[Alpha]

Whenever my car gets to two gallons left, the fuel reserve light comes on. People say that it is bad to drive on fuel reserve but I feel like it really isnt the reserve but just the last two gallons of the car. All my previous cars have never had a light saying I have two gallons left. Anyway my question is whether you guys think this is a bad thing as I have heard before that it is good to let your fuel tank come to almost empty once in a while as this clears out the old gas. Maybe this doesn't apply to direct fuel injections but I wouldn't know.

Ok next question, My 335i shifts at 7 or redline when it is in DS mode and I floor it, is it supposed to do that as I heard that shifting at that high a rev is not good for our 335i's(as they have small turbos or something). Remeber this is only when I floor it(not much).

OK last question, I always drive with dsc and dtc off, is this bad for the car? I do this because like someone previously stated, our 335i's shift from first gear too fast. So when you turn of dsc and dtc it goes a bit more before it shifts and this feels more comfortable driving around. I guess this should be okay as it just turns off traction control?

[3lusive]

To respond to your "next" question, the reason redline exists is to prevent you from damaging the engine by revving it beyond its limits. Thus, going to 7000rpm, or any rpm as long as it is under or at the redline, should be OK for the engine. Of course, you'll see a drastic increase in consumption if you go that high, so it's better for everyone if you don't.

For the DTC/DSC question, it doesn't hurt to turn if off but why? You increase the risk of losing control because traction control is inoperable. I think my 325i shifts quickly from 1st but I think this is because BMWs have a short 1st gear. Just my thoughts, not sure.

[Alpha]

I turn dtc and dsc off because the 335i shifts too fast for me from first gear. As for the safety reasons, I don't drive fast around the city or take fast turns, so I have had no problems with losing traction yet. The only time I lost it was when I floored it starting off but I only do that rarely and for fun.

[blue2fire]

Q1. Not good as this lets the particles that are in the bottom of the fuel tank into the system.
Q2.BMW programmed it to shift at that level, so no harm done there.
Q3.Dont do it unless you are doing some spirited driving at that exact point of time.

[methodtim]

Originally Posted by Alpha

Whenever my car gets to two gallons left, the fuel reserve light comes on. People say that it is bad to drive on fuel reserve but I feel like it really isnt the reserve but just the last two gallons of the car.

Just fill up your tank and call it a day.

Originally Posted by Alpha

Ok next question, My 335i shifts at 7 or redline when it is in DS mode and I floor it, is it supposed to do that as I heard that shifting at that high a rev is not good for our 335i's(as they have small turbos or something). Remeber this is only when I floor it(not much).

Revving up to redline is fine. Drive it like you stole it.

Originally Posted by Alpha

OK last question, I always drive with dsc and dtc off, is this bad for the car?

Leave the electronic nannies on. They'll save your life one day.

[galahad05]

All my previous cars have never had a light saying I have two gallons left.

Yes they have. In those cases though it was simply a yellow or red fuel low warning light when your gas gauge shows on the "E".

And the actual fuel left varies a bit from car to car, but around 1-2 gallons is normal.

[Oulixes]

An opinion on general questions posted by Alpha:

"Fuel Reserve"
So far, on the forum, there were two reasons given for not letting fuel level go down to the lower limit. I shall only list the opinions not critique them.
(a) Some people have suggested that impurities might be accumulated at the bottom of the fuel tank and stirred into suspension when the fuel level is low, and could under these conditions enter and damage the fuel pump.
(b) Others suggested that the fuel pump could possibly overheat when it has ceased to be fully immersed in fuel.
Both (a) and (b) are speculations supported so far neither by the fuel delivery design blueprints, nor by opinions of experts. Unlike lesser companies, BMW does not sell shop manuals; from other postings dealing with design-related problems, it is certain that expert members of the forum could clarify both of these points.

"335i shifts at 7 or redline"
My car has a manual transmission and no turbos, but I am sure the members of the forum using automatic transmission will confirm that you engine is safe.

"I always drive with dsc and dtc off, is this bad for the car?"
To leave the DTC/DSC engaged will not harm the car. In certain situations it may be to your advantage to disengage the DTC or DSC or both, but until you know for sure how the functions work, it might be prudent to leave the controls in default condition (engaged). The functions have been explained in detail several times on the forum. Search for the discussions, read them, find a safe location and enjoy testing the functions.

