is this true: a broken pipe affects your gas mileage

[stillfox]

Hi, there,

I got a subaru 1997 outback recently. I know it is not supposed to be a very fuel efficient car, however, I still feel it is using too much more gas than average.

I smell some gas when I got off the car, so I looked at the bottom. I saw there is somewhere broken (problem the connection) in between the catalytic converter and the pipe.

 

Someone told me before that a hole on the pipe or the exhaust system that leaks will cause gas mileage to decrease. However, I think exhausing system is just throwing sth. before cleaning it up and it wont affect gas mileage at all.

 

Can someone make it clear for me, please?

THanks,

Joe

[Legacy777]

An exhaust leak might affect mileage slightly, but shouldn't be too noticable.

 

How much of a drop are you seeing?

 

You mentioned you smelled gas. Was it a raw gasoline smell? Or exhaust smell?

[WagonsOnly]

Legacies and Outbacks have a bad reputation for rust near the fuel-filler neck--and a hole in your fuel storage/delivery system has been rumoured to negatively impact gas mileage. I'd guess you're leaking unburned fuel as opposed to the backpressure from the exhaust doing in your mileage. How much gas are you using, on average, and what kind of driving do you do? Mileage? Last tuneup? Tire pressure right, and is the CEL on?

[Ranger83]

You'll be dead long before you notice the mpg change.

 

Carbon Monoxide bonds so much more readily than Oxygen with the hemoglobin in your blood that a concentration of only 9% will kill you.

 

Driving a car when you can smell gas and have an exhaust leak under the passenger compartment is riskier than anything I've ever done. But YMMV.....

[nipper]

heheheh..

 

If your running an open exhaust system, the gas mialge will drop as ewell as performance. You will gin upper end performance, but you need that back pressure to help make bottom end power. a minor leak you wont notice, unless its before a cat then there is that entire death thing mentioned eralier.

The gas leak will afect gas mileage , especially when the fire trucks show up.

is the leak from the front of the car or the back of the car.

 

nipper

[OB99W]

As Ranger83 said, CO (carbon monoxide) poisoning is a real health risk (as may be the gasoline leak). A CO level in the air you breathe of 800 ppm (parts per million), which is only 0.08%, can cause dizziness, nausea and convulsions within 45 minutes, and be deadly within as little as 2 hours. As others have suggested, mpg shouldn't be your major concern.

[stillfox]

wow, thank you all for your information.

The smell is not so strong and it smells just like what the muffler sends off. I cannot smell it in the car. I only smell it when I get out.

I saw some white smoke coming out from the connection between the catalytic converter and the pipe. There seemst to be a rubber ring there, the white smoke comes right our of the ring. I am not sure if the ring is part of the connection, or it is just some protection for the connection within.

 

To be more precise, from the back the car, it is muffler, pipe, connection, catalytic converter. It is that connection.

 

Or from http://www.rockauto.com/ref/Walker/Detail.html?1505.gif

It is 31358 between 16090 and 54062.

 

So I should take it to garage, right? It seems that the highway mileage is ok, about 25mpg, but local is very bad.

Thanks,

[Dr.Outback]

There is a metal mesh donut gasket between the cat and mid pipe section. Sounds like your is bad.

[OB99W]

To be more precise, from the back the car, it is muffler, pipe, connection, catalytic converter. It is that connection.[...]So I should take it to garage, right? It seems that the highway mileage is ok, about 25mpg, but local is very bad.

Where you are saying that the exhaust leak is located, after the catalytic converter (and assuming the cat is working correctly), the CO levels are not as high as before the cat. Nevertheless, an exhaust leak isn't a good thing and should be fixed. It may be contributing slightly to the mileage problem, but your earlier mention of a smell of "gas" is probably more directly related (or did you mean "exhaust gasses", as opposed to "gasoline"?). Anyway, it seems that you should have someone with experience look into the problem(s).

[WoodsWagon]

Your car probably has at least one oxygen sensor. If the break in the pipe is before the O2 sensor, it will allow air into the pipe, leaning out the mix in the exhaust. The sensor will give the computer a lean signal, and the computer will richen up the mix of gas into the engine. This will lower your milage. Any exhaust pipe after the O2 sensors (there is often at least 2, one just before the cat, and one after) can be removed without affecting the sensor's readings.

[Tiny Clark]

I had a broken hash pipe in the 70's that caused my gas mileage to go down, but that was because I'd pull into a gas station, reset the odometer and leave, forgetting to fill up.

[stillfox]

All right. I took my car to cole muffler and took a look.

Yes, the gasket between the converter and the pipe is open. There are two sensors there.

 

BUt, that is not the reason i smell strong gas. The gas tank is somewhat leaking. It wont leak when you start the engine and let it run. It only leaks when the engine is shut off. I did a test. After shuting off the engine, the gas will dribble about 3 drops in 2 seconds. And this slows down until after 20 minutes it. I was told that it will be costy to repair since the axles have to be removed in order to access the tank and the fule line.

