Hot answers tagged

61

There is absolutely no reason to use higher-octane fuel unless your car explicitly requires it. The higher the octane, the more compression/heat required to combust the fuel. High-performance engines (turbo-charged, high compression cylinders, etc), a higher octane fuel is needed so the fuel doesn't combust prematurely (knocking). If you put this fuel in ...


54

Both previous posts are pretty good. I'll add a few more considerations though. On a low tank, during hard cornering, some cars will uncover the fuel pump pickup and starve for fuel. There's been some discussion for years now about keeping 1/4 tank as your minimum as the fuel provides cooling for the fuel pump. Some people argue that additional cooling ...


35

If the car is equipped with a modern fuel injection system, it will likely use less if left in gear and allowed to run against the transmission with no throttle as modern fuel injection systems can and do shut down the injectors completely thus use no fuel whatsoever. If the engine is at idle in neutral, the ECU will have to use a small amount of fuel to ...


33

There is an unexpected effect to running with a full tank all of the time: fuel is heavy. The actual weight per gallon depends on temperature (and thus on density) but it's on the order of six pounds per gallon (or about .7 kg per liter, if you like doing all your math in base 10...). Obviously, the total weight depends on your vehicle's tank. In my car, ...


24

Use the recommended gas for your car. Going lower than the recommended may reduce fuel economy as the engine may have to retard timing to avoid detonation. Going higher than recommended won't help as your engine is unable to take full advantage of it, as well as the fact that higher octane fuels actually contain slightly less energy (they just offer a more ...


24

The reason is that motorcycles traditionally have the fuel tank higher than the carburetor, and the fuel feeds with gravity alone. What risks does this introduce that necessitates a manual shutoff? Without the shutoff, if the carburetor float failed to close the valve tightly enough to stop the fuel flow, then gas would continue to trickle into the carb, ...


22

I left my Mazda Protege unused in my garage for over a year, and the fuel filter was clogged when I went to start it again. It started fine, but would not rev and was basically undriveable. I'm sure it wasn't great for the fuel injectors, too. Also, I once bought a motorcycle with 10 year old gas in the tank, and the bike wouldn't run at all. I could hear a ...


20

High octane is required for some cars: e.g., a turbocharged car will likely require higher octane to reduce risk of detonation with higher charge temperatures. High octane is also required to get the optimal power out of a tuned car: properly advanced timing will enhance power and economy (obviously, not at the same time). Some cars are capable of ...


19

Knowing that gasoline does not freeze (Ok, it will start freezing at -180 degrees, but this is more than you or your car can tolerate) but that a small amount of water can accumulate in yout tank over time. So, in cold winter weather condition, like here in Canada, if you have a low level in your tank, that accumulated water could freeze and cause some ...


15

Lean and Rich Symptoms in Motorcycle Carburetors In your post you indicate that some of the symptoms you have read are contradictory. I will try and clarify between the two conditions and attempt to give you guidelines in troubleshooting between the two. Background Motorcycle carbs have a few circuits that effect different throttle positions. Idle ...


15

Some aspects of this question have been covered previously. In my previous answer, I pointed out that using octane that is too low will lead to retarded timing and higher emissions. With respect to fuel economy, you can never trust someone's casual anecdote about fuel economy. As Mark points out, they're almost certainly going to be operating under a case ...


15

I would suggest that the original problem was not the use of E10 (the vast majority of all gas sold in the US is E10 fuel due to federal mandate), but rather you received a ration of bad gas which probably had water in it, or was old gas (had been sitting for a while without new gas infused in the mix). I don't think there are any remnants of the bad gas in ...


15

Carburettors are very crude in comparison to EFI systems, and so the amount of fuel entering the engine is simply a factor of the amount of air going in, which is controlled by the position of the butterfly (and hence by the throttle position). At a completely closed throttle, there will therefore still be some fuel getting in, enough to keep the engine ...


15

At a base level, carburetors meter the amount of fuel they let into the engine by the amount of air that is moving through them. Vacuum is created by the piston moving in the engine and creating an open space. As the piston moves down, it creates an empty volume which pulls in air through the only opening it can find, which is the passageway through the ...


14

So-called "octane number" is a measure of how much the air-fuel mix is resistant to detonation. The higher the "octane number" is the more resistant it is and the more is can be compressed without exploding. The higher the pressure is at the point the air-fuel mix ignites the more efficient the engine works. Modern engines are designed for some rather high ...


