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Discussion Starter #1
I just got this done last Friday.

Since then, I've noticed about a 10% reduction in my gas mileage. I was getting around 46, now getting around 42.

Now I know there's variation depending on where I'm driving, how I'm driving, etc., but today I drove to work and back as usual, and tried to be as "gentle" as possible, and it just seems like it's getting somewhat less mileage.

Just wondered, has anyone else noticed this?
 

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Discussion Starter #3
Good question. I did have an oil change, plus they adjusted the rear brakes. No significant weather changes.
 

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I'm also currently at "lower than usual" mileage, but drove home in the pouring rain tonight (first round trip to work since last fill-up Sat, after SSC 40D on Fri). Willl keep an eye on it (as usual), but I'm not expecting any changes as it was supposed to be a diagnostic issue.

[email protected] My eye! What happened to my eye?!
 

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I've taken my 2001 Prius to several different dealers. I have yet to even get the tires set to 35psi front, 33psi rear, let alone to the 40/38 that I prefer. IF they change the tire pressure (often they just rotate, don't change the pressures at all, which makes the f/r bias really off!), they seem to like 32psi all around, if not lower... Perhaps your tire pressures have changed and you didn't know it?

Another possibility is that they used the wrong grade of oil (common problem). Prius is 5W-30, but some dealers prefer using the cheaper bulk 10w-30, which is a heavier oil and can reduce your MPG a bit. Same problem if they overfilled your oil (another common problem).
 

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mrv said:
I've taken my 2001 Prius to several different dealers. I have yet to even get the tires set to 35psi front, 33psi rear, let alone to the 40/38 that I prefer. IF they change the tire pressure (often they just rotate, don't change the pressures at all, which makes the f/r bias really off!), they seem to like 32psi all around, if not lower... Perhaps your tire pressures have changed and you didn't know it?

Another possibility is that they used the wrong grade of oil (common problem). Prius is 5W-30, but some dealers prefer using the cheaper bulk 10w-30, which is a heavier oil and can reduce your MPG a bit. Same problem if they overfilled your oil (another common problem).
All good points, Michelle. My 2004's tire pressure stems all have caps that say 32 in big green and white. I wouldn't be surprised to hear that the dealer's check them and let some air out each time.
 

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I was getting a consistant 52 mpg before and now a consistant 48.5. Supposedly the 40d had nothing to do with this, but my driving has not changed. the weather has been the same. I have not checked tire pressure, i will in the morning for cold psi and get back to you.
 

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46.5 mpg (display) and climbing since SSC-40D and last fill-up; approaching 47.0 mpg (display) of last tank. To be continued...

P.S. Tires at 44F/42R; still on original oil (< 5K miles)
 

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I didn't think to connect the two, but my mileage took a hit immediately following the upgrade as well. Before the service was performed I was averaging better than 51 mpg. Following the service it dropped to 45mpg for a day or two and then started a slow climb back up to 51mpg. I did have an oil change at the time. The weather has been hot lately, so I've been using the A/C and I figured that was what casued the drop. But I was using it while the mileage climbed, too. Interesting.
Drive happy,
Moo :)
 

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I wonder if upgrading the ECU program clears its memory of your car's peculiarities, either every time it's upgraded, or if something isn't done right?

This could easily appear as a sudden drop in mileage that slowly rises to the previous performance.
 

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Discussion Starter #11
Robert, could you please elaborate? How could clearing the memory, etc. affect the gas mileage?
 

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hbark said:
Robert, could you please elaborate? How could clearing the memory, etc. affect the gas mileage?
Well, I don't know if it can. Many ECU controlled cars (and I think the Prius is probably included) store information in memory about measurements and operating points so they have a better starting point in all the feedback loops when the car is first started. A change in a program often means a change in parameters monitored or at least their location.

I have no access to the Prius programs, so can't determine this first hand.
 

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My mileage actually went up immediately after the SSC 40D. I had the 5K servicing at the same time. Made sure tires were at 42/40, and requested synth oil. But after the first 2 tanks immediately after the 5K, when mpg was 50-52, the last several days have been 45-47. Maybe I need to check the tires again? Why is it that a few seconds accelerating uphill can pull mileage down way faster than minutes of downhill coasting can pull it up?! :?
 
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