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-   -   How to increase my mpg?? (98 civic LX 5-speed, AC always on) (

mattrich67 10-14-2012 04:21 PM

How to increase my mpg?? (98 civic LX 5-speed, AC always on)
I have a 98 civic Lx 4dr lowered timing at 14* (runs a little better then12*)
Tires at 45 psi synthetic oil full tune up valves adjusted new filters.
Just installed my vacuum gauge last week (still trying to figure out the best shifts)
I have to run my a/c since its so hot here in Vegas and I have two kids always with me.

Couple questions.
When I use my vacuum gauge is it better to

I guess what it all comes down to is a higher vacuum 12-25 reading and a higher rpm 3000-3500 reading better then a lower 0-8 vacuum reading and a lower 2000-2500 rpm reading

While shifting should i Keep my vacuum closer to 15-20 (idle) and hold the gears longer and then shift at 3500 so it stays in a good vacuum range after shift or shift at 23-2800 and have the vacuum go closer to 5 in the (poor )

Also when climbing a hill on freeway do I try to stay in fifth and have vacuum readings in 5 poor/ fair or shift to 4th and 3000-4000 rpm and feather the pedal to stay in good 12-18 vacuum readings

Thanks for all your responses and your help

Gealii 10-14-2012 06:03 PM

I couldn't tell you how to drive with a vacuum gauge cuz i never had one but you want to do short shifts. This is basically saying that you want to be in the highest gear you can without lugging the engine. People say they can cruise at a very low rpm without lugging, but as soon as they accelerate it lugs. The goal is to be in the highest gear you can while accelerating without lugging. When i was in my 5speed i would hit 5th gear at 37mph and accelerate in 5th all the way up to cruising speed.

I couldn't tell you about hills only did 1 extreme hill and lets just say i should've shifted down 1 more gear when i got to the top i could smell the clutch.

bestclimb 10-14-2012 08:20 PM

unless you need to shift down to avoid slowing down too much on the highway leave it in 5th gear and let the speed drop off just a tad while going up hill, you can get the speed back up on the next down hill or flat. Really the best thing to help your mileage is data, get an instant fuel consumption display of some sort you will be able to see for your self. It will pay for it self.

nmtmechengineer 10-15-2012 02:35 AM

I used to use a vacuum gauge back in college on my 87 Celica, so I can relate to this question. Although it depends on if you are driving in the city or high way. I used to use the hypermiling techniques before I read about them. Driving with load or rolling to an intersection without stopping.

What looked at was the engine dyno for the engine in my car which was a 3S-FE Toyota engine. It had a pretty flat torque across the RPM range. Thus I shifted at a lower RPM. In addition, it made sense to me because for most calculations regarding force the velocity is squared.

BTW the vacuum gauge I mostly used on the open road or highways because it is very sensitive to the gas petal input.

Just my 2 cents.

California98Civic 10-15-2012 04:05 AM

Use the search function for other threads, but here is one that will help you:


mattrich67 10-15-2012 04:42 AM

Thanks for all the replies.

I have tried for a week and a half now to get the best mileage I can and I'm not gaining as much as I would have liked. I have gone from 25 mpg from the first tank after I bought it. ( it was sitting for 6 months ) these last two tanks I have only got 32 mpg withy the a/c on and that's with coasting to lights 65 freeway prob 60 town 40 freeway. I have been using the vacuum gauge and try very hard to keep that vacuum anywhere from 5-15 driving and then feather the pedal after I hit my speed goal.

How are you guys getting such awesome mpg. I thought with me driving like a grandmas grandma would get me maybe 40 with the mix driving and a/c but when I only saw 60 miles and its already in between full and 3/4 tank I don't know if its worth driving that cautious and that much concentration.

Is it me or something up with the car. I have changed everything and did all the fluids. It seems a little sluggish when I hit any type of incline. Seem like I always have to shift down??

mattrich67 10-15-2012 04:45 AM

I have a Mac tools scanner that has live data is there anything I can look at or test to see of something is not correct? O2s iat load or short fuel trim long fuel trim?

Thanks again

MetroMPG 10-15-2012 12:31 PM

First: consider more active use of the a/c - shut it off on grades or other times when the added load would otherwise make a downshift necessary. Turn it back on when cruising or when you have to decelerate in gear (DFCO).

Second: going by the fuel gauge is a lousy way to estimate your current fuel economy. It's not accurate enough. You really need a digital MPG gauge - ScanGauge or equivalent if you want to know fuel consumption use in-between fill-ups.

Third: in my opinion, focusing on how to use the accelerator is not where you should be spending your efforts (at least in city driving). Get in the highest gear you can, then worry about the brake pedal - It's the enemy of good city MPG. You should be driving without brakes as much as possible, looking far ahead in traffic, planning & anticipating, and coasting as long as possible in neutral when approaching stops/turns (without impeding traffic!). Every time you hit the brakes, give yourself a dope slap.

Fourth: how realistic are your expectations? 25 mpg to 32 mpg is a pretty big improvement already. That's a 28% increase! And you're apparently beating your highway MPG rating now.

When you ask "How are you guys getting such awesome mpg?", which guys are you talking about?

The Civic owners getting extreme MPG are not using the A/C, they're definitely not cruising at 65 mph on the highway, and they're definitely not driving like Grandma ever did! They're using advanced techniques that may not be appropriate for you or your driving environment.

mattrich67 10-15-2012 01:09 PM


The best way to calculate fuel mileage is how much fuel you use on gas gauge. And if I only go 150 miles on a half a tank I know I'm not getting but more then 30-35 mpg. If I got like 200 miles on half a tank I know I'm doing right.

Anybody can trick a on board computer. I do it all the time in my scion xb. I can get that to read in the 30 mpg range but when you do the real math and calculate the miles to gallons and read 24 mpg not 30 then you know you can't fully trust a on board gauge.

When my civic is supposed to get 28 mpg city only that's what I expect on a average driver. Now since I'm driving slower at takeoff, coasting to a stop, shifting under 3000 rpm, and driving the most efficient as I am able to do. I would think that I could make at least 5-8 mpg better.
Also my 32 mpg is 40% freeway

Fourth : thanks for that advise

Fifth :
I have seen over and over civic owners non hybrid getting 40- 50 mpg with only changing driving habits and maybe a grill block.
That's why I am asking and if they can get 50 mpg why can't I get 40 mpg.

OR are they going by a scan gauge readout!?

And yes the ones I saw did go 60-65 mph on freeway.


Are these people live in a town that's all flat ground no hills just smooth drive nice wheather

This is the stuff I am asking.

MetroMPG 10-15-2012 01:38 PM

Of course you're right: the final word goes to miles divided by gallons at fill-up time.

But if you want the most useful feedback between fill-ups, use a resettable, properly calibrated digital fuel economy gauge. The overwhelming majority of "high MPG" drivers here use them for that reason.

Saying "I'm not getting but more then 30-35 mpg" by the position of the needle on the fuel gauge just isn't accurate or timely enough to use as feedback.

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