Keeping Gas Tank Full during Winter on newer cars

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quote:

Originally posted by olympic:
Condensation is only a real issue if you park your car in a heated garage. The drastic temperature changes from winter cold to room temperature a couple times a day can cause moisture to build up in the tank. So either park it full of use some gas line antifreeze with each fill.



At work I park in an underground garage, which stays at between 40-60 degrees for most of the winter months. At home I park outside, so it can often get down to below 0F.

FYI, Fuel Power also doubles as a gas line antifreeze. So if you're using it already there is no need for anything else to be added to the fuel.
 
quote:

Keep in mind one thing that's different about today's cars. The tanks are no longer vented directly to the atmosphere.

Matt makes a good point, here. The evaporative emissions systems controls do not allow the air in the gas tank to freely mix with outside atmospheric air.

The amount of condensation that can form on the inside of a gas tank is limited to the moisture/humidity of only the approx. 12-16 gallons of air within an almost empty tank.

Here is an example from an EPA site dealing with the issue of ethanol blended gas absoring moisture from the air.


EPA Memo - Water Phase Separation in Oxygenated Gasoline - (as quoted from page 4)

Since the solubility of water in both gasoline and air decreases with a decrease in temperature, water can enter a fuel system through condensation when the atmospheric temperature changes.

For example, assume a tank containing conventional gasoline contains only one gallon of fuel. Assume also that it is closed while the outside temperature is 100 degrees F with a relative humidity of 100 percent. If this tank is left sealed and the temperature drops to 40 degrees F, water will likely condense on the inside of the tank, and dissolve in the fuel.

In order for enough water to condense from the air to cause gasoline-water phase separation, however, there must be approximately 200 gallons of air per gallon of fuel over this temperature drop (100 to 40 degrees). Since oxygenated fuels can hold even more water than conventional gasoline, it is even more unlikely that enough water will condense from the air to cause gasoline-water phase separation.

http://www.epa.gov/otaq/regs/fuels/rfg/waterphs.pdf
 
**** , $500-800 for a fuel pump??

I had mine replaced with a higher-flow Walbro unit (and even paid labor to have it installed) for a total of about $180; I suppose if you had to buy an OEM pump and have a dealer install you might get raped. But still, I'd never pay that much.

On topic though, I run my car down till the gas light comes on (1/8th of a tank) before I even think about filling up. Less weight = better gas milage, and I've never really had a problem with gas line freezing.

Would using a tank of Ethanol gas every so often help?
 
Well Blue, looks like we'll just leave it at that.
lol.gif
 
quote:

Originally posted by sxg6:
every so often ill run my car down to E as much as possible..for some reason i think it'll get rid of any extra crud that has accumulated at the bottom of my tank..anyone else do this or think its worthwhile?

I think you are asking for problems. I would not recommend doing this.

A few have replied that when the low gas warning light comes on there is still some gas in the tank. (implying that one can keep on driving)

They are missing the purpose of the low fuel warning light. I'll post more detailed info about this in the next replay.
 
For what it's worth, I usually try to burn down as much of each tank as I can.

As for keeping it mainly full to cool the fuel pump... maybe for some cars that is true, but on mine, the fuel pump lives in the top 1/2 of the tank. Using that logic, I would have to keep the tank greater than 1/2s of a tank full to keep the pump properly cooled.

Now letting it totaly run out of gas is another thing. That will cause the pump to over heat and die an early death. I had always heard that the pumps were cooled by the flow of gas through them, not by keeping them surrounded with gas.

Completely non-scientific statistics, but in the large extended family of vehicles here that see the regular 100+ degree summers.. I have yet to see an electric fuel pump die due to not keeping the tank full for the majority of the time. Die due to letting things run dry? Yes, but not from running it through the range of the fuel guage between fillups.

Also in this completely non-scientific statistical data, we see winter temps dip into the teens every winter and occasionally will see single digits and below 0 temps from year to year in this part of the country. Have yet to have anyone that I know suffer a frozen fuel line problem caused by the same practice.
 
