Another gas mileage thread

[ProDarwin]

Maybe someone on here can help me. This is my 4th daily driven Saturn. I've put probably 150k miles on different S cars at this point, and my two main DDs have always gotten exceptional mileage. Back and forth to college I could easily get 38-40mph averaging over 70mph. Both cars also returned ~34-35 commuting.

My current beater wagon, which I have had for around 15K miles does not do as well. Its a 95 SW2 Auto with around 150k on it. My last 10 tank average was 31mpg, and it seems to be going down. Several fill ups I have seen 26-28mpg. Even all highway trips I'm barely hitting 30mpg.

Attached is my maintenance history since I've purchased the car (Dec. 2008). I'm pretty sure I've covered all of the basics. No codes, no performance problems. The car runs great. Am I missing anything?

[DonP]

My last 10 tank average was 31mpg, and it seems to be going down. Several fill ups I have seen 26-28mpg. Even all highway trips I'm barely hitting 30mpg.

Attached is my maintenance history

Maybe it is my browser, but I do not see a maintenance history.

In any case, I would expect MPG to drop in summer, and winter, and peak in spring and fall. (See graph in my photos) for my '95 SL2.

A couple issues for sudden poor MPG not attributed to changes in driving profile or seasonal variations could be failed/stuc-open t-stat and/or a lazy O2 sensor. Neither of these would be likely to show up as a noticeable driveability issue or set a code on an OBD1 vehicle.

[ProDarwin]

Originally Posted by DonP

Maybe it is my browser, but I do not see a maintenance history.

In any case, I would expect MPG to drop in summer, and winter, and peak in spring and fall. (See graph in my photos) for my '95 SL2.

A couple issues for sudden poor MPG not attributed to changes in driving profile or seasonal variations could be failed/stuc-open t-stat and/or a lazy O2 sensor. Neither of these would be likely to show up as a noticeable driveability issue or set a code on an OBD1 vehicle.

I posted an image of my spreadsheet. Here is a direct link: http://i12.photobucket.com/albums/a2...aintenance.jpg

I'm aware of mileage changes during seasons. As I said, I have been daily driving Saturns for many years. This is not a sudden drop. I have owned the car for over 15k miles, and the mileage has always been bad. I have addressed what I believe to be all of the common causes, and I'm still getting crap mileage.

If you could see the maintenance log, the issues you mentioned have been addressed.

[Slammin96]

its probably a lazy 02 sensor. I know my MPG has been dropping lately and its the only culprit i havent checked/replaced

[DonP]

What were your other two Saturns?

I would expect the SW2 to get significantly lower MPG than a SL1 for example, especially as a daily driver in the Fairfax County area. And in NVA, summer weather with its impact on economy did not really arrive until nearly August.

[ProDarwin]

Originally Posted by Slammin96

its probably a lazy 02 sensor. I know my MPG has been dropping lately and its the only culprit i havent checked/replaced

The O2 was replaced ~1000 miles ago.

Originally Posted by DonP

What were your other two Saturns?

I would expect the SW2 to get significantly lower MPG than a SL1 for example, especially as a daily driver in the Fairfax County area. And in NVA, summer weather with its impact on economy did not really arrive until nearly August.

93 SW2 and 97 SC2

I am aware of the weather. This is not a seasonal change. Mileage also sucks on highway trips as well (66 or 7 to Winchester, 270 to Frederick, 95 to Aberdeen, etc), so its not just a driving cycle problem.

[Leafy]

its an automatic, getting 30 mpg is pretty good. now if this was a 5spd I'd be concerned with that mpg figure.

[lil_buddy]

What about cleaning the throttle body and the EGR?

I feel your pain by the way, I'm only getting 30-32 mpg and I have an SOHC. Wish I knew why.

[ProDarwin]

Originally Posted by lil_buddy

What about cleaning the throttle body and the EGR?

I feel your pain by the way, I'm only getting 30-32 mpg and I have an SOHC. Wish I knew why.

TB has been cleaned, but could probably use another cleaning. I don't think I have ever cleaned the EGR, its worth looking into. I'm not sure either would affect mileage as much as driveability.

[Pitcher]

Two things:

1) I would run a full bottle of Amsoil P.I. (Performance Improver) in a full tank of gas. It will help your gas mileage.

2) What is the air pressure in the tires? Let us know and fill them up to 39-42 if the sidewall says 44 max. It will help your gas mileage also.

Do both and post back the next MPG calculation.

[Leafy]

or you could use any brand of fuel system cleaner, read the label they all have the same crap in them, for the most part. next step would be to sea foam it.

[ruley73]

Did you replace one or both of the coolant temp sensors? The temp sending unit is the one-wire sensor unit near the water outlet on the cylinder head and the engine coolant temp sensor is the two-wire sensor that is mounted a little lower. The latter is the one that always causes problems and should be replaced if it hasn't been already.

I would also suggest replacing the fuel filter.

[ProDarwin]

Originally Posted by Pitcher

Two things:

1) I would run a full bottle of Amsoil P.I. (Performance Improver) in a full tank of gas. It will help your gas mileage.

