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  #1  
Old 04-05-2002, 09:07 PM
DPH
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Question Gas Mileage

I used to monitor my gas mileage with every tank and found it to fluctuate very little from 21.5 mpg - so I stopped monitoring about 8 months ago. The last 3 tanks I have been quite surprised to be getting 16.8 mpg! I drive in Southern California, always burn premium gas, and have noticed no change in the cars performance.
Any suggestions as to what has caused this sudden 20+% drop in mileage.
Thanks
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  #2  
Old 04-05-2002, 09:46 PM
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Engine coolant temp normal?
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  #3  
Old 04-05-2002, 09:58 PM
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O2 sensor. I'd bet $$ on it. When was it last changed? It's recommended replacement interval is every 60k miles
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  #4  
Old 04-06-2002, 01:09 AM
DPH
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gas mileage

I replaced the radiator last year and the car continues to run cool. The O2 sensor has never been changed...the car still has less than 60k miles. Though things seem to wear out with time as well as mileage, like me .
Thanks for the tips, I will look into the O2 sensor more. Someone suggested to me that the gas in California has changed!
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  #5  
Old 04-06-2002, 02:02 AM
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For the winter months here in California (if you can call them that) the fuel is oxygenated. Oxygenated fuel produces lower MPG, for the summer months we have 'normal' California gas. I just don't recall if we are on winter or summer gas right now.
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  #6  
Old 04-06-2002, 09:12 AM
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<<
I replaced the radiator last year and the car continues to run cool.
>>

When a car runs cool, it uses more fuel.

If your thermostat is original, replace it. In my experience, 60kmi is how long it typically lasts. It is inexpensive and easy to replace on most of the 4-6 cylinder gas models.

When the thermostat gets fatigued, it cannot close completely, so your car cannot reach or takes a long time to reach the operating temp. That makes your fuel mileage lower. Different gasoline could be a factor too but I doubt it will be a 20% reduction.
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Old 04-06-2002, 12:38 PM
natsman
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California is now back on "regular" gasoline as opposed to the oxygenated stuff. Check the 02 sensor first. 9 out of 10 times it will be the reason for a the big drop in gas mileage.
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  #8  
Old 04-06-2002, 01:00 PM
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I don't normally check to see which ful (winter/summer) is pumping, but will take note today when I hit the fuel depot. Normally I see about a 1-1.5 mpg drop with the winter fuel, which on my Benzes is a good 10% drop in mileage.
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'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.
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  #9  
Old 04-06-2002, 02:20 PM
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It might be a good idea to replace your O2 sensor anyways, as 60,000 miles seems to be its useful life.

But in my experience and those of others I've talked to, a bad O2 sensor will result in huge drops in mpg, like down to 10 mpg. A drop from 21.5 to 16.8 to me doesn't seem like a big enough drop, but who knows?

It may be the gasoline, it may be harder driving...
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Old 04-06-2002, 02:44 PM
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I've been thru 3 O2 sensor cycles (bought car @ 67k, changed @ 120 k and just changed it again @ 178k) and the mileage deteriorates on my wagon from 18-19 down to 15-16-changed it out and it's right back to 19 MPG
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  #11  
Old 04-06-2002, 09:23 PM
DPH
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gas mileage

The O2 sensor sounds like one of the 'usual suspects'. I won't be able to crawl under my car for several weekends, but plan to do so. To that end, I did a search on this site for 'oxygen sensor'. This led to MANY hits. It seems that some of folks here have used an O2 sensor from a ford mustang - though some refer to it as a 302 mustang and some a 5.0 mustang, and the years vary a whole bunch. Does anyone have any experience with implanting a mustang sensor (ie part numbers or model and year, and which mercedes engines) into an E model mercedes?
Thanks.
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  #12  
Old 04-07-2002, 05:40 PM
Clauser1
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Mustang 02 sensor..

I tried it in my 2.6,ain't worth a sh*&^%#t.
(In my case anyway)
The chk.eng.light keep blinking.Went to OEM.
and everything went fine.$49.bucks went to
waste.
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  #13  
Old 04-07-2002, 05:56 PM
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A bad O2 sensor usually trigs a Check Engine light.
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  #14  
Old 04-07-2002, 09:15 PM
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Bo,

FWIW, be advised that an O2 sensor can go pretty bad before it throws a code. In my 300TE, my mileage goes to pot long before it ingnites the "check engine" light; in my 500E, the car ran like crapola at 1/2 to 3/4 throttle until I replaced the O2 sensor. It appears that the MBZ computers are fairly tolerant of an underperforming O2 sensor; in this case it's gotta be time
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