Oil Level/Tire Pressure MPG Myth

i have had my Prius a little over 3 weeks now. it has 1400 miles on it, original oil, original tire pressure, and i have a life time 48.3 MPG and on the trip i just returned from, over 400 miles round trip, I averaged 49.7 MPG, all interstate miles. I understand the EPA mileage for highway is 51, so I'm not that far off with dealer pressure, oil, etc. and I'm still in the break in period.

anyway, i'm still as happy today as I was when we first put out deposit down. What a wonderful car!!

 

Even if there was no MPG gain at all from the higher tire-pressure or the lower oil-level, there is still a reason to maintain that anyway.

Tire wear has been proven to slow as a result of never allowing the pressure below the minimum (35/33). Keeping it at 44/42 helps out even the most forgetful of owners.

As for having the oil level lower, you are simply using less oil. That's a good thing no matter how you look at it.

 

Overinflated tires produce a harsher ride and I wonder if they cause rattles and may cause suspension problems later on. Using less oil than recommended means that the same oil is circulating over and over, so that you may need to change it earlier.

My experience over 44,000 miles is that dyno oil and 35/33 work just fine.

 

Tires run at less than their design pressure will wear unevenly.
.
An overfull crankcase will cause more thrashing and foaming, as well
as a viscosity-friction hit. And more oil may show up in that sump
that seems to form in the bottom of everyone's intake manifold.
.
This stuff ain't a myth. Go snoop around cleanmpg.com for some
vindication.
.
_H*

 

<div class='quotetop'>QUOTE(jamarimutt @ Aug 8 2006, 09:24 PM) [snapback]299960[/snapback]</div>

Not in a Prius. 5,000 miles is actually premature. The engine simply doesn't get worked anywhere near as hard as a traditional vehicle, which have the same change interval. Take a look during the next service. It comes out surprisingly thin & clean compared to what you'd expect.

 

<div class='quotetop'>QUOTE(jamarimutt @ Aug 8 2006, 09:24 PM) [snapback]299960[/snapback]</div>

I've posted Used Oil Analysis run a bit over 1,000 miles past the recommended oil change interval. At least with my Prius, there is no issue at all.

Consider that the EU market Prius has an oil change interval of 12 months or 16,000km, twice as long as our North American Prius cars. It's all in the quality of the oil. And - essentially - all the motor oil does is endlessly circulate around the motor

 

I put my tyres up to 42/40 for a few hundred miles and didn't notice a big difference in MPG.. ok so it wasn't for very long but that's because I DID notice a big difference in everything else. I can't decide wether the alarmingly skittish handling through bumpy corners was worse than the road noise or the vibrations rattling the trim all over the car...!

As for oil - I doubt a couple of cups extra would hurt. I've only done 5k miles in mine so haven't had the chance to check it out. I'm assuming the dealer changed it at 4.5k when they passed it on to me.

I do notice some tyre wear right on the edges of the tyres though, about an inch in maybe. People are saying that 35/33 is too low in terms of tyre wear, regardless of mpg.

 

Short of extensive testing it is nearly impossible to quantify the results of a couple of pounds of tire pressure or a half quart difference in oil....

A person making the exact same 200 mile trip two days in a row could easily achieve a 2-3 mpg difference simply by changes in the bp or humidity... Too many variables happen during the course of a tank of gas (especially in a Prius)m to accurately quantify subtle changes short of simply following through over and over again to see a trend or change.

If someone can quantify results then that is great. All I know is from my racing experience where if I fail to extimate the performance of my vehicle within .01 or .02 I will probably lose. Such factors as weather, tire pressure, amount of fuel, and hundreds of other variables come into play and until the variables can be accurately quantified any changes, such as tire pressure, cannot be accurately evalulated.

On the street, if a person drives the same route for a month, makes a change, and drives the same route for a month, the variables often will equalize so the person has a good idea (although not conclusive proof), of how a change, such as tire pressure, affects economy.

 

I've seen no problems with oil up to the full mark but I never overfill beyond that.
For tires I see 2-3 mpg difference from Toyota spec to tire sidewall spec.

All of you are making up stuff without measuring it. It is very simple to to measure but you can't do it by tankfuls. There are too many variables. You must measure 1 change at a time and do it so nothing else varies.

I check every change I make at constant speed on level road with no wind, and at matching conditions.
I use the car mpg readout and reset it to measure over a short test route. This way changes of 1 mpg are meaningful and repeatable every time.

Over a tankful I see variations way beyond what I am trying to detect.

The car is very predictable and on any regular route if you get 42 mpg when you normally get 50 you can be sure something changed.

 

<div class='quotetop'>QUOTE(jamarimutt @ Aug 8 2006, 07:24 PM) [snapback]299960[/snapback]</div>

When I asked someone at the Toyota dealership where I have my oil changed, I was told 42/40 would probably cause too much wear in the center of the tread, as well as cause a very rough ride. The streets in both Spokane and Cheney (where I live) are far from smooth.

