TurboJeff had oil tests done, showing 10% fuel in 2K miles as I recall. Likely not unusual.

For an oil test 2% is the usual amount allowed, and 5% is considered bad. Fuel is not a great lubricant.

From FSM, FD oil capacity is 5.7 Q for twin coolers, and 5.2 for singles. Oil change drops 3.7, 3.9 if filter is removed (breaks vacuum in passage from pump). Little oil is left in the filter.

--- 3 oil change cases for twin coolers ---
--- assume 3.4% dilution/ 1k miles, based on Jeff's numbers ---

O&F change will remove 68% of the oil.
Just oil change removes 65%.

Case 1: O&F chg every 2K miles.

-> dilution after chg = 3.2%, ... aft 2K 10%, ... ave = 6.6%

Case 2: O&F chg every 2k, but chg oil only 2nd time after 1st ~20 miles.

-> dilution aft chg = .9%, ... aft 2K 7.7%, ... ave = 4.3%

Case 3: Oil chg every 1K, filter chg every 2K.

-> dilution cycle is 1.7% O&F, 5.1% -> 1.8% Oil only, 5.2%, ... ave = 3.4%

I just did "case 2" on my single cooler, and this was first time no slight fuel smell in oil filler neck aft oil change. I use synth blend, vs synth, due to frequent changes.

Note dilution will not be 20% with a 4 K change, since some will evaporate, and 3.4% per 1K is a really for Jeffs cars only, but likely not unusual.

fwiw

 

Interesting perspective. Oil dillution is the only reason I change my oil every 3,000 miles and is also the reason I don't bother using $$$ synthetic as it would just dillute as well.

Late in its life my old motor reaked of fuel whenever the oil was changed. My reman now has 30,000 miles on it and there is no fuel smell when changing the oil. Seems somebody mentioned side seals as the main contributor to oil dillution. Been meaning to have mine tested but never remember.

 

Kevin, think about oil dilution much?? good info, I guess

I found that if you run the fuel vapor purge system with out the solenoid (haltech) the oil will smell like fuel pretty quick, as fuel vapors will invade your motor while it's just sitting there.

Since I've reinstalled the purge solenoid I have no fuel smell. Just one more thing to check if your oil has an oddly strong fuel smell. Solenoid could be stuck open <---is that possible? I don't have a clue what the fail mode is.


*(I'm a dumbass, now that I think back...wtf, was I thinking about )

 

FWIW

a friend has a 20bfd and was talking to Cam Worth of Pettit last week about oil dilution..
according to my friend, Cam said that leaking primary injectors are the primary source of oil being diluted w gas.

i have found over the years that you can take most everything Cam says to the bank.

howard coleman

 

I change my oil every 1500 miles. But I drive my car very hard. Also it has dual oil coolers. One time I went as far as to drain the oil, fill it back up, and drain the oil again. This oil was as dark as the oil I drained the first time. Oh well oil is recycled and it is cheap.

 

Hmmmmmm. That could account for it too because my new (30,000 mile) motor that doesn't reak has new injectors in it.

 

Would be interesting to test oil from non stinkers. I remember a lot of tests in the past, and most all had higher than 2% dilution.

 

I can smell the difference between changing oil every 1k and every 2k. The oil that has seen 2k miles smells like fuel, the oil that's seen 1k doesn't. I know this isn't very scientific, but it's the best I've got for now. I'm using cheapo Chevron 10w30 oil bought at Costco, by the way. I usually change it every 1k.

Looks like I've got another couple projects this winter break: change the oil twice in the same week, and look into having the injectors serviced.

 

I think it would be interested to run an electric vacuum pump for crank case vent that goes to a catch can then to atmosphere.