Below is a very long re-post of some information about fuel levels by Jim Hopkins. Mr. Hopkins is retired after a very long and distinguished career as a trainer and troubleshooter for Toyota of North America (I think this is correct - applogies to Mr. Hopkins if I ommited something.) What follows is a long read but may clear up some issues discussed in this thread. =======


Warning: The "low fuel" warning light was NOT put on your car so that you could avoid the embarrassment of having to be rescued by
the AAA because your engine quit from fuel starvation (many people somehow think it was put there just for that very purpose). Avoid
using it for this purpose. It was never intended to encourage driver neglect. It is not there to release drivers from their responsibilities and encourage bad driving habits. It is there
because it was "mandated" by "corporate lawyers" to meet emission control regulations in the early 1980s. That's why it's there!

The law required that all car manufacturers, warranty all emission controls for 5 years to assure compliance with emission control
regulations.

Now! The engineers were fully convinced that all the right components ( platinum spark plugs, EGR, fuel injection etc., etc.) would easily meet and surpass all the legal specifications, and warranty requirements for emission controls, with only "TWO" major conditions: #1 absolutely NO leaded fuel (poisons the catalytic onverter), and #2 only very limited amounts of raw unburned) fuel should ever be permitted to reach the catalytic converter (overheats the converter).

The unleaded fuel problem was eventually resolved by the installation of a smaller diameter fuel filler inlet into the fuel
tank filler neck, and appropriate "unleaded fuel only" customer warning stickers, were strategically placed, With the cooperation
of the fuel suppliers, providing smaller gas pump filler nozzles ONLY for unleaded fuel, consumer mistakes were hopefully minimized.

However, the raw fuel problem was much more difficult to resolve since "fuel starvation" (misfire) causes unburned fuel to enter the
catalytic converter.

If there ever is "NO" fuel available at the fuel pump pickup inlet inside the fuel tank, the fuel pump simply cannot pump any fuel! That's just elementary! With a loss of fuel delivery, the fuel rail "residual" pressure is quickly depleted, especially if the engine's demands for fuel are high, This fuel pressure drop causes a drastic reduction in the amount of fuel delivered by the injectors by each fuel pulse. The fuel mixture then becomes very "lean" (the same amount of intake air, combined with less fuel). "Lean" fuel mixtures burn much "hotter" than rich fuel mixtures, and must therefore be avoided, especially at high engine loads, and high engine RPM (more power pulses per minute) to prevent overheating the combustion chamber, and burning the valves, etc. (also exhaust emissions can increase). Lean burning is the first stage of fuel starvation.

If the mixture becomes even "leaner" ignition suddenly becomes impossible, and "lean combustion" instantly becomes "lean misfire".
If a fuel charge fails to ignite the unburned gasoline and air mixture then passes right through the engine combustion chamber
completely unburned. This mixture rapidly cools the overheated combustion chamber, and continues right on through the exhaust manifold, and reaches the catalytic converter, where the mixture is then burned, likely causing the converter to overheat in it`s attempts to prevent tailpipe emissions.

Now! The if fuel pump constantly delivers several times as much fuel as the engine could possibly ever use to generate it's maximum rated
horsepower, fuel starvation under high loads is virtually impossible. Only if someone has somehow outrageously tricked up the
engine with larger fuel injectors, overridden the computers RPM limiter, force fed the engine (turbo-super charger), etc. etc. etc.
doubling the engine's rated horsepower, or restricted the fuel pressure line or fuel filter, installed an ultra strong drive line
and tires with colossal tire grip, etc. etc., could they ever create an engine load that even approach the limits of the fuel pump
delivery capacity to supply. So, forget larger fuel pumps promising increased horsepower. I have seen mechanics quickly drain a fuel
tank just by opening a fuel line and directing it into a storage tank , and then running the fuel pump (a neat trick). I will explain how to do this later on in this post. Only a drag racer
could ever consume fuel that rapidly. Don't buy a larger fuel pump to increase performance.

Since fuel starvation will ALWAYS occur when the fuel in the fuel tank becomes DEPLEATED. The design engineer is very limited in what
he can do to prevent this "driver" initiated problem. A larger fuel tank will only delay the problem, as eventually all cars will run
out of fuel (even solar powered cars, when the sun doesn't shine).
This ultimately always becomes a driver education problem, and not really an engineering design problem. Driver education is however
very, very difficult!

