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Old 03-13-2018, 02:47 PM   #1
PrestonIII
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Default Poor Fuel Economy compared to everyone else.

I'm sure this has been covered before, but I'm asking about my specific situation:

I drive a 54K mile '94 SL2 HCE, with an automatic and all the options. I've had this car 6 months, purchased from an estate.

I live 10 miles from Columbus Ohio via mostly 4 lane highways. I live 18 miles from work via mostly 4 lane interstates. I do very little city driving, maybe 15 percent of my overall driving.

I drive the speed limits, usually 55 or 70 mph.

The best fuel economy I've seen with my car is 24 mpg. Why isn't it better?
I had a '93 SL2 auto, and mpg was about the same as this one: 23 mpg.
I had a '94 SL1 stick and got 28 mpg with it, though I saw 46 mpg once on a round trip from Columbus to Indianapolis (350 miles, all interstate).

I have a '93 GMC Suburban that gets about 11 mpg overall, mixed driving.

I live near Columbus Ohio, where the weather is always cloudy overcast, higher humidity, and generally moderate (very few extremes).


Why is my mileage so bad compared to all the stories I read in here?

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Old 03-13-2018, 03:01 PM   #2
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Default Re: Poor Fuel Economy compared to everyone else.

Did you check for the original (faulty) two wire coolant sensor? If idle remains above 800 rpm and the temperature gauge stays close to the 1/4 mark, these are two signs of a faulty (cracked) sensor. There's also a worn seal on the thermostat that allows coolant to seep around to keep coolant temps colder than ideal (185F-195F). Both parts are failure prone when the original coolant sensor cracks, allowing the engine to overheat, never turning on the cooling fan and ruining the t-stat seal. Another symptom of t-stat seal failure is heater output is lower in freezing temps. Once replaced, heater operation returns to full output with many complaining of too much heat, the way it should be to allow temperature and blower control to modulate heater output (all Saturns use a constant coolant flow thru the heater core - no shut off valve with the temperature door adjusting air flow thru the heater to blend with outside air). one or both in faulty condition reduces fuel mileage.

Last edited by fdryer; 03-13-2018 at 03:10 PM..

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Old 03-13-2018, 03:39 PM   #3
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Default Re: Poor Fuel Economy compared to everyone else.

I agree with the above reply, however; one must also look at how heavy we might tromp on the gas pedal.

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Old 03-13-2018, 03:58 PM   #4
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Default Re: Poor Fuel Economy compared to everyone else.

Haha, yup. The driver is the largest factor, IMHO. I used to get a consistent 35-38 in my SL2. Get my mom or wife behind the wheel, and it went into the upper 20s.

Drive like an aggressive ******* and you get to buy extra gas.

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Old 03-13-2018, 08:50 PM   #5
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Default Re: Poor Fuel Economy compared to everyone else.

Quote:
Originally Posted by toggenburg View Post
I agree with the above reply, however; one must also look at how heavy we might tromp on the gas pedal.
One might consider the losses associated with having only 15 working valves, out of the 16 contained in the cylinder head. It dropped my economy from 33-35mpg, down to 26mpg and an extremely rough idle.

It happened, because I Tromped on my gas pedal, when leaving work, two weeks ago.

Columbus traffic is brutal, as well. Yeah, they have 4-lane highways. They also have bumper-to-bumper, rush-hour traffic jams, road construction, and an airport to deal with. When you see the orange "Lane Merge" signs, in Columbus that means: "Floor your car right up to the orange barrels, and IMMEDIATELY swerve over into the large line of traffic, full of responsible drivers trying to obey the construction zone speed limits."

Been there, plenty of times, myself. You couldn't pay me to drive on I-70, I-270, or I-71 regularly. Cops patrol with helicopters, and drivers are about as "courteous" as they are in downtown Pittsburgh, PA.(Pittsburgh, much like its football fans, is considered the city with the worst drivers in the entire country)

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Old 03-14-2018, 10:35 AM   #6
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Default Re: Poor Fuel Economy compared to everyone else.

