Fuel dilution harm and remedies

[Shannow]

Best that I've been able to find so far is that HTHS gets affected at about half the percentage loss of KV100, regardless of the mechanism (typically). And fuel dilution typically helps things like MRV and CCS while it is there as fuel.

I tried ages ago to try to model at least the KV100 changes with fuel dilution% as a "mix", and it's really not doable/that simple, as different oils and chemistries respond differently...e.g. VII molecules are more "active" in thinner basestocks than thicker, as they are sheared less in action.

Other characteristics of particular oils make the results non predictable also. (This paper is for diesel, and biofuels and blends, but what happens with one oil can be completely different to another.

http://www.transport-research.info/sites...vity_Report.pdf

As to "burning off" fuel with highway operation, here's a distillation curve of some gasoline and alcohol components. So clearly, SOME of the fuel has to stay, regardless of sump temperatures.

Best defence is Miyagi's "best defence is no be there"

Another brief paper FYI
http://hrcak.srce.hr/file/75680

 

[Ducked]

I said all that in the other thread.

https://bobistheoilguy.com/forums/ubbthreads.php/topics/4211628

Mind you, unlike you, I was guessing

 

[FCD]

I think one of the first 20W-60 Oils was made in order to compensate for fuel dilution, certainly for example in a high mileage old Alfa twin cam motor with twin webers i wouldn't mind using a 20W-60 , originally they specified 10W-50

 

[fdcg27]

Originally Posted By: Danh
Originally Posted By: KingCake
Best way to combat fuel dilution is to take it out on the interstate for a 30-60 minute romp now and then. The fuel will bake off, get sucked in through the PCV system and burned.


Yeah, except in my case the >5% dilution samples were drawn immediately after a 400 mile mostly-Interstate highway run. Three times. Curious, isn't it?


In the other thread you wrote:

John Deere says this about how to prevent fuel dilution:

1) "Stay away from operating vehicle in short trips with light engine loads. The reason for this is that the engine oil temperature does not get hot enough to boil off fuel and moisture in the crankcase. Running the engine at operating temperature and under load for long enough periods will allow the fuel to evaporate."

John Deere's other suggestion if to use high quality, fresh fuel.

Maybe John Deere has it all wrong, but they seem like a credible source to me.

You still see significant fuel content after a long run most of which would have been at pretty lean conditions. Clearly, fuel does not readily evaporate from the oil once there by whatever mechanism. It is as I and others wrote in the other thread. Fuel is solvent in the oil so is not easily and never completely evaporated out.

 

[Ducked]

Originally Posted By: fdcg27
Fuel is solvent in the oil so is not easily and never completely evaporated out.


No arguing with the observational bit, but I doubt solvation is the whole story as to the mechanism.

If you put, say, ether in your sump the oil is very soluable in it, but I'd think the ether will boil off pretty quickly. BP 35 (C. I don't F-about)

Conversely, if you put, say, mercury in your sump, the oil isn't very soluable in it, but I'd think it'll boil off fairly slowly. BP 357 (C. I don't F-about).

Please note I am not suggesting using mercury as a viscosity improver.

 

[bmwpowere36m3]

Originally Posted By: Ducked
Originally Posted By: fdcg27
Fuel is solvent in the oil so is not easily and never completely evaporated out.


No arguing with the observational bit, but I doubt solvation is the whole story as to the mechanism.

If you put, say, ether in your sump the oil is very soluable in it, but I'd think the ether will boil off pretty quickly. BP 35 (C. I don't F-about)

Conversely, if you put, say, mercury in your sump, the oil isn't very soluable in it, but I'd think it'll boil off fairly slowly. BP 357 (C. I don't F-about).

Please note I am not suggesting using mercury as a viscosity improver.


Isn't that how distillation of crude works... heat it up and the various bits separate based on volatility.

 

[kschachn]

Originally Posted By: bmwpowere36m3
Isn't that how distillation of crude works... heat it up and the various bits separate based on volatility.