2) What is the air pressure in the tires? Let us know and fill them up to 39-42 if the sidewall says 44 max. It will help your gas mileage also.

Do both and post back the next MPG calculation.

1. Thats just injector cleaner. It has been done several times.

2. I don't run with air pressures that high. Its not a safe practice IMO. Even autocrossing I almost never cross 40psi hot. Lets just go ahead and cross air pressure out of the equation as I always have an eye on my tire pressures, and it hasn't seemed to affect the other two DDs I've had. Note that the other DDs were on tires that ranged from high wear 195s to 205 Z1s to 225/50 RA1s (at 24 psi )

Originally Posted by ruley73

Did you replace one or both of the coolant temp sensors? The temp sending unit is the one-wire sensor unit near the water outlet on the cylinder head and the engine coolant temp sensor is the two-wire sensor that is mounted a little lower. The latter is the one that always causes problems and should be replaced if it hasn't been already.

I would also suggest replacing the fuel filter.

I replaced both.

I will look into the fuel filter. Does this normally have an effect on performance? I would guess that this would manifest itself as a drive ability issue as well.

[Slammin96]

a dirty fuel filter will indeed have an affect on performance and MPG. At least I know it did on my 94 GT.

[nmikmik]

Sorry to her you still have a problem after all the maintenance you've done to it.
I noticed you mentioned caliper problems @138101, I assume you "cut" the rotors when you did the brakes, what color where they and what color they are now? If the problem is with the calipers pins or rust inside'em you are going to have a drag on your rotor that is major contributor to the decreased MPGs. Probably more noticeable on the freeway. Also I've noticed you added the hitch, what kind was or more important how heavy is it, more weight usually don't help MPGs either.

[Pitcher]

Originally Posted by ProDarwin

1. Thats just injector cleaner. It has been done several times.

2. I don't run with air pressures that high. Its not a safe practice IMO. Even autocrossing I almost never cross 40psi hot. Lets just go ahead and cross air pressure out of the equation as I always have an eye on my tire pressures, and it hasn't seemed to affect the other two DDs I've had. Note that the other DDs were on tires that ranged from high wear 195s to 205 Z1s to 225/50 RA1s (at 24 psi )

I always run tire pressures ~2 psi under the tire sidewall max, 30 years worth. In snow, ice, etc and have great traction. No accidents. If you don't want to, that's fine. What pressure do you run in your tires and what does it say for max on the sidewall?

The Amsoil is wonderful in cleaning combustion chamber deposits, intake valve deposits and port fuel injector deposits. Have you ran the PI which has a lot of PEA in it or other lower quality injector cleaners?

Good luck, I hope you improve your MPG!

[ProDarwin]

Originally Posted by nmikmik

Sorry to her you still have a problem after all the maintenance you've done to it.
I noticed you mentioned caliper problems @138101, I assume you "cut" the rotors when you did the brakes, what color where they and what color they are now? If the problem is with the calipers pins or rust inside'em you are going to have a drag on your rotor that is major contributor to the decreased MPGs. Probably more noticeable on the freeway. Also I've noticed you added the hitch, what kind was or more important how heavy is it, more weight usually don't help MPGs either.

No, I didn't "cut" the rotors. I just replaced the pads. The rotors were not warped, "cutting" them was not necessary. I cleaned, then later replaced all of the pins, boots, and bushings. I've eliminated all of the drag from the front. Regardless, you'll notice that all 4 rotors were replaced very recently, at that time I inspected the brakes and there was no abnormal wear.

The hitch weighs 26lbs.

[ProDarwin]

Originally Posted by Pitcher

I always run tire pressures ~2 psi under the tire sidewall max, 30 years worth. In snow, ice, etc and have great traction. No accidents. If you don't want to, that's fine. What pressure do you run in your tires and what does it say for max on the sidewall?

The Amsoil is wonderful in cleaning combustion chamber deposits, intake valve deposits and port fuel injector deposits. Have you ran the PI which has a lot of PEA in it or other lower quality injector cleaners?

Good luck, I hope you improve your MPG!

I usually run a bottle of cheap FI cleaner every oil change or so. I can give a higher-quality one a shot though. Its only a couple bucks.

What pressures I run in my tires depends on what tires are on the car. Crappy OEM sized 195 60 15s... 30psi all around. It also depends on how the car is loaded (although for the purposes of this thread... assume the car is empty. I don't complain about my mileage if I am towing something... I know its going to suck).

[geartooth94]

SFI vs. MPFI of earlier DOHCs ?

[ProDarwin]

So, skimming back through, I should:

A) Clean the EGR (link to linear EGR cleaning thread please?)
B) Clean the TB again
C) Replace the fuel filter
D) Run a can of high-quality injector cleaner through the car

Today at a stoplight the car started stuttering like crazy at idle until I revved the engine. I'm suspecting EGR based on past experience, possibly fuel filter. Luckily, both are on the list above. If not, I suppose I could have a coil-pack going bad.

Originally Posted by geartooth94

SFI vs. MPFI of earlier DOHCs ?

Umm, what?