Quote:
Originally Posted by toggenburg View Post
I agree with the above reply, however; one must also look at how heavy we might tromp on the gas pedal.
^^^ This.

If EVERY vehicle YOU drive is getting less than the expected MPG, you either have extremely bad luck or you have very bad driving habits.

The lady friend and I can get a HUGE swing in MPG driving the same vehicle. Observe us both drive and it will not be hard to determine why. She constantly has to be stomping on something, whether it be the brakes OR the gas pedal. Yeah, her brakes wear out much faster than mine too.

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Old 03-14-2018, 10:59 AM   #7
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Default Re: Poor Fuel Economy compared to everyone else.

Several MPG difference between when my wife and I drive the same car.

She warms the car up, idling extensively.

Keeps her foot on the gas until the last minute, then switches immediately over to the brake. I spend a lot more time coasting when coming towards a stop sign or red light.

She does not use cruise and her speed will vary from 5~10 mph below the limit to 5 over.

She is also a left-foot braker and I suspect her foot is occasionally on the brake when driving, though I can't prove it and have been married too long to think proving it is a good idea or will change anything

I did get her to stop shifting out of Reverse and into Drive while the car was still rolling, though.

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Old 03-14-2018, 07:48 PM   #8
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Default Re: Poor Fuel Economy compared to everyone else.

I thought about the coolant temperature sensor, but discounted it because the car runs perfectly, idles nicely, and shows no codes for the PCM. The idle speed is normal, though one can only guess about the exact speed by reading the tachometer. At such a low rpm, there are no marks on the gauge. The temperature gauge hovers around the 1/4 mark when running, though I've seen it climb to nearly half in slow traffic. And there simply isn't enough heat from the heater core. I can barely keep the windshield defrosted in this cold humidity. This car has 2 temperature senders doesn't it? Other posts I've read have indicated that the temperature gauge and amount of heat I get are normal for the car. I remember my previous Saturns never getting warm in the interior (and one of them had a new radiator and thermostat).

As I said, I drive predominantly interstate at the posted limits, so acceleration and braking aren't issues. As a matter of fact, I have a fuel economy monitor on my Garmin GPS, and regularly get well above the 90% range while driving and just as high total at the end of a tank of gas.

Nobody else drives my car since I'm a single guy, and over 60 years old.

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Old 03-14-2018, 08:19 PM   #9
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Default Re: Poor Fuel Economy compared to everyone else.

Your choice to check these two parts.
Attached Images
File Type: jpg plastic-brass cts.jpg (82.8 KB, 7 views)
File Type: jpg t-stat 1.jpg (119.5 KB, 5 views)

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Old 03-14-2018, 10:13 PM   #10
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Default Re: Poor Fuel Economy compared to everyone else.

Yeah, i say to check the ECTS and thermostat anyway. The 1994 shouldnt be running at 1/4, it should be somewhat higher than that, and either one will cause bad heat, lowered fuel economy, and hovering 1/4 on the coolant temp gauge.

Its basically free to check, and if its not the issue, well you can move on from it.

...
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Old 03-14-2018, 10:46 PM   #11
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Default Re: Poor Fuel Economy compared to everyone else.

1/4 on the gauge is too low for any 1st gen, no matter who says what. The majority of 1st gens run at the 1/2 mark, though it was also common enough to run at the same mark as the rest...around 3/8.

The gauge is run off 1 sensor and the PCM use's another sensor (the same sensor that '96-'02's kept) so it's possible the low reading is just from a bad gauge sender. Stick a thermometer in the coolant reservoir when cold and let it warm up (bad idea to open a hot coolant system...) and see what it says the temp is there...if much below 190f there's a problem with the system if 185-190f then there's a problem with the gauge sender.

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Old 03-15-2018, 01:21 AM   #12
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Default Re: Poor Fuel Economy compared to everyone else.

