep 2, 2006
24,638
6,016
136
dfanatic86 said:
maybe a tune up. spark plugs, wires, cap&rotor and fuel filter. also maintaing proper tire psi help a little bit. gl
Click to expand...

i did the plugs/wires a couple years ago, but not the cap and rotor or filter, maybe i will try those. always keep my tires maxed around 40 psi.
 
exdeath

exdeath

Lifer
Jan 29, 2004
13,679
10
81
260k miles I'm betting the compression is probably down a few psi from normal wear. Also things like valve seals or PCV leaking oil into the combustion chamber reduces octane and causes timing to be pulled by the knock sensor. Slow O2 sensors, low coolant temp due to thermostat, accessory drag from worn bearings, all sorts of things can add up to affect fuel consumption when you are talking just 4 mpg.

Only way to know for sure is data log with a scanner and compare to a lower mileage version of the same car (or Honda diagnostic manual if it has target values)

Have you moved at all? Differences in elevation, weather (hot, cold, humid, etc) have an affect as well.

Any transmission issues? etc.
 
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F

Ferzerp

Diamond Member
Oct 12, 1999
6,438
107
106
exdeath said:
all sorts of things can add up to affect fuel consumption when you are talking just 4 mpg.
Click to expand...


Yes, and especially getting in the 30's and 40's of mpgs, the reciprocal version makes a ton more sense. 4 mpg at 36MPG is not a lot. 2.777ga/100mi for 36, and 3.125ga/100mi for 32. It's a difference, at current average prices of $1.21/100mi. It's a 96, meaning it's around 17 years old at this point, so it's averaging about 15.3k miles per year.

The net cost to you is around $185 per year (compared to when it was getting 36mpg, but are you sure your driving habits have been totally invariant, because it doesn't take muct at all to use an extra 1/3 gallon over 100 mi ?). Now, if you check it out, and it's just normal wear and nothing problematic, consider that cost per year before sinking something like $1k in to it ;)

That $185 is out of around a $2100 fuel bill per year at today's prices for perspective.
 
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brianmanahan

brianmanahan

Lifer
Sep 2, 2006
24,638
6,016
136
exdeath said:
260k miles I'm betting the compression is probably down a few psi from normal wear. Also things like valve seals or PCV leaking oil into the combustion chamber reduces octane and causes timing to be pulled by the knock sensor. Slow O2 sensors, low coolant temp due to thermostat, accessory drag from worn bearings, all sorts of things can add up to affect fuel consumption when you are talking just 4 mpg.

Only way to know for sure is data log with a scanner and compare to a lower mileage version of the same car (or Honda diagnostic manual if it has target values)

Have you moved at all? Differences in elevation, weather (hot, cold, humid, etc) have an affect as well.

Any transmission issues? etc.
Click to expand...

nah havent moved at all, and the tranny is still working as good as when i got it.

sometimes its actually dipped down to 28-29 mpg for a month or two at a time, then back up a little.

maybe i will try replacing the o2 sensor and doing a full tuneup and see if that fixes anything

or maybe ill just let it go as it is and get myself a newer honda fit in the next year or so :awe:
 
dfanatic86

dfanatic86

Member
Jul 2, 2012
91
0
0
exdeath said:
260k miles I'm betting the compression is probably down a few psi from normal wear. Also things like valve seals or PCV leaking oil into the combustion chamber reduces octane and causes timing to be pulled by the knock sensor. Slow O2 sensors, low coolant temp due to thermostat, accessory drag from worn bearings, all sorts of things can add up to affect fuel consumption when you are talking just 4 mpg.

Only way to know for sure is data log with a scanner and compare to a lower mileage version of the same car (or Honda diagnostic manual if it has target values)

Have you moved at all? Differences in elevation, weather (hot, cold, humid, etc) have an affect as well.

Any transmission issues? etc.
Click to expand...

Good call, these are secondary things to look in to.
 
J

JCH13

Diamond Member
Sep 14, 2010
4,981
66
91
I'd run a seafoam treatment on the intake and engine oil, get sludge out of both. Likely the transmission is due for a flush too.
 
T

thomsbrain

Lifer
Dec 4, 2001
18,148
1
0
Don't forget to check your air intake filter and make sure it is clean.

I went on a road trip recently and got noticeably better mileage with non-ethanol-diluted gas (Scangauge verified).
 
S

soccerballtux

Lifer
Dec 30, 2004
12,553
2
76
Soundmanred said:
Most 18 year olds have no desire to work these days.
Click to expand...

jobs don't pay like they used to.
$12 to eat out, $13 to see a movie, $3.50/g gas, 5-digits-per-year-college-tuition, why bother? Take bus, play video games. Who needs more? My minimum wage job taught me the value of an hour of freedom. When I tell older people that now they scowl at me, suck it old farts, the world sucks now and you wouldn't work an 8 hour shift at McD for minimum wage, either so get off my case.

I make an engineer's salary now. Still would make same decision given the chance. Those summers of working in high school are summers I'm never going to get back. Work work work till you die. No thanks.
 
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brianmanahan

brianmanahan

Lifer
Sep 2, 2006
24,638
6,016
136
JCH13 said:
I'd run a seafoam treatment on the intake and engine oil, get sludge out of both. Likely the transmission is due for a flush too.
Click to expand...

thanks i will look into this. is that hard to do? i can do a few things (oil, brakes, plugs, tires) but i aint that great at maintenance/repair.
 
J

JCH13

Diamond Member
Sep 14, 2010
4,981
66
91
brianmanahan said:
thanks i will look into this. is that hard to do? i can do a few things (oil, brakes, plugs, tires) but i aint that great at maintenance/repair.
Click to expand...

The seafoam treatment is easy, video here.

I would take it to a shop for a transmission flush.
 
hanoverphist

hanoverphist

Diamond Member
Dec 7, 2006
9,867
23
76
JCH13 said:
I'd run a seafoam treatment on the intake and engine oil, get sludge out of both. Likely the transmission is due for a flush too.
Click to expand...

this. it would do a lot to just pull the intake and clean it all, throttle body and all. at that point you can clean out the IACV and TPS while youre in there, and get that sucker running close to new again.

the o2 sensor will kill your mpg as well, even if it isnt tossing a code for it. its nto too hard to soak and clean tho.

another is the lockup solenoid for the trans, but that will usually toss a code. the solenoid is what locks the torque converter in 4th gear and cruising so it doesnt move. when this happens the rpms drop a bit (about 400) while cruising between 45-65.

there is no MAF in that car, it runs off of MAP instead. there is an Oring on the sensor tho, could be an issue there giving it a bad reading, changing the tune.

cylinder compression could do the same, but i think youd have other things going wrong besides just a mileage drop i think. either way, that sucker has 260k on it, theres lots that is worn down, as well as lots you can do to refresh it easily. and honestly, those things are so easy to rebuild its almost a no brainer. you could rebuild it for cheep and get that body up to 400k i bet.

i have a 98 civic HB with 250k on the body, but i have recently redone the head and other things.
 
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