SentraSE-R

O2 sensor failures are pretty common among Toyotas. I've heard them mentioned as the commonest cause of smog check failures, and they're linked to poor mileage complaints, too.

Your CAI works against mileage. Colder air is denser, and your car drinks more fuel to maintain its stoichiometric ratio.

Jan06xB

Yeah I still use the acetone but the idea that is melts paint off the car is probably from someone that used some spray can paint to paint their car. Acetone is one of the mildest petrolium solvents there is which is why it is used as a nail polish remover and the carrier/solvent for the nail polish paint. The factory paint will get nice and clean if some gets on it and the repainted surface from the body shop on mine that was oversprayed on my roof would not come off with acetone either - I had to wet sand it off with 1000 grit and then buff it smooth. It does make my engine run a lot smoother - gets rid of the little stumbles that it can have at low speed when in traffic or when cold.

I think the use of Synlube may have another influence on my mileage too. The stuff seals the rings really well and as a result I burn very little oil in fact so little that it may be a problem since I end up NOT adding the Add Oil often enough to replenish the sacrifical components of the Synlube which prevent corrosion. But having less oil burning keeps the cat working better and the O2 sensors cleaner. I have one of the cleanest tipe pipes I have even seen and once the cat is warmed up the exhaust has no odor at all.

On the topic of oil from what I was reading about the tC and the oil pressure at idle I would think twice about changing to a 0w20 or a 5w20 - there are posts here about 9psi at idle and some getting down to 6psi which starts to get to be an issue if you don't have enough film strength in the oil to prevent metal to metal contact.

SentraSE-R

'06 owners can use 5W-20W per the TSB, but '04 and '05 owners are playing Russian Roulette.

blown_xa

That it not entirely correct. Cars from the factory including the xB have ducts drawing cool air to the factory air box. Cool air and cool fuel is much more efficient. More ignition timing is utilized which results in a better combustion burn. When you have a better combustion, less fuel is needed to expell the same amount of energy. That is why most modern cars have a returnless fuel system, the fuel is not circulated from the hot engine bay back into the fuel tank. That is also why economy cars such as the Yaris, xA, xB have composite intake manifolds... less heat soak. There is a factory air intake temperature sensor on the maf sensor. Dense air provides better mileage, that is why many tractor trailors use water injection.

blown_xa

You will know if your o2 sensors are bad if you throw a CEL which says o2 sensor stuck lean/rich or o2 sensor heater circuit low/high. Until then dont waste your $ replacing the sensors.

vintage42

Is that because of a difference in the '04 and '05 engines? As far as I know, there is no difference. And as I read the TSB, it is perfectly OK to use 5W-20W oil in all Scion engines of any year. The TSB is just to say that Toyota has begun to use the thinner oil for its '06 and '07 models.

Technical Service BULLETIN
TSB #ENG01-06
March 29, 2006
Title: ILSAC GF-4 ENGINE OIL RECOMMENDATION
Models: All ’06 – ’07 Toyota & Scion

Toyota Motor Corporation manufacturing plants have begun using ILSAC GF–4 engine oil. This engine oil is recommended due to its superiority in terms of fuel economy and engine protection and due to its benefits for both the customer and the environment. ILSAC GF–4 can be used in all Toyota and Scion engines.

Applicable Vehicles: 2006 – 2007 model year Toyota and Scion vehicles.

Recommended Engine Oils: ILSAC GF–4 SAE 5W–20
This oil has been set as the Toyota genuine engine oil, starting in February 2006 for the U.S. This oil is superior in terms of fuel economy, engine protection, and cold starting performance.

bugandxbandme

I don't know if the CAI is good for gas mileage or not, but our first long trip after we put it on we got 37 mpg! A few months after is when our mpg went down, and I thought it would improve in the summer but it really didn't.

SentraSE-R

Note that TSB EG001-06 was superseded by EG018-06. Follow this link and note the links to the actual TSB in the last message in the thread.

Your quote above seems to cite the wrong TSB. In any case, its applicability is clearly only to 2006 and 2007 Toyotas and Scions - not to 2004s and 2005s.

Basically, the TSB page 1 and TSB page 2 says ILSAC GF-4 is recommended for all Toyota engines, but owners should use the viscosity on their oil filler cap, unless their engine is listed in the table in the TSB. The table then includes the 1NZ-FE engine in 2006 and 2007 Scions - not the same engine in '04s and '05s.

