15w-40 in Prius

[oggb]

Changed the oil in my Prius today. I've used 5w-30 synthetic (whatever's cheap) up to this point, aside from a few thousand miles on Toyota 0w-20.

Put Rotella 15w-40 in the sump. It'll be in there for at least 10,000 miles.

Drained out a QSUD/QSAD mix that had been in for around 10,000 miles. I've stopped keeping tabs on it, really. Oh, and I didn't change the filter. Didn't feel like buying one, honestly. It has a Bosch DistancePlus or whatever they're called mounted right now.

MPG has been 48.1 - 48.3 over the last few tanks (5w-30). I don't hand calculate anymore, as the Prius is fairly accurate as long as I remember to correct for tire size -- mine are 1% taller than OEM.

Guess my MPG is going to be terrible until I drain the 15w-40 out.

Oh, and if you're wondering "Why in the heck did you put 15w-40 in your PRIUS!?" ... It was free.

 

[JHZR2]

You rebel!!

 

[Geonerd]

Yea, 47.x MPG is gonna be SOOOOO awful!

Please report the results of your gas guzzling debauchery.

 

[friendly_jacek]

I think this "free" oil will cost you plenty in gas money, LOL!

 

[uart]

Originally Posted By: JRed
Guess my MPG is going to be terrible until I drain the 15w-40 out.


Don't know but it will be interesting to see. Make sure you haven't disconnected the 12V battery (it effects the calculated MPG accuracy for some time) or overfilled the oil and please post the results averaged over several tanks. I'm certainly interested in the results.

I'm guessing a drop of about 2 MPG.

And BTW. Change the filter!!!!

 

[JAG]

The Prius ECU is going to discover what horror you've subjected the engine to and will refuse to allow the car to budge! Just kidding. Yes, please let us know what effect it has on gas mileage.

 

[Artem]

I vote 1-2mpg loss at the most.

Wouldn't be surprised if the OP reports the same MPG average with the thicker oil...

 

[JHZR2]

Originally Posted By: Artem
I vote 1-2mpg loss at the most.

Wouldn't be surprised if the OP reports the same MPG average with the thicker oil...


Especially in the summertime with the heat we have been having!

 

[gregk24]

Mileage wont drop much, but my goodness....just because it was free? your doing more damage to you motor than "free" is worth.

 

[WiskyBadger]

How much damage Greg?

 

[Bandito440]

What kind of damage are we talking about here? I'm skeptical.

 

[147_Grain]

Even IF the 15W-40 was free, I'd still cut it with a 20-weight during the hot summer months.

 

[Shannow]

Originally Posted By: gregk24
Mileage wont drop much, but my goodness....just because it was free? your doing more damage to you motor than "free" is worth.


Care to quantify that assessment ?

 

[daves87rs]

Won't hurt it a bit.

 

[Garak]

I might worry if it were -40 out or if one were actively seeking 15w-40 for the vehicle, but at this time of year? I can't see a major issue.

 

[The Critic]

The only concern is that the engine will technically crank slower with 15w40 vs 5w30. While I don't see it being a true issue, I'm sure that the Prius ECM software has a specified range that it likes to see (cranking speed) due to the frequent start/stop cycles. I supposed if you have not already gotten a check engine light, all is well.

 

[supercity]

Toyota Hybrids are manufactured right here in Melbourne. Toyota allow 15w40 and even 20w50. Id say it will probably be OK.

 

[friendly_jacek]

Now if the OP is doing high speed hwy driving, there will be near zero MPG change. If short city trips, huge drop in MPG. This is what I saw in Subaru going from 5W30 to 5W40. Prius should not be different.

But, I would change that oil before winter for sure.

 

[JOD]

Originally Posted By: friendly_jacek
Now if the OP is doing high speed hwy driving, there will be near zero MPG change. If short city trips, huge drop in MPG. This is what I saw in Subaru going from 5W30 to 5W40. Prius should not be different.

But, I would change that oil before winter for sure.


I'd expect it to make a bigger difference in a Prius than in your Subaru, since engine internal friction is a more significant portion of fuel use in a Prius than a Subaru, particularly at highway speeds; 2 drive axles, lighter weight and significantly better aerodyamics mean the engine is a bigger source of losses in the overall system (as a %). If anything, short city trips should be LESS affected than highway, particularly since he'll be on battery power more often.

Interesting if you do the maths. If he loses 2mpg over the course of a 10K OCI, the "free" oil is actually costing him about 10 bucks compared to M1 0W20.

 

[BillyTheKid]

It will be fine. I'm even doubting noticeable mpg differences. I'd have no worry if it were mine.