Poor Mileage Since Oil Change

[cfvettes]

We recently bought an '04 with 75K. We have been getting right around 49 - 51 mpg regularly. We live in Southern California and have put on 5000 miles since. The mileage numbers on the MFD have pretty well matched up with manually calculated numbers so far.

We took the car in for an oil change and right afterwards filled up the tank. Now ... halfway through the tank, the mileage is only showing 36.4 mpg. Could something done or not done during the oil change have adversely affected our mileage?

Bewildered,

Charles

[JimboK]

There are many things that cause variation in fuel economy, especially driving conditions and weather. Has anything changed since the oil change? Hotter temps? More wind? More AC use? Different routes? Heavier traffic? Different drivers?

As for anything the shop might have done, two things come to mind. First, reports of overfilling the oil are common, with drops in fuel economy resulting. I would check the dipstick. Second, is there a chance the shop did a courtesy tire pressure adjustment -- downward?

[alevinemi]

Absolutely.

If the oil is overfilled, MPG will drop. Check the dipstick, it shouldn't be over the high mark.

If the oil is crappy or thick, MPG will drop. Use 5w30.

If the previous owner used 0w20 (which is not recommended by Toyota, but some do it), MPG will increase.

-->Adam

[Bob.H]

What I have gleaned from oil and tire threads, is that the best you can hope for in optimizing each is around 2 to 4 percent fuel savings for us average drivers. With everything stock, low tire pressure and all we have not gone below 44 MPG in my 08.

Check the dipstick to be sure it looks reasonable and like fresh engine oil. Low tire pressure is easy to rule out. Gauges are cheap or even given away promotionally at some automotive stores.

Look for something else in addition to possible oil and tire inflation errors. Simple MFD error, try resetting the MPG calculation. Breaks dragging, how does it glide now compared to before?

I have not experienced your problem but from reading here: If you get a couple of confirmed consecutive low mileage tanks it might be a sign to take it to the dealer to investigate.

[richard schumacher]

*Always* check the oil level yourself before driving away from every oil change. This can catch egregious mistakes before they become annoying or expensive. And yes, overfilling is a mistake.

Assuming that the oil is not over full, check the tire pressures. Service techs often reduce them to the factory setting of 35/33 PSI front/rear, whereas something like 42/40 noticeably improves MPGs.

[ETP]

Originally Posted by cfvettes

We recently bought an '04 with 75K. We have been getting right around 49 - 51 mpg regularly. We live in Southern California and have put on 5000 miles since. The mileage numbers on the MFD have pretty well matched up with manually calculated numbers so far.



We took the car in for an oil change and right afterwards filled up the tank. Now ... halfway through the tank, the mileage is only showing 36.4 mpg. Could something done or not done during the oil change have adversely affected our mileage?

Bewildered,

Charles

This is a common problem. Check the air in the tires and be sure the next time to take your own oil. I had a Honda dealer put 5W30 in my 2003 and I dropped 10 MPG. I took my 0W20 the next time and the mileage went up. 0w30 is good to go for the Prius as is says on the can good for all 5W30 and 10W30 appilcations.
They probably put bulk 10W30 crap in your Prius and set your tires to 32PSI

[ETP]

Originally Posted by richard schumacher

*Always* check the oil level yourself before driving away from every oil change. This can catch egregious mistakes before they become annoying or expensive. And yes, overfilling is a mistake.

Assuming that the oil is not over full, check the tire pressures. Service techs often reduce them to the factory setting of 35/33 PSI front/rear, whereas something like 42/40 noticeably improves MPGs.

I believe this for the Prius, but my Honda Hybrid actually got better mileage with a 1/3 of a quart overfill. Dealer did it so I left it alone.

[yardman 49]

So this brings up another question for me: why trust the dipstick?

I just had the first oil change done on my 2009. I told the Toyota dealer's shop that I didn't want it overfilled. In response the service writer told me that they had to put in the recommended amount.

When they finished, he gave me me a printout from Toyota that clearly states that an oil and filter change should take 3.9 quarts of oil. When I checked it when I got home, the dipsticked showed about 1/4 to 3/8 inch over the full mark.

So should I leave it as is, or drain some out. And if I should take some out, can I use one of those oil suction pumps to pull it out through the dipstick tube?

Thanks

[Shawn Clark]

Originally Posted by yardman 49

So this brings up another question for me: why trust the dipstick?

Because the manual and warranty rely on it for the indication of proper fill. The manual says keep it between the marks, not below or above. If you bring it into a dealer with the oil over the top of the dipstick, Toyota could deny warranty coverage if that was deemed responsible for a particular failure.

I just had the first oil change done on my 2009. I told the Toyota dealer's shop that I didn't want it overfilled. In response the service writer told me that they had to put in the recommended amount.

Don't use them again, they are clueless and failing to check their own work.

When they finished, he gave me me a printout from Toyota that clearly states that an oil and filter change should take 3.9 quarts of oil. When I checked it when I got home, the dipsticked showed about 1/4 to 3/8 inch over the full mark.

Toyota's dipsticks and their fill amounts are at odds in the Prius. A competent dealership would recognize this and not overfill...or fix it if they discovered they had. An incompetent dealership would use some lame excuse to justify what is defined as an overfill in the manual.

So should I leave it as is, or drain some out. And if I should take some out, can I use one of those oil suction pumps to pull it out through the dipstick tube?

It's your call. I got a "free" oil change at 1,000 miles and had mine filled with 3.5 quarts of synthetic, dropping it about 1/4" below the overfill line as memory serves. The car had originally been delivered 1/4" overfilled, as is the norm for most Prius' according to many reports here.

At 6,000 miles I went to 3 quarts which puts the oil level right in the middle of the dipstick range. I saved a few bucks on oil and my mileage is up several mpg from what it was. This could be break in of tires, drivetrain, etc. or even weather...although I've tried to account for the weather in analyzing it. Whatever the cause, I won't be adding excess oil to determine if more oil actually reduces mpg again.

If you tell the dealer you will read the dipstick before leaving the lot they are likely to read it right in front of you. (That's what they did for me, I thanked them and went on about my way.)

[Shawn Clark]

Originally Posted by cfvettes

We took the car in for an oil change and right afterwards filled up the tank. Now ... halfway through the tank, the mileage is only showing 36.4 mpg. Could something done or not done during the oil change have adversely affected our mileage?

There are several other possibilities beyond oil level and tire pressure. One thing that can happen at dealerships is the vehicle might be set idling with the AC on or something like that. That could throw off the MFD for some miles.

A related possibility is that the tech turned up the AC or blower or defog settings and you haven't changed them back to what you normally use. This sort of thing will hurt most in short range stop and go driving.