First off, I want to say that normally, I fuel up with a quarter tank left. but recently I've been busy and today i was driving until the last light was on. It says for the range i have 10km (6.2mi) remaining. I was wondering if anyone know if there is a reserve that it goes on even after no lights on the gas meter?
Gas Tank Reserve
- Thread starter kefun
- Start date
Yeah, there's plenty left when it says "0 miles to empty" and the gauge is on empty. Likely almost two gallons. But it's not a good idea to suck it all the way dry on any modern car so I only plan on 1 gallon once I hit empty. Never had an issue doing it like that.
Not sure of other years but at least for '15 fuel capacity is as follows:
FWD: 56.0 L (14.8 US gal, 12.3 Imp gal)
AWD: 58.0 L (15.3 US gal, 12.8 Imp gal)
I imagine other years are the same.
FWD: 56.0 L (14.8 US gal, 12.3 Imp gal)
AWD: 58.0 L (15.3 US gal, 12.8 Imp gal)
I imagine other years are the same.
If the CX-5 uses an "in tank" style fuel pump, running your fuel very low or dry may damage it as these pumps are cooled by the gas they sit in. I'm new to this car, but in theory this is not a good practice.
I hope this wasn't serious...
No, the fuel pump is not cooled by the fuel it sits in but it does depend upon the fuel that is flowing through it to lubricate the impeller. It's O.K. to run it low but not real good to run it dry.
Fuel pumps don't generally fail from impeller failures. They fail from heat to the motor or just plain wear out. Impellers themselves do not necessarily cool electric motors which fail from heat. They do move liquid which cools the pump end, but not necessarily the electric motor. Electric motors in static conditions must be cooled by a source (air, water, fuel, heat exchanger, etc.) and are usually cooled by flow inducers or sleeves that produce "movement" over the electric motors when used in liquid. Some pumps have internal cooling systems. I doubt these fuel pumps do. A type of cooling could be fuel sloshing in a gas tank. Thus the need to immerse the "motor end" and not necessarily the "pump end" in fuel. Thus the point of not running them dry=heat= motor failure.
Skyactiv engines utilize many technologies to increase efficiency across the board. One of these is pulse control modulation to control the low pressure fuel pump. Traditional injection systems pump far more fuel than is ever needed through the fuel rail near the injectors. Whatever fuel is not used is returned to the tank. As you can imagine, over time, and with a small amount of fuel in the tank, the fuel that is circulated through the fuel rail becomes very hot and so does the fuel in the tank when there is only a gallon or so remaining. All of the fuel that is being circulated is forced through the micron level fuel filter which requires a lot of work due to the high volume of fuel being continually circulated. The 2.0L Mazda 3 (not Skyactiv) requires a 30 amp fuse and the fuel pump runs at full power continuously.
Skyactiv engines have two fuel pumps, the high pressure pump driven by the camshaft mechanically and the low pressure pump located in the fuel tank which is driven by an electric motor protected by a 15 amp fuse. This pump does not run at full power constantly but is modulated using a PCM controller to pump (and filter) only as much fuel as is actually needed. Under normal operation it is only running at 10-20% of capacity and there is no return fuel line to cause the fuel remaining in the tank to become hotter and hotter except for a small amount of warming generated by the electric fuel pump. By using far less electricity than a conventional fuel pump the vehicles efficiency is increased and very little heat is created inside the electric fuel pump motor. Keeping the internal tank temperature low has the further benefit of reducing fuel vapor in the tank thereby reducing evaporative emissions.
For these reasons the fuel pump can be cooled in the same way that most electric motors are cooled, by the air that surrounds them. There simply isn't much heat being created internally (or via a return fuel line). Electric motors typically are made of components that are very heat resistant. They conduct heat to the motor casing where it is harmlessly radiated away. Even if there is no fuel surrounding the fuel pump, it will not overheat.
Thanks for the explanation. Very detailed. Two fuel pumps sounds more like a diesel application. However I will say that after being in the industry of pumps/water and liquid transfer for 40 years, the number one killer of pumps-any pumps, is heat, first usually related to stopping and starting (cycling) and secondly, lack of cooling, whether they are running at low or high capacity. So the lessen here would be the same given any course of logic: Don't run them dry.
