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post #1 of 17 (permalink) Old 02-09-2019 Thread Starter
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gas in oil

It seems that there might be a problem with direct fuel injection engines in general with regard to excessive gas making it into the engine oil. This has surfaced in Hondas and Subarus with direct injection. Has this been an issue with the Mustang DI engines? A quick check is to smell the oil on your dipstick for a fuel smell. Some have even experienced an increase in the oil level over time as registered on the dipstick.



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post #2 of 17 (permalink) Old 02-09-2019
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It seems that there might be a problem with direct fuel injection engines in general with regard to excessive gas making it into the engine oil. This has surfaced in Hondas and Subarus with direct injection. Has this been an issue with the Mustang DI engines? A quick check is to smell the oil on your dipstick for a fuel smell. Some have even experienced an increase in the oil level over time as registered on the dipstick.
I am unable to equate this problem with EFI; would not carburetors have contributed an even greater degree of it? Starting cold, for example, with whom knows how much liquid fuel being washed down off cylinder walls......

Just wondering!

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post #3 of 17 (permalink) Old 02-09-2019 Thread Starter
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I am unable to equate this problem with EFI; would not carburetors have contributed an even greater degree of it? Starting cold, for example, with whom knows how much liquid fuel being washed down off cylinder walls......

Just wondering!
EFI includes port injection and more recently direct injection where gas is squirted directly into the cylinder rather that having to pass past an open intake valve as with older engines.


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post #4 of 17 (permalink) Old 02-09-2019
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In short, yes...a common issue with all DI systems and especially pops up when there are multiple cold starts in cold climates and the engine oil does not reach 150 F for 15 minutes.

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post #5 of 17 (permalink) Old 02-12-2019
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I wonder if it will effect the newer mustang gt sense they have both multi port and direct injection.
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post #6 of 17 (permalink) Old 02-12-2019 Thread Starter
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I wonder if it will effect the newer mustang gt sense they have both multi port and direct injection.
Since my engine is DI and my driving is 90% city, my oil service is classified as "severe" hence a 3K mile or 3 month oil change interval is recommended. That should help prevent damage to the engine caused by oil degraded by gas.


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post #7 of 17 (permalink) Old 02-23-2019
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The Coyote 5.0 V8 is a hybrid engine with BOTH direct and port injection. Neither squirts fuel into the oil, k=just the cylinder. If fuel is getting from the cylinder into the oil, then you have a failure of the compression or oil rings. It's about the only way for fuel to get to the crankcase. The valves are overhead cam type, so i ois unlikely they are the source of fuel, but it COULD be. Maybe an intake valve is leaking badly, bringing too much fuel into the a cylinder.

Probably needs a teardown to confirm the source. Good luck!
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post #8 of 17 (permalink) Old 02-24-2019
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The Coyote 5.0 V8 is a hybrid engine with BOTH direct and port injection. Neither squirts fuel into the oil, k=just the cylinder. If fuel is getting from the cylinder into the oil, then you have a failure of the compression or oil rings. It's about the only way for fuel to get to the crankcase. The valves are overhead cam type, so i ois unlikely they are the source of fuel, but it COULD be. Maybe an intake valve is leaking badly, bringing too much fuel into the a cylinder.

Probably needs a teardown to confirm the source. Good luck!

I don't think the original poster said he had a problem with gas in oil. He just wanted to know if anyone else has noticed if this happens with Direct Fuel Injection Mustangs like it does with Hondas and Subarus. I have yet to see a poster in this thread saying they have the problem with gas in oil.


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post #9 of 17 (permalink) Old 02-24-2019
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You'll get gas in the oil in any type of fuel system if the engine never gets up to operating temperature with multiple starts. And it doesn't matter the make/model of car. Excessive gas in the oil can come from tune specs, internal fuel leaks, leaking injectors, etc. but will be noticed by poor performance. Since gas is a solvent and blends with oil, the oil/gas mix will have to be warm for the gas to evaporate in a short time. If you let a gas/oil mix sit undisturbed, the gas will slowly separate and evaporate.
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post #10 of 17 (permalink) Old 02-25-2019 Thread Starter
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You'll get gas in the oil in any type of fuel system if the engine never gets up to operating temperature with multiple starts. And it doesn't matter the make/model of car. Excessive gas in the oil can come from tune specs, internal fuel leaks, leaking injectors, etc. but will be noticed by poor performance. Since gas is a solvent and blends with oil, the oil/gas mix will have to be warm for the gas to evaporate in a short time. If you let a gas/oil mix sit undisturbed, the gas will slowly separate and evaporate.
Although my oil has a slight gas smell, I doubt much unburned gas gets blown past the rings into the oil as evidenced by its apparent negligible oil "usage" between changes. But to mitigate any negative consequences of this phenomenon I am using an oil with a very low volatility index (NOACK rating) which will also address excessive crud buildup on the intake valves. The Oil is Valvoline 5W20 full synthetic. It's NOACK rating is at 7.6 vs. Mobil 1 at 10.


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I want to tag onto the comments and add that some fuel bypass into the crankcase is not unusual. However, E15 and E85 will exacerbate fuel intrusion into the crankcase. So, if anyone uses that on a recurring basis in a vehicle they can expect a little more bypass of fuel. Just shorten oil change intervals.

Just to clarify: anything over 15% ethanol (E15) is not suggested in a non-flex vehicle but some locations have percentages over 15% that are not true 85% ethanol but can do damage in a non-flex fuel vehicle. I believe E85 includes any fuel with ethanol content above 50%.

Addressing the topic about DFI and oil level increase in the engine: I do not think there is any correlation between Direct Fuel Injection and fuel intrusion in the crankcase causing fluid levels to increase on the dip stick. If the contamination of fuel into the crankcase is that much to see a fluid level increase then it would be enough to substantially thin the oil causing oil consumption which would then be indicated by lower fluid level on the dip stick.

FYI - the 2018 5.0 is now a 10 qt system due to changes in the fuel delivery system resulting in more low-end torque and rpm which adds more demand on the lube system to lubricate and keep internals under control.

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post #12 of 17 (permalink) Old 02-25-2019 Thread Starter
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I want to tag onto the comments and add that some fuel bypass into the crankcase is not unusual. However, E15 and E85 will exacerbate fuel intrusion into the crankcase. So, if anyone uses that on a recurring basis in a vehicle they can expect a little more bypass of fuel. Just shorten oil change intervals.
Fortunately in the Tulsa area tier 1 ethanol-free gas is readily available which is what I use (Sinclair or QuikTrip). As far as the OCI I am doing 3K miles or 3 month interval which is what the manufacturer recommends for "severe" service (constant short trip city driving). I hate throwing away oil in that short an interval, but mitigation of any GDI collateral damage is more important and cheaper in the long run.
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The Coyote 5.0 V8 is a hybrid engine with BOTH direct and port injection. Neither squirts fuel into the oil, k=just the cylinder. If fuel is getting from the cylinder into the oil, then you have a failure of the compression or oil rings.


I short, no....the rings are designed to seal against vapor, not liquid as the thickness of gas is much thinner than oil it will slip by the rings..... a very common event with DI engines during startup in cold weather when an increased amount of fuel is injected into the cylinder at startup (although small, it happens...and well publicized in journals)
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I'm guessing it probably also has to do with the extreme high pressures used to squirt the gas in, which pushes it past the rings under the right conditions

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I'm guessing it probably also has to do with the extreme high pressures used to squirt the gas in, which pushes it past the rings under the right conditions
You may be right...myself, I'm thinking more in line with because of the colder conditions the fuel condenses into droplets much faster and some slips past the rings during the upstroke on compression before ignition.


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