Toyota obviously thinks there's a difference between the '04/'05 engines and the '06/'07 engines. Most likely it's in finer polishing of the bearings, allowing the newer ones to receive adequate lubrication with the thinner 5W-20W oil.

SentraSE-R

The secret, as in all things, is moderation. An IAT of 140ºF is what I've seen cited as best for fuel economy. Colder denser air may be desired for power and/or efficiency. Many fuel system mods are just to keep fuel from vaporizing too early and causing vapor lock - something completely aside from fuel economy.

bB2NER

Cold air intakes do little considering the dang TB heats the income air anyhow with engine coolant.

blown_xa

I can see your point. But Im pretty certain a returnless system on todays cars is not in place to prevent vapor lock, that may have been an issue in the 1970's but not today. Controlling the point of vaporization of the fuel is important. The only thing that can change that point (on a givin car) is temperature. If the fuel vaporizes before it enters the combustion chamber then that is a waste of energy, it can do so if air intake temperaures are high and fuel temperatures are high. The fuel injectors in our cars are more than capable of atomizing fuel very well regardless of temperature or viscosity. What you said was contradictory to itself, you stated (in more or less words) that efficiency was seperate from fuel economy... that doesnt make since because efficiency is what provides good fuel economy . Some manufactures are using direct port injection to control the vaporization of the fuel, it can only vaporize in the combustion chamber.

Hot motor is good when combined will cool fuel and air because the vaporization will have a better percentage of occuring in the combustion chamber and the energy potential is most efficient... fuel burns correctly and not wasted.

Many cars get worse gas mileage in the winter time simply due to the fact that warm up takes longer therefore the car stays in open loop for a long time, and in cold weather the ecu tells the car to run rich to stablize a potential rough idle. And with many day to day driving will yeild worse gas mileage. That is my bet on the fine lady's problem with her xB. Yes it does require more fuel to compensate for denser air, but the equilizer is that less throttle is needed to expell the same energy (hp). So it is in turn the same result. Highway mileage can be gained though, like I said many truck drivers install water injection to increase gas mileage. They are only doing highway miles and benifit greatly from a reduced air intake temperature.

Jan06xB

The only problems with what you just said are the following. Smaller throttle opening with cold air increases pumping losses - the energy wasted trying to suck the air into the cylinder - diesels run full open throttle and control the fuel is one reason why they run more efficiently. Colder intake air make more power since the expansion ratio of cold air and fuel to burnt fuel is greater and you can cram more cold air molecules into the cylinder however at low power levels the cold air reduces the ability of the fuel to vaporize and more completely burn so at low power levels warm air is better plus it helps increase combustion temperatures more to burn more completely. I think you will find that the injection system in our cars warm up and run closed loop right away no matter how cold the engine is but there is mixture issues, idle speed and oil temps that lower initial mileage in cold weather. As far as the return fuel it just isn't needed these days for our fuel injection systems since the fuel pump can handle the pressure control without a regulator in the engine area to return excess pressure. You end up saving fuel lines and wasted excess fuel pump power if you don't pump extra gas around and there is less fuel heating as a result too.

lazermule

+1 Quite good, couldn't have said it better myself...

LM

bugandxbandme

Wow, this is deep. Anyway, we just filled up, gonna try to let the engine warm all the way up before we drive like maniacs. Hehe

blown_xa

combustion temperatures are over 3000 degrees, you think 70 degrees of air temperature makes that much difference on when the fuel vaporizes in the combustion chamber? The compression stroke is what brings the fuel up to the temperature. You stated exactly what I said, colder air reduces the tendency for the fuel to vaporize... the air is only cold before the combustion chamber though (as is should be ). Combustion chamber design and compression pressures result in better homogenization of the fuel and air molecules, and that is what you want. It should only vaporize in the combustion chamber.
Denser air provides faster burn, the advantage of a faster burn is ignition spark is doesnt need as much advance, resulting in less time to build pressures before reaching top dead center. That reduces braking action to compression pressure which in turn increases pumping efficiency of the engine... this results in less power wasted to pump the engine, and better fuel economy.
So there you have it

Another thing you said doesnt make since to me.. you stated that the suctional loss (small throttle body "sucking in cold air" ) reduces the efficiency of the motor, but what is confuzing me is that you also stated that colder air has more air molecules cramed into it... so isnt that statement irrelivent? It is irrelivent because it becomes more efficient (as I explained in previous paragraph).
The goal is to generate the same energy output (horsepower) using less consumables. That is what makes fuel economy.