13

The ECON button is not a placebo, though the wording from that specific web page is a bit vague. The key is that the ECON button and the Eco-Assist system are two separate things. According to Honda, pressing the ECON button configures your car to improve mileage at the cost of performance. Turning it off will improve power and reduce mileage, which you ...


12

Background Multi-cylinder vehicles with multiple carbs To port this question over to applicability with cars. This is the same issue that has plagued older Ferrari and Jaguar mechanics over the years. The 'balancing act'. If you have a V12 and 6 or 12 carbs, getting them all balanced and uniformly restrictive in terms of allowing air into them can be ...


12

Most modern diesel engines (ie: engines after mid-80s) require some electricity to run because they are electronically controlled. This is due to computers controlling the fuel charge and monitoring of the engine itself. Without this, the diesel engine has no control. They also require electricity to power the primary fuel pump, to move the fuel from the ...


12

You should be fine¹ The beauty of fuel-injection management systems is that they can compensate for slight deviations in operation via feedback. The amount of compensation is commonly referred to as "fuel trim" (because the fuel injector pulsewidth is controlled ("trimmed") by the fuel-injection management). It is not uncommon for vehicles to accommodate ...


12

IMO you have a fuel starved vehicle. Perhaps some blockage in the gas tank at the petcock filter or an inline filter between your gas tank and the carburetor. When you run the bike the fuel might not be filling the float bowl at the rate that the engine is consuming fuel. When your bike stalls the fuel is trickling into the float bowl and then you can ...


11

Any oil change place should be able to take it off your hands for a small disposal fee. You can also try calling your local fire department, they may either be able to take it, or they will know of a licensed disposal site in your area.


11

Unless you've got an extraordinary circumstance or legitimate reason for using it, don't. Chances are the usage will temporary make the symptoms subside, only to return again later. The way I see it, if your vehicle required it you would find it listed in the recommended maintenance items list in your owner's manual. I think another side to this question ...


11

The problem is, the crossfire isn't just high compression, I believe its supercharged as well. Forced induction motors like octane - the high pressure, high compression, and most importantly high combustion temperatures make you more prone to detonation. There are enough electronics in the engine (knock sensor for one) to realize that something is amiss ...


11

No, the tachometer can not be related to fuel efficiency as the tachometer is measuring the amount of rotations per minute (RPMs) of the engine. In the same gear and at the same speed your tachometer will always be at the same RPMs. However, you can be at 2000 RPMs and be barely touching the gas pedal (or completely off of it) because you are coasting down ...


11

As already stated, the ignition source between gasoline/gas engines and diesel engines are different and this is the primary reason for the difference in sound. I will try to explain those differences so you you'll understand why the sound is there with one, rather than the other. NOTE 1: There is a diatribe here, but bear with me as I attempt to answer the ...


11

He is mostly right and here's why ... There is an old saying about Harley Davidson Motorcycles. They call them the "Milwaukee Vibrator" because of they way they run. These engines are a 45 deg V-Twin engine (45 degrees is the angle between the two cylinders). In the HD engine, the two connecting rods attached to the pistons share a common journal or "pin" ...


11

Regulations limit the amount of unburnt hydrocarbons that can be released into the atmosphere, therefore fuel tanks on cars now have to be sealed to stop these emissions. The noise you hear is air rushing into the fuel tank, due to the low pressure caused by the use of fuel.


11

Background You asked Why is the effect of a bad fuel pump more noticeable at higher speeds? I assume that by 'higher speeds' you mean engine speeds or RPM's. During high RPM operation an ICE consumes more fuel so the flow rate into the fuel injection system or carburetor increases at higher RPM's. This taxes the fuel system and puts more load on the ...


10

Yes, you can buy additives that can be mixed with unleaded fuel. I found a list suitable products on the AA website: Suitable additives There are several proprietary lead-replacement additives available for 'DIY' dosing of unleaded petrol – these will increasingly be found in accessory shops and filling stations. Additives have been in ...


10

As an everyday buyer you won't be interested in the high performance end of diesel or petrol, so here goes: Diesel engines typically rev lower and have more low speed torque - so you are less likely to stall off the line, for example. Petrol engines usually rev higher and get more power at 3-4 thousand revs Diesel seems to be getting more expensive - ...



Only top voted, non community-wiki answers of a minimum length are eligible