I have a 1990 Honda Civic, 4door, 1.5L, 4 speed automatic, A/C, PL, P/W, P/S, P/B, Cruise/Tilt. This car use to get 35-38 MPG when newer. Now it seems to get 27-31 MPG. This car has 105,000 miles. I have completely serviced it installed new spark plugs, main relay, fuel pump & screen, new air filter, fuel filter, new tires stock size (35psi).

Anyway, this car belonged to my Mom. So I have only driven it a few times since she bought it new in 1990. Anyway, I have noticed that at 70 MPH the tach. reads 3100 RPMs. Is this right? I feel the trans shifting through all gears. My buddy owns an ex cop car with a certified speedo. Today we checked the speedometer in the Honda & when he is going 70 MPH the Honda speedo reads 73-74 MPH.
Anyway, does any of this sound normal.
I'm trying to figure out why we can't get better mileage, or is this about right. I notice with the A/C on the mileage drops about a few miles per gallon.
Any input would be appreciated, thanks.

 

Do you have the stock size wheels on?
different sized tires will throw the speedometer off.

And yeah The AC runs off the motor, so when you turn it on, it engages and uses power from the motor to run the AC.
so yeah it wastes a bit more gas then with nothing on.

 

Yea, Everything is stock including wheels. I'm wondering more if the mileage & RPMs at the speed are normal, or I'm I missing something.
thanks

 

The speedometer error you are experiencing is normal. Happens on most 90s Hondas, If I remember correctly. My 93 del Sol does it too, and so did my old 93 Civic.

 

Hey man, the wheel bearing is worn and dragging a bit, the glass is a little bit off and not providing "perfect" slipstream. Same with worn weatherstrips. U also have to compare apples to apples. U driving it a "few times" probly not a good measurement. Speed also affects mileage alot. The mileage the dealer quotes u are tested at 55 mph.

 

Just gonna jump in with some info too.

I have a 97 civic with a d16y7 motor. At 100kmh (about 70mph) I'm spinning pretty much 3000rpm. I also have slightly undersized tires on (stock is 185/65/14, but I got a great deal on rims and tires in the 155/80/13 size - which are slightly shorter)

So it seems your rpms vs speed is pretty close.

 

Thanks for that info. That is what I was wondering, was that normal RPMs for that speed.
trustdestruction: Thanks for confirming the speedo error. I'm not really concerned about the speedo error. I just want to give as much info as possible. Well I will see what the wife does for mileage this week. It could be that this car sat for 18 months with no driving at all. We have only put about 2500 miles on it since we started driving it. With her slowing the speed back to 73-74 MPH by speedo actual 70 I see if that helps the mileage. She was running 80 MPH by speedo which was closer to 75 MPH.
I figure we should be able to get 35 MPG with NO A/C on. Maybe 31-32 MPG with it on. It is only a 1.5L engine. Speed effects gas mileage.
Thanks guys. I'll post this weeks mileage on Friday.

 

Well after my wife's last week the Civic got 32 MPG & 70 MPH A/C OFF. So that looks like that is the mileage. I'm a little disappointed I was hoping for 35+ MPH. I talked with my mom the other day & she said when she would get 38 MPG she was only driving around 60 MPH. So I guess if we drove like an 80 year old women maybe we would get better mileage.
Thanks for everyone's input

 

When was the last time spark plugs, wires, and stuff like that were changed?

Also check the tire pressure, that could rob you of a few mpgs.

And it's true, MPGs drop when you get over 55-60 or so. That and quick take offs from stoplights will hurt too

 

I just did spark plugs. Haven't changed plug wires, I'm not sure how long it has been since they or the cap & rotor have been changed. I think about 40,000 miles ago but not sure. Plugs were shot. They were burned up with a gap of over .075. Fuel pump, pump screen, main relay, plugs, fuel filter, air filter, & complete LOF. (I installed a set of Bosch standard plugs. Autolites were in it.) In the last 1500 miles.
As for tire pressure, I just had new Kumho KR21 tires installed & they are running 35 psi.

Thanks,