Hi,

I recently sold my 2005 997 C2 and upgraded to a 2007 C4S cab. My old 997 C2 was giving me around 18 mpg and just found my new C4S cab is giving me only 12-13mpg which seems really low. It is rated 16/24 city/hwy so 12 seems really low. I wonder if there is something wrong with the car? I expected a higher fuel consumption being it's a C4S cab and is heavier, but what are others getting? Is this a normal consumption for the C4S cab?


Thanks,
Jon

 

You are probably taking good advantage of the wider/higher torque in your new 3.8l engine.

 

Actually I'm comparing my usual commute to work drive which I don't push the car hard and it's combined city and highway driving. I would expect lower fuel economy if I was pushing the car but I'm not.

 

Your driving style and conditions control the mileage; I suggest you check the tire pressure. Are you calculating the data or just using the computer ? My old 997.1 c4 got + 19 mpg driving aggressively on non-city roads with traffic and + 22 mpg at steady +75 mph on the highway (summer). The new 997.2 has the direct fuel injection and gets about 1.5 to 2 mpg for the same conditions. I drive about 260 miles into the mountains regularly and the mileage drops as I hit the steeper roads. I've gotten over 410 miles from a tank at least twice this past summer.

Enjoy the new car ! How many miles were on the car when you got it and was it a private sale ?

 

I'm not calculating the mph, that's what is showing on the computer. This is my first tank of gas but it's going fast and the computer tells me I'm getting 12.4mpg avg. It was a CPO car and it has 32k miles. Maybe there is a problem with it. Your numbers are significantly higher. Tire pressures are showing on the computer as 29 front 36 rears.

 

Your cold pressures (measured with an accurate tire gauge) should be 33/39. You are running too low.

 

Thanks. Would that minor tire pressure difference translate into such lower gas mileage?

 

I don't know, but low pressures do reduce gas mileage and reduce grip of short-sidewall high performance tires.

 

There isn't a chance your tire pressure being off a couple PSI would account for that much loss in MPG. Your MPG is around what I get right when I put a new tank in after the track, which isn't good...

 

I found out the wheel/tire size made a big difference on my '03 Boxster. On the stock 16", it got 30 MPG on the Hwy. With 19" summers, it dropped to 25 MPG. My '06 C4S is a similar story, with the 18" snow tires I can easily get 25 MPG on the Hwy but struggled to get 23 with the 19's. For your kind of commute, though, I would expect 19 MPG average. 12 is WAY too low! These things are pretty sophisticated so should 'know' why it is using more fuel if it is engine related. My guess is something mechanical, like a brake dragging or low tire pressure or ??

 

My previous 997's ,2 which were Turbo's did around 21mpg. When I got my 2010 C4S Cab the first tank computed horribly around 14 mpg.

Now I am averaging 21.5 over 3000 miles mainly short trips. I think these cars are so economical for the performance they afford.

Unlike the CGT which can suck it down at under 10mpg easily. Even the Gallardo Spyder drinks it at about 14 mpg.

I think the car that most surprised me was my Ford GT40 which would average around 19mpg. Not bad considering it makes you want to drive it like a **** most of the time!!

 

My 06 C2S cab averages around 18+ mpg in day-to-day driving around Orange County, combination of freeways and streets. If I take streets like Moulton Pkwy for my commute (about 6 miles) I average closer to 12-15 mpg for that trip, depending on waits at lights. Taking a combo of streets and freeway (about 7 miles) I average 18-20 mpg. The highest I ever recorded on a trip is around 25 (with speed in the 70-80 range).
Bottom line, the mileage varies drastically with driving conditions. I've learned to ignore it and just enjoy the car.

 

This

 

As a daily driver, my '06 C4S Cab typically gets 10-12 mpg in my brief (3 mile) daily commute to/from work on surface streets. I tend to drive in a "spirited" manner, shifting just north of 4K rpm. My best performance is on the open highway, where I can cruise at 70-80 mph and average 18-20 mpg.

Economy for theses cars, especially the beastly heavy C4S cab, is terrible - even worse (in town) than my hulking Land Rover LR3. The sound & fury of those 3.8 litres growling behind me more than makes up for it however!

 

Just askin', Did you did reset the computer when filling up the first time and have you driven far enough that it's averaging your driving rather than the previous owner/dealer. That actually can take more miles than you might think.

My TT generally gets 20++ mpg on the road even at elevation and mtn passes. On the track, 7- 8 mpg is customary. When coming off the track it takes 100 - 200 miles before the computer figures out we're not going fast anymore and provides a representative reading. My ex - 08 C4S behaved similarly.

I'd do a manual calculation and go thru a couple of tanks before becoming concerned.