Very Poor Gas Mileage

[Hitman]

Carrying around dead weight makes a difference. If you have to repeatedly accelerate that dead weight its going to add up.

Even after filling up at E, there is still over 2 gallons of fuel in the tank. That should be plenty to submerge the fuel pump.

Dead weight? All the weight of a vehicle is dead weight, except for the unsprung weight (wheels, tires, brake rotors etc..) But my point is that you're talking about less than 2% weight of the vehicle.

Also, the fuel pump does not sit at the bottom of the fuel tank. In fact, it "hangs" from the very top of the fuel tank and is mounted vertically. Only the fuel pump pick-up sits at the bottom of the tank.

 

[JungleJim]

Don't fill up until you are almost at E on the Fuel Gauge.

Be careful about doing this. On newer vehicles, this is not a problem. But as a vehicle gets older, sludge builds up in the bottom of the gas tank. You can ruin a fuel pump quickly by running it down too low on an older vehicle. There's no benefit to running any vehicle down to below a quarter of a tank.

 

[4RunnerOU]

Finally finish up the 1st full tank filled by the dealership. So, I went to fill up the gas, it stopped at 19.9 gallon. Total trip mileage is 357. Therefore, I was getting 17.9 MPG. My driving was approx. 60% HW and 40% CITY.

Hope MPG will get better once I reach 1K.

 

[pbm317]

My mileage has been pretty poor lately too. A couple 300+ mile trips on the highways and I was averaging 16. I was going at a moderate pace too, nothing too crazy. I am going to recheck my air filter soon... could that make a big difference?

 

[p53mustang]

poor gas mileage

Guys,
thought this might help I used to have a 02 Subaru Outback (very good car) which from the very beginning i've been averaging 21mpg. And for some reason I noticed that my average mpg started to drop to 20 first then 19 (and this was a year and half into ownership) i took it to the dealer and they couldn't find anything wrong (no lights on dash) and then for a while (approx 3 mos.) my ave. mpg stayed at around 19 and then it got worst to 16 . By this time i had this thing checked out again and again they couldn't find anything wrong. I used to put a clean cardboard under the engine bay area in my garage and I couldn't find any spot or any drop , I left it at the dealership overnight more than one occasion and they still couldn't find anything wrong (by this time i've been to 3 subie dealers)
Anyhow make long story short by the time I got down to ten miles to a gallon the dealer finally solved the problem there was a very fine leak (gas ) on the injection port right on top of where the exhaust manifold that when the car is at still with the engine off you can't see any drop and then with the engine idling the leak was so fine that the exhaust manifold just melts it before the leak could make it to the ground. However at hight rate of speed when the throtle was wide open the leak pours out more some of it get burned and some (i assume falls to the ground) however you can't smell anything because the car is in motion.
Sorry if this is too long , hope this helps.
Good luck.

 

[PT2002]

I have a 2004 4Runner V6 2WD. I know i don't have the same engine but i do share the "bad Mileage" experience. i get 15-17 MPG on my 2wd v6. That's running by myself normally to and from work. I live in Los Angeles and most of my driving are on the highway. Never the less, i suspect there is something wrong somewhere when the Gas mileage falls out of range.

Do you know we can bring it to the dealer and have them look it up?

 

[Iowa4Runner]

Dead weight? All the weight of a vehicle is dead weight, except for the unsprung weight (wheels, tires, brake rotors etc..) But my point is that you're talking about less than 2% weight of the vehicle.

Also, the fuel pump does not sit at the bottom of the fuel tank. In fact, it "hangs" from the very top of the fuel tank and is mounted vertically. Only the fuel pump pick-up sits at the bottom of the tank.

If the pump is near the top of the tank, then I wouldn't think submersion is very critical. Am I missing something?

 

[Iowa4Runner]

Be careful about doing this. On newer vehicles, this is not a problem. But as a vehicle gets older, sludge builds up in the bottom of the gas tank. You can ruin a fuel pump quickly by running it down too low on an older vehicle. There's no benefit to running any vehicle down to below a quarter of a tank.

I've never quite understood this, since the pump sucks fuel from the bottom (or near the bottom) of the tank where the sludge would collect. Does bringing the fuel level down stir that stuff up or something?

 

[Hitman]

If the pump is near the top of the tank, then I wouldn't think submersion is very critical. Am I missing something?

I said that the fuel pump hangs from the top of the tank. It is mounted vertically, which means that it hangs straight down into the tank where it can be cooled by the surrounding fuel. Almost every modern vehicle uses this same design. Gas tanks are usually fairly shallow, so they don't need to be kept near full to keep the pump cool, especially considering that a moving vehicle tends to splash fuel around in the tank.

