ls430lover

just some observations that are interesting, Would you like to pay for a free oil change with synthetic. after my observations using mobil 1 ep and oem air filter i have been changing the oil around 7500 miles, i noticed my round trip gas mileage from work and a little local has been down to 20 mpg, with 80% highway. i have newer plugs with 20 k on them. i pushed the life of the air filter usually change it around 15 k to 22 k.. yesterday with oil change and and new air filter i am about 1 mpg more per gallon round trip. interesting because if you take 1/21 of a gallon of gas at 3.65 gallon thats 17 cents a mile. i do 800 miles a week x .17 mile is 13 bucks a week or 52 month
i am sticking to 6000 oil changes and air filter at 15k in 2 months i see 100$ in savings seems like no brainer
cheers safe driving

fensterlip

I'm not sure how to factor the variables. Based on what you say, that's completely true, but I know air filters don't change mileage like they used to in the pre-MAS days. Are you thinking there's a minute change in the oil viscosity or lubricity that's making that difference?
I happen to use around 7500 miles between changes with M1 5-20 or 5-30 (i have both and don't remember at the moment) and average 22 to 24 mpg but driving habits, hills, tires, weather and our crappy Cali gas all make a difference. This is North of SF in Sonoma County.
It would be interesting to parse this further.

ls430lover

hi just wanted to respond, its a combination of the two that you mentioned, quite simple the more air flow that uninhibited and the oil fresh that is creating less friction add to better gas mileage more the first, if you research air filter changes you will notice the threads on mpg for other cars. for us with our v-8 i started using premium more frequently because as i posted in past i get better gas mileage with mine using premium vs regular unleaded. the point of this thread was that if you stay up on oil/air filter changes and save lets say 30 to 40 bucks over the oil change it basically pays for a air filter or the labor on the oil change seems like a a no brainer to me. second your mpg numbers above remember you have a 6 speed auto pre 04 have the 5 speed so last night coming home i got 22.5 combined city/highway.

chunkyda

While I appreciate your efforts to save money, I think your math is flawed. Very simply if you get 20mpg and notice an increase to 21mpg you are approximately 5% better off. So take your weekly expense of $146 (800miles / 20mpg x $3.65) and you will see that 5% improvement is about $7.30 less per week on gas. How much more is the synthetic oil vs conventional per quart?
I would also submit to you that one or two tank fill ups is not enough to make the determination that your oil change is the single factor in your percieved milage increase. Do this over the course of a full year and report your findings. There are much better (and free) ways to increase your milage a mere 5% over the long term.
Your A/C compressor is about a 10% penalty to mileage on its own.
easy on the jack rabbit starts
take the extra crap out of your trunk
manually turn off the A/C when not needed
eliminate excessive idling on startup, at the drivethrough...
As far as using premium fuel to increase mpg, again I think you are not spending wisely. Premium is now about 10% added to the cost of regular and I don't think you will get 10% better mpg using it. The benefit of premium will be in engine performance but you are looking to save money so don't stomp on the gas and you will save even more money.
BTW, I have an Excel spreadsheet where I have tracked every single car expense for the past 5 years, you might want to give it a try to see what you can find out about driving habits, environmental factors, fuel additives, etc. Notice how mpg changes from tank to tank even as mpg averages over the course of a few months or years.

jayclapp

Excellent data you have there. You have enough data to convert the chart to a statistical chart. First you need to determine the average for the year shown and plot that average as a single line. Then compute the upper and lower control limits (plus and minus 3 standard deviations) and plot those lines on the chart also. If the process is stable, then the variation within those lines is the normal variation, which means that you have no control over those results and trying to make it go up or down within those limits will be fruitless.

However, your process many not be a stable process. If you have 7 or more consecutive data point that go either up or down, the process is not stable. If you have 7 or more consecutive data points on one side of the average then the process is not stable. In either case, the rules I stated above don't apply.

If the process is stable, then the statistical chart is of great value. If you than have an occasional data point that is outside of the upper and lower limits, that means that something abnormal happened. If you look for that quickly you will be able to determine what the cause was (in that case, it might be a trip that have a much higher mpg). If you have a sudden data point below the lower limit, it should cue you to look for a mechanical problem.

I suspect that you will find that the process is not stable and you cannot apply statistical rules to the process. It man very well be that the process is stable for only short periods of time and changes from winter to summer for instance. In that case you need a period of at least 20 data points to determine the average and upper and lower limits.

