Another milage thread - Great hwy MPG horrible city MPG

[KEWROCK]

I live in NYC also. In my V70 wagon with a turbo and AWD I get around 15 City and 22 Hwy. I do about 50/50, I'm on the Grand Central a lot. My trip computer settles in at 19 mpg consistently after a few weeks of various driving. The trip computer is surprisingly accurate too. I don't notice any difference in the ethanol months.

Have you checked your brake calipers, to see if there's any drag? Also parking brake cable and links.

If you have a 6 cyl two-wheel-drive sedan, I would think you should be doing considerably better that me.

I just noticed you have a manual stick too. I think there's definitely a problem.

[aewoodhouse]

I guess then O2 sensors are next. I got the car from my brother who had it from between 50K and 117K. He kept all repair receipts and in looking through them I couldn't find any evidence that the sensors have been replaced. (Its got 150K now.)
Though with impending need for a clutch and a timing belt as well, I'm wondering whether to just get a different S70.

[jkdjim]

I have a 2000 S80 T6. I was going to ask this very question and was concerned with O2 sensors as well. If no codes, should I replace anyway? Also, there seem to be several options based on what I've seen on IPD/FCP and others. Do I need all 4?

[jblackburn]

I had bad gas mileage (low teens city/20 highway) from my S70 and no codes. I replaced the FRONT O2 sensor only, and both performance and gas mileage improved. It was pretty normal for my car to get numbers near 18/30.

The rear O2 sensor on a 1998 doesn't do anything but monitor the catalyst. Don't waste money on that one.

An S80 is different - 2 front O2 sensors and 2 rear ones. That can get expensive, but I'd still start with the front ones. I believe the S80 rear sensors may play a role in fuel management as well, though.

[E Showell]

aewoodhouse -- If you have your brother's maintenance receipts, and he did a reasonable job of keeping up with things, I'd not be inclined to walk away from this car simply because it has some expensive maintenance coming up. If you're going to keep a car for hundreds of thousands of miles, you'll need to do some periodic maintenance.

Things on the horizon after timing belt and water pump most likely include, O2 sensor, complete PCV service and new suspension parts -- springs don't need to be replaced unless they are broken (some will disagree with me on this) but you are likely to need new struts and associated bits, as well as new rear shocks at c. 150K -- you probably already need them if you've been cruising the pot hole laden streets of NYC for any length of time.

Once you do those things, you've got a pretty solid ride for another 100-150K.

P.S. My original clutch went to 229K miles and wasn't yet down to the rivits. I just had two new exhaust valves put into the cylinder head in my car and had the head reconditioned with all new valve seals and all valve seats reground, and with 241K on the clock, it drives like it had half that mileage. Of course, I had previously done the PCV and replaced major suspension components at about 180K miles. My mechanic says from the way it drives, you'd never know my V70 has nearly 250K miles on it.

[aewoodhouse]

Regarding NYC street conditions: I just changed the spring seats for the second time in three years. The original OEMs are useless on bad urban streets. A very helpful member of these forums pointed out that the OEM's for the S70 were eventually superseded by the stock XC70 ones. That cleared a lot of confusion and the ride is MUCH nicer now. If you ask FCP to send OEMs they won't send the proper XC70 ones. Not to veer too far off topic but I figured it was worth mentioning.

And yes... the front end was devoured too so its gotten struts, shocks, tie rod ends and ball joints/control arms in the last 2 years. Not to mention the heater core (FUN job!) brake lines, tires and all the other stuff mentioned in the OP. Youre right showell... probably best not to walk away...

I'm shocked that the clutch is slipping at 150K considering that my dad was the ultimate clutch drill master when teaching us to drive. Two years of clutch balancing drills on the steepest hills in the neighborhood. We know how to treat a clutch nicely.

[E Showell]

IPD heavy duty sway bar end links are another useful upgrade.

[War Iron]

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

On a flat highway the engine only has to put enough power through the drivetrain to overcome wind and rolling resistance. Around town, the torque required to accelerate is much, much greater and the clutch will slip a lot more, turning a great deal of energy (torque) into heat at the clutch disc. Your O2 sensors may very well be bad, but substantial slip at the clutch is just pouring gas down the street.

[mrbrian200]

aewoodhouse post hinting that you might look at your alignment/checked. Highway econ is highly influenced by parasitic rolling resistance. My FWD S60 gets mid-high 30's on the highway. I've discovered while tweaking the alignment myself that toe error (both front and rear) doesn't have to be off by too terribly much or econ will tank down to EPA rating (mid-high 20s) even though the car still seems to handle well.
An overt simple way to gauge whether you have issues here (or a possible dragging brake or wheel bearing starting to go south) is on flat level pavement (and no strong headwind) put the car in neutral at 40 mph. It should keep rolling for quite a distance without slowing much (at least a couple hundred feet). These are relatively heavy cars for considering their size/low wind profile, the mass of the vehicle will continue forward momentum (physics). If I put mine in N at 40 it'll roll a good 1/8 of a mile or more before coming to a stop.
Now I have Pirelli LRRs on mine pumped to 38psi, so your experience may vary somewhat depending on tire type/air pressure. But even with comfort tires at 32psi it should still continue forward for a considerable distance.

[wizechatmgr]

Replace the thermostat if you haven't yet. Possibly the cheapest fix you can attempt. Sounds like it isn't fully closing. How long is this trip time-wise? My car is up to temp in about 5 minutes on a ~30-40 F day.

Are you having any other performance issues beyond the clutch? When was the fuel filter last changed? What weight oil and what drain interval?

Before replacing an O2 sensor I'd take a multimeter/VIDA to it. They can be tested without too much issue.

My '99 V70 XC loves the highway, hates the city...