Fuel starvation occurs long, long before the fuel in the tank is ever actually exhausted. The fuel pump pick up cannot be located at the very bottom of the fuel tank, as it would then suck in water and sediment, etc. So, the fuel sloshes merrily around (in spite of baffles) up the sides of the fuel tank every time the vehicle is
affected by any inertia forces, leaving the fuel pump pickup pipe high and dry. Way before you ever actually "run out of fuel" your engine can suffer real fuel starvation, misfire. etc., and dump a lot of your costly fuel right down the exhaust manifold and into the catalytic converter to be converted into wasted heat (so that at least it won't pollute the environment).

An engine turning even 2000 RPM fires 1000 times in a minute, so the driver will probably never even notice 50 misfires (5%) per minute.
But the driver looses 5% of the engine's horsepower, and wastes 5% of his fuel. Note: Low fuel levels in the fuel tank will "NOT" cause
lean misfire at idle (when the car is stationary / no inertia forces), where engine misfire is usually easily detected. Also fuel
starvation will not show up at emission control test stations because they test on a rolling road (no inertia forces) Always keep the TOP half of your fuel tank full!

If you don't believe me, just try holding an open cup of coffee (even a quarter full) while the driver weaves around through busy
traffic, over potholes, rounds curves etc. (without spilling any coffee). Imagine what is happening inside the car's fuel tank, as
the fuel pump pick up pipe gasps for fuel. Fuel also runs to the rear of the fuel tank when ascending hills, further aggravating fuel
starvation. A lot of poor fuel economy is caused by fuel starvation. as well, as contributing to catalytic converter overheating. Always
keep the TOP half of your fuel tank full!

Inertia forces from rough roads can be reduced by: smoothing the road surface (municipal problem), softening the suspension (an
engineering compromise), reducing vehicle speed (driver education). These inertia forces are very difficult to predict. When driving on rough "back country" roads always keep the TOP half of your fuel tank full!

Braking can generate very large inertia forces, but when the throttle closes (very likely under hard braking), fuel injection is
completely terminated by the engine computer until the engine RPM slows down to near idle speed. Then at idle, so little fuel is
injected that any air entrained in the rapidly circulating fuel stream is quickly released back into the fuel tank with very little consequence. So braking inertia (although very high) is not really a fuel starvation factor.

Cornering forces can be very high and can easily cause fuel starvation (just ask NASCAR drivers). Acceleration forces are particularly nasty for fuel starvation. Acceleration forces are
limited by both engine torque and tire adhesion (two wheels) , and are therefore much lower than braking forces (four wheels). Acceleration forces are usually of much shorter duration than
cornering forces because they cannot be sustained, but since, acceleration forces correspond directly with a very high fuel demand
by the engine, they are therefore very, very likely to cause fuel starvation and lean misfire. When both acceleration and cornering
forces are combined on a rough road, chances of fuel starvation greatly increase. For aggressive driving, always keep the TOP half of your fuel tank full!

If you have installed stiffer shock absorbers, stickier tires, increased your engine's power, or drive more briskly than normal, you are very likely to experience even more fuel starvation and lean engine misfire from inertia isplacement of fuel inside the fuel tank. "Savvy" street racers often challenge a competitor if they
spot a low fuel gauge reading in his car. With a full fuel tank, they likely have an advantage. Always keep the TOP half of your fuel tank full!


The design engineers ESTIMATE the fuel level at which "THEY" anticipate fuel starvation "MAY" become problematic and lead to catalytic converter overheating. They consider the vehicles
intended use (family sedan, sports car, etc.), engine horsepower, tire adhesion , etc. Based on this (original equipment) prediction, they appropriately locate a fuel level sensor inside the fuel tank to monitor the "low fuel" warning level. This "low fuel sensor is located very near the fuel pump pickup as this is the point
requiring monitoring.

A float gauge (as is the fuel gauge) would not work, since it would be all over the place as the fuel sloshed around in the tank, and would need very heavy damping (like a normal fuel level gauge), which would make it very slow to respond and too inaccurate.

Instead a tiny electrical resistor, encapsulated in a plastic cover is used as a "low fuel level" warning sensor. This resistor is continually (ignition on) fed a very small voltage, which causes the resistor to heat up, as the resistor heats, it's resistance increases, when it's resistance increases it's current flow
decreases because the applied voltage is kept constant. Therefore it's current flow reflects it's temperature.

