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Old 10-05-2019, 12:49 PM   #1
Banksy
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Default Would replacing my air filter improve my mpg?

Hi everyone,

I have a 2002 SL2 with a manual transmission.

The car has a little over 180k on it and I probably have put like 20-30k on the car since I have owned it without replacing the air filter. Don't know how recently it has been changed before buying it.

Didn't really look dirty and I hit it with some compressed air a while back to try an clean it out which is why I never replaced it.

As of right now it's getting about 35 mpg. My old 99 SL 2 at 200k was getting about 41 so I'm wondering what's going on.

All my mpg calculations have been done using the same gas station (more or less) without using the AC and with the drivers side window down for a for bit of the driving (dunno if that makes a difference or not)

I have done the following recent things to the car.

New gas filter

New valve cover gasket

New rear 02 sensor last year

Patched exhaust leak


I have not done a compression test on the car and really don't plan to due to not having one.


The front drivers side tire was low (like 23 psi) and rear passenger tire was REALLY low during most of this testing (like around 20 or something). So I'm assuming that had an impact.



Also this car before replacing the valve cover gasket was going through 1qt over oil every 5k

Just changed the oil and it looks like it burnt 2 qts.

The valve cover gasket doesn't appear to be leaking from any part that I've checked and I pulled the plug wires and the wells that the plugs go into look dry (had some oil in them before the gasket change).

Dunno what is causing that or if it should be a big concern.

I'm going to run another 5k through the engine and see what the oil consumption is after that because I honestly don't know if that was happening before I changed the gasket. I used a Fil Pro (dunno if I spelled that right. Got it at Advanced Auto) gasket if that is some useful information.

This is my 3rd SL2 and this car has been pretty much bullet proof the entire time I've had it.

Thanks for you time in advance

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Old 10-05-2019, 01:06 PM   #2
SlayZombi
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2001 SL
Default Re: Would replacing my air filter improve my mpg?

Yes, improper tire pressure makes a noticeable difference. Remedy the issue and retest.

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Old 10-05-2019, 02:31 PM   #3
Saturn Night
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Default Re: Would replacing my air filter improve my mpg?

Ain't no stock twin cams getting 41mpg, even my automatic has barely turned 37.0 on an all-highway trip to Toledo, OH. And the automatic has better gearing for economy than the 5-speed manual.

That being said, yes, a clean air filter will improve overall fuel economy by about1-2mpg

...
"What does a Saturn owner do, at the gas station?"

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

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Old 10-05-2019, 02:44 PM   #4
fdryer
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Default Re: Would replacing my air filter improve my mpg?

I like your world art. Where's your latest statement?

Unless the air filter was completely blocked with fine dust strangling air intake, I doubt the reasonable fuel mileage is caused by a relatively clean filter. I'm inclined to believe two tires running lower pressures are contributing to lower fuel economy despite getting 35 mpg. Underinflated tires create more rolling resistance. If tires could have 4,000 psi and don't return a hard ride, every vehicle would benefit with higher fuel mileage. Great for learning how to slide around at the slightest jerk of the steering wheel, losing traction quickly in slick road conditions, and scaring the life out of anyone trying it.

AutoZone has a tool loan program, free when leaving either a cash deposit or credit card charge. Cash returned or credit refunded when a tool is returned. I borrowed a compression gauge but it was faulty and voiced my concern but still not charged for damage. It's presumed wear and tear takes its toll on tools loaned to everyone not caring when its not personally owned. I have a very old rubber cone type compression gauge, still in operating condition but unusable with deep spark plug wells requiring a plug fitting with flexible hose. Borrow one. Most diyers have good experiences borrowing tools from AutoZone. Advance Auto has a similar practice. My nephew didn't know about O2 sensor tools and spent two days trying to remove a seized sensor. A few minutes with a loaner sensor tool loosened the sensor a minute after leaving the store and trying it in the parking lot. For occasional use, tool loaner programs opens up new opportunities for everyone attempting diy car maintenance with less costs in buying seldom used tools.

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Old 10-05-2019, 04:59 PM   #5
Waiex191
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Default Re: Would replacing my air filter improve my mpg?

My 99 SL2 has been over 40 many times. Not lately though. The 55 MPH era was awesome for fuel economy.

...
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Old 10-06-2019, 07:49 PM   #6
Psycho
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Default Re: Would replacing my air filter improve my mpg?

Changing your air filter will help your car breath better and will help with gas mileage. With a dirty air filter the computer is trying to keep the air to fuel ratio where its suppose to be. The less air the car has the more fuel its going to spend. Should change every 3,000-5,000 miles or if you live in the country on dirt roads like I do sooner then that.

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Old 10-07-2019, 02:40 PM   #7
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Default Re: Would replacing my air filter improve my mpg?

Quote:
Originally Posted by fdryer View Post
Unless the air filter was completely blocked with fine dust strangling air intake, I doubt the reasonable fuel mileage is caused by a relatively clean filter. I'm inclined to believe two tires running lower pressures are contributing to lower fuel economy despite getting 35 mpg.
+1

The "dirty air filter costs you x mpg" comes from the carburetor age, when carbs where calibrated for a certain amount of air coming in, and gets repeated every year by newspapers repeating the previous years stories. Modern, computer controlled, fuel injection systems can accommodate a variety of operating conditions.

https://blog.esurance.com/5-gas-myths-busted/

Quote:
Reducing airflow causes the engine to automatically reduce the amount of fuel being used. A dirty air filter may hinder your acceleration speed, but according to Consumer Reports, driving with a dirty air filter no longer has any impact on fuel economy.
Quote:
Originally Posted by Banksy
Also this car before replacing the valve cover gasket was going through 1qt over oil every 5k

Just changed the oil and it looks like it burnt 2 qts.
I hope you were not 2 qts low when you changed the oil. If so, you are killing your engine. The added heat and friction cant be good for your mpg, either. Engine oil provides considerable cooling to internal parts. Check your oil frequently and top off as needed - keep it full at all times.

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Old 10-07-2019, 04:38 PM   #8
onlinebiker
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Default Re: Would replacing my air filter improve my mpg?

You can get 41 mpg by inflating the tires slightly over 42 psi - running 0% alcohol -in warm, dry weather.


Or any day with a 25 mph tailwind....

...
92 SC2
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96 SC2
97 SL2
97 SC2
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