Quote:
Originally Posted by PrestonIII View Post
I thought about the coolant temperature sensor, but discounted it because the car runs perfectly, idles nicely, and shows no codes for the PCM. The idle speed is normal, though one can only guess about the exact speed by reading the tachometer. At such a low rpm, there are no marks on the gauge. The temperature gauge hovers around the 1/4 mark when running, though I've seen it climb to nearly half in slow traffic. And there simply isn't enough heat from the heater core. I can barely keep the windshield defrosted in this cold humidity. This car has 2 temperature senders doesn't it? Other posts I've read have indicated that the temperature gauge and amount of heat I get are normal for the car. I remember my previous Saturns never getting warm in the interior (and one of them had a new radiator and thermostat).

As I said, I drive predominantly interstate at the posted limits, so acceleration and braking aren't issues. As a matter of fact, I have a fuel economy monitor on my Garmin GPS, and regularly get well above the 90% range while driving and just as high total at the end of a tank of gas.

Nobody else drives my car since I'm a single guy, and over 60 years old.
If your coolant gauge is hovering at the mark, that means the thermostat needs to be replaced, or the ECTS sensor is bad.

Note: Either condition will NOT always send a code to the PCM. It will run the engine very rich, will foul the plugs quicker and return very poor fuel economy.

A 1994 Saturn S-Series should be just below the mark, when it gets up to temperature.

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"He checks the gas, and fills the oil....."

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Old 03-15-2018, 07:50 AM   #13
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Roll Eyes Re: Poor Fuel Economy compared to everyone else.

The OP should really listen to the above. It is good advice.
That is a clear indication that both the coolant temperature sensors and the thermostat are suspect.
And if the sensors are plastic, they need to be replaced, period.

Also I strongly second the statement that either or both of these being defective may not necessarily set codes.
The PCM will simply act as if the engine is in the process of warming up which is not a fault condition.

As for economy being dependent upon the driver.
Oh yes. Same situation in our household.

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Old 03-15-2018, 12:47 PM   #14
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Default Re: Poor Fuel Economy compared to everyone else.

Quote:
Originally Posted by DIYguy View Post
Also I strongly second the statement that either or both of these being defective may not necessarily set codes.
Third. Neither a bad ECTS or bad ECTS connector will set a code.

Lack of heat is not normal on an SL2. At ambient temps of 10F, I've got warm air in about 5~7 miles of driving. Shortly after that, it can get to "uncomfortably warm" very quickly

I understand the the SL1 and other SOHC cars produce less heat but I have no experience iwth them

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Old 03-15-2018, 02:49 PM   #15
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Wrench Re: Poor Fuel Economy compared to everyone else.

^^^^^^^^^^^ what alordofchaos said about defective parts ^^^^^^^^^^^.
Especially if the OP still has plastic bodied sensors, the connectors for them could be polluted and corroded.
And as has been discussed many times on this forum, they really can't be cleaned once they get contaminated or corroded.
Replacement is the only good option.
If you pull the connectors and they have green (or wet) on them, they are beyond salvage already.

Another side note about all of this.
If the engine is running chronically rich, regardless of the reason, the cat can eventually fail.
And because it is OBD-1, you don't have the secondary O2 sensor to help warn you.
Spend a few $$ now or potentially $$$$$ later.

Speaking of that, I don't think anyone has mentioned the O2 sensor.
The car may only have 54k miles on it, but at that sheer age low mileage alone does not mean the O2 sensor is still OK.

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Old 03-15-2018, 10:17 PM   #16
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Default Re: Poor Fuel Economy compared to everyone else.

On all these recommendations, I think it's time to replace 2 sensors and a t-stat. Should I replace the one in the transmission at the same time, as I've heard that they're all 3 the same. Any recommendation on a brand or place to get a "good" one? Are there more? Intake Air Temp Sensor?

I know that one of the sensors is in the driver's side end of the cylinder head. Where is the other? AND, which is which?

I only have the P.O.S. Haynes book, and I know it's not worth a damn. It's really bad about not giving enough information.

Actually, I'd love to get hold of a set of Factory Service Manuals, especially the Electrical Wiring volume.

And by-the-way, thanks guys!

