1998 S70 Bad Gas Mileage

Gazoogleheimer · Post by **Gazoogleheimer** » 23 Jan 2010, 19:05

I have a 1998 S70 with 70,200 miles and I have kept it as a habit ot check the gas mileage every time I fill up. With 93 "octane" (RON/AKI) gasoline, I only get about 15 MPG (this is calculated via trip odometer, not trip computer.) What's wrong? Do I need new plugs? I performed the airbox mod to try to improve things but nothing really changed.

Most of my driving is, however, city driving--so that might simply be the cause.

Post by **jblackburn** » 23 Jan 2010, 19:26

I get about 17-18 between the 200 downtown stop lights we have here, and I have the T5 model that eats gas like crazy.

New plugs could help...check around for vacuum leaks as well. It could be a bad O2 sensor as well, but likely you'd get codes for that.

Gazoogleheimer · Post by **Gazoogleheimer** » 23 Jan 2010, 21:27

Yes, I have checked around the engine bay for vacuum leaks but did not find any. My thermo-vacuum valve on my airbox thermostat had failed and was a vacuum leak, but upon plugging that there was no change in gas mileage.

salts850 · Post by **salts850** » 23 Jan 2010, 22:05

A couple other things that can contribute with poor fuel mileage are your tire pressure and if your alignment is off. I understand your situation is more than just the two I listed, but something to keep in mind that is often simple and overlooked.

Gazoogleheimer · Post by **Gazoogleheimer** » 23 Jan 2010, 22:13

Yes, my pressure is right at 36 but I haven't checked my alignment.

salts850 · Post by **salts850** » 23 Jan 2010, 22:25

Not sure how long you've owned your vehicle for, but if never done, the fuel filter is a good idea too. I've worked in various shops and people never seem to get the filters replaced. A fuel injector service works great, especially if never done. I'm not too familiar with the volvo injectors, but gm's 3.8/3.1 would get so clogged it would trigger the ses. People take them out and clean them by hand, but from my experience it's not even close to what you get with the cleaner running through the entire injector. If i keep my trans switched to econ. on the highway i get anywhere from 29-31 mpg.

Gazoogleheimer · Post by **Gazoogleheimer** » 24 Jan 2010, 22:50

Yeah. I've only owned the vehicle since late last summer and I am the 3rd owner. As I said, it doesn't have too many miles, but perhaps that would be a quick and easy fix--or at least my Haynes makes it look that way.

Gazoogleheimer · Post by **Gazoogleheimer** » 26 Jan 2010, 11:28

Any other ideas?

C@lvin · Post by **C@lvin** » 26 Jan 2010, 11:55

I see you're in Atlanta. Do you spend a lot of time stuck in rush hour traffic? Is most of your driving city, urban, highway, mixed? From my experiences getting stuck in traffic in Atlanta I wouldn't be at all suprised by 15 MPG if your experience is similar.

For comparison, my commute in my 98 S70 with 190K is about 23 miles each way in what I would call "urban" environment -some 55MPH, some 50MPH, some 45MPH speed limits and about 10-15 stop lights without a lot of congestion. I leave it in "sport" mode and exclusively use 93 Octane fuel. I did the air box mod as well as the 960 throttle plate swap and recently installed a K&N filter. My MPG average is right around 22. The fuel filter and plugs were change at about 184K and I changed to synthetic (Mobil 1 10W40) at about 186K.

In addition to what others have mentioned, have you checked your PCV? Wouldn't think it's an issue with only 70K but could influence MPG if clogged.

I'm sure you know your'e due to replace the timing belt at 70K, but feel obligated to mention is just in case......

9394volvo850s · Post by **9394volvo850s** » 27 Jan 2010, 18:04

get your cam timing out of the retarded setting its in. slightly advancing cam timing shifts power lower in the RPMs, making city driving require less throttle.