Very low mpg, help plz
 

Hello I just bought a 01' Boxster S about 2 weeks ago. I changed the oil a few days later and I drive at around 3k rpm. I'm still only getting about 16 mpg and I drive mostly on the freeway. Am I doing something wrong or is it the car? and how do I fix it? thanks!

Did you have a PPI done before you bought it?
Is it running properly?

Changing the oil has very little to do with MPG. Yea, maybe a little impact, but...

What RPM are you shifting at?
Are you in 6th gear at freeway speeds?
how fast are you going
uphill? downhill?

Also without pics, the car is not real

No PPI. I'm shifting at around 3.2k and I use 6th gear on the freeway. I'm driving at around 25 using 3rd Downhill also. I'm driving around 70 to 80 on the freeway.

was the MPG better before you changed the oil?

Not really sure I didn't have it long enough and I only filled the tank once.

If your check engine light is off & in working order, (insure it is on when you 1st turn on the ignition switch) it may be injector or sparkplug related. Put injector cleaner in gas tank & then fill tank with Chevron premium. This is designed to clean fuel system & combustion chamber in cylinder heads. The debris that is cleaned can get past piston rings into the oil sump so you should change oil soon after that tank of gas is gone. Replacing the sparkplugs should improve efficiency also. Search this forum to decide which oil to use.

These cars can get anywhere from great mileage to low. If you are in 6th on the highway and mostly doing highway driving the mileage should be better than 16 though. I notice a significant difference when going from city to highway driving in the boxster, a much larger difference then any other cars i drive.

How are you factoring the mpg? Does your car have a computer or are you figuring your mpg manually?

The check engine light is ok and I changed the oil almost 2 weeks ago. I used Mobil 1 0w-40. I also have lucas oil injector cleaner I can use, I don't know why I didn't think to put some in the tank. I haven't been using chevron gas though it's expensive. Since I got the car I've been using arco 91 premium.

I've been doing it manually. Even with city driving I don't think it should be 16mpg.

What's your elevation? Can you not get 93?

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Bingo!! :barf:

Mike; Are you smelling fuel around your car? Any leaks? You should have a CEL lit if that much fuel is being unburnt in the engine and your Cats should be glowing red! Why are you shifting at 3.2k strange engine noises? I would wonder if an exhaust valve is stuck open, but like I say your cats would not like it. NOT those cats! :eek:

In CA!, that's more illegal than pot! :eek:

No gas smell and no leaks. I probably would've noticed it when I changed the oil. The engine light is also fine. Are you asking why I'm shifting at 3.2k? What is cats? Not sure I've heard that before.

Lol I don't have 93 in my area and I think CA it doesn't go over 91. It shouldn't matter though because the engine has the octane knock sensor thing right?

Ok I saw the other posts while I was typing. Last thought would be to not shift until at least 4.5k and get your car off that knock sensor. At those RPMs and low quality fuel your timing could be retarded from lugging the engine. Lugging this engine is worse than revving it up due to load on the engine.

Cats are catalytic converters.

Does it really matter that I'm using arco?

Sorry I messed up on the quote thing and had to fix it. Wouldn't 4.5k burn more fuel not helping with mpg?

No, I use ARCO gas sometimes and it is not a problem
Mostly I put in VONS/Safeway or Costco and its 91 octane. Other than a few odd places, 91 is the max around. There is one station that has 100 and its around $9.00/gal. Its in a very wealthly area and there are lots of supercars there

Lets not make this in to a What Gas should I use thread

In my 04 S I get around 18 city, 20 mixed and 28 Hwy
I have a reasonably heavy foot and generally am 10-15 over the limit

That is all based on the onboard computer

Depends on what the throttle is at. I of course like to use a lot of it! :) Mike I think you may be shifting your car too early. There is a lot of load on these engines at low RPMs The load on the engine (chains) is lessened when the engine is revving. I would suggest occasional bursts to 6500 RPM but don't shift before 4.5k. If you have your owners manual it has minimum speed to shift at.