The beauty of a statistically stable process is that it can predict the future. If the process doesn't change, future results will remain within the control limits. If the process starts to change (see the rules I stated above) you can look for the reason.

Also, a control chart will give you peace of mind concerning the variation in mpg you see and when the variation is significant and action should be taken.

ls430lover

chunky da appreciate your insight i don't have the patience or time to create expenses over gas or an air filter, was simple math and observations so appreciate your thoughts,
as fyi to your 5% to 10% i am getting 1 or 2 mpg better in the last week spend 40 hours with your spreadsheet my math tells me the air filter will pay for itself.. one other simple formula for you to save $$$$
synthetic mobil 1 ep or penzoil ultra, new air filter and michelin primacy mxv4 with good fill with air I'm no harvard grad but bet you save 50$ month at 3200 miles a month
just saying
peace

ls430lover

and jay fyi
you seem like a smart cat thanks for the input

username32

Only 20? I been avging 23.5 with about 80% highway and even those 80% of the highway is crappy LA traffic on 405 and 605 freeways. And mine is the old 01 with the 5 speed, i heard newer models get even better mpg with the 6 speed. My best was to and from Vegas i got 26.8mpg steady 75mph.

chunkyda

I guess what I am trying to show with the chart is that from one fill-up to the next the mileage is almost always plus or minus 1-2 mpg. For your theory to be valid you need to track more than one fill-up.

ls430lover

and i appreciate your thoughts, been a week now i am getting about 1.5 mpg more a gallon since oil change and new air filter, my numbers still apply, even if it was .4 miles to a gallon it would pay to change the air filter at 15k is the point of the thread, people and garages thinking air blowing the filter will get make it go longer the reality is the air flow inhibits with mileage and the filter getting saturated thus decreasing air flow
if anyone has switched to the k and n with good results please post, i know it will increase air flow but is it filtering as well as the paper?

CowBoE

Getting 11-12 MPG is very abnormal, unless you are constantly in a stop and go traffic,
and rarely get it on a highway speed.

Heck with the gas price emptying our pocket these days, this is definitely worth getting resolved,
and likely it's going to be more of a maintenance/tuneup than costly repairs.

Here are sequence of steps I would take:

1. Go to the autopart store and check for any enging error/warning codes.
I've seen cases, where the error code shows up in ODB reader,
but didn't light up the Check Enging Light icon on dash.
I won't be surprised if the ODB reader finds P0172 code.

2. I know you replaced the air fitler, but that's not enough.
Check the entire air passage from the entry at the front bumper area
and follow it all the way to the throttle body.
Use a flashlight, use flexible stick, or even remove the air passage hoses
and besure that animals didn't leave something in the passage that blocks the full air flow.
This happens quiet a bit on cars that sit a long period and do not get regular driving.
39K miles is extremelely low miles for 13 year old car.

3. Clean MAF (mass airflow sensor). This is a simple task.
MAF constantly controls and adjusts the air/fuel mixture ratio.
If this sensor is dirty or malfunctioning, the a/f ratio will be out of whack.

4. Clean Throttle Body. There is a flap that controls amount of air going into the
combustion chamber, and if this is not opening up sufficiently for the speed that
you are driving, then you'll be in "rich" condition and burn more fuel than necessary.

5. Check spark plugs. These Iridium spark plugs are designed to last 100-120K miles.
I highly doubt that you need to replace it, but do check each for massive corrosion
or oil/carbon buildup. Also check for gap, as wrong gap will definitely not
fire at perfect time, and will cause misfire or incomplete burning of fuels.
If you have to replace it, which I don't believe, only get the matching OEM.
This car is sensitive, and I've tried slightly cheaper OEM Iridium plugs,
and it caused misfire, so I had to get the matching OEM.

6. Replace PCV, and check all vacuum lines. Broken or leaking vacuum could disguise
all sorts of problems.

7. Engine oil and gasoline have shelf life. So if the car sits a long time,
the condition of oil and gasoline won't be optimal. Even if the car is not driven much,
the car should be started at least once every couple of weeks, and preferably,
at least drive it for about 30 minutes.


Here are videos on 3,4,5, and 6.

Throttle Body and Mass Airflow Sensor cleaning:

Spark Plug replacement

PCV replaement

If you happen to break connectors during the work,
here are videos on how to replace them.