As long as this sensor remains submerged underneath the fuel inside the fuel tank, it's heat is continuously absorbed by the surrounding
fuel, so it cannot heat up and it's current draw will remain relatively high.

Should the fuel level drop, exposing the sensor to the air inside the fuel tank, the resistor will soon heat up, causing it's resistance to increase, less current will now flow, and the computer will interpret the low current flow as an indication of a low fuel level in the fuel tank, and respond by turning on the "low fuel"
warning light. This light will never come on at start up, even if the fuel level is low, because it requires several seconds for the sensor to warm up sufficiently to signal the computer to turn on the warning light. This process will take a little longer on a very cold morning.

While rounding a very long curve at high speed you may have noticed the light come on after a few seconds delay as the fuel is drained away from the sensor by inertia allowing it to heat up, and turn on the warning light, to warn the driver of impending fuel starvation (do you always heed this warning?). As the car then
resumed a straighter, stable course the sloshing fuel returned to a more tranquil state, quenched the sensors heat and extinguished the warning light. Did you then forget about the warning?
This process will occur much more rapidly if the fuel in the tank has been previously heated by engine heat absorbed from the engine fuel rail.

Most people assume that the owner's manual says "Warning! You can only drive about 50 km more before you run out of fuel" It DOESN'T!"
Check your owner's manual. What is printed there???

It reads "Warning! "DO NOT DRIVE" when the "low fuel" warning light is on. Car manufacturers assume no legal liability whatever for any damage to the vehicle's engine or emission control components etc. caused by owners who do not heed this warning light. It is considered, driver neglect! Read your owner's manual "very"
carefully, and always keep the TOP half of your fuel tank full!

Catalytic converters are engine garbage disposals. Don't risk turning your costly fuel into garbage, and tossing it away into the
catalytic converter for disposal! Always keep the TOP have of your fuel tank full!

I have actually fielded owner complaints that their "low fuel" warning light was incorrectly calibrated at the factory, because (they assured me) there was still lots of fuel remaining in the fuel tank after the light came on. They complained that they found the warning light very annoying, and distracting while they proceeded to consume all of the fuel remaining inside the fuel tank. Have you ever felt this way about your low fuel warning light? Better change!

Not only are you at great risk of inducing fuel starvation, but the fuel remaining inside the fuel tank is also at greater risk of being
overheated and vaporizing etc. Also, there is much greater air space inside a fuel tank with a low fuel level for water vapours to condense, causing water to collect in the bottom of the tank to freeze in fuel lines, etc. Add a half cup of methyl hydrate once or twice a year, and keep the TOP half of your fuel tank full!

If you must continue to drive with the "low fuel" warning light on, drive at reduced speeds, avoid sudden manoeuvres etc. and fuel
up "just as soon" as you possibly can. If you are an exuberant driver fill up much, much sooner. In hot weather, on long fast drives, fill up much sooner. If you have modified your car to achieve more cornering "Gs" fill up much, much sooner. If you experience any loss of power during hard acceleration, fill up "immediately". If the "low fuel warning light ever comes on
during hard acceleration, your fuel is probably both too hot, and too low, so forget any racing till you fill up your fuel tank.

Many a Sunday drag racer has been defeated by much lesser cars because the fuel in his fuel tank simply flowed away from the fuel pump pick up under hard acceleration, or taking a fast corner. Many street racers experience fuel starvation and are then sold "humongous", expensive fuel pumps as an "upgrade". They then
fill up their fuel tanks, and will swear that it was their trick fuel pump installation etc. that delivered a terrific performance improvement. That is, until the next time they race with a low fuel level.

Few racers like to admit that their tricked out car, lost out simply because they neglected to fill up the fuel tank, and they just ran
out of gas under hard acceleration. A new key ring would probably have done as much for their performance as a the " humongous" fuel pump! The cheapest performance "upgrade you can ever make to your car is to keep the TOP half of your fuel tank full!

If you really must race with low fuel levels, change your fuel tank over to one engineered specifically for racing. It may not sound as
sexy as many other highly advertised performance products as a racing fuel tank cannot promise more power, but it is the best cure for fuel starvation. Do not install racing fuel tanks with a much smaller fuel capacity, unless you install an appropriate fuel heat exchanger on the fuel pressure regulator return line to the fuel tank. Make sure your replacement fuel tank installation is safe and has the appropriate openings for fuel vapour collection, etc.

