Lets's talk MPG....or lack there of

As you guys may know this is my 3rd C4S. Had an 02, 03 and now an 04. The first two were coupes and this is a cab. All had the same wheels and tires and suspension. My first two got anywhere between 23 and 27 around town and just over 30 on road trips. This one is 17 to 18 around town and 26ish on the highway. My car has 60k on it. In the AM it smells rich on start up. But other than that it runs just great. I have reset the ECU and no change. I have new plugs and coils to go in next. Have run several BG44k's thru it and has fresh oil. Any ideas?

23-27 is very optimistic IMO in city driving. You should look at all the MPG threads here to come to your own conclusion. What does your avg speed indicator say on the trip computer?

It was great on those cars. I joked that I like my econo Porsche

Quotes source post: 11784100

CEL is off I take it? Did all 3 cars have the same transmission? If this latest car has a Tip... Next question concerns the accuracy with which you measure the fuel consumption. It is very important you fill the tank the same way and to the same level each time you fill the tank. I have found the most consistent filling comes from turning the nozzle around 180 degrees. Note my 2002 Boxster was just fine filing the tank with the nozzle in the traditional orientation. But my 2003 Turbo was quite prone to causing the nozzle to shut off prematurely unless I spun the nozzle around 180 degrees. With the nozzle oriented this way filling is quite consistent and doesn't result in overfilling -- brimming or worse -- the fuel tank. This can damage the actives charcoal in the vapor recovery canister. Some more observations. The Cab is heavier. Would this make a difference? Around town probably. Also, I note this is your first Cab. With the top down the car is not as aerodynamically as smooth as a coupe. Around town this won't matter but on the highway... You have to also be on top of the tires and their inflation pressure. Low tires can really affect fuel mileage. I note you are in CO and if it has recently turned cool/even cold there tire pressures might be low. Approx. for every 10 degs F. drop in air temperature the tire loses 1psi. Have you changed gasolines? Have gasolines changed where you live? I'm thinking maybe 15% ethanol has made an appearance where you live? BTW, the engine will get the best mileage using the proper octane grade. IIRC while some regions of CO do not sell 91 octane let alone 93 or 92 you must use the highest octane available where you live and drive. Using a lower octane grade of gasoline is false fuel economy. The rich smell is probably normal absent a CEL and no other untoward behavior from the engine. A cold engine is going to run rich and cold converters are not going to process this rich exhaust gas and you'll smell fuel some until the converters get hot enough to work. Roughly this takes as long as the secondary air injection pump runs. What else?... Oh yes, plugs. While the engine is not misfiring and chances are good the coils are just fine, plugs go off after so many miles. Even if the engine doesn't misfire it can run less efficiently and this can cost you MPG. If the plugs are due, change them. Use the appropriate plugs. If your tech believes coils need to be changed have them replaced. While you are there replace the engine air filter. If you want to run a bottle or two of Techron through the gas tank, following directions on the bottle, that may not be a bad idea. I like to change the oil/filter after doing this. While we are at the engine what oil is in the engine? Do not dismiss this. There was post by a 993 owner who insisted on running 15w-50 in his car's engine even thought he admitted it caused the engine to run slower at the track. Oil friction accounts for a lot of the engine's friction. Where you live 0w-40 is more than sufficient and will provide proper protection on cold starts then protect the engine when warmed and given the whip. A lot of things to consider. Chances are it is not just one thing that accounts for the difference in MPG, provided of course it is real and not due to human error. It could be tires and the Cab's heavier weight and less efficient aerodynamics. Or you could have just changed your driving style, or the route you take to work. Even less obvious is traffic. I know where I live and drive every day the work commute has gotten a lot worse. I spend more time in stop and go traffic and MPG has dropped 1 or 2 MPG.

Mac Good info. My fill ups seem to be consistent and I have tried different gas brands (yes we only have 91 in CO). I have factory plugs and coils to put in. And the tires are at the correct pressure. I had thought about the extra 154#'s it carries around and the dynamics. Now that the weather is getting cold I will watch it as the top is up most of the time. And good point about traffic. It has gotten real bad here (my wife thinks it is all the people moving here for Pot) Thanks for the feedback. It will be interesting to see what the plugs look like when I take them out.

Unless your plugs are severely worn or damaged, they will not make up the 5+ mpg difference.

I would tend to agree but good maint can't hurt

Tim, Mileage on my 04 C4S Cab is the same as yours. And it has new plugs, new air filter, and gets nothing but 93 octane top tier gas. And the tires are set to Porsche recommended settings. I am not complaining since I recognize this is a P-car, but admit I sometimes wonder why a car that is so light and aerodynamic doesn't do better.

