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post #1 of 9 (permalink) Old 07-07-2008, 08:34 AM Thread Starter
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Better milage or garage myth?

A friend was saying that he shielded his o2 sencer from the cold air, and it is now getting better milage!

Does this make any sence to you?
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post #2 of 9 (permalink) Old 07-07-2008, 10:26 AM
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Quote:
Originally Posted by gn300 View Post
A friend was saying that he shielded his o2 sencer from the cold air, and it is now getting better milage!

Does this make any sence to you?
There are a lot of things that can be done to increase mileage - minimally - and that may work, but to the detriment of the emissions output, and also possibly the engine, since it could very well cause a lean condition when cold, which will, over time, not do the gengine any good.
Probably get the same increase in MPG by inflating the tires from 32 to 36 - 38 or by removing exess weight; driving at the optimum speed for the car, or driving "ahead" of yourself to avoid unnecessary braking and accelleration.
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post #3 of 9 (permalink) Old 07-07-2008, 10:43 AM
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"very well cause a lean condition when cold"

I think is the other way around: cold= rich (same as choke in older veh)


How can be a ox sensor be shielded from cold if the "reading" tip is inside the exhaust?
someone is pulling your leg
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post #4 of 9 (permalink) Old 07-07-2008, 12:14 PM
 
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O2 sensors have a vent for reference air. In order to work, an O2 sensor has to have a way of comparing the O2 reading from regular air to that which is in the exhaust. I heard about this myth, wrapping the O2 sensors with aluminum foil to increase mileage. I have not tried it though.

Question:
How does the oxygen sensor work?

Answer:
The sensor works as a result of the varying quantities of oxygen in the exhaust verses the amount in the atmosphere. Voltage is produced by the difference in the two amounts. If the amount of oxygen in the exhaust is closer to the amount in the air, the engine is lean and the voltage is low (under 250mv). If the engine is rich the voltage is high (about 950mv).


My guess on this myth or theory would be by wrapping the sensors they become insulated. The air around the sensor becomes hot and hot air is less dense, having less oxygen molecules. Since the outside air will have less oxygen, it changes the reference point. It must be that the exhaust appears rich under these outside conditions and the computer would actually try to go lean in order to stoich, which in reality it isn't.

Last edited by froggy81500; 07-07-2008 at 12:23 PM.
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post #5 of 9 (permalink) Old 07-07-2008, 02:48 PM
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Quote:
Originally Posted by 234on87 View Post
"very well cause a lean condition when cold"

I think is the other way around: cold= rich (same as choke in older veh)


How can be a ox sensor be shielded from cold if the "reading" tip is inside the exhaust?
someone is pulling your leg
You missed the point - with the sensor unsheilded (normal), engine would be rich from the ATS when cold, but if the O2 shielded, could cause it to run lean, since it would not sense the correct exhaust content for the actual temp. Not saying it WILL do that, just that it is a possibility, as is any other wacky thing that could happen with sensors that are "tricked" into doing something they are not supposed to do. You don't just alter that parameter, but also all of the things that read it and try to compensate for what they think they see (which, of course, is what your last statement says in effect)


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post #6 of 9 (permalink) Old 07-07-2008, 04:05 PM
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OK then my bad, so the idea is to unplug the sensor, wrapping it n putting it back. then is possible..somentimes just a colder t.stat will make some cars go faster (sensor read Cold=rich) of course bad for efficiency but who cares this days
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post #7 of 9 (permalink) Old 07-07-2008, 04:29 PM
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Quote:
Originally Posted by gn300 View Post
A friend was saying that he shielded his o2 sencer from the cold air, and it is now getting better milage!

Does this make any sence to you?
Is there a polite way of telling a friend that he's a moron ???
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post #8 of 9 (permalink) Old 07-07-2008, 08:33 PM
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I can only see one way this would work: an O2 sensor is a galvanic battery. It creates a voltage based on the differential of O2 between the inside and the outside of the sensor. Every battery increases its output and speed of reaction as it gets hotter. So if you get the outside really hot, you increase the speed with which the sensor can react to changes.

But the idea falls apart when you consider: they're already hotter than anything else under the hood by virtue of conductive heating from the exhaust gas impinging on the inside of the sensor. And these sensors are heated to get them up to the right temperature to begin with. And if you insulate the sensor too well you deprive it of O2 on the outside, which will degrade it's performance. With the heat-budget available inside the exhaust system, I can't see the outside air temp making a lot of real difference to the sensor's performance. And finally, like everything else, O2 sensors have a heat range in which they function best. Too hot and they fail more quickly, and probably don't work as well as normal before they fail.

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Is there a polite way of telling a friend that he's a moron ???
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post #9 of 9 (permalink) Old 07-11-2008, 04:30 PM Thread Starter
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Thats what i thought, his car is an old colt with the sensor very exposed to cold air and wasn't working all that good.

so the electronics might not be as advanced, i don't know!
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