But continually running the tank near E will definitely cause the fuel pump to run hotter than usual because of the lack of fuel in the tank acting as a cooling agent. This is not just my opinion, this is a fact known by many auto techs and engineers.

I always thought it was strange that there is an electric pump inside a fuel tank in the first place..... as we all know, electricity and gasoline just don't mix....

 

[Hitman]

I've never quite understood this, since the pump sucks fuel from the bottom (or near the bottom) of the tank where the sludge would collect. Does bringing the fuel level down stir that stuff up or something?

The end of the fuel pump pickup has a mesh covering that is designed to stop anything foreign from being ingested by the pump. This is important because modern fuel injectors cannot tolerate anything more than the tiniest particles imagineable.

Did you ever stop to think about which is heavier, water or gas? Think about it....they don't mix, so one tends to "float" on top of the other...

 

[Hitman]

Many years ago, I had a vehicle that wasn't sending fuel very well. It acted like a clogged fuel filter but wasn't. To make a long story short, I'd dropped the tank to replace the fuel pump which was inside the gas tank. The intake had a fine wire mesh sock over it and it looked like it was smeared with vasoline from a distance. It wasn't, it was WATER. The surface tension in the mesh was stronger than the pump's ability to draw it through. Water is heavier than gas and sinks to the bottom of the tank. If you run your tank to near empty AND there's water inside the tank, you can have the same thing happen.

I don't know about sludge, but I learned the hard way about water. I never go below 1/4 tank unless it just can't be helped.

Exactly... I just read your post and it makes a lot of sense...

One other thing to consider-- water tends to condense on the inside of the fuel tank. The more "room" available for this condensation, the more water that will end up mixed with the fuel. That's just one more reason to keep the tank filled with gas--less space available for the condensation of water in the tank!

 

[Pinuz]

I have a little suspect looking at my minumum RPM.

We know that in the first 5 - 10 minutes the RPM is in the range of 1200 - 1300 and after will slow down to under 1000.

When the engine is hot, in a V8 the minimum RMP should be around 500-600 RPM! without A/C.

Mine never goes under 1000! so can be a problem with electronic choke.

What RPM you guys see putting in neutral when the engine is hot (of course in the V8 model since the V6 has higher minimum RPM)

 

[bulldog-yota]

I have a little suspect looking at my minumum RPM.

We know that in the first 5 - 10 minutes the RPM is in the range of 1200 - 1300 and after will slow down to under 1000.

When the engine is hot, in a V8 the minimum RMP should be around 500-600 RPM! without A/C.

Mine never goes under 1000! so can be a problem with electronic choke.

What RPM you guys see putting in neutral when the engine is hot (of course in the V8 model since the V6 has higher minimum RPM)

Does your 4R actually reach operating temp when you drive. I was thinking about it. It may just be the fact that you drive short distances in cold weather and the FI will compensate by making the mixture richer. I would say maybe drive a couple of miles extra once or twice a week, to make sure the engine heats up properly.

Also for general longlivety I would say hit a good few miles of highway at least once a week. It is not good for an engine just to be used for short distances, especially in the cold. Your engine oil will get a lot more moisture in and you engine will build up carbon from constantly running at low rpm with a rich mixture.

Just take it out for a spirited highway drive every week, and do a few miles extra to make sure it heats up properly a few times a week.

Does the temp gauge get to halfway when you do your daily trips for at least half the trip?

 

[Sac State]

I have a little suspect looking at my minumum RPM.

We know that in the first 5 - 10 minutes the RPM is in the range of 1200 - 1300 and after will slow down to under 1000.

When the engine is hot, in a V8 the minimum RMP should be around 500-600 RPM! without A/C.

Mine never goes under 1000! so can be a problem with electronic choke.

What RPM you guys see putting in neutral when the engine is hot (of course in the V8 model since the V6 has higher minimum RPM)

My RPM is around 700 when hot and at idle.

 

[bulldog-yota]

My RPM is around 700 when hot and at idle.

Mine is in the 600 range as well, when at operating temp.

 

[Iowa4Runner]

Originally posted by Hitman
I said that the fuel pump hangs from the top of the tank. It is mounted vertically, which means that it hangs straight down into the tank where it can be cooled by the surrounding fuel.

OK well the fact that it hangs from the top doesn't tell us anything then. It's got extension hoses and might be hanging low enough to actually be right at the bottom.

[/i] Almost every modern vehicle uses this same design. Gas tanks are usually fairly shallow, so they don't need to be kept near full to keep the pump cool, especially considering that a moving vehicle tends to splash fuel around in the tank.
[/QUOTE]

What??? Splashing aside, a shallow tank would be bad for cooling as it would require more fuel than a tall skinny tank to submerge the pump.