I am sure many people reading this are wondering why on earth, I have devoted so much time detailing what seemingly appears to them
to be the obvious. However, when I am asked by people for a good tip on maintaining their cars I often reply: "Keep the TOP half of your fuel tank full!". They usually look amazed and just snicker, and reply: "Oh I know all about that, I once ran out of gas about 3 years ago, but lately I have been very lucky. A few close calls. But I haven't run right out of fuel!" for along. "Now! Tell me something exotic, and exciting, like: How to get more power and
acceleration, better handling, better gas mileage, how to make it start faster in hot weather, what additives to use to clean my fuel
injectors, etc., etc."

Then I tell them that I have just told them how to do this, but they just didn't understand why I said it, and obviously, a much more in
depth and detailed explanation is required for them to fully appreciate the full significance of this advice. This advice is very well known, but very few people will ever give you this detailed an explanation, probably because it serves no commercial market, and may even adversely impact on their future sales. Yet, I think it is necessary information, in order for a drivers to FULLY appreciate the full consequences of their neglect. How many times do drivers breathe a sigh of relief as they reach a service station just in time, and then congratulate themselves for getting away with it.
Truth is, they probably really didn't get away with it! They just think they did! Actually they probably unwittingly cheated themselves out of some "free "gasoline.

I can also, positively guarantee that if you always keep the "TOP" half of your fuel tank full, you will NEVER, ever "run out of gas".
I can also guarantee that it will cost you much less money to keep the TOP half of your fuel tank full than the bottom half. You have
my word on it! If you have any friends that you think would benefit from this information, please pass it along. I always hate to see
people senselessly dumping their good fuel down their catalytic converters.

I`ll bet when you refuelled on a hot day, the fuel cap went "whoosh" releasing the high pressure built up by the hot vaporizing fuel
during your long drive, both by the sun`s heat and that carried away from the engine by the rapidly circulating fuel combined. Now,
at a constant fuel temperature a slight vacuum would always be left behind as the fuel vacates the tank. That "whoosh" however, is a good sign that the fuel storage system is well sealed and that fuel vapours inside the tank, are being effectively controlled, but it is also a sign of very "HOT" fuel inside the fuel tank. Note: The
evaporative emission control (EVAP) will allow quite a high , but limited amount of pressure to develop inside the fuel tank before fuel vapours are allowed to escape out into the charcoal canister, this residual fuel tank pressure reduces the formation of even more fuel vapours under hot fuel conditions.

Should a vacuum develop as the fuel cools or as fuel is used up, with no temperature increase, the "fuel tank cap" has a little valve in it to let atmospheric air into the fuel tank, so that the tank is not crushed by atmospheric pressure. This valve also requires a little vacuum to open it, so it is not unusual to sometimes find a
slight vacuum inside the fuel tank, if fuel temperatures are fairly stable. This slight vacuum "hiss" is also the sign of a good fuel
tank cap when refuelling.

Remember to always tighten the fuel filler cap till it "clicks" to assure a positive fuel filler cap seal. If you never hear a "whoosh" or "hiss" replace the fuel filler cap, or cap gasket, immediately, because, you are wasting the fuel you have paid for and are just polluting the atmosphere with it.
 
That's a good article, Cressida. I have one thing to point out, though. Many cars, mine included, actually do pick up the fuel from the very bottom of the tank. The fuel pump is mounted vertically inside a plastic cage with the inlet at the bottom. There is a carbon-filled sock attached to the bottom that lies on the bottom of the tank. The cage is also pressed against the bottom via springs. With this design, the fuel pump would only suck air if you're in imminent danger of running out of gas, at which point the gauge would be bottomed out and the low fuel light would have been on for some time.

So what I'm saying is that the details of the fuel pickup don't apply to all cars. The information overall is very informative, though. It's a good, read, albeit long as you said.
 
Also if your in a state with the possiblity of hard snows and blizzards, it's a good idea to have a full tank of gas in case you go off the road, and can't get help. That gas is your only source of heat.