 

Wagonsonly, it seems that you claim is true. I smelled the drips and they are raw gas.

 

I d like to hear all your opinions. Is there anyway I can get around this without costy repair?

THanks,

Stillfox

[Legacy777]

It depends on where the leak is. More then likely the leak is at the fuel neck filler hose. if so, you can replace that in an hour...easy.

 

If it is in the tank....then the entire rear crossmember/suspension/etc needs to be removed to drop the tank.

[stillfox]

Thanks,

So for the first case leaking at fuel neck, I do not need to remove the axle, right?

[Legacy777]

If the filler tube is where it's leaking, no you don't have to remove the axle.

[crazymjb]

I agree with Loyale, If it is OBDII then the sensor after the cat could be reading that there is too much O2(since some of the CO is leaking out) and telling the engine to run richer. Is the engine shaking at all during idle?

[stillfox]

No, the engine is not shaking. The hole is after the cat and before the pipe towards muffler, I guess it has already been cleaned.

I drove it to Albany one time. It is about 230miles, and I used less than 10 gallon gas (The tank is just 12 gallon for my outback. Yes it s small). So I guess the gas mileage is fair. However, the local mileage is low.

 

Since the fuel return line is leaking afer I shut off the engine, everything makes so much sense now..

 

BTW, where can I buy those hoses and fuel line connections? I dont see them showing up in autozone and advanceautoparts? Do I have to order from dealer? Mine is 1997 subaru legacy outback.

 

Thanks,

 

I agree with Loyale, If it is OBDII then the sensor after the cat could be reading that there is too much O2(since some of the CO is leaking out) and telling the engine to run richer. Is the engine shaking at all during idle?

[stillfox]

First, thank you all guys for your advice.

 

Second, I am afraid that the leak is not from the return fuel hose. Now it becomes more serious. When I started the engine, it starts to leak/dribble. And when I jacked up one side of the car, the leak is more serious. When it is flat, the leak is slower. When I stopped the engine, the leak will gradually stop.

 

I released the fuel pressure by disconnecting the fuel pump connector under my rear seats. I saw three hoses there, I guess they are the fuel hose, fuel return hose and some other hose. These connections to the fuel pump seem to be good. There are no leak there.

 

 

I got under the car, and when the engine is turned off, I can hear some small sound of hissing around the gas tank. There is a tank cover down there, I removed it. However, the source of leak is on the upper side. I can only put my fingers into there and feel the leaked gas, but I still dont know the leak source. I tried to reomve the rear seat, but it seemed that I still cannot access the upperside even if they are removed.

 

So can anyone give me any advice on how I can access the tank, or the middle section of fuel hose/connections without removing the axle?

 

Thanks,

stillfox

[friendly_jacek]

Please fix this sooner than later!

[outback_97]

(The tank is just 12 gallon for my outback. Yes it s small). So I guess the gas mileage is fair. However, the local mileage is low.

 

Since the fuel return line is leaking afer I shut off the engine, everything makes so much sense now..

 

BTW, where can I buy those hoses and fuel line connections? I dont see them showing up in autozone and advanceautoparts? Do I have to order from dealer? Mine is 1997 subaru legacy outback.

 

Stillfox:

 

Your gas tank is actually 15.9 gallons, unless you have a non-standard tank installed or you hit some very big rocks and bashed four gallons of volume out of the tank. Your fuel gauge might be inaccurate, that's a common problem on these cars, sometimes mine shows the tank nearly empty at <200 miles.

 

I got 24 mpg on my last tank, which was mostly highway miles. Speeds ranged from 40-80 (some clear roads, some snowy / icy / slushy) and there were a lot of hills, high elevation, and winds. A lot of semis to pass and a lot of variable speeds. Around town I get around 19-22 mpg, this time of year is the worst for mileage. This is on 85 octane (we're over 4000ft here) which seems to work just fine for my car. So, unless you're significantly lower than 20 mpg around town, your mileage isn't too far off normal IMO.

 

There are numerous places online to buy parts that are much better choices than the local stealership. Try http://www.subarugenuineparts.com or http://www.subaruparts.com or http://www.1stsubaruparts.com to name a few. Prices are usually better, and sometimes much better there.

 

Steve

[Storydude1]

In the rear of the vehicle there are 2 access ports under the carpet. Remove those, and there will be the sending unit/s.

 

check the hoses coming off of them, check the hoses under the car(especally the one with a round disk in it..That disk is a one way valve that allows pressure to bleed off of the tank. If it's plugged, you'll force gas out of many places) and check the transfer pump line(IIRC the middle one on the pass. side sending unit)

 

Sounds like you may have a leak in one of those lines. There is enough room to get rubber lines beside the tank, and down to the metal lines if you are patient.