Reducing oil dilution in priusII

I've been using torque apk for many years continously.
Short Term Fuel trim is one of the guages I keep my eye on.
I've seen short term fuel trim as high at -19 (19% added fuel) durring engine warm up (86-150 degrees F).
My prius has 98k miles with orignal maf,plugs,injectors and I have never cleaned the maf yet.
My fuel trim might be higher than yours if you have changed maf, plugs or injectors.
To reduce oil dilution with unburnt gasoline I drive my prius in braking gear (B mode) while the engine is warming up.
When releasing the accelerator pedel in B mode durring warm-up (at speeds above say 25mph) the injectors stop injecting gasoline which normally only happens once the engine is warmed up (150 F and above and in D=drive mode).
But durring engine warm-up injectors don't stop injecting gasoline while in D (drive) gear unless the engine is warmed to 150 F and above.

If I happen to get stuck at a red traffic light while in B (down hill engine braking) mode/gear the gasoline engine (ice) will not stop running. So I will put the transmission back to D (drive) mode to let the engine stop running while at a red light.
If you left transmission in B mode while at a red light and engine is under 150 F the fuel trim will remain high and the engine will not stop running and injecting extra fuel thus diluting the oil.

Also I do not use the cabin heater till the engine is warmed above 150 F. Running the heater durring warm up cycle will keep engine running while stopped at a red traffic light (regardless of selected transmisson gear when engine temp is below say 145F) injecting extra gasoline which doesn't all get burn't resulting in more oil dilution.

I've always used mobil 1 ep 5-w30 synthetic since the prius had 2500 miles.
Without this special warm-up procedure I would start hearing slight engine noise 2500 miles after each oil change.
Doing this special warm-up technique I have gone up to 5500 miles on an oil change and not heard any engine noise.

I also no longer smell gasoline on my oil dip stick.

 

valde3
I mean to say its short term fuel trim that I'm talking about.
Neg short term fuel trim on prius genII (displayed with torque apk) is adding fuel.
My prius burns about 8 ounces per 5k miles
and my st fuel trim is high (neg.19) only durring warmup. Not after engine is above 150F.

I should also say that oil dilution was not a problem with the SM rated oil (no engine noises heard with SM oil) oil still smelled gassy but no engine noise.. But when the government made reductions of zinc and phosporus (SN oil) then I started hearing engine noise after only 2000-2500 miles on mobil 1 5-w30 synthetic oil. No more engine noise using special warm-up technique.

We also have prius genIII never had any fuel dilution on our prius genIII.
54k miles (genIII) using mobil 1 0-w20 synthetic.

 

vaide3
Just as you say watching the st fuel trim when engine is cold to determine which way fuel is added or subtracted is how I know is neg. adding fuel when cold as shown on torque apk.

If you carfull read my orignal post you would see I'm specifically talking engine cold conditions.
I've had torque apk running for probably 6 years now. continously I dont leave home without torque apk.

I agree its not logical that neg st fuel trim is adding fuel (torque apk)but It is.
I is not logical hv battery regen charging is also shown as a negative number on torque apk, scanguage, etc.

All backwards. but it doesn't take a rocket scientist to figure out which sign is what.

 

Over 7 years of prius chat posts.
I've seen many posts over the years reporting this neg st fuel trim (when expecting pos. numbs) durring warm-up from perfectly running prius's / owners questioning why is it backwards.

The many posts were not regarding problems with there prius but mearly observations.

Myself baffled with this backward sign-age (back approximately 2011) I did an interrnet search and found there were other car manufactures that reported backward fuel trims but warned technicans so they could interpet results appropiately. I don't remember which other manufactures they were but toyota wasn't one of them listed.
But still have been many posters reporting the backwardness of the fuel trim.
I believe the long term fuel trim to have the correct sigh-age cause it follows what is expected.

Maybe there could be different software/firmware with genII years 2004-2009 but I dought it.
I also watch injector time durrring warm-up 5ms (-3 stft) = 25-30mgh. After warm-up 5ms injector open (0-1 stft) = 55-60 mph. fuel trim only hits -19 going downhill no accelator pedal and traveling 40-60 or more mgh and engine temp below 150F. I also watch air to fuel ratios look (at all times hot or cold) great mostly 14.5:1 (suspiciously to good).

After warm-up stft goes neg climbing hills. goes positive decending hills and follows injector timing.
The inclineometer (I think it is the gas fuel float) adds fuel (neg. stft) for climbing overpasses and subtracts fuel (pos stft) while decending (stft).

I've never had any codes set on my prius. I always get 50+mpg and my drives are 99% city driving.

Hope this helps.

 

valde3
I was using a scanguage back around 2010 is also shows stft negative while warming and other times when additional fuel is injected.
Again long term fuel trim shown on scanguage and torque appear to show the correct sign.
Its only the short term fuel trim (stft) showing the wrong sign on scanguage as well as torque apk.
Back 2010 I was using scanguage my prius probably had only 15000 miles probably less.
Over the years I have watched stft increase only durring engine warm-up say 1 or 2% per year.
While long term fuel trim has remained stable over the years.
Yes I do have a problem (stft sometimes -19%). GenII prius's have a history of oil dilution I thiink mostly city driven under 10 miles per trip where the engine rarely reaches operating temperature. .
My genII prius appears to have 180F thermostat and 183F is the normal warmed-up engine temperature and it takes about 10 miles with outside temperature 40-50F to reach operating temperature.
Our GenIII seems to have a 190F thermostat and also takes about 10 miles to reach operating temperature (say 192F).
My wife drives the GenIII. So I only have 10 or 20 hours of torque apk operating on the GenIII but oil dilution is not a problem like with the GenII.

Its very important that engine oil reach operating temperature (extended drive or at least 10 miles) so that gasoline in the oil will have a chance to be burned off (evaporated).

Valde3 How many hours of operation on your prius have you; while watching short term fuel trim?
How many hours of (your personal prius) driving while watching long term fuel trim?

I have thousands of hours watching stft. Dont you thing I might posibly know what I talking about?

The internet search I did years ago where I found other car manufactures reporting negative instead of positive values for fuel trims was not specific to torque apk or scanguage but specific to certain manufactues ecu's.

I think we are geting off topic. This tread in specific to reducing oil dilution. It should have nothing more to do with Negative or positive fuel trim ecu coding errors.

My results are long lasting oil (no more gasoline smell on my dipstick), long lasting engine (no more engine noise on older oil). And oil dilution on genII prius is a known problem.

And yes there is a problem with my stft durring warm-up. however after I fix the fuel trim problem I will continue to use my special warm-up procedure as it definately extends oil quality and reduces oil dilution.

I was hoping Anyone with oil dilution may benifit from this post (unless there check engine light is on) there is other problems .

Also mobil 1 oil company considers frequent drives less than 10 miles duration as severe service duty on oil. And says severe service duty of oil requires earlier oil changes.

Hope someone gets benifet from all this.

 

Yes Gasoline getting into oil.

 

Valde3

This discription from your manual follows exactly what I'm stating. Negative value adds fuel. Positive reduces fuel.
Example should my fuel trim reache -30 it will set a rich fuel code. Meaning to much fuel is being added.

Durring engine warm-up any car (any model) fuel should be rich condition (adding fuel for faster warm-up). genII prius shows this as negative number (my case under certain conditions -19) should my prius reach -30 according to your prius manual will set error code rich fuel (exacty right too much fuel being added). I do not see your confusion?

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