I have hydronic heating in my home. Whenever the gas boiler is operating there is a 120 volt pump that circulates the water throughout the house. The pump motor is air cooled although it is enclosed in a steel case without fan or air circulation. It gets very warm to the touch through most of the 8 month heating season. The boiler expert tells me this pump is original to the 1957 gas boiler. It has been running for 57 years without cooling or failure.
My hot tub which has been in constant operation for 8 years has three water pumps, two large ones that run intermittently (whenever the jets/skimmer run) and one small one that runs 24 hours/day. The small one was replaced two years ago and the two large ones have never failed. None of them are water cooled.
I have two 2002 fuel injected Ducati motorcycles. The fuel pumps are mounted in the tanks and are often not covered with fuel (I like to use the full range of the 5.5 gallon tanks). These are not direct injected engines so the fuel is constantly being circulated between the tank and the fuel injectors before being returned to the tank. After being run on a sunny day (the tank is in full sun, unlike CX-5), the tank is often too hot to hold your hand on it without getting burned. Even though this is a very high temperature application and one of the bikes has 60,000 miles on it, I've never experienced a fuel pump failure.
I'm afraid your statistical group is much smaller than mine. (screwy) and your summation of lack of failures does not reflect electric motor industry findings. Since you are near Portland, you may wish to attend the Cornell Pump School (2 days x 8 hours each day). You may find their motor failure "statistics" differ greatly than your small sample may indicate.
My own "hydroponic" Laars radiant floor boiler system Grundfos circulator pump failed last year. Unfortunately it's on the third one since 1992. The other pumps you refer to in your spa system have (or should have) a cooling fan built into each unit. Try covering up the "exhaust" holes on the casings and see how long the motors last.
And as far as your Ducati's go...well, you must just plain like to work on things (guitar). Always been in love with the 996 myself.
The two big motors do have narrow vanes on the output shaft. The pump that runs 24/7 does not. It just radiates heat from the metal enclosure.
And the Ducati fuel pumps just keep going. Of course there are no vanes on those fuel pumps because they are designed to be run either submerged in fuel or in the air (when the tank is less than half full).
I only need to service the Ducati's once a year and I would do that with any brand motorcycle. These are modern Ducati and they are very reliable. The tires are usually getting near bald by the time they're ready for their annual service. The tank gets so hot with all that fuel flowing through the feed and return hoses which are crammed between the cylinders and fuel tank, I'm surprised the pumps keep going. But they do. They don't seem to mind being run down to a shallow puddle of fuel in the bottom of a burning hot tank that's been soaking up engine heat from below and solar heat from above. The pumps use high temperature materials they are designed to handle heat. The CX-5 tank remains very cool by comparison and the fuel pump is not running at 100% due to the pulse modulation controller. Running the tank low will not overheat the fuel pump. If you go to my fuelly page you will see I run it quite low with regularity without pump failure. In fact, I've never heard of a single fuel pump failure in a CX-5.
When the CX-5 is running out of fuel the pump will not be able to deliver the gas at the requested pressure so the controller is going to keep raising the pulse to 100% generating max heat in the pump and pump motor. At the same time the pump will start sucking air which will likely allow it to over speed adding more stress. If the design is to be cooled by liquids and it is now in the air the transfer of heat to air is not nearly as effective as heat transfer to liquid like gas. I think there is a bigger potential problem if air gets in the high pressure pump and rails as unlike gas, air compresses. This means that at the top of the engine piston stroke the electric injector will open up and instead of spraying fuel into the cylinder the air in the lines will also compress and the dirty compression gas from the engine will be fed into the injectors potentially clogging and overheating them. Hopefully they have some type of pressure monitoring system that will turn off the injectors if there is not adequate pressure in the high pressure side of the injector rails. Has anyone ran the CX-5 out of gas, had it quit and not damage it?
In case you were not aware, this discussion is about running the tank LOW, not running it dry.
Nothing bad happens from being run low but, I agree, running it dry is bad. The injectors get their high pressure from mechanical fuel pumps running off the cam shafts but the injectors are electrically operated. I would assume the injectors would not be opened if there was not at least 34 PSI in the low pressure system, a pressure that would be impossible to reach if the low pressure side was full of air.
Well now, if you run the tank very LOW and turn or stop or start the fuel left will slosh away from the pump and it will pull air and be dry.
Interesting they are using a mechanical high pressure pump. It must be a negligible parasitic MPG loss from this.
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True, but that's how I define running the tank dry (the fuel pump starts to suck air). You can never get the last little bit out so the tank is never actually dry.
