Oil/Fuel Dilution Concerns...

[Franko Manini]

I ran pennzoil ultra platinum 5w30 this summer. Only thing I noticed was a quieter engine. Back to pennzoil up 0w20 for the winter.

I think that's reasonable, especially if you don't have a fuel dilution issue. See my reply to @MustardTiger for more detail.

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[Franko Manini]

Here is my last two changes. Notice the first change was 396 miles, column to the right. Fuel dilution much better and contributed to proper driving to seat the rings.

Tim, you're 100% correct. fuel dilution will be high until the rings seat properly. with only 0.6% fuel in oil after 2700 miles I think you will probably be just fine going forward unless your driving habits or environment change. That can also influence the results.

What did you change in your driving habits during the break-in period?

 

[TimC.]

After the first 396 miles I conducted multiple dyno simulations driving in manual up hill and full rpm red line. You must be smooth on the throttle just as if you were in the dyno room. Frequency was 2-3 times per week until the 2700 mile mark. I let oil analysis determine when I stop this. I know my piston rings are sealing quit nicely now.

 

[MustardTiger]

Checked my oil temperatures while driving highway yesterday. After 20 mins it settled on about 198-200f. Doing some hard pulls from 3k-redline, in 4th, up some grades, I got it to 210f. But cruising speed it’s kept close to 200f. Ambient temps were 39f.

So in reality then, even at highway driving, any fuel in the oil will barely begin to evaporate at those oil temps. I’ll be curious to see the engine oil temps when it’s -30c

 

[Franko Manini]

Checked my oil temperatures while driving highway yesterday. After 20 mins it settled on about 198-200f. Doing some hard pulls from 3k-redline, in 4th, up some grades, I got it to 210f. But cruising speed it’s kept close to 200f. Ambient temps were 39f.

So in reality then, even at highway driving, any fuel in the oil will barely begin to evaporate at those oil temps. I’ll be curious to see the engine oil temps when it’s -30c

I apologize in advance, but being Canadian, and a science guy, I use Celsius, so if you wouldn't mind doing the conversion on your own, I'd appreciate it!

It's not quite as simple as reaching a given temp for the boiling point of gasoline and then all the fuel in the oil evaporates. Gasoline is made up of a lot of different hydrocarbons (often called fractions), but to simply things, we can categorize them into carbon chain length (yes, I know some are branched, some are cyclic, etc.) and they all have different boiling points. The shorter the chain (less carbon atoms) the lower the boiling point. The mixture that makes up gasoline also changes from season to season (winter and summer gas). Winter fuels have more C4 to lower the vapour point, summer blends have more C10 - C12 to increase vapour point.

The lower the carbon count the lower the boiling point. So when you're running at 80-95C most of the shorter fractions (which are the really bad ones for fuel dilution) evaporate relatively quickly. The longer chain molecules will take longer to evaporate at that temperature. Note that just because the boiling point of something is say 90 degrees C, doesn't mean none if it will evaporate at 80C. In fact, some of it will evaporate at the lower temperature ranges. But the MAJORITY will require reaching the boiling point. Here is a general makeup of gasoline and the approximate boiling point of each fraction:

C4 hydrocarbons
Boiling range: roughly –12°C to –1°C

C5 hydrocarbons
Boiling range: roughly 36°C to 41°C

C6 hydrocarbons
Boiling range: roughly 60°C to 71°C

C7 hydrocarbons
Boiling range: roughly 90°C to 100°C

C8 hydrocarbons (octanes)
Boiling range: roughly 125°C to 150°C

C9 hydrocarbons (often cyclics)
Boiling range: roughly 150°C to 180°C

C10 to C11 hydrocarbons
Boiling range: roughly 180°C to 200°C

Note that the operating environment of the oil is OFTEN, not always, under a slight vacuum, and that REDUCES the boiling point of the fuel, so the temperatures listed above will be higher than real-world numbers. So at 80-95 degrees (which is the observed operating temp of the oil for my use case) you're probably getting rid of most fractions C4 and C5. C6 and C7 will take longer to evaporate at normal operating temperatures. Those from C8 to C11 are a smaller part of dilution, but once in the oil they are stubborn.

Because winter fuel has more of the C4 and C5 fractions to help with cold starts, and the environment is cold, meaning the oil takes longer to heat up and - if it's really cold - may actually be at a lower operating temperature, winter is worse for fuel dilution.

 

[MustardTiger]

@Franko Manini thanks for the detailed response! Canadian here too, I just listed in F because it’s more common for the general audience here. So all in all, sounds like oil dilution will be more of an issue in the winter…which is why I’m noticing it now vs the absence during the summer.

Moral of the story…if you primarily do short trips in the winter, cut your OCI in half!

 

[Franko Manini]

Moral of the story…if you primarily do short trips in the winter, cut your OCI in half!

Well, shorten it anyway. This is where UOA can really help inform you of intervals.

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