Oil analysis on my second oil change showed >2.5% fuel with around 1500 miles or thereabouts.

Direct injection engines are prone to dilution. The problem with the Z06 is the fuel system. If interested, I can go into detail.....

 

Those LT6 engine failures/problems, how common are they? Is it a very small % or?

 

Fuel diluters: what r ur oil temps? Ambient operating temps?

 

In my ad-hoc research the driving conditions prior to sampling and oil collection technique will affect the fuel dilution percentage. If you do an internet search for "C8 Corvette Z06 Blackstone oil analysis" you should find some good information on multiple samples analysis from different people. There is also a discussion of how driving and sampling conditions affect the fuel-in-oil percentage.
Here is a short version of my theory:

• Direct Injection startup, especially cold, uses a lot of extra fuel to "light-off" the combustion. Some of this excess fuel is not burned
• Some gasoline will migrate into the crankcase and oil under overly rich conditions when the fuel is not completely burned
• Normal light-duty driving of the Z06 does not heat the oil to full operating temperature. Typically less than 170 degrees F. At this low temperature it will take longer for any fuel in the oil from start-up to evaporate.
• Many Z06s are driven for lots of consecutive short trips without getting the oil above 170 F. This can cause more fuel to accumulate in the oil.
• Oil lab companies like Blackstone recommend the oil be sampled at operating temperature
• Samples taken after multiple short trips without a long run at 170 degrees F, or hard run at full operating temperature of 190+ degrees F for at lease 30 minutes will show higher % fuel-in-oil.

I have preliminarily confirmed (though not enough samples to be statistically significant) this theory by comparing several analysis reports. The ones with higher fuel-in-oil percentage of 0.5-3% were typically sampled from the drained oil without a long run at 160-170 or a shorter run at 190+. The ones with a lower percentage of trace (TR) to <0.5% were sampled with a suction pump from the oil tank, or the oil drain stream, immediately after a long run at 160-170 or a shorter run at 190+, without restarting.
I believe even one start-up just prior to the oil change can increase the fuel-in-oil slightly.
For reference 8 quarts is 256 ounces, so 1% fuel-in-oil would be ~2.6 ounces gasoline to 256 ounces oil.

Conclusion:
Smell -- Most people can smell gasoline at less than 0.5 parts per million (PPM) in air. That's 0.0000005 to 1, or 0.00005%. It takes very little gasoline present to smell it, so smell is not a reliable tool.
Dipstick level -- In my experience the dipstick level will vary depending on operating conditions so a higher than normal level may-or-may not indicate fuel in oil.
Oil analysis reports -- To use and compare analysis reports for fuel-in-oil percentage, the sampling method and driving conditions prior to the collection must be known.

 

One YouTuber was saying that there are 2 high pressure fuel pumps, one for each bank. These are powered by the cam. These just multiply the lower pressure feed, there is only one low pressure pump. The theory is that if you get cavitation on one bank, the low pressure pump adds pressure so the bank with cavitation doesn't run lean. The problem is that the second bank now will run super rich and then you end up with fuel in the oil.

Seems like it could be easy to fix, but I know nothing of fuel systems.

 

Yikes that's high fuel in only 1500mi. When you are pulling your sample to send is the oil cold or do you drive it before changing it and get it nice and hot?

 

They need two low pressure pumps

 

The only purpose of the low pressure pump is to get the fuel from the tank to the engine. The high pressure pump increases the pressure necessary for DI.

 

Negative. Two high pressure pumps at the engine (one per bank) and one single low pressure pump in the tank. Its even the same low pressure pump as the LT2 cars.

 

I’m not sure I accept fuel dilution of the oil as a factor in engine failures. As an avid boater, I’ve owned 4 stroke Yamaha 4.2L v6 outboards that made oil like they’re directly connected to a Saudi oil well. 50 hours of run time and oil levels would be 3” past the high mark on the dipstick. We’re talking a quart of fuel in 7 quarts of oil. It’s been and continues to be a known issue with the engines. But it doesn’t kill them. Yamaha just tells customers to run wide open more often to seat the rings and remove oil if the level gets too high. Even the diluted oil at those levels of dilution provides enough lubrication to let those outboards run high rpm almost all the time.

 

The total runtime of a boat's engine is a tiny fraction of that compared to a car's engine. So not really a valid observation when we are talking longevity. If an issue surfaces in a car's engine at even a low 10,000 or 20,000 miles, you would never reach that runtime in a boat unless you used it everyday, which virtually no one does.

 

Why? The 2 high pressure pumps are inches from each other and connected to a common feed pump. How could one HP pump cavitate (insufficient inlet flow) and the other one not? Its not about 1 or 2 feed pumps, the HP pumps either have sufficient flow to keep the inlet fed, or they don't. Are you trying to say GM undersized the in tank pump and it cannot provide sufficient flow to the HP pumps? I think you will find the feed pump is specified with sufficient capacity overhead to properly feed the HP pumps.

Yes, fuel dilution is an issue but its not a need for 2 pumps vs 1.

 

There will never be any resolution to this argument because people put too much faith in what Chevy does. Forget the issue of one or two in tank pumps. When one bank runs super rich, why doesn't this set a diagnostic trouble code, aka check engine light? And, under the conditions where full voltage is commanded to the single lift pump in response to the control system chasing a lean condition, why does this not set a check engine light? Can someone inside GM answer this? It looks like the allowable window for errors in a host of the fueling parameters have been opened way up so as to be insignificant. Under these conditions, as such, you will never have a 'problem'.

 

How do you know one bank is running super rich while the other is not? How do you know the low pressure pump is hitting its limits?

 

Would be good to see some data logging on that.

 

Without getting into this which would create further controversy, lets look at something much simpler: On any of the cars - lets take south Florida where several cars went back to dealers with grossly overfilled oil sumps heavily diluted with fuel and where the dealers were instructed to simply drain out the excess, why is it none of these cars that had obvious issues - lets not even assume it was a fueling issue, why is it none of these cars set any codes? No codes at all. Explain this to me. I am not asking how the severe dilution happened. I am asking why a control system as sophisticated as the one used on the Z06 never recognized there was a serious deviation from normal engine operation. Tell me, I want to know.

 

Fuel rail pressure sensor is supposedly the cause of my Z’s problem. Cars still at dealership …. I still have NOT ever driven my Z yet 🧐


https://www.corvetteforum.com/forums...ick-it-up.html

 

And your car threw a code indicating a problem.

 

yup

 

Because there is no sensor that can sense this. The cars were running fine despite the diluted oil. I am not saying there is no problem because there is. Just that so many here think they know the whole issue and GM refuses to implement their simple fix. Its not so simple.