04 40th Anniversary model, 65k miles, 17mpg street driving. Note: X51 engine package. I tend to cruise at 4000 rpm. Guys that are shifting at 3000 rpm say they get much better mpg. Personally I suspect that keeping the engine at low rpm is bad for IMB-IMS. Cheers, Paul

Wow. I get about 10MPG in the City (stopping at every block and big hills in SF) and just got my highest ever of 30MPG on the freeway last night. Manual '99 cab.

14.5 MPG in my 40th AE in City and 26 +/- highway. However, I measure smiles NOT miles per gallon.

Quotes source post: 11784100

That's pretty astounding unless your "around town" is mostly 50-55mph with very few stoplights (and/or you're in the UK on the Imperial gallon). Around here most of the roads on my daily commute are 30-45mph limit with lights every mile or so, and the best I ever get is 16-17. Straight interstate driving at 65-75 gets me at best 24-26. (The higher figures are in Jan and Feb when I don't need to use the A/C very often). All the gas here is 10% ethanol which probably drops the mileage a few percent.

Quotes source post: 11784617

that must be barrels of fun, having a stick in SF.

Quotes source post: 11784315

Cruising at 4K unless you are in top gear and on the autobahn is a bit extreme. You'll pay a price in fuel consumption for that kind of driving style. Around 3K is OK. There are some owners who can have the thing in 4th gear before they are out of their driveway, and I'm not talking about a driveway that would put the one used for the Goodwood's Hillclimb to shame, either. Just buzz the engine up once in a while after its fully warmed up. I sometimes run 1st up past 4K to even 5K and then short shift the remaining gears. ('course, sometimes I don't short shift either...) I avoid operating the engine under 2K in any gear but 1st. And then I try to keep RPMs above 1.5K if at all possible.

03 Cabrio, 93 Octane gasoline (Shell most of the time), brand new tires alignment with proper PSI , recent 2 year major service, new spark plugs, no mods, city 23 MPG. Driving style average. I did the MPG measure just for the heck of it but is the last thing I worry. MPG/Sports car doesn't match unless if your buying a Tesla roadster!

Ben, Denver area is pretty open (kinda). But more crowded now. I suspect that has some to do with it as I am on a more stop and go route now to work. I am not really concerned about the MPG as I love to drive the car. Just interesting the big difference from my other two cars.

2003 C2 Cab consistently get 24mpg+ in town driving. Typically shift ~4k with goal of maintaining ~3k while driving. Highway pretty consistent @ 29-30mpg with cruise set @75mph

Tim have you lived in Denver while owning the other cars? If so maybe this car's barometric adjustment is a little richer. Do you get the rotten egg (sulfur) smell often/ever?

I never really thought about my MPG too much. It don't matter to me what it is, the car is worth it!! I'd push start the car every drive to have the opportunity to drive a 911.

In our '01 C4 cab tiptronic, I see 17-18 in real "in town" driving which is 25-35 MPH with stoplights every 1/4 to 1/2 mile. On the highway, 26 is possible. I thought these were pretty decent numbers because my lighter, newer Cayman S does about the same in town, but can only manage 23-24 on the highway. They both have 3.4L engines. The difference is in the gearing. The 996 Tip has gearing such that at highway speeds, it is turning around 500-700 RPM less than the Cayman. So even though it is heavier, and probably less aerodynamic, it gets better mileage.

Quotes source post: 11784749

Yes. We go through clutches like crazy here. I used to live right on the corner of a bad hill and the smell of burnt clutch was always in the air. After a while you get pretty good at it. Starting on 30% grades is a challenge though. After you know the area well you can avoid the really steep parts if you want to. The long route may also be the flat route.

Quotes source post: 11785038

This is where the hill holder option would truly be useful. Especially in rush hour traffic.

I average 16-18 in my 2001 with a GIAC flash, EVO intake, and FabSpeed headers and mufflers. Oh, I keep my foot in it most of the time too! The mileage sucks (the way I drive it) and it is worth every dime!

I've always maintained that if you're NOT getting under 15mpg, you're not driving it hard enough. Drive it like your angry/pissed off is the best way IMO.

FPB, yeah I have had all here in CO. Regardless I love my car

Since no one asked... I will. Any of the occupants put on extra weight recently? Sorry... couldn't resist....

HAHAHAHA 12 maybe. So not really

Quotes source post: 11786199

I always take a crap and do the anorexia throw up technique to shed a couple pounds if I take out my car on a Saturday night to give me the edge in stoplight to stoplight racing against those pesky kids with their mom's V6 Accords.

