What range can I get on the highway with a full tank?

driving 80 with the ac blowing in a 99 cab top up. Can I get 350 miles on a tank? What do you guys think?

Yes.

doing 75 on cruise...the best I've seen is 680 Kms before the light went on. That about 422 in Amer-can

Really depends on speed. Generally I would say if you are running under 75, yes. Over 75, maybe. Over 80, no.

Driving 65-75 mph with cruise control, AC on, 2004 C4S, range was 400-500 miles. Went a little over 250 miles with under 8 gallons used. Trip computer indicated similar results on the previous similar highway journey also.

Quotes source post: 8696928

Maybe. Try it. 350 miles at 80mph is 4.37 hours of driving though and I find that I'm better off stopping every 3 hours or so of driving and if I stop I like to fill up the tank so I generally don't stretch out a tank that far. Oh, I do not like to stop for gas when driving up (or down) through Oregon and last trip up there I drove over 300 miles -- in my 03 Turbo -- from just inside the CA border where I filled up the Turbo's gas tank to a few miles into Washington (all on I-5) between fillups. I was not able to drive 80mph though because the speed limit in Oregon on I-5 is 65mph and in places even lower than that and towards the end of my north bound drive I encountered some heavy traffic through the Portland area and as a result didn't come anywhere near averaging anywhere near the speed limit for miles and miles. On a recent drive east up on I-80 my car averaged 25mph or a bit more mph driving at 75mph+ and this is with the A/C on. (Modern car A/Cs (at least those in Porsches -- the A/C system is really good) do not really affect fuel economy all that much.) However, being unfamiliar with that more northern route (I usually take I-40) and unsure of where I'd find the next gas station I filled up more often usually before the tank level dropped to 1/4 tank. There were plenty of gas stations though (and offering sometimes 93 octane at prices less than 91 octane gas here in CA!) and from NV all the way across NE speed limits were in most areas 75mph! I made good time and the car got good gas mileage. Anyhow, had I wanted to run longer assuming I could get the car to deliver 26mpg leaving say 3 gallons for reserve that gives me (about) 13.5 gallons of usable gasoline so 26mph times 13.5 gallons works out to 351 miles. And your car might (should) deliver even better fuel mileage if you drive it reasonable. So the answer's maybe. Try it. Sincerely, Macster.

Question on the radio last weekend on whether driving on almost empty is a bad thing. The answer was no, although mine remains yes; who wants junk at the bottom of the tank vacuumed into your engine, even if there is a filter? That said, the argument was that theoretically with less gas, your car is lighter when empty, and gas mileage might improve. IIRC, the US interstate highway system originally set its speed limit at 55 mph not because of safety but because of the 1973 oil crisis. Quoted online, "The National Maximum Speed Law (NMSL) in the United States was a provision of the 1974 Emergency Highway Energy Conservation Act that prohibited speed limits higher than 55 mph (90 km/h). It was drafted in response to oil price spikes and supply disruptions during the 1973 oil crisis." The point being: lower mph in most cars improves efficiency, so I'm unclear why a "specific" speed would make your trip more likely to succeed. That said, cruise control will cut your fluctuations and yes, a "set" speed higher than 55 mph can improve efficiency. If it's true that the 911 no longer spontaneously combusts when the rpms drop under 3K, why not try to get your gas consumption as low as possible when driving straight, in sixth gear, at 65 mph? Is it not possible to refill during the trip? $0.02.

