My 98 civic LX has had a recent tune up. When I 1st bought this car I was getting approx 36 mpg. It is a 5 speed. It started getting worse the past few months. around 30. I figured since it's paid for, I should fine tune everything before getting a paint job. Here is what I have recently done to it as of 8/23/10
1) new NGK plugs
2) new battery (old one was getting weak)
3) new PCV valve $2
4) Switched to castrol full synthetic oil 10W30
5) New tires. 15" aluminum rims 195 50 R15
6) took out the huge speaker box. Approx 150lbs.
7) New clutch kit / rear main seal + there are no oil leaks at all
8) Flywheel also changed
9) Transmission fluid change w/ honda genuine fluid manual trans.
10) Timing belt change & drive belts.
11) K&N intake (this is the only aftermarket mod on it)

The car drives so smooth now with all of this. Yet I am still getting 28mpg every time I check it, Something must be off to have almost 10mpg less than when I got the car. Any tips appreciated

 

is your timing set correctly?

 

+1 on the timing. Also does the engine warm up to normal temperature? If it is staying too cold it will run in warm-up mode which reduces mileage. With an intake mod be sure the IAT sensor is still connected so it will measure intake air temperature.

5W30 oil is recommended. Heavier oil will slightly reduce mpg.

Also if the final OD of the tires is larger than stock, the car will actually have traveled more miles than the odometer says. That can lead to a perception of low mpg. Check your odometer calibration by driving a few miles on the interstate and comparing it to the mile posts.

 

Make sure your tires are properly inflated. I went up 4 mpg just from filling mine up right.

I'm running 205/50/15 tires. That might be making my mileage off a little too.

 

Ok, I thought it was all set when they changed the belt, but how would I set timing without pulling off timing cover?
Engine warms up about a quarter of the way up, new radiator too. & yes I put the intake sensor back on the tube, it's a short ram intake. I may try a cold air all the way into the bumper. Next time I change oil, I will try 5W30 syntec instead. I always thought the older the car the heavier the oil.
Also what is the average pressure of the tires suppose to be that you guys normally use? I usually stay at 30-32

 

I also finally put up pics of the car as well

 

Spark timing is set with a timing light. Normal temperature is halfway up on the gauge. Replace the thermostat, make sure the new one is a 193 or 195 degree. Low profile tires can need a lot more pressure than stock ones. Honda's sticker on the car only applies to the stock setup. Check the markings on the tire and ask the tire dealer. You'll always get better mileage with higher tire pressure, but the car's road handling can be degraded.

 

Your tires can also affect your mpg as well. If your new tires are a higher rolling resistance than your old ones, your mpg may suffer slightly. Also, if your new wheels are heavier than your old ones, this could also decrease efficiency slightly. But the combined effects of these both would probably contribute to 2-3 mpg in the absolute worst case scenario.

mk378 is right about the thermostat. Mine always tops out at half-way up. I haven't changed mine yet, but it looks easy to fix on our cars.

Good luck figuring it out! Let us know what works.

 

Thanks guys. Ye ever since I got it the temp just went up slightly, never to half. I always thought this was good. A few months back my radiator developed a crack so I changed it & the temp is still low.
I will look for one like you spoke of, thanks

 

every single car ive owned except v8 motors the temp is always a quater of the way up that is 100% perfect temp it should only go up to half(rarely) on an extremely hot day if its at half u need to get the right thermostat, try putting ur old tires back on and see what it does, if it goes back up with stock tires then have your odometer calibrated for the larger ones, i run 40psi for highway driving for spirited driving 32psi, n 5w30 is the best oil to use 10w30 is ok but not recomended, also the lighter the wheels/tires the better performance and gas mileage.