[/i]
But continually running the tank near E will definitely cause the fuel pump to run hotter than usual because of the lack of fuel in the tank acting as a cooling agent. This is not just my opinion, this is a fact known by many auto techs and engineers.
[/QUOTE]

I have a feeling this "fact" is a lot like the NiCad scare that convinced people they have to completely discharge their battery packs every time or they'll suffer from the dreaded memory syndrome. There's some truth to it, but it's not gospel.

If driving with low fuel is so bad, why doesn't the owner's manual advise against this? What purpose do you suppose the subtank serves?

 

[Iowa4Runner]

The end of the fuel pump pickup has a mesh covering that is designed to stop anything foreign from being ingested by the pump. This is important because modern fuel injectors cannot tolerate anything more than the tiniest particles imagineable.

Did you ever stop to think about which is heavier, water or gas? Think about it....they don't mix, so one tends to "float" on top of the other...

Actually the mesh does nothing for the fuel injectors, it only protects the pump. Downstream from the pump is a fuel filter, that's what protect the injectors.

Yes Hitman, gas floats on water. That's why simply changing the fuel volume alone can't cause water to be sucked into the fuel pump. Maybe YOU should think about it. Like I suggested before, there has to be a contributing factor like sloshing. Draw yourself a diagram, you'll figure it out.

 

[Hitman]

OK well the fact that it hangs from the top doesn't tell us anything then. It's got extension hoses and might be hanging low enough to actually be right at the bottom.

No, it doesn't. I've replaced many fuel pumps before and they are all basically the same design. I'd say the average in-tank fuel pump is no more than 8 or 9 inches long, which is hanging from the very top of the tank. Only the pick-up (which is not part of the pump that needs to be cooled) reaches the bottom of the tank.



What??? Splashing aside, a shallow tank would be bad for cooling as it would require more fuel than a tall skinny tank to submerge the pump.

Unfortunately, most modern vehicles have to package their fuel tanks within the space available, which pretty much dictates the shape of the fuel tank. The result is never a tall, skinny tank. They are usually fairly shallow and wide, with an odd shape to them.



I have a feeling this "fact" is a lot like the NiCad scare that convinced people they have to completely discharge their battery packs every time or they'll suffer from the dreaded memory syndrome. There's some truth to it, but it's not gospel.

You can choose to believe whatever you wish, but doesn't it make sense that an electic pump will benefit from a cooler environment? I'm not saying that a fuel pump will fail in a year because of driving with a low fuel level all the time, I'm simply saying that evidence supports the idea that the cooling of a fuel pump can prolong its life. Logic is on my side, here....



If driving with low fuel is so bad, why doesn't the owner's manual advise against this? What purpose do you suppose the subtank serves?

Does the owner's manual advise against anything and everything bad? I don't think so.... I wouldn't think of the owner's manual as the only thing you should follow to care for any vehicle.

The "subtank" as you call it, is simply reserve fuel supply for those who cannot or will not fill the tank in a timely manner. In other words, if you find yourself running low of fuel (according to the fuel gauge) it will provide you with a small reserve to avoid running out of fuel completely.

Do you think manufacturers put this reserve there to use it all the time? If so, you should drive your 4Runner well past E and get every last drop out of your tank.

Personally, I would hope not to have to use the fuel reserve. But in the event that I did, I'd sure be glad it was there. Sorta like my spare tire, if you know what I mean....

 

[Hitman]

Actually the mesh does nothing for the fuel injectors, it only protects the pump. Downstream from the pump is a fuel filter, that's what protect the injectors.

Yes Hitman, gas floats on water. That's why simply changing the fuel volume alone can't cause water to be sucked into the fuel pump. Maybe YOU should think about it. Like I suggested before, there has to be a contributing factor like sloshing. Draw yourself a diagram, you'll figure it out.

Actually, the mesh is the first line of defense. The mesh protects the more than the pump, it protects the fuel filter, which in turn protects the injectors. So it is correct to say that the mesh protects the injectors M>F>I

As for the fuel/water debate:

Do you really think that the fuel and water in your tank stay completely separated? No, they do not mix very well, but they also do not stay completely apart. Even oil and vinegar will mix if shaken, which is exactly what happens with a moving vehicle.

Now, lets use some logic. If our tank is 23 Gallons and we fill our tank with fuel (assume 100% fuel, no water from the gas pump), but we have a half liter of water in our tank, what is the ratio of water to fuel?

Now consider the same situation (half liter of water) mixed with just 3 gallons of fuel. Are you starting to see the point? Or do I have to draw you a picture?

 

[bulldog-yota]

Ok guys, lets get back to the topic an that is Pinuz's gas mileage.

Pinuz, check my post on my thoughts and see what you think and if it applies to your condition.