why such Bad gas Mileage - 986 Forum - The Community for Porsche Boxster & Cayman Owners

flmont · 01-28-2023, 09:58 AM

GM...I drove my 02' 2.7 5 Spd in a round trip of 60 miles, mixed driving some Interstate and surface streets,and used a 1/4 tank of 91 octane fuel from Cheveron, that cant be normal..Ive never taken this car on any type of trip, so I don't really have a gauge for mileage RPM range was 3K to 5500. ?? any Info would be Great...Thank's Frank

Starter986 · 01-28-2023, 10:58 AM

You own a sports car and you're worried about mileage? I haven't done the mileage equation since... ever.

Seriously... you have to fill up the tank... drive a few hundred miles... fill it up again... look at the diference in fill amounts... and do the math. Look up the equation on the internets.

The math? I'm not sure because I've never much oncerned myself with mileage in this car (smiles per mile...).

Further... 60 miles is not much of a trip to be calculating mileage. The fuel level guage starts going low quickly as you get to that last quarter tank and, if corectly I recall... when it's filled up. When the gauge is in the middle 50% slowly it moves... down. I don't know... I don't pay attention to it. I just try to keep my tank at least 1/4 full.

Look up the math equation... online... and try it. Let us know the real results... not the seat of the pants answer.

blue62 · 01-28-2023, 04:12 PM

Quote:

Originally Posted by flmont

GM...I drove my 02' 2.7 5 Spd in a round trip of 60 miles, mixed driving some Interstate and surface streets,and used a 1/4 tank of 91 octane fuel from Cheveron, that cant be normal..Ive never taken this car on any type of trip, so I don't really have a gauge for mileage RPM range was 3K to 5500. ?? any Info would be Great...Thank's Frank

going by the fuel gauge is not the way to figure fuel mileage.
I have a 2000 S 3.2 6spd.
I get 20-25 mph depending on how I drive it and where I drive it.

flmont · 01-28-2023, 04:45 PM

Ok .I will try that method Sarter..I was just surprised it dropped that much in 60 miles..I thought I may have Injection issues or the timing is off..or something we shall find out Thank's

Thank's ! Blue62

Gilles · 01-28-2023, 07:11 PM

Quote:

Originally Posted by flmont

Ok .I will try that method Sarter..I was just surprised it dropped that much in 60 miles..I thought I may have Injection issues or the timing is off..or something we shall find out Thank's

Thank's ! Blue62

Fill it up, zero the odometer and drive the thing for a couple hundred miles :-) when you fill up again, you divide the mileage between the gallons used..

blue62 · 01-28-2023, 08:14 PM

Quote:

Originally Posted by flmont

Ok .I will try that method Sarter..I was just surprised it dropped that much in 60 miles..I thought I may have Injection issues or the timing is off..or something we shall find out Thank's

Thank's ! Blue62

If your getting poor fuel mileage... to jump to conclusions about possible injector issues or timing issues is way, way over the top.
With any automotive issue always, always, always, simplest things first.
poor fuel mileage can happen from many many things.
driving style for one.
If I was to start getting poor fuel mileage.....
I would look at my air filter, my plugs, and do a vacuum test as some simple firsts.

flmont · 01-28-2023, 09:24 PM

Thank's Guy's..I will ck it out to determine my mileage and Ill get back with a answer

paulofto · 01-29-2023, 07:57 AM

The fuel gauge is far from accurate. It will tell you when you approach empty but to use it as a consumption gauge to determine fuel efficiency will not work. Do what the other posters suggest and do the math. Btw, my 03 S gets close to 30 miles per gallon if doing a steady state highway long distance drive at or around the speed limit. If I drive ‘with enthusiasm’ that mileage drops to well under 20.

flmont · 01-29-2023, 09:53 AM

Thank's Paulofto,..Ive heard of the Temp gauge being off,..but everyone is now saying the fuel gauge too,And the another question is,why are the gauges off..I know thats a completely different topic,and I understand they do not need to be exactly dead on..but you would want pretty close especially for the Temp gauge. ??, anyway Thanks..I plan a run next weekend to see what's up..

elgyqc · 01-29-2023, 10:00 AM

Quote:

Originally Posted by blue62

... I get 20-25 mph depending on how I drive it and where I drive it.

You should get great mpg if you only go 20-25 mph

blue62 · 01-29-2023, 12:56 PM

Quote:

Originally Posted by elgyqc

You should get great mpg if you only go 20-25 mph

LOL didn't even notice that.
never use the top 4 gears either.

dbear61 · 01-29-2023, 06:18 PM

On my '01S, the gauge is at 3/4 after about 75 miles. Because I do a lot of long distance road trips on back roads, I have to be aware of my car's range to make sure I don't get to the orange refill spot too far from a gas station.

The best mileage I ever got was 29 mpg on a 300 mile, non stop drive on I-80 through Nevada. Typical highway mileage is 24-26 mpg. Twisty road, aggressive driving is around 18-19 mpg.

With the base model, you'll probably see 1-3 mpg more than that. Just learn the range of your car under the most aggressive driving. Once you know that, don't worry unless you see a dramatic dropoff. My range, depending on driving conditions, is 270 to 340 miles.

DBear

flmont · 01-30-2023, 08:49 AM

Thank's Dbear...I can live with that..I'll be testing soon..my driving style is 75-80 on interstate as able and 40-50 surface street as permitted,..Frank

Rob175 · 02-02-2023, 07:28 AM

Hell....my 25 year old 5-speed Boxster (w/91,000 miles) gets 27-28 miles a gallon and always has.

flmont · 03-09-2023, 07:56 AM

As it turns out, I get about 26-27 MPG as well, plus my oil analyst states no fuel delusion, which is what I thought was happening,..Thank's Frank

Smallblock454 · 03-09-2023, 10:38 AM

2003 S, MT

Fuel consumption really depends on how you drive.

At 80-90 Km/h i get an average below 7.5 litres / 100 Km.
Full throttle on the Autobahn i can get up to 15 litres / 100 Km.

In general in daily use the car is at around 10 litre / 100 Km.

It's up to you gentleman to convert to mileage per gallon.

PLP · 03-10-2023, 09:07 AM

Quote:

Originally Posted by flmont

I don't really have a gauge for mileage RPM range was 3K to 5500. ?? any Info would be Great...Thank's Frank

Here is your problem - rpm range did not go below 3000... so the engine must eat.
Keep it below 3000 and it will give you much better results.
The engine is just fine at 1500 rpm pulling in 4th gear.

Bill Ladd · 03-10-2023, 12:37 PM

Quote:

Originally Posted by PLP

…The engine is just fine at 1500 rpm pulling in 4th gear.

But not much fun, lol.

My 2000S gets terrible mileage. Turns out the nut connecting the steering wheel to the seat has a leadfoot.

JayG · 03-11-2023, 06:18 AM

Quote:

Originally Posted by PLP

Here is your problem - rpm range did not go below 3000... so the engine must eat.
Keep it below 3000 and it will give you much better results.
The engine is just fine at 1500 rpm pulling in 4th gear.

Driving these cars at 1500 RPM s not really a good thing

PLP · 03-11-2023, 11:48 AM

Quote:

Originally Posted by JayG

Driving these cars at 1500 RPM s not really a good thing

Date to elaborate as to why?

I support my statement with... AT shifts mapping. If Porsche believed their engines are not supposed to experience low RPM they would upshift at 3000 RPM range, yet they upshift much lower.

Sure, I am not talking about running WOT at 1100 rpm - if you need power, rev it. But for everyday use - keeping between 1500-2500 is just fine.