Poor Mileage Since Oil Change

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?

 

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

 

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.

 

*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.

 

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

 

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.

 

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

 

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.

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

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.

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.)

 

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.

 

What Shawn wrote: It's an error that Toyota never corrected. The dipstick does not agree with the owner's manual or the shop manual. I finally decided to trust the dipstick, because the dipstick design comes direct from the design engineers, whereas the information in the manuals went through two translations: one from the design engineers to the technical writers, and again from the Japanese manual to the English manual.

You can ask that dealer to drain out some, but they did warn you in advance that they would add the recommended amount. If they won't do it, do it yourself or have another dealer do it. For future oil changes use a dealer who will add oil per the dipstick. You can increase the odds of success by buying *three* quarts of oil and giving them to the dealer to use. Warn them not to add any of their own oil and tell them that you will check the dipstick before leaving.

 

Thanks, Shawn, Richard, and anyone who answers the following questions.

Any advice on removing the oil? On cars I've owned in the past, I've quickly removed the drain plug and put it back in again.

Is there any problem with doing this with the Prius? I hear that the seal is an o-ring. So I have some questions for those who have changed the oil themselves:

- Any danger of the o-ring not staying on the plug when I remove it?
- Is the o-ring good for many uses, or does it get replaced every time the plug is removed?
- Is the plug easy to get started in the drain hole, or is it "finicky" and easy to cross thread? As there will be oil pouring out when I'm trying to install it, this could cause an issue.
- Any particular torque setting specified, or just the usual guestimate?
- What's the best way to access the plug: front, side, jack or no jack? I also have ramps.

Thanks for any advice here. I'm leaving tomorrow on a long trip, and want to drain some before I leave.

Thank you!

 

The crush gasket in the plug should reseat. Some folks reuse them repeatedly. I have used one for 2-3 changes on other vehicles. If you go that route, then torque the plug back down to recommended setting (28 ft-lb -- for some reason Toyota deigned not to put this in the owner's manual, but it can be found in their procedure and in the Bentley manual.) The concern I would have is that it might leak a little if done as you describe, but that's just me being cautious.

I think it would be difficult to remove the plug and get it back in again with the oil pushing its way out--I've tried to do something like that before for other reasons and it was a mess when I fumbled the plug. (It's especially hard to do if the oil is hot...)

 

Would it be easier to remove the filter and take some oil out that way? Just a thought. I've never done such a thing.

 

I am new on DYI car care and find using a pump to suck up oil through the dipstick hole very easy to do. Good luck!

 

Thanks, everyone. That's exactly what I ended up doing. I have a a Craftsman "oil siphon" jug that I use for sucking the oil out of my yard equipment engines instead of trying to drain it from underneath. The hose was the perfect size to snake down the dipstick tube. Very easy to pull out the right amount.

I have another free oil change left at the dealer. So the next time that I get it changed, I'll probably just let them do their thing, then come home and pull a little out. They'll be happy ("we have to put in the Toyota recommended amount..."), and the Prius will be happy.

After that I'll probably just start changing it myself.

Best wishes,

 

I have yet to buy a lawnmower that will take all the oil the tag on the block says it will. So what is correct? I think the people that throw this stuff together are not as accurate as we think. And unless we take an engine apart and measure the volumes we would never know. We just have to guess and hope that we are right.
If it runs, gets good mileage, and does not make noise then leave it alone.