I've talked to a few people that run a catch can and most of them say that the majority of what it catches is fuel. I think its from very heavy vapor that gets in the crank case then eventually turns to liquid when it cools. If you had a catch can the vapor would go there then turn to fuel. That is the only thing I can think of because some have reported having nothing but liquid fuel in the catch can and if the fuel was entering the pan in its liquid state it would mix with oil and never go to the catch can. For it to be pure fuel it would have to go to the can as a vapor then turn to liquid as it cools inside the can.

Also, the reason I said using a vacuum pump is because you have to vent the catch can...a lot of people vent to the intake but then your diluting your charge air big time and going to lower VE. If you vent to atmosphere then there is nothing to suck on the crank case and bring it to vacuum. If you run a vacuum pump your going to have a crank case under vacuum so your turbos can drain better and in addition your going to get more of the vapors out of it. Then you can run the can to atmosphere.

If you do a search its not uncommon for V8 cars and many other race cars to run a vacuum pump when they go forced induction for this reason.

Stephen

 

I'll do this, I need too and my first born motor is approaching 3k (just changed the oil when purge solenoid went back in)...It'll take me a few weeks to rack up miles, but plan to drive to Louisiana for xmas (600mi one way)

other than that most miles are hard driven.

where to send oil?


*subscribed to thread for rememberance

 

first time I change the oil in the car it had such a strong scent of gas, I changed the oil after a thousand miles and scent was a lot weaker than the first time...

 

My car had ~45K miles on it when I started testing IIRC, started in 1999 or so. If the injectors are leaking badly after that few miles then we have bigger problems.

 

My can only catches during hard cornering and high rpms at de events. The catch looks like thinned oil, maybe 20% fuel on my fresh oil charge. I would say fuel vapors purge through continuously, and get mixed with percolating oil in fill tube at high-g rights. At least in my case, suggests rotor side seal leak, vs FI leak, although I value Cam and Howard's opinions.

If the dilution is blow-by related, not sure vac pump would prevent vapors from mixing with return oil dripping back to sump from bearings, rotors, etc.

A better purge would help. Stock PCV will take excess air from sump, but will also just bypass sump due to other vent line to same oil filler neck location. Never purges sump with clean air. A small air pump could draw filtered air into the crankcase, away from the filler neck (ex: front cover), triggered by boost, wot, etc. Vapor could be returned thru catch can to existing turbo inlet point ...... easier to just do frequent oil changes!

 

That would be me . An improperly clearanced motor definitely won't help things.

Fyi, I am now running the Idemitsu oil, and am happy with it's performance thus far.

 

So yeah, Goodfella, I remember it was you going over the clearancing issue on the side seals, and how you made yours to be exactly as long as the grooves in the side, yes, rather than shorter? After some miles on your engine, do you still have low gas smell?

My rebuild from Pineapple has had bad gas smell after only 1500 miles, right from the get go too. Way I figure it, maybe the turbos won't coke as soon, right? Right? Sigh... at least it runs nicely....

 

for all those who say their "exacting tolerances" reduced or essentially eliminated fuel dilution, I want to see the PROOF....I ain't buyin' it....a nose test is highly subjective, maybe the wind was blowing the wrong way or maybe your had a sinus infection that day and didn't realize it

let's see the the analytical data boys....unless then I'm throwing the flag

 

That's a hell of alot of trouble to go to just to impress some lone gringo. Why don't you go ride your bike into the nearest lake of holy water ?

 

LOL

it's only a $30 test ain't it?

 

It is also very common on V8 race cars even without forced induction. Very high compression engines create very high cylinder pressures similar to forced induction. I have a crankcase evacuation system on my NA V8 (~14:1 CR) in my Nova. You tend to get a little better ring seal when the crankcase is under a slight vacuum. It improves performance, keeps fuel out of the oil, and prevents that milky white stuff (condensation) common to rotaries.

I have also seen people use smog pumps as crankcase evacuation pumps. They seem to work relatively well, and I have heard that this is a trick that NASCAR engine builders have used. And all of you thought that the air pump was good for nothing but mooing...