Fuel Dilution

[X49]

I've got a direct injection turbo engine that is known to have fairly high significant fuel dilution (Subaru FA20DIT).

What I want to know is whether fuel dilution trends upwards over long periods of time or whether fuel contamination will hit a certain percentage then maintain an equilibrium where fuel evaporates as quickly as it is introduced. In other words, will changing the oil more frequently prevent high levels of fuel dilution?

I've been looking for some good scientific papers that cover this but I haven't really found anything relevant.

 

[turtlevette]

Run e85 it'll flash off quicker.

 

[Rolla07]

Im no expert on the topic but ideally get the oil hot enough (avoid short trips). Doing a UOA is likely best to test and find out if your current habits result in fuel dilution in your oil.

 

[Quest]

did you perform a UOA to verify?

 

[Garak]

Originally Posted By: turtlevette
Run e85 it'll flash off quicker.

And the ethanol will deplete the TBN in short order.

 

[OneEyeJack]

A bit of fuel dilution now is not the real problem, for for a longer drive. The real problem is what happens in a few years when stuff starts wearing out and needs replacing. Sounds expensive.

 

[Greasymechtech]

I'm a short tripper and my car's dipstick makes oil constantly. I can also lower the oil level with a good 50 mile highway run. And, when the oil is diluted with fuel, it is very noticeably thinner when checking the cold oil level.

Hows that for a scientific paper?

If you're a short tripper, you need regular highway runs to evap that fuel. Another option is to change oil more frequently. And, I'd recommend a thicker oil.

GM's OLM reprogram hints at the issue with wear vs dilution vs interval vs ...

There are several bypass filters with 'heated' elements that cook and vent off the fuel vapors, moisture... Work great but not worth the investment for all.

And, you could always use the combination engine block heater and oil pan heater, to get vehicle up to temperature quicker.

Makes me wonder if I should use an oversized oil pan heater to boil off the fuel when vehicle is parked in the driveway. Wouldn't want to cook off the fuel in the garage and then light a pipe or cigar.

 

[redbone3]

I have a 2014 VW Passat gasser with a turbo. When the oil lubes the turbo it's gotta get hot. I wonder if that ameliorates fuel dilution from the direct injection???

 

[Rand]

Constant fuel dilution will "wear out" oil faster
It will cause changes to the oil that dont reverse simply by evaporation.
yes I used a generic term.

That all being said modern motor oil is good stuff and usually manufacturer oil change intervals are conservative.

If you short trip all winter its a good idea to follow the severe service interval even if you get a longer trip once a week.

 

[Pontual]

Originally Posted By: Garak
Originally Posted By: turtlevette
Run e85 it'll flash off quicker.

And the ethanol will deplete the TBN in short order.


Why? Ethanol has almost no Sulphur as opposed to gasoline, that has a lot. TBN should keep better.

 

[edhackett]

Originally Posted By: Pontual
Originally Posted By: Garak
Originally Posted By: turtlevette
Run e85 it'll flash off quicker.

And the ethanol will deplete the TBN in short order.


Why? Ethanol has almost no Sulphur as opposed to gasoline, that has a lot. TBN should keep better.

Here's the structure of an alcohol:

Here's the structure of an organic acid. One of the byproducts of incomplete combustion(oxidation) of alcohol is acid.

Ed

 

[BrocLuno]

The biggest problem with fuel dilution is increased cylinder wear. The fuel attacks the oil film on the cylinder wall before it gets to the crankcase... There is far more oil in the crankcase to absorb this dilution than there is on the cylinder walls and the ring pack.

I'd be doing 3K OCI's with synblend oils to get the diluted oils out of the system. Keep the crankcase full of "cleaner" oil on average ...

I don't know of a specific oil that resists fuel dilution better than others. But if it turns out it's a full syn, you have to weigh the cost of syn changes vs mileage with increasing dilution. My gut says more changes more often is better than running even full syn for longer ...

 

[X49]

Thanks for all the responses. I haven't done a UOA yet, but they typically measure 1-4% dilution in these engines. TBN never seems to be an issue with
I do take a lot of short trips, but plan on using a block heater religiously in the winter.

I'm not too worried about low viscosity since the car's got and oil cooler and my oil temps never get above 100 degrees C, but I'd still love to see how fuel dilution trends over time, for curiosity's sake.

I might end up taking a few samples in a single change interval just to see.

 

[bluesubie]

I agree with BrocLuno on the short OCI. Does Canada still recommend the severe service interval for all Subaru's? Based on the DIT UOA's on subaruforester.org and nasioc, I think I'd be going with a low SAPS ACEA C3 oil changed at a maximum of 8k km's or 5k km's for a GF5 oil.

A few samples during a single oci would be helpful, but I don't think there would be that much difference in fuel levels from what I've seen. Fuel doesn't seem to burn off in these engines with longer trips like it does in port injected engines. The 2015 WRX thread on nasioc in the Service & Maintenance forum and the 2.0 DIT uoa sticky at subaruforester.org would be good places to see some uoa's.

And if you do uoa's, I would recommend a lab that tests for fuel using gas chromatography. This guy appears to be the Subaru DIT fuel dilution champion.

With all that said, the WRX's and Forester XT's seem to be doing ok with fuel contamination and 20 grade oil! So far.

 

[X49]

The Canadian manual actually doesn't mention severe service intervals. 10,000km or 6 months is required. I plan to do 6-7k km changes with Pennzoil Platinum 5W-30. I want to stick with a warranty-approved GF-5 oil.

Looking at UOA's of this oil and comparing the viscosity to some fuel dilution charts, it doesn't seem to shear down to lower viscosity at all. All viscosity loss can be explained by fuel dilution. This is why I'm interested in whether fuel trends upward over time. If it doesn't, there's not much point in going with short intervals.

 

[Pontual]

Originally Posted By: edhackett
Originally Posted By: Pontual
Originally Posted By: Garak
Originally Posted By: turtlevette
Run e85 it'll flash off quicker.

And the ethanol will deplete the TBN in short order.


Why? Ethanol has almost no Sulphur as opposed to gasoline, that has a lot. TBN should keep better.

Here's the structure of an alcohol:

Here's the structure of an organic acid. One of the byproducts of incomplete combustion(oxidation) of alcohol is acid.

Ed


Right Ed. Would you be kind enough to show the "between structures" (ethanol oxidizing to acid, and if that resulant acidification is way more than gasoline, causing depletion of the TBN quickier) chemical reaction formula?