[bsamoul]

Originally Posted by methodtim

Just fill up your tank and call it a day.



Revving up to redline is fine. Drive it like you stole it.



Leave the electronic nannies on. They'll save your life one day.

in regards to #2: don't redline if you're still breaking her in.

[Blue Streak]

I agree with generally everything that was said here already. However, I will say that I'll never leave the DSC and DTC fully off anymore. I thought it was fun for a while, but one time when I made a 90 degree right turn onto a street I gave it some full throttle and totally lost all control. I counter-steered like a drift king, but waaaaaay too much power was spinning the wheels and I ended up going up onto the curb. Both my right side wheels where way out of alignment and I couldn't even drive the car except to go home and then just over a mile to get an alignment. The wheels have an extreme case of road rash too that need repair (although it's just cosmetic). This was a hard lesson for me... I'll at least be using DTC if I want to have some fun and not have the engine cut on me during hard acceleration.

[methodtim]

Originally Posted by bsamoul

in regards to #2: don't redline if you're still breaking her in.

That's too much nuance for OP. Just rev away. Vroom, vroom, yeah!

[akhter]

1) its pure speculation. driving with low fuel is fine.

2) if you have AT, you can't hurt the engine--it won't let you.

3) while driving in DTC mode or *ALL OFF* mode is not at all bad for the car, ppl do it more to get better performance in track conditions. If safety is not a concer, then drive as you will--you won't damage your car. if you are so finicky about gear shifts--drive in manual mode. many i know with AT drive in manual mode for that reason (myself included can't stand D or DS except for highway cruising).

[SteveC]

Every load of fuel will contain a certain amount of particulate matter, which will slowly settle to the bottom of the tank. As the fuel tank empties, the fuel moves around as you drive, resuspending some of the particulates which get drawn through the fuel lines to the engine. This is why you have a fuel filter. If you run your tank close to empty each time before filling up, your fuel filter will block gradually, hence it is changed at prescribed service intervals. If you keep your tank 'topped' you will draw less particles with your fuel and the particulates will accumulate so the first time you do run near empty the last couple of gallons will tend have a high particulate load that could conceivably block your fuel filter, depending on how long the sediment has been accumlating for and how dirty the fuel you use.

Redline is where the most wear occurs for your engine. Heat generated is maximum, your turbos are spinning at their fastest, engine lubrication is at its most stressed and the transmission is having to deal with maximum loads. When redlining a car, it should be fully up to temperature, there should be good traction and you should make sure you run the car for some time after redlining to remove some of the heat from the engine. Switching off an engine right after its been producing maximum power will leave local hotspots (like turbo bearings) which will 'cook' the stagnant oil.

The reason BMW build in devices like DSC and DTC is because they manufacture cars capable of breaking traction in the first 2 gears on normal dry roads and the first 4 gears on wet roads. Hit a patch of spilled diesel and all bets are off. Like power, traction is not a constant. Whenever maximum power meets minimum traction your liklihood of losing control is high. DTC is your only way of ensuring that maximum power only meets minimum traction for 1/100th of a second, which is about how fast the car needs to react to avoid an 'event' .
By the time you've noticed that something is wrong, you'll already be sideways, whereas DTC would already be making its 100th correction.

The ability to switch off these safety devices is required for special situations like snow and ice, deep sand and mud and when circulating on a closed circuit where the driver may be willing to take more risk in order to exploit the chassis's full performance envelope. For normal roads, where traction conditions can change in less than the blink of an eye, you need to keep them switched on.

[Alpha]

Well Damn, Thanks a lot guys I learned a lot from this thread. And thanks SteveC for taking time to write that detailed explanation of things. I really appreciate all the answers by everyone even if they differed.

[bspaceman]

I think i read something in Bimmer magazine that said BMWs are made to be driven hard. The harder they are driven, the better (less) the emissions readings. Interesting but trivial stuff.

[Payroll]

With regard to the first question, I agree with everything already said, but I would like to add another (that is, if I haven't missed it). Some parts of the fuel pump are lubricated by the fuel, so if you run it dry it wears on the pump pretty bad. Coming from a Chevy Tahoe that had a notoriously loud fuel pump, you can hear when they're about to go. I ran that bitch out of gas a couple times and had to have it replaced, which was expensive because you have to remove the fuel tank.