-T
 
That article was a joke. Racers go with a mostly empty tank because gasoline weighs 6.7 lbs/gallon. It ignores calibration issues as well. When my light comes on there is still 8 gallons in the tank! I run it down to E and it still has 4-5 gallons. OTOH, it drops like a rock from F then slows down in the end. It's not well calibrated and I'm not taking a page from some yay-hoo to tell me how to do it differently.
 
i was under the impression that the main reason for running a full tank was to limit corrosion of metal tanks. since most gas tanks are plastic now this isnt a concern.

my dakota is something like 22 gallons. if i always filled at 1/2 a tank i would always be hauling around an extra 73 lbs. i suspect this would consume more gas than the vapor that escapes when i open the gas cap.

as for moisture for the air condensing in the tank, probably not a big deal in the winter (dry air). even so, during the winter they usually oxygenate gas. since mtbe is being phased out, i suspect there is enough ethanol to take care of any water issues.
 
You should always consider driving until the warning light comes on and then push it just a little bit, you know hard braking, fast turns and bumpy roads. How else can the fuel pump get the sediment and crud sucked off the bottom of the gas tank. If you always drive with a near-full tank you will always have a dirty fuel tank. Don't worry, when the filter on the fuel pump is full the pump will fail, a signal to change it for a new one.

On some cars you can rig a sediment level indicator. Let's say your pump has a 15A fuse. Replace it with a 10A fuse. When that fuse blows you are half full, replace it with a 12A fuse. When that one blows you are three quarters full and you might want to consider scheduling a change. There should be nothing between you and a clean fuel tank, except, maybe a tow truck.
 
quote:

Originally posted by Brons2:
That article was a joke. Racers go with a mostly empty tank because gasoline weighs 6.7 lbs/gallon. It ignores calibration issues as well. When my light comes on there is still 8 gallons in the tank! I run it down to E and it still has 4-5 gallons. OTOH, it drops like a rock from F then slows down in the end. It's not well calibrated and I'm not taking a page from some yay-hoo to tell me how to do it differently.

The guy should write fiction. He's wordy enough and sounds convincing to people who don't know better. He certainly has a good imagination. The low fuel lamp was put there for emissions compliance...
lol.gif
 
quote:

Originally posted by Forkman:
Please tell me you don't do this in the summer time since in many vehicles the fuel pump is designed to be cooled by the surrounding fuel in the tank. Running tanks to near empty on a regular basis (at least in the warmer months) is a very good way to shorten the life of the in-tank fuel pump.

Heck, many of the owners manuals on certain models of GM vehicles specifically caution against this practice. I do recall my 98 Grand Am had that warning in the owners manual.


I'd like to know how gas surrounding the pump is more useful as a coolant than the gas getting sucked through the pump...
 
quote:

Originally posted by weatherdude:
Now letting it totaly run out of gas is another thing. That will cause the pump to over heat and die an early death.

And in the case of running out of gas and the engine dying, the fuel pump control will usually shut down the pump after 2-5 seconds of the engine shutting down, further minimizing the risk.
 
quote:

Originally posted by Cressida:
Below is a very long re-post of some information about fuel levels by Jim Hopkins. Mr. Hopkins is retired after a very long and distinguished career as a trainer and troubleshooter for Toyota of North America (I think this is correct - applogies to Mr. Hopkins if I ommited something.) What follows is a long read but may clear up some issues discussed in this thread. =======

Wow, what a long winded way to explain something that doesn't really apply to running a fuel tank low. I only have one thing to say about Mr. Hopkins theory on low fuel lights - BS. My 93 Caprice has no fuel warning light, though it was optional with a low fluid level warning center. My 95 Camaro, on the other hand, has no warning light nor was one available. It is a convenience warning and NOTHING MORE. My Caprice is notorious for starving the fuel pump for fuel during hard cornering. I've done it MANY times. It does not misfire when the fuel pump sucks air. The engine simply stops making power, at all. As soon as fuel is available to the pump, instant power. Maybe other cars are different, but this is my experience. Not to mention running with a lean misfire for a few seconds is NOT going to hurt the cat. Maybe early cats were extra fragile...
 
So.... if the fuel pump is such an important "emissions" component, how come it isn't covered by a lifetime warranty like all emissions components are?

There may be some truth in the emissions part of his story, but to claim that the low warning light is primarily emissions-related is more bizarre than I can even imagine.
 
what about external fuel pumps? how do those not overheat if the sorrounding fuel is what cools them?
 
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