Quotes source post: 8697249

The interstate speed limits were dropped to 55mph during the gas crisis to save fuel. Before that they were of course set higher. Thankfully they are higher again with some states permitting 75mph or even 80mph speeds (west Texas on I-10 and I-20) and IIRC (maybe it is Texas (I love Texas!) is considering raising the limit to 85mph across some sections. The concern with driving around with a low gas tank level is that since the fuel is used to cool the fuel pump with less fuel in the tank the fuel will heat up more and as a result the fuel pump will run hotter and this works to shorten the fuel pump's life. While I oftentimes run the fuel level down to 1/4 tank and sometimes even lower I don't make a habit of going much below 1/4 tank just to help keep the fuel pump cooler. Sure, the car is lighter with an lower fuel level but not by much. Besides I would have to believe that the fuel consumption penalty in stopping to fuel more often when striving to keep the fuel tank level low would be higher than the fuel consumption penalty from hauling around a few more gallons of gas. The particulate matter at the bottom of the tank remains there no matter the level of the fuel. When I had my Boxster's fuel pump replaced (after over 170K miles of service) the in-tank fuel filter (a fine mesh which was part of the fuel pump housing) had some tiny particles of trash in its mesh but not much. There was plenty of open mesh so no way would the fuel pump be starved for fuel. The tech told me there was not a large amount of particulate matter at the bottom of the fuel tank. He also told me there was no sign of any water in the tank. I note too, the old fuel pump, which I have next to me desk here at the office, but which spent 170K miles sitting on the bottom of the fuel tank, shows no signs of having been in contact with any water. So, I just keep the fuel tank above 1/4 tank most of the time and when I do fill it up I elect to fill it full (but not to the brim) to reduce the hit to fuel consumption a fill up represents. As for the cruise control it actually costs gas and gas mileage unless one is driving on level road and is in a very light traffic area. What happens with cruise control is as the vehicle starts up a grade the control adjusts to keep speed constant. This results in acceleration and fuel consumption goes up. (I see this with cars that have instanenous fuel consumption display.) As the car continues to climb the fuel consumption numbers get worse. I've seen it drop from say 20mpg to under 15mpg. Now then the most economical way to drive a car is to get the vehicle up to speed, then back off a bit on the throttle to reduce pumping losses arising from the butterfly valve. How much this helps in modern cars with e-Gas is unknown. As the car begins to climb a grade keep your foot pressure on the throttle constant. The car's speed will drop but surprisingly the fuel consumption does not go up and sometimes even goes down. As the vehicle reaches the top of the grade and begins its decent the vehicle's speed will increase even with a constant pedal pressure. (Might add depending upon the terrain the speed can incease considerably.) The fuel consumption will really improve in this situation. This technique results in less fuel consumed than using the cruise control. The problem is that in many places with hills (and especially in the mountains) doing away with the cruise control means the vehicle's speed can drop considerably climbing a long grade. In some cases at the bottom of the beginning of an upgrade the car's speed is at the limit, 75mph. At the top of the grade it can be down to around 55mph or possibly less but I get ansty when the speed drops below that the big rig drivers like to maintain and can maintain. In the mountains they like all the momentum they can get and do not like to lose it due to some butthead trying out fuel saving driving techniques. This means as the car climbs and with constant gas pedal presure it loses speed and now faster moving vehicles will catch the car and pass the car. On the downhill grade as the car gains speed and if one can avoid applying the brakes or even lifting off the gas pedal the car's speed increases. Of course it can depending upon the grade steepness and its distance result in the car gaining enough speed to catch up with the vehicles that passed the car on the climb up and to keep the car's speed up these vehicles must be passed again. One has to watch the car's speed too, that it doesn't get too high, too far above the limit (and it can on some grades). Even if one is saving gas if the car's speed is too high through a radar trap a ticket is the result. Often times the passing doesn't go well -- there is enough traffic even on the open interstate to interfere with smooth passing -- and one has to brake then accelerate again and the benefit from trying to keep the throttle constant is lost. Plus the trip becomes a bit of hectic in some respects because of all the pasing back and forth. If one stays with this technique for a distance the same cars and trucks pass you and and then get passed, over and over again. So I use the cruise control and absorb the small bump in fuel consumption though sometimes on particularly long and steep grades I'll suspend the cruise control and let the car coast, in gear (6th), to save fuel until the bottom of the grade is reached at which time I'll engage cruise control. That 140 miles from Flagstaff AZ to Kingman AZ and beyond is almost all downhill (7700+ feet at Flagstaff to around 600 feet at the AZ/CA state line) and allowing the car to coast down the downhill grades results in good fuel mileage numbers. My cars can gain a couple of mpg easy with this technique. (Of course since I drove the other direction the car had to burn more fuel going 'up' that 140 miles of distance too.) Sincerely, Macster.