If toyota wanted to draw in hot air, they would have put the intake manifold right on top of the exhaust manifold instead of using a cross port design. Older cars utilized that method, but then people got smarter. And they would have routed the air box intake tube toward the exhaust manifold, oh oh and they would have run the metal fuel line all the way to the fuel rail in the engine bay(instead of insultaing it) ... but hmmm i wonder why they didnt do it that way????????

Jan06xB

Ok the 3000 degrees is probably correct at the very center of the cylinder combustion flame - the outer edges drop off a lot cooler. There is a video of a combustion chamber firing and the flame is on the intake valve because the fuel coats it since it is the cooler part of the combustion chamber - there isn't a lot of flame in there. At light throttle even at highway speeds my xB engine is timed at 35 degrees before Top Dead Center - there is not a lot of pressure at that point maybe a little above atmospheric since I am running maybe 40% load which means pretty high intake vacuum so not much air to compress to create high temps. The intake is getting air from behind the headlight which is a little warmer than ambient temperatures due to the air flow coming through the radiator and since there are some openings in the bottom of the airbox I am sure some air also comes in from above the tranny. If you had a Scangauge and monitored the AI Air Intake temperatures you would know that it runs a little warmer to very hot on hot days. With a plastic intake manifold hot air is not a good thing and like I said for light throttle you want warm air since the timing is very advanced (as much as 38 degrees) and the very small amount of fuel being injected may not mix very well with the tiny buff of intake air so enter the variable valve timing of Toyota which reduces the pumping losses and lets the intake valves stay open longer as I understand even as long as after bottom dead center. This helps reduce pumping losses. Now for thermal efficiency cold air is better IF you are trying to create a lot of power because with a lot of cold air and a lot of fuel you can get a lot of heat and compression but most of the time you don't need a lot of power so the equation changes to getting the tiny amount of fuel to just burn completely. That is why I run with some Acetone in my gas to help with the light loads to atomize the fuel better when that injector fires for a few milliseconds. I want the fuel to turn to a gas and burn clean and it appears to work well - the problem is that everyone tries to run acetone at highway speeds and expects to get better MPG then but it doesn't really help much or at all at highway speeds. Mythbusters tested it at highway speeds and found no improvement DUH! What I said!
Pumping losses occure during the intake stroke when the piston is traveling down from the head trying to draw in fresh A/F mixture. The vacuum is created by the piston drawing in the mixture - the wider open the throttle plate and the more free flowing the intake and air filter is the lower the vacuum and the less power that is lost drawing in the A/F mixture. Works great at full throttle but like I said we don't operate at full throttle much. The only way to reduce pumping losses a little is to keep the intake valve open past BDC so that the vacuum can also pull the piston up on the compression stroke but that happens anyway even if the valve is closed.
As far as the intake temperature goes when compression occurs the temperature rise from the change in the A/F charge volume is multiplying the temperture of the A/F charge so the warmer it is the even higher temperature it gets to under compression and there probably is a minimum intake temperature where the compression gets it very close to ignition temperatures or at least closer to ignition temperatures which increases efficiency of combustion. I would have to crunch some numbers to know for sure.

blown_xa

I have a simple solution so you can get better gas mileage... trade the box in and get an xA
All good points. But I guess the engineers who do that for a living would be best to inform. Bottom line, everything is in place on our vehicles for a reason. VVT-I only changes when the intake valves open though (just to specify one thing you were not sure of).

bugandxbandme

Well, it appears that driving style has much to do with our decrease. We drove very reservedly for a whole tank, and got almost 32 mpg! The thing is, it seemed to get better as we got to the end of the tank, like the car was catching on that my husband wasn't driving aggressively any more. Now I've finally convinced him to slow down! Yay! At least until he gets his sway bar.

vintage42

I don't see how cold air intakes could do much at steady cruising speed. I have ScanGuages in both my xB and Forester, and it shows the OEM intake air temperature to be only 7*F higher than outside air. I have to estimate the outside air temp with the xB, but the Forester has a display for it.

So at cruising speed, a cold air intake would merely reduce the intake air temperature by something less than that 7*F.

SentraSE-R

! I've got 40 tanks in my gas log, and my worst tank wasn't 32 mpg. I've got more tanks over 50 mpg than I have under 40 mpg.

Here's what you'd see if we all rode in the same xB with your husband and me driving. He used to shift at 4000 rpm. Now he shifts at 3000 rpm. I shift at 2000-2200 rpm.