In tank fuel pumps, a fire danger??

[NIsaacs]

I recently replaced the electric fuel pump in my EX's Dodge Neon, my first one. I completely disassembled it to see what made it tick, even cut the motor apart with a hack saw.



I was amazed and appalled that the fuel passes through the motor, that it is not sealed from the gas. How in the world can this be safe? I sorta understand that a spark that is submerged in gas can't light, but what about if the tank is low or out?? In a bad crash scenario when maybe there is no liquid, just fumes... is this crazy or just me??? I wonder if the Crown Vic and the older Chevy pickups with the outside the frame tanks were set on fire by this or just the impact? Even if the motor is not submerged in the gas and is sealed from it, what about the wires leading to it?? Thoughts?



Nick

 

[BarryG]

Yeah that has always struck me as odd to put an electric motor in a fuel tank. I had a Pontiac years ago like that. It broke down on a road trip and when I got it towed to a shop was suprised at how much it was going to cost. When I asked wtf for a simple fuel pump then they informed me they had to drop the tank to r & r since it was inside the tank. My old 74 chevy 4x4 with 350 engine I used to have had the saddle tanks outside the frame rails but the pump was mechanical on the side of the block like a 12 valve.

 

[rscurtis]

The reason it is not a fire hazard is that the mixture is too rich to burn. It's like trying to start a flooded engine- even the spark plugs can't light the fuel. If the tank was completely dry, and the fuel/air mixture was in the correct ratio, the fuel pump could blow the tank. How often is that going to happen?

 

[tempforce]

also the fuel lubricates the pump helping it to last longer.
the smart thing to do is never let your fuel tank get below 1/4. so that the pump doesn't get hot.

 

[NIsaacs]

The reason it is not a fire hazard is that the mixture is too rich to burn. It's like trying to start a flooded engine- even the spark plugs can't light the fuel. If the tank was completely dry, and the fuel/air mixture was in the correct ratio, the fuel pump could blow the tank. How often is that going to happen?

Yes, I can see the reasoning behind the submerged pump, but even once is too many. I can't help but think it happens more often. How about when the vehicle is on it's side or up side down, will the pump run dry trying to fuel the system. I would think the brushes would be sorta like flint in a lighter. Plus if the wires come loose or broke in a collision and arced. Maybe I am just thinking too much of a "what if" but I still think it is a dumb bell system.



Nick

 

[CKelley1]

as stated above you have to have 15 parts air to one part fuel to ignite. i weld on fuel tanks every once in a while. and when we remove a underground tank for the military they have us cut a 3 foot square hole in each end of the tank. there is usually about 4 inches of rust, sludge and gas in the bottom when we drop the plates that was cut with a chopsaw showering the fuel with red hot sparks.

 

[Wingate]

Yes, I can see the reasoning behind the submerged pump, but even once is too many. I can't help but think it happens more often. How about when the vehicle is on it's side or up side down, will the pump run dry trying to fuel the system. I would think the brushes would be sorta like flint in a lighter. Plus if the wires come loose or broke in a collision and arced. Maybe I am just thinking too much of a "what if" but I still think it is a dumb bell system.



Nick

The fuel pump is in the tank for several reasons. One is that its more cost effective (cheaper!!) to put it there vs. a mechanical pump on the engine. Its also easier on the pump to push fuel the length of the vehicle vs. sucking it from the tank...

EFI engines have a roll over switch that shuts down the fuel pump in the event of a flip... I have seen the switches get tripped from a wreck on level ground when the vehicle didnt flip, so they DO work. .

As others have said, although you have the ignition source and the fuel... you are missing the other required piece of the puzzle to support a fire... Oxygen!. The gas vapor displaces the oxygen in the tank... so theres no oxygen to support a fire.

 

[Missouri Mule]

My 88 ford van had electrical pumps (one in the tank and one on the frame under driver's seat). There was a cut off switch by the passenger door that would cut off the power to the pumps in case of an accident (this switch could be reset just in case it acitvated for no reason. )



I agree, you need oxygen to burn something.

 

[PBJ2500CTD]

I believe the in tank fuel pumps are brushless, so there is no spark.

 

[NIsaacs]

I believe the in tank fuel pumps are brushless, so there is no spark.

I was wondering about that, why they weren't brushless. The Neon does have them, it was a Wabco pump, the original. I replaced it with an Airtex, not sure about it.



When I inspected the motor and pump, they both looked good and was running fine, just no fuel being pumped. It had a filter (sock) on the main canister inlet and another one inside the canister to the pump inlet and a metal filter with normal filtering media on the pump outlet. When I cut it open it appeared to be mostly plugged up with motor generated debris. It is not serviced separately but would be easy to change if one was available. I think it was plugged, so no fuel.



Thanks for all the scientific info, they are starting to make more sense now. However I am still somewhat unsure of fires in perfect combustion scenarios. Especially with gas, diesel not so much.



After the fact, there would be no way an investigation could pin point the combustion source in the case of a wreck and fire. My pea brain just can't seem to wrap itself around all this complexity.



Nick