Quotes source post: 11784901

I'm only going by what the PCM computer says is the mileage. Right now it's 17.1 and I haven't reset it in about 1000 miles since the last oil change. I never bother to calculate gas mileage, I mean, I can see considering it before buying a car, but once you own it, it is what it is

The only car I have that gets any mileage is a little MBZ Slk 230 at 31/hwy. The S55 AMG gets 12, '70 Corvette gets 12, '74 Trans Am gets 10, GL450 gets 14. The 911 gets upper teens to mid 20's... I can't worry about it..

Quotes source post: 11785968

I like the cut of this man's jib.

Quotes source post: 11785968

You drive this to your anger management classes right Have a good driving weekend gang

Not worried at about the cost here in the ME but monitoring your gas mileage can give an early clue to something being amiss with the car.

I posted some of these numbers quite a while ago, but I'll do so again 2002 C2, 99,500 miles as of today. Partial daily driver (I don't work every day) around town 22-23 MPG Road Trip: 27 MPG , 5,500 miles, 79 hours driving time = 69 MPH average (including getting stuck in Chicago & Milwaukee traffic for a couple of hours), no traffic tickets (kept it under 125 MPH-Garmin verified). I suspect at Joan Claybrook's preferred 55 MPH, the mileage would be a bit over 30. In summary, you can hyperbole a 996

Quotes source post: 11789110

MPG might be better at 55mph but it might not. My Turbo does quite well even running at 75mph. The times -- not often but once in a while -- I end up having to drive slower, 65mph or less for extended periods of time fuel economy doesn't seem to get any better in fact it gets worse. While my 1972 Datsun 510 managed around 50mpg running at 55mph -- back the day of the 1st (or was it the second?) fuel crisis and strictly enforced 55mph limit -- my Turbo (and my Boxster) seem "tuned" -- inclined at any rate -- to deliver their best fuel economy at a higher speed.

Macster, I find the same with both my Cayman and 996. In my case 70 seems to be better than 60. I really haven't tried 75+ for an extended period to see what that would yield.

Quotes source post: 11784100

My '87 ranged from 16 most of the time to about 20-22 very best with highway driving. The current '02 (all stock) gets an average 22 with a little stop-and-go driving and mostly freeway (75 mph) and a few spirited on/off ramps. On freeway alone it gets 26, measured by putting it on cruise control and resetting the mileage indicator. The original window sticker says 18/26 so I've been pretty happy about the mileage now. I was actually thrilled because before Flat6's rebuild it got 18 and 23 respectively. In CA we have 10% ethanol everywhere as far as I can tell from a little research. I do remember that when ethanol showed up all our cars' mileage suffered at least 10%.

I do a lot of freeway driving, but sometimes it is 90 mph and sometimes 5 mph, depending on traffic. I drive my cars pretty hard. Not abusive, but "spirited" as they say. The mileage computer always settles on 19.8 mpg after a period of time. If I really want to milk it for mileage, I can get 28 mpg on the Freeway. On the track, it came out 14 mpg last time, which I though was pretty freekin' amazingly high. It's a 2003 C2. Just turned 118,000 miles last week. Not a garage queen at all. Driven the way it was meant to be. Political Soap Box Commentary: Ethanol... what a freekin' government scam. Much lower lower BTUs in ethanol vs gasoline. Gov't subsidies to sell corn for ethanol rather than for food or animal feed. Ethanol is for drinking, not burning in cars. Dinosaurs nobly gave their lives for this purpose, and I believe in the proper honoring of their memory.

Quotes source post: 11789682

I agree with your soap box sentiments. However, just a tiny nitpick: No dinosaurs were harmed in the making of oil. Oil comes from the remains of tiny marine organisms, lots and lots of these over the millennia that over time were buried under sediment and broken down and transformed into crude oil. This oil migrated upward through porous rock and fractures and accumulated in porous rock, sandstone, under a water, oil, and gas tight layer of impervious rock, shale IIRC. (Well, while I'm nitpicking, I can nitpick myself: Some experts believe it is possible some dinosaurs -- land based or sea going -- ended up in the same marine organisms muck on the sea floor and thereby contributed to this crude oil but the contribution was very very small. And dinosaurs played a similar very very small role in coal deposits. Large accumulations of land based plant matter -- like peat bogs -- turned into coal deposits.) 14mpg on the track seems quite high. Were you trying? My Turbo would probably deliver about 18/19mpg if I drove it like you drive your car. In fact, once in a while I do and it does. If I'm good mpg can reach 26mpg and maybe a bit better if I'm really good and doing my high miler imitation. My Boxster delivers several mpg higher numbers under similar circumstances.

With stop and go driving in Los Angeles the milage is about 15.2 mpg. I haven't had any long freeway trips where I could check highway milage. In perspective, this is about the same city milage as my 2007 VW Rabbit with the 2.5 engine and my 95 993 back in 1998..