Gas mileage vs Car's Mileage

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Apr 10, 2005
Fremont, CA
Do cars get worse gas mileage when they are new? I heard someone day that your car won't get it's optimal gas mileage until it's fully broken in at around 10,000 miles is this true? I didnt start monitoring my gasmileage until 5,000 miles...and from 5,000 till 10,000 gas mileage has been around 25 to 30mpg. Rising slightly from 5000 to 10000
My Subaru Outback Sport has been getting at or close to the EPA estimate since it was new. Most of the variations come from weather conditions or trailer towing. I now have nearly 12K on it and it's about the same as new.
I just looked back at the mileage on a few of my vehicles. My 1995 4Runner gets about 11% better mileage at 300,000 than it did when new, but the jump was when I started using a diesel conditioner. It is somewhat distorted by my increasing the tire size twice, so it is really going about 8% further than the odometer reads. My 1999 4Runner is only about 10% better at 85,000 than when I bought it, but again the jump was with the diesel conditioner.
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