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?

[/B]

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.

3.2k is really low. Keep your shifts between 4k-5k+. At about 5.5k, that engine really sings. ;)
Even with that said, you should be getting better mileage.
My 2.5 gets roughly 20 city, 25+ highway, even on 91 octane.

I guess I'll use some injector cleaner, fill up the tank with chevron a couple of times, and replace the spark plugs. I hope this takes care of it.

On 6th gear going 65mph the RPM is around 2.5k. Should I be using 5th gear then?

how is your air filter / tire pressure?

Yes; Listen to your engine and feel the pressure you are using on the throttle. The engine will communicate back to where it wants to run. You will have much better results. I have driven my 2.5 into So CAL down the 215 rarely using 5th gear and have gotten 32 calculated freeway. I believe you are so low in RPM the knock sensor is retarding the ignition timing. Try keeping at 3.2k +. I don't think your plugs are an issue since you just bought car so had to pass CA smog. Of course new plugs are always good.

PS; I used to have an air cooled 911 with weber carbs hat would load up below 3.5k. This was during the famous 55mph speed limit days. I used to have to shift constantly between 2nd and 3rd that car really hated that speed limit. Now at 90 Yahoo!

So that's why they all drive teslas when they want to go fast!

I honestly did not know that such a socialist thing could happen in the land of the free [emoji33]. (I kid, however I do enjoy my right to 93 octane, no front plate, and no emissions test, then I regret that right when a truck carrying a confederate flag "rolls coal" across the intersection.)

The tire pressure is fine I checked it 2 days ago. I should probably change the filters though.

Damn I'm such a newbie lol. I've driven a manual car before but it wasn't a sports car and this my first car with manual. So I've been lugging my engine for like 3 weeks I hope I didn't screw things up too bad.

LMAO! I thought u were being serious for a second there.

Damn I'm such a newbie lol. I've driven a manual car before but it wasn't a sports car and this my first car with manual. So I've been lugging my engine for like 3 weeks I hope I didn't screw things up too bad.[/QUOTE]

Mike; I went and looked at your original posts and hopefully without starting a war I noticed you are aware of the IMS. There is lots of informative reading on this subject in here when you have time and popcorn. Jake Raby is a very knowledgeable resource. I hope he doesn't mind my referencing him but he has stated that the IMS has the most loading at low RPM. IMHO This is why there is a theory that engines that have been driven hard have less IMS failure than a garage queen, Lugged around engine. Hence the statement Drive it like you stole it! These cars love to rev! Their pedigree is racing. Get out and enjoy the way it was meant to be driven! :cheers:

Thanks. I hope to get the IMS and clutch replaced as soon as I have the money. I had a mechanic tell me a LN and the pelican parts bearing both failed on him. I don't think I believe him lol.

Mike there is something else that is bothering me about your thread. You say you have filled up once in 3 weeks and getting 16 mpg. That only works to a maximum of around 240 miles a week or around 10 miles a day. Are you only driving around 5 miles one way? Sorry I'm not trying to pry, but, short trips are also bad.

It couldn't hurt to disconnect the battery, turn the key in the ignition to drain all power, and then reconnect the battery to reset the car's learned driving/throttle values. That, combined with your new gas type, injector cleaner, trying a different gear on the freeway etc will rule out all of the easy things.

Sorry I don't mean to hijack OP's thread, but since this is here, I need to ask. I know short trips are bad, but from my understanding, it's because the engine hasn't had time to warm up properly, so basically short trips are cold driving trips. I currently do 5 miles one way too, no freeway, takes a bout 12 minutes. But the engine temp always get to 180 on the gauge when I get there, so I assume my engine is safe?

Hancock; You are correct. Now I don't wish to pass off my idiosyncrasies I've developed from my years of driving an shall we just say array of vehicles. This was crucial in older carbureted cars where chokes caused raw fuel etc in the oil pan. Current fuel injection has gone a long way to deal with the cold start issues. However the logic still continues that lots of freeway miles are much better than many short trips. Reason is systems haven't stabilized at "Normal" temps to cook off the contaminates that have condensed into oils, trans included, forming corrosive contaminates in the engine etc. 5 minute trips hardly recharge the battery from the start! Many opinions, mine included, but I try to drive no less than 20 min after normal temp achieved. SO get out there and paste a grin on your face a little longer! Oh the horrors!:eek: LOL.

Interesting comments about shift points

If I am doing just regular cruising, I shift right around 3k. For performance, I'm looking around 5.5-6.5k shifts. On the track, I may hit the rev limiter every now and then. On the freeway in 6th, 3k =~78 displayed, 75 actual mph, right at the bottom of the power curve.

According to the manual you aren't supposed to warm up ur car idle. It says to drive the car immediately after start and don't go over like 4.5k rpm for first 5 minutes.

That's how I've been driving, I'm a little confused. Do you have the base model or an S? Wouldn't the rpm and shifting change?

Hey JayG; Good to have an instructor chime in! I hope I'm not giving bad info. :( Some of my style may be due to my driving a 2.5 so keeping it in the power band (3.2k+) is a job. When on the freeway I typically don't use 5th until above 75 indicated where I can keep in the aforementioned power band. That said in response to the OPs question regarding poor fuel mileage my thought is he is shifting just as he is entering the power band but more importantly may be spending too much time below the power band and in the lugging range of the engine with the knock sensor picking up the gears/chains lashing, then retarding ignition timing causing the poor fuel economy? If he is shifting 3.2 k then he is 2.2k after shift. OP lives in Monterey so as I'm sure you know it is not all sea level driving there. Viva Laguna Seca!:dance:

I have a S with a 6 speed, so yes, the shift points could be a little different as to speed. In any case I don't see why you need to rev high for just cruising other that the wonderful sound at higher rpm. Certainly don't want to lug the engine either.

IIRC many that track the 986 prefer the 5 speed because of the gear ratios

Not an instructor (yet, maybe one day) but an enthusiast.

I don't see how shifting below 3.5 will reduce MPG. If anything running at higher RPM will decrease MPG. My 996 has a tip ( same tranny as 986 tip) and unless I am putting my foot into it, will shift right around 3k My guess is the tip in a Boxster will shift pretty much the same.

I would think that higher RPM = lower MPG n matter what gear or tranny you are using