2000 S70 Base Getting 12mpg

thankswww · Post by **thankswww** » 13 Oct 2013, 04:43

I picked up a 2000 base model S70 in amazingly good shape, with 99,500 miles on it.

Thus far, I've done various maintenance on it, including the timing belt/tensioner, replaced all the shocks, changed oil and filter, even swapped out the heater core (which was leaking) myself. I changed the plugs with OEM volvo plugs about 500 miles ago. I've changed the air filter and cabin air filter. I fixed the stuck button on the gear selector. Basically, my S70 had all of the typical S70 "issues".

The thermostat in my airbox was dead, stuck sucking air in from the "hot" side of the airbox. I fixed this, and now it only gets air from the "cold" side. I've reset the ECU recently as well. I wonder if the constant hot air being introduced to the airbox eventually cooked the MAF sensor.

I've got the car running how I want, in pristine shape, but I'm at my wit's end trying to figure out why this car is getting 11.5-12mpg under typical city driving conditions. From what I've seen, this is roughly half what everyone else seems to be getting, and indeed, I have a turbo Porsche that gets MUCH better gas mileage, which just doesn't seem right.

I've done the following in hopes of getting better mileage:

-Plugs
-Air filter
-Oil and Filter
-Checked tire pressure
-"Fixed" airbox thermostat
-Fixed a vacuum leak on one of the airbox vacuum lines

Using fuel which is approximately 93 octane, so it's not a fuel quality issue as far as I can tell.

No check engine light, though last time I was at the mechanic, he told me that there was an issue with the knock sensor (I've ordered it). The car however, doesn't display any symptoms of a bad knock sensor. It runs smoothly, no smoke out the back, starts and idles well. There aren't any exhaust leaks. I hear what I think sounds like some type of vacuum leak coming from either the fuel rail area, or the exhaust manifold side of the head, but after searching and searching, I cannot find a leak anywhere. It sounds kind of like a whining sound. If I had to guess, I'd say that it sounded like a leaky gasket in some area that is otherwise pressurized. Though again, no rough idle or stuttering acceleration.

I've had the plugs out, check the hoses under the plugs cover, checked the hoses around the intake manifold area.

At a loss. Could faulty signals from a knock sensor cause such poor gas mileage, without throwing a CEL or displaying any other symptoms? It would be a real shame to get rid of this car, which otherwise runs beautifully!

Post by **rspi** » 13 Oct 2013, 05:05

Is it running cold and rich from a bad tstat?

thankswww · Post by **thankswww** » 13 Oct 2013, 05:08

Nope, it heats up in a reasonable amount of time, and does not run hot or cold. The temperature seems quite consistent.

Post by **rspi** » 13 Oct 2013, 05:15

Is it running rich from a vac leak, or does it have a fuel leak?

I would hook up a code reader to make sure it's getting up to 185°.

thankswww · Post by **thankswww** » 13 Oct 2013, 05:18

I'd be surprised if it had a fuel leak. Nothing visible and no smell of a fuel leak. If I were to buy a volvo code reader, how would I find out if the car reached 185 degrees? I'm assuming a typical OBDII reader wouldn't be able to give me this information.

Post by **rspi** » 13 Oct 2013, 05:43

Almost every code reader will report live data. You can have an auto parts store scan the system and give you that data.

The Volvo temp gauge is calibrated to lock in at the 3 o'clock position when the motor reaches 175° and will stay there through 222°.

Is the PCV system in good condition? Have you done the glove test?

thankswww · Post by **thankswww** » 13 Oct 2013, 07:15

I've done the glove test. Glove didn't inflate in the slightest. No smoke from dipstick tube either.

Post by **precopster** » 13 Oct 2013, 07:26

A out of tolerance coolant temp sensor can report incorrectly to the engine's ECU resulting in rich mixtures.

Another avenue to pursue may be gummed up injectors giving a poor spray pattern. They're easy enough to remove and test if you can rig up a fuel supply that won't catch on fire

My 2000 V70 base gets read beautifully with Torque and an ELM 327 bluetooth adaptor. All the live readings you'll ever need are in the paid version of this App.

Post by **rspi** » 13 Oct 2013, 08:18

Good to read that your PCV is in good shape.

Run some Lucas injector cleaner through the next two tanks. My bet is on the temp. As stated a bad sensor can make it run rich. Keep at it, sounds like a nice car to not get fixed.

difflock54 · Post by **difflock54** » 13 Oct 2013, 19:12

Have you checked your o2 sensors, especially the pre cat' side.?
After just under 100,000k they may be needing replacing unless already.
Condition of the catylytic convertor? clogged?