Dave


<div class='quotetop'>QUOTE(john1701a @ Aug 8 2006, 08:03 PM) [snapback]299989[/snapback]</div>

In spite of the 5000 miles being premature, every time I get my oil change at just under 5000 miles (to be certain I'm keeping my warranty) they slap on a sticker indicating the next oil change in 3000 miles.

Dave

 

<div class='quotetop'>QUOTE(dmckinstry @ Aug 9 2006, 09:58 AM) [snapback]300149[/snapback]</div>

Lots of evidence (pictures, user experiences) on this site showing that keeping tires at spec will cause more edge wears.

Dealers want you to change oil at 3000 miles because they want more business. The maintenance booklet stated 5k miles intervals. Many on this site (including myself) did used oil analysis showing the oil is still good at 5k miles and can last a lot longer.

Overfilling the oil above full mark can cause problems too. The oil can get into the intake manifold and cause engine not run properly.

You can search around the site to see the posts I mention above.

 

<div class='quotetop'>QUOTE(dmckinstry @ Aug 9 2006, 06:58 AM) [snapback]300149[/snapback]</div>

Recommendation for oil change every 3K miles as a “cheap†way to protect your engine is one my pet peeves. It’s really a total waste and a way to use up oil for nothing and a way for dealers and oil change outfits to make more money by scaring the wits out of us half-witted car owners! Any – and I mean ANY dino oil is good for over 10K – maybe even 15K-20K miles. The same cars sold in the US with the recommendation of 3K or 5K oil change when sold in Europe or Japan has a recommendation of 10k miles oil change interval. I first learnt of this in the early 80’s when I worked with a visiting scholar from the UK. . He bought an Escort, identical to the one he had at home – just ‘cos he’s familiar with it – and to his surprise the dealer (and the owner’s manual) recommended oil change interval was listed as 3K miles. He couldn’t belief it, he was sure he’s being ripped off. His Escort at home had a recommended interval of 7500 miles. Now is their oil that much better? No. Is their road and driving condition less harsh – no – in fact much worse. I decided to look into this and realized that indeed we have all been ripped off. Yes, 50 years ago, 3K miles oil change interval is about right. But today’s engine technology and metallurgy have advanced and so has oil formulation. After 3K miles in ANY engine, the oil drained will test like new. In 1995 when I bought a brand new Infiniti Q45, with a recommend oil change interval of 5000 miles, I told the dealer that I will bring my car in to them for all oil changes (and all repairs) but that I’ll only do it every 10,000 miles and I don’t want any hassles. Why, because the same car sold in Japan (as the Nissan Cima) has a recommend oil change interval of 15,000 km (about 10,000 miles.) The dealer has no problem with that and never threatened to void my warrantee. When I sold the Q45 last year with 160,000 miles on it, it purred like a kitten and ran like new. I bought a Honda Civic Hybrid and it comes with a recommended oil change interval of 10,000 miles – finally I’m glad to see Honda stepping up to the plate and debunk this 3000 mile oil change interval nonsense.

Goggle info about oil change intervals and you will find many research that say that even after 20,000 miles, the oil is barely “used†– so we Americans are just so desensitized to wasting perfectly good oil that we can be easily scared into submission about changing oil every 3K miles as “cheap†insurance for our engines. Nonsense – just a way for us to waste natural recourses. But we are all scared sh**less and brainwashed to “protect†our investment and will continue to dump perfectly good oil once every 3000 miles. What would it take to deprogram us? Well how about taking the oil to a lab for analysis after 3K, 5K, 7.5K, 10K or even 15K miles and let the result show that really, the oil not contaminated, the oil molecules not sheered and viscosity not diminished even after 10k miles and we really really don’t need to waste so much oil.
Here’s some links:
http://www.nordicgroup.us/oil.htm
http://www.motoroilbible.com/pre-one.html Exposing the 3000 mile change myth
http://www.carjunky.com/news/motor_oil_myths.shtml Same article here - better layout
http://www.amsoil.com/testimonials/409000.aspx Here’s Amsoil running their syn oil in Cummings truck for 400,000 miles – but wait don’t they want to sell more oil?
http://www.practicingoilanalysis.com/artic...p?articleid=562 Built-in sensors for cars to determine when oil needs to be changed.
http://freshalloy.com/club/editorials/snake_oil.html

 

I used to have that same eighth-inch bilge of oil at the bottom of
my intake plenum, but more recently I've run about 5000 miles with
the oil at about a quarter-inch below the full mark on the stick,
i.e. the correct level, and the bilge is *almost* gone. It's clear
that an overfill gets sucked right up the PCV hoses, and it evidently
takes a *long* time to re-vaporize out of the manifold and get
burned up. Since I had my throttle-body off today to check it out
and lube the pivots, I was able to swab out the minor remainder so
now my intake chamber is close to DRY and I hope it'll stay that way.
.
_H*

 

<div class='quotetop'>QUOTE(yauman @ Aug 9 2006, 11:52 AM) [snapback]300344[/snapback]</div>

agreed.