Sudden, significant drop in MPG after an oil change

<div class='quotetop'>QUOTE(JasonCon @ Nov 29 2006, 12:02 PM) [snapback]355275[/snapback]</div>

It could be the gas. The winter formula has more additives that result in less energy per gallon. This results in less mileage. Also lower temperatures will lower your mileage. This happens with all cars, but is a larger drop with the Toyota hybrids.

 

how overfilled was it? if it was pretty bad oil might have gotten into the throttle body, but you should be seeing a check engine light in that case.

screw-ups are not a warranty provision. toyota will fix any problems that exist, but jiffy lube will end up paying if they caused the problem, likely not until you push them pretty hard about it. a toyota shop is not going to clean up after jiffy lube's mess for free.

 

<div class='quotetop'>QUOTE(JasonCon @ Nov 29 2006, 01:02 PM) [snapback]355275[/snapback]</div>

I haven't gone to any quick oil change place for years, not since some high school high-on, working in the well at the very last quick oil change place, forgot to put the plastic wheel well cover back on when he was done. Every time that I turned left there would be this really loud and scary scraping noise. Flipping idiots, I'll always go to the dealership because they're a lot less likely to make a screw-up like that and probably won't hire high school kids on minimum wage who smoke skinny cigarettes on their break.

 

<div class='quotetop'>QUOTE(JasonCon @ Nov 29 2006, 10:30 AM) [snapback]355292[/snapback]</div>

That doesn't sound like it would contribute to such a dramatic MPG drop. I will however share a story about an oil change done at Valvoline on our Avalon. While checking our air filter, the rocket scientist didn't know how to operate the super complex hinges on the housing and had to yank it so much that he ripped out an air sensor. My wife didn't think too much of it when she was watching the idiot struggle with it under the hood, but when she drove out, it became apparent that something was wrong. She returned to Valvoline and the manager on duty was able to re-align the sensor and clear the codes from the computer. The point of the story: Perhaps the guy who worked on your car also fouled up an air sensor, or something else that might now not be able to mix the air and fuel in proper proportions, manifesting itself as a drop in MPG.

 

<div class='quotetop'>QUOTE(JasonCon @ Nov 29 2006, 01:30 PM) [snapback]355292[/snapback]</div>

Of course, the problem that I had initially was that I'd gotten the OEM tires replaced with tripletreds which require a higher air pressure (42 instead of 36 or whatever) and when I took my Prius to the dealership for its first oil change, they set the tires at the OEM pressure without bothering to check or notice that the tires were different. That reduced my mpg somewhat significantly until I checked to see for myself what the problem was Just shows you that you gotta watch those dealership people, even if it is a Toyota dealership.

 

I dont know about the Prius ,but in my F150 pickup the viscosity of the oil affects the mpg drastically . Its designed for 5-30 weight and after an oil change the mpg went down about 20%.I had guessed that a new air filter, that the oil changer had installed was at fault.When I went to buy an OEM air filter,the Ford parts guy informed me about the oil viscosity.

 

<div class='quotetop'>QUOTE(JasonCon @ Nov 29 2006, 10:30 AM) [snapback]355292[/snapback]</div>

This is a topic of heated debate here over the years, but what you describe is not an overfill, especially if every Prius that has ended up on US shores has had this condition. Now I can't speak to every Prius, but mine was over the full dot when it arrived and every oil change has been over the full mark and I have had no performance issues. I didn't expect any performance issues with this oil fill condition and I do not anticiapte any in the futhre.

The dipstick is not a precision instrument. And the oil level in the pan at 1/4 inch "overfill", as indicated by the dipstick, does not interfear with any of the moving parts in the engine. In addition, when an engine is operating the oil level in the sump is lower than at rest because a good quantity of the total amount of oil in the system is up in the top of the block doing its job. The Prius block is also not a dry sump system. Dry sump engines require fairly precise quantities of oil. Never below a certain amount, and not too much above a certain amount. But that is not an issue for us either.

Your issue with FE going down drastically is definitly related to some other issue. Tire pressure, fuel quality, fuel additives, and as was suggested earlier, oil viscosity, are going to be much more likley factors than oil level. I would wait and drive through a couple of tanks of gas before taking it to Toyota for a once over.

Good luck!

 

I rather doubt putting in 10W-30 would affect fuel economy that much compared to 5W-30, unless maybe in temps below 0 F.

However you can't be sure what sort of oil is sitting in the bulk oil tote bin out back. Could be 15W-40 or even 20W-50 for all you know.

I had an issue around a year ago with strange used oil analysis results. I let the dealership handle the first three oil changes, using their own Mystery Oil, then switched to Mobil 1 0W-30. I had the Mobil used oil analysed and it had weird Na readings.

After chasing a lot of dead ends, the testing lab finally suggested I have the dealer oil tested. I was surprised the dealer agreed to this.

That dealer oil was garbage, really nasty stuff. Even had free moisture and iron in it. The Na was sky high too, around 400 ppm if I recall.

I know when I change to Mobil 1 0W-20 for fall/winter, from the Mobil 1 0W-30 I normally use, I get around 5-10% better city fuel economy, with no difference in highway fuel economy, at the same temps.

That drastic a change for you shouldn't have been caused by the oil itself though. Does that part of CA use winter fuel blends??

 

If the fuel economy remains that low, something is going on. Not sure if it's worth another oil change done yourself.

 

<div class='quotetop'>QUOTE(JackDodge @ Nov 29 2006, 03:29 PM) [snapback]355340[/snapback]</div>

Yes. I was in Montana for 6 weeks in 1998. Drove my '92 Corolla. Put 5k miles on it, so needed oil change while out there. Not gonna mess with jiffy changes; go to dealer. Don't want any messups spoiling my working vacation.

The day after the change, I was headed for Glacier National Park from Missoula. About 50 miles up the road, saw a lake view that I wanted to go back to. Did. Wasn't worth it. Drove on.

Short time [thankfully] later, I stopped to take a picture. But what's that rising from under the hood? :blink:

They had left the filler cap more or less in place [I assume; otherwise, why no smoke before?], but not screwed on. When I made the turn to go back to that lake, it fell off the filler hole.

What a mess. Oil everywhere. A roll of paper towels later, I drove off, got oil, went on to park. One day ruined; other 1.5 fantastic.

Back in Missoula, the dealer apologized and agreed to steam clean the engine. Case closed? No way.

It gets better.

A few weeks later, "on my way home" via Glacier NP [had to see it again after losing a day the other time], was driving up Going-to-the-Sun road to the Continental Divide. Steep. Oil light comes on. :blink: Checked oil, no problem. Had as much fun as I could till I could call the dealer next day.

He assured me that, given the otherwise normal operation, it was a bad sensor, possibly messed up by the oil spill. "Enjoy yourself," he says. "We'll pay to have it fixed." [That should have told me right there that it wasn't possible that the light was correct.]

All easier said than done when, every time I go down hill or use the clutch, on comes the light. Cut trip short to get to the bottom of it.

Yeah, it was the sensor. Still have car, 200k miles. So I bought a Prius. Love it and its 50 mpg for 4000 miles.

To reiterate:

"Just shows you that you gotta watch those dealership people, even if it is a Toyota dealership."

Dave S.

 

Makes me wonder what they have sitting in their bulk oil tote bin out back? Perhaps 15W-40 or maybe 20W-50??

Happy to hear all is well.