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Old 03-16-2018, 07:11 AM   #17
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Default Re: Poor Fuel Economy compared to everyone else.

ECTS has 2 a wire plug. Any auto parts store has this sensor for under $14.
Yes, it's the same sensor under the air snorkel in front of the battery area, nearby the trans spin-on filter.

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Old 03-16-2018, 08:14 AM   #18
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Default Re: Poor Fuel Economy compared to everyone else.

Quote:
Originally Posted by PrestonIII View Post
On all these recommendations, I think it's time to replace 2 sensors and a t-stat. Should I replace the one in the transmission at the same time, as I've heard that they're all 3 the same. Any recommendation on a brand or place to get a "good" one? Are there more? Intake Air Temp Sensor?

I know that one of the sensors is in the driver's side end of the cylinder head. Where is the other? AND, which is which?

I only have the P.O.S. Haynes book, and I know it's not worth a damn. It's really bad about not giving enough information.

Actually, I'd love to get hold of a set of Factory Service Manuals, especially the Electrical Wiring volume.

And by-the-way, thanks guys!
The Air Intake Temp Sensor, the Transmission Temp Sensor, and the Coolant Temp Sensor are all the same.

Do NOT mess with the Thermostat, until you verify the coolant temp sensor has been replaced with a brass replacement.

Do NOT waste the money on replacing the Air Intake Temp sensor. These sensors rarely fail, and they are installed with RED thread locker. You will destroy the housing to your air cleaner well before you will break that sensor loose for replacement.

As far as the O2 sensor, it is probably ok. One of the few codes that actually seem to work on OBD-I systems(cars built from 1982-1995) are the codes for the oxygen sensor.

If you don't have trouble codes for your O2 sensor, leave it alone.

Do one thing at a time, as troubleshooting a poor fuel economy issue can be die to multiple causes. All troubleshooting is about isolating the root cause of the symptoms.

So, it is process of elimination.

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Old 03-16-2018, 12:28 PM   #19
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Default Re: Poor Fuel Economy compared to everyone else.

Quote:
Originally Posted by PrestonIII View Post
........... The temperature gauge hovers around the 1/4 mark when running, though I've seen it climb to nearly half in slow traffic. And there simply isn't enough heat from the heater core. I can barely keep the windshield defrosted in this cold humidity. .........
Remove the two wire coolant sensor for comparison to pictures posted. Replace it if it's a round, bullet shaped nose. Replace the t-stat to have real heat.

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Old 03-16-2018, 01:12 PM   #20
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Default Re: Poor Fuel Economy compared to everyone else.

Quote:
Originally Posted by PrestonIII View Post
On all these recommendations, I think it's time to replace 2 sensors and a t-stat. Should I replace the one in the transmission at the same time, as I've heard that they're all 3 the same. Any recommendation on a brand or place to get a "good" one? Are there more? Intake Air Temp Sensor?
auto trans temp and intake air temp (IAT) sensors rarely fail.

The IAT is usually mentioned because, if you need a good connector (pigtail) for the ECTS, you can either pay for a new one, or get an IAT connector for a dollar or so from a junkyard.

If your ECTS shows corrosion, it is possible (likely?) taht just replacing the ECTS won't fix the problem - you may have to solder in (and shrink wrap) a new connector, too. I did - cleaned teh corrosion off the connector but it did not fix my mpg/stalling/hard start problems until I changed the connector

Some links from a previous post - last link shows clearly both temp sensors (follow the top radiator hose back to the block, just past that. You only need to replace the 2-wire one, as stated - your one-wire one seems to work fine as your instrument panel is showing the correct temp.
Also see this thread, esp post 14 and below
http://www.saturnfans.com/forums/sho...d.php?t=191883

It is quite possible that the parts store person will get confused when you say temp sensor, since your car has two (one for teh instrument panel and one for the PCM). open the box in store and take a look, might save you a trip later
Both sensors have two prongs, even though one has only one wire

OldNuc has mentioned Standard Motor Products part #TX73 as a good number to cross reference for teh ECTS. OEM part numbers provided in link above

...
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