Another milage thread - Great hwy MPG horrible city MPG

aewoodhouse · Post by **aewoodhouse** » 27 Feb 2013, 06:38

Hello all....

Well, the subject says it. And i'm so tired of trying to solve it that i'm ready to give up on the car - a 1998 S70 non turbo 5 speed manual.

The car runs wonderfully but I am hardly getting 12 mpg around town and that's with lots of coasting and gentle driving. ON the highway I can count on 26-28. Here's what's been done so far:

Plugs, wires, cap, rotor, fuel filter, air filter, lucas injector cleaner, checked brake calipers and tire pressure, mechanic found and repaired a vacuum leak around the throttle body. After the vacuum leak was repaired I thought I was home free. However, it was only the highway milage that went back to normal.

What's left? I have not replaced either O2 sensor but figure that those always throw codes if they're bad, (am I wrong?)
have not replaced the charcoal canister, and have not replaced the fuel pressure regulator.

But again.. its fine on the highway so I'm not sure if this eliminates any other obvious factors.
I should mention that it is due for a timing belt any day now with 151,000 miles, and the clutch is starting to slip in 4th and 5th mostly. This has been going on for about 1.5 years - long before the clutch slipped.

I'm so tired of watching this thing devour gas but have dumped so much into it over the last year that would have a hard time walking away - especially since its probably worth only about $700 with the slippery clutch. Have also replaced almost every component in the front end in the last year.

Any insight would be most appreciated. Thanks for reading.

Post by **rspi** » 27 Feb 2013, 06:52

What is your average distance and speed around town?

Yes o2 sensors that are going out will cause poor mileage.

The worn timing belt will have nothing to do with gas mileage.

Is the motor warming up to temp?

Bottom line is, until a car warms up to temp it will get between 12 and 14 mpg. So, if your trips are less than 5 miles and the motor is cold most of the time, any car will have low mileage except for hybrids.

aewoodhouse · Post by **aewoodhouse** » 27 Feb 2013, 08:04

All this time and no one has suggested that its that simple? I live in NYC. Lots of trips are slow - avg 25 mph, lots of stops and starts and indeed, many short trips under five miles. While I know that NYC is especially bad for driving conditions, I'd have guessed that it should be getting 15mpg at worst given other's claims of 17-21 city.

I just got 210 miles out of a full tank of 91 octane combined highway / city.

Still doesn't seem right.

Is it worth swapping o2 sensors even though there are no codes?

Post by **rmmagow** » 27 Feb 2013, 09:13

How bad is that slippery clutch? I'd say 12 MPG in NYC is roughly par for these. I get 18 MPG in town but I don't have to put up with frequent stops etc and the car gets warmed up. My wife has gotten as low as 15. This is on a V70 wagon w/190K. I use it mainly on the highway now and get 23~24 mpg at highway speeds. I don't think you can do much to help your car in this situation. New O2 Senors would buy a lot of gas.

aewoodhouse · Post by **aewoodhouse** » 27 Feb 2013, 09:58

The clutch is another story because the slip seems to vary. Which i know is technically impossible considering i've had the rear main seal checked. Its gone from almost impossibly slippery (unsafe to drive) back to perfectly drivable just a little revvy in 3rd and 4th. But all this for another thread in which i'm sure people would be more inclined to question my mental health more than anything.

Thanks for the very useful points of reference rmmagow. Knowing that i've done what i can do still feels better even if the milage isn't great.

Post by **erikv11** » 27 Feb 2013, 10:05

Agreed, my 850s get 13-15 in the winter if they don't see the highway. Around town driving here is all short trips. Same car gets on the highway and clocks 25 mpg.

Adler · Post by **Adler** » 27 Feb 2013, 15:28

erikv11 wrote:Agreed, my 850s get 13-15 in the winter if they don't see the highway. Around town driving here is all short trips. Same car gets on the highway and clocks 25 mpg.

I get about the same in my 98. The engine gets to operating temp for only half the trip.

aewoodhouse · Post by **aewoodhouse** » 27 Feb 2013, 15:34

Nice to know i'm not alone. And regardless, I'd still much rather be driving my car than my dad's 2011 Prius.

Post by **JRL** » 27 Feb 2013, 16:45

You need to be at stage 0 before you can discuss mileage and you're not!
Bad 02 sensors AND a slipping clutch is a recipe for disaster

Post by **E Showell** » 01 Mar 2013, 08:56

I second JRL on the bad O2 sensors. They are considered a maintenance item that should be replaced at 100K miles. All sorts of bad things can happen -- like burned valves -- if you simply let the 02 sensors hang around until they decide to throw codes. Also, failure modes vary on the o2 sensors. Sometimes they start to lean out the mixture, sometime they over-enrich the mixture on their way out. Best not to mess. Replace in pairs at 100K miles. I learned this the hard way.