Getting only 15-16 MPG combined driving...

Volvich · Post by **Volvich** » 14 Mar 2013, 13:17

Hi all,
I'm only getting 15-16 miles per gallon of 91 octane fuel on my 98 c70 coupe turbo.
I had a CEL on (evap large leak) and I thought that would be the reason, but no, I've fixed it a month ago
and I'm still getting the same 15mpg.
I have a turbo failure, oil gets sucked into intake tube as my mechanic said. Also recently i disconnected the
intercooler hose, and it was all oily inside. Would that affect efficiency?
What is the average mpg on these T5 turbos? The milage on mine is 119K.
What else should I look at? Any advice would be greatly appreciated!

Post by **mercuric** » 14 Mar 2013, 15:20

Really depends on your driving style... and how much time you spend sitting at lights.. short trips really bring it down too!
What do you get cruising on the freeway if you reset the counter as you come up to speed, post o2 sensor warmup?

Volvich · Post by **Volvich** » 14 Mar 2013, 15:32

On the freeway I hardly get 20mpg. Realistically 18-19..

Post by **jblackburn** » 14 Mar 2013, 20:44

Turbo's probably fine; it's more likely a plugged up PCV system at the oil trap.

Freeway for how long? If you reset the average MPG and cruise at a steady speed, what's it showing>

Mine averaged about 16 city/28 hwy. 23 mpg in mixed driving.

Volvich · Post by **Volvich** » 15 Mar 2013, 15:45

I drive around 50-70 mi fwy and 100 mi city a week and have to put ~11 gallons a week. I plan to clean the throttle body, inspect and possibly change the spark plugs before I smog test the car.
Not sure if that will contribute much to efficiency. Btw, yes, the car has power, but I believe it can do better.
Sometimes it feels like it's nose is congested, it can't breathe freely... donno, maybe it's just me wanting more out of the engine. But when you step on the gas there is a hesitation for a second before it responds.
Pcv is such a pita... but yea I should do that too.

Post by **EstVolvo** » 15 Mar 2013, 22:59

Try to test the oxygen sensor.

Post by **mercuric** » 16 Mar 2013, 00:25

o2 sensor sluggishness would definitely explain the hesitation and poor mileage.. should be more pronounced when warm, after the o2 sensor has heated and you've gone into closed loop in that case.

air intake leaks also come to mind, as does low or inconsistent fuel pressure.

Post by **cn90** » 16 Mar 2013, 04:12

For an 850, S/C/V70 with automatic...
With:
- tires at 35 psi or
- single driver (+/- passenger)
- no heavy cargo
- car properly aligned
- uninterrupted highway speed of 65 mph

You should get approx. 28-30 mph.

If not, do a complete tune-up first:
- spark plugs (Bosch vs NGK copper)...about $2/each.
- cap/rotor (Bosch only)...about $55.
- spark plug wires (Bougicord only)...about $55.

Once you have done this refresh of the ignition dept, troubleshooting gas consumption is much easier.
Remember that fuel mileage problem can cost you a lot of gas money, so at 120K miles, the above is a good investment regardless.

Volvich · Post by **Volvich** » 19 Mar 2013, 13:58

Thanks all for replies!
Is there a way to test o2 sensor other than with a butane torch? I'm afraid it'll damage the sensor.
I was thinking of hooking some tiny wires to the sensor ports and hauling them into the cabin so i can monitor the signal with a multimeter while I'm driving. But what voltage should I get?

... and what is a "closed loop" mercuric had mentioned?

anmartin44 · Post by **anmartin44** » 19 Mar 2013, 17:16

When was the last time you changed your air filter? Let's keep it simple first!