Real close but I doubt it. You will be on fumes. I drive from Erie PA to Birdsboro pa, 361 miles.. I have to refuel about 30 miles from home on the way back. Its a 90% highway drive

It's not that hard to find out. Try it and let us know what happens. Lots of variables that can affect results +- 10%.

Just took a 948 mile highway trip. Top up, air on, cruise set at 75mph most of the way. We used 35.8 gallons, 26.5mpg (usally fill it after light comes on ~13 gal) so ~345 miles with out getting to fumes. This includes rest stops and gas stops. (Wife's tank does not last as long as Porsche's) Side note: I am working on a 1972T, carburated, fuel pump. I had it recirculating 1 gallon of diesel fuel for about 1 hour. The pump pulls 1/2 amp free running and 1.5 amp (6-18 watts) pushing 5lbs pressure. While this pump is not a submersable it is cooled by the fuel running through it. I was surprised to feel that the diesel was very warm after an hour. Hot gas is one reason to keep more fuel in the tank for our fuel cooled pumps.

Just a data point. I drove from Minneapolis to Peoria and back last weekend doing 75 with the AC and Cruse in a 1992 968 and was able to go 375 miles on a tank. Its a 3 liter 4 banger, water cooled.

Running the fuel very low is bad for the pump, due to proper cooling. IIRC, it even states in the Owner's Manual, that once the low fuel warning is activted, not to drive in a spirited fashion and reduce full throttle inputs. Something like that.

Quotes source post: 8698440

that is ~20 mpg if you used the full 19 gallons. ~23 mpg if you used 16 and kept 3 gallons in reserve.

Just did a 320 mile trip today and as I was one mile from my destination the fuel warning message came up. I averaged 75-80 MPH, most of it with cruise control. So I think your 350 mile goal is attainable with the right conditions.

At 80MPH I think it would be close. No worries, there are gas stations everywhere just waiting to sell you some $4 to $5 a gallon gas.

So I had to drive the car from Bentonville AR (My Work) to Dallas (my home) and asked if you guys thought I could make the 350 on a tank. Reason being at most gas stations they don't have 93 octane in AR or OK but if I had to stop and fill up I wanted to do it in these ratty states before hitting the higher speed highway coming into Texas. I did not stay anywhere near my 80mph goal exceeding it substantially throughout the trip. (what can I say). I pay state income tax in AR, property taxes in Texas and pay a speeding tax almost every time I go through OK. So, I hate to pay a gas tax also. So......went through all the way actually 365 miles at high speeds with no issues on the gas. Could have probably gotten 400 miles. In the winter when cooler air generates a little more HP and no AC blowing it would be even better. Will continue to fly home on the weekends so I hope to not find out! Hope this data helps someone.

just back from 400 miles from home to france / 400 miles in france then 400 home & was staggered with the frugality of the 996 C2 6speed , wasn't even trying & 360miles covered before light on (80/100mph) my guess brim to brim was 33mpg ish which more than makes me happy with the power available , doubt many other performance cars could get near & if any owners haven't stretched their 996,s touring yet they are missing a treat , the deserted lanes of normandy were def made for the flat 6 machines some pics here http://p101tv.com/view-album/147/french-invasion

Quotes source post: 8696928

I think with some instruction you could get that WAY DOWN - maybe into the low 200's if you really try !!!!

yeah , pretty sure my average was boosted with the 800 mile commute & not the blasting through deserted french countryside at 120mph , fantastic mode of transport for touring though ,

The best/average I'm getting is about 300 miles and 14-14.3 to fill up. About 22 mpg I guess... this is averaging about 80mph