Do I believe the evidence or the dealer?

If there is an award to be given for top first posts, this one has got to be in the running.

Congratulations on making such an effort to educate yourself, identify issues, take action, etc. Clearly, you've been able to make the changes that should make a difference. One thing that you cannot change, though, is likely going to make your "low" numbers stick: You only drive in 5-minute intervals. In the winter, this really shows up as a "problem" for those striving to increase MPGs.

One thing you can change is your dealer. Either go to another dealer or take the time to educate the dealer. You are not going to be able to increase the mechanics' abilities or knowledge of automobiles (unless you are a mechanic yourself), but you will be able to educate the dealer about YOUR INTEREST in having the Prius achieve its maximum potential.

I have been wondering myself why I've experienced a noticeable drop in MPG since my first (5,000 mile) oil change. I've put on about 1,000 miles since then, and I still see this decrease. Some is likely weather related, but could all of it be from the cold? I increased the tire pressure the afternoon after the oil change (the dealer had dropped it, but only to about 40/38). I had blocked the grill prior to the oil change (and since increased it to a full block). I turn the heat on low only after the first five minutes (if at all). And I wonder what happened at the dealer's garage.

I am thinking (and hoping) that it really is just due to the very cold weather. Just yesterday I had two 55-minute drives, mainly expressway. Normally, I would have seen MPGs in the upper 50s. Instead -- outbound was in the low 50s and the return was in the upper 40s. I think the cold and, the sloppy roads combined to drop the mileage. Just as I've noticed lower MPGs in rainy conditions, I think MPGs drop when I drive on sloppy roads during and after snow storms.

Like you, though, I'd be interested in some other views about what could be done.

Yes, the EBH is on order and will be arriving soon!

 

Ah ha. Maybe I'm not crazy. Even when the roads were perfect, but it was just colder out I had been noticeing shorter gliding distances. I too had checked my tire inflation, but that wasn't the culprit.

To address the OP, I would guess that you *might* not be able to make any definite determinations until next spring when temps have moderated to what they were when you were getting 45-48 mpg.

 

I apologize for the assumption I made about being a new Prius owner/driver.

You've now taken an interesting post and made a real mystery of it!

 

Thank you for a gracious reply.

You've probably read through the numerous posts regarding oil changes on PC. Many people have written to complain and warn against going to quick-change shops. Many others have complained about dealerships, but feel their warranties are not in trouble if they go to Toyota dealers for service. A very vocal group says: "Change the oil yourself -- it is easy and cheap!" There is a rather recent thread showing you just how to do this easy task.
I used to do all the maintenance on my cars. I also used to get very cold and dirty doing it all outside. Now I wait in the heated room at the dealership and try not to think about it too hard.

 

You might try that to rule out problems with the oil the present dealer is using.

If you do switch where you go to have the oil changed, you might want to consider synthetic oil such as Mobil 1. Also, a block heater could be something to consider, even though your mileage last year was not as bad as this year. Lastly, did your area recently switch to ethanol additive in the gas?

 

Did the dealer do any software upgrades that they forgot to tell you about? I noticed in the '04 that when they re-programmed the computer, we got much worse mileage.....

 

If they put the wrong oil in, that would explain everything. A higher viscosity oil would really be noticable in the MPGs.

If that happened to me, I would either have the oil sampled or ensure that I got it changed with oil I bought. You have eliminated just about every other factor that would cause that big of a change, other than a computer update...and that should not cause it to drop that much.

 

I hadn't thought of this as a real issue. Would there be a noticeable change in MPGs if the oil was changed from 10W30 to 10W40?

 

Having changed the oil on a 2001 Prius for 7 years, I noticed a ~1 MPG improvement with the new oil of the same viscosity. This required lots of oil changes and lots of data to verify since a 1 MPG change is so easily affected by many other factors. The Prius gets such high MPG that it is sensitive to everything (temp, oil, tire psi, etc)....and something really big had to change to cause that much drop.

So, yes changing the viscosity does change the MPG. Now what would happen if they put in 20W-50? Big changes in MPG. Now I am guessing like everyone else, but you really have eliminated just about everything else.

(Search for posts by jayman to get a firsthand description of a Toyota Dealer putting bad oil in a Prius.)

 

Welcome to PC.
How is your parking brake? Did that get higher after the oil change too? It is possible the park brake is adjusted too tight causing friction in the rear brakes. Check for heat in the rear brakes after a drive, they should be reasonably cold with normal Prius driving.

Hey wrong oil wont just reduce mileage but it can damage the engine. I have seen engine damage caused to an engine that should have had 10w-30 but 20w-50 was used. The 20w-50 oil is too thick for the fine clearances in a modern engine

 

The correct oil would be 5W-30. Don't forget to check the air filter

 

Thanks for the further explanation. Had no idea you had already been through a winter. Oops.

At this point I would want to change variables one at a time. I might see what happens when the oil is changed again, but not make the switch from dino to synthetic as that's changing two variables at one time. You might not know which one of those made a difference if you suddenly get another change. But that's just me being methodical.


What all in the engine needs to be checked if it was the wrong weight of oil? Or too much oil??

 

I wouldn't think that changing the oil from 5W30 to 10W30 would cause a noticeable difference. I have a crankcase full of the heavier oil and mpg did not decrease.

 

I should not because the running viscosity (30) is the same. The cold, starting viscosity (5W or 10W) determines how fast the engine gets lubricated on startup (I am sure you knew this already, so this really is not aimed at you).

In the case of the OP, if the dealer put in the wrong oil, it could have been really wrong rather than just slightly different. It looks like the OP knows what he is doing so I expect we will find out before too long.

 

standard dealership oil stock is
0w20
5w20
5w30
10w30

make sure they put 5w30 in there, but concerns about extremely heavy stuff are probably not worth thinking about.

you should get an itemized list to see if they did anything other than change oil and rotate tires.