Sure, but only if the fractions have somewhere to go outside of the system. If they are being condensed and re-introduced into the oil then it's more like reflux condensation than distillation.

 

[SonofJoe]

Originally Posted By: kschachn
Originally Posted By: bmwpowere36m3
Isn't that how distillation of crude works... heat it up and the various bits separate based on volatility.


Sure, but only if the fractions have somewhere to go outside of the system. If they are being condensed and re-introduced into the oil then it's more like reflux condensation than distillation.


What happens in the crankcase is a complex but very inefficient form of extractive distillation. You have two similar hydrocarbon liquid phases (lube and fuel) plus one dissimilar liquid phase (condensed water) and one constantly renewed gas phase (you can aggregate the blow-by and purge air). It's probably fair to assume (because the crankcase is a violently mixed system) that the gas that leaves the crankcase into the PCV system is in vapour-liquid equilibrium with the liquid phase (so it will contain some fuel, some water and a teeny weeny bit of lube). Changing the engine conditions (eg higher oil temp, higher blow-by rate & temp) will shift the equilibrium point to favour more fuel/water/oil being transferred. The problem with engines from a chemical engineer's perspective, is that there is no reflux stage. If there was, it would be much easier to rid the oil of fuel & water and keep lube oil out of the PCV system and creating subsequent downstream problems such as inlet valve and combustion chamber deposits.

 

[kschachn]

I guess I was just thinking of the engine as a whole, where there are surfaces (such as the valve covers) that are relatively cooler and would allow condensation to occur.

This may be a really ignorant question, but if it is really like distillation where exactly do the "lighter fractions" (whatever they may be) get out of the engine? From the PCV system into the combustion chamber and then out the exhaust system? I guess I was imagining some of them condensing and just recirculating in the oil.

Originally Posted By: SonofJoe
What happens in the crankcase is a complex but very inefficient form of extractive distillation. You have two similar hydrocarbon liquid phases (lube and fuel) plus one dissimilar liquid phase (condensed water) and one constantly renewed gas phase (you can aggregate the blow-by and purge air). It's probably fair to assume (because the crankcase is a violently mixed system) that the gas that leaves the crankcase into the PCV system is in vapour-liquid equilibrium with the liquid phase (so it will contain some fuel, some water and a teeny weeny bit of lube). Changing the engine conditions (eg higher oil temp, higher blow-by rate & temp) will shift the equilibrium point to favour more fuel/water/oil being transferred. The problem with engines from a chemical engineer's perspective, is that there is no reflux stage. If there was, it would be much easier to rid the oil of fuel & water and keep lube oil out of the PCV system and creating subsequent downstream problems such as inlet valve and combustion chamber deposits.

 

[bmwpowere36m3]

Originally Posted By: HKPolice
Gasoline vaporizes at low temps and goes through the PCV system causing carbon deposits on your intake valves. That is the main harm of high fuel dilution, nothing will show up in UOAs. Carbon deposits are unpredictable, some models start showing driveability problems after ~30K, other DI engines are less prone to deposits.


I'm thinking oil being recycled thru PCV...

 

[SonofJoe]

Originally Posted By: kschachn
I guess I was just thinking of the engine as a whole, where there are surfaces (such as the valve covers) that are relatively cooler and would allow condensation to occur.

This may be a really ignorant question, but if it is really like distillation where exactly do the "lighter fractions" (whatever they may be) get out of the engine? From the PCV system into the combustion chamber and then out the exhaust system? I guess I was imagining some of them condensing and just recirculating in the oil.

Originally Posted By: SonofJoe
What happens in the crankcase is a complex but very inefficient form of extractive distillation. You have two similar hydrocarbon liquid phases (lube and fuel) plus one dissimilar liquid phase (condensed water) and one constantly renewed gas phase (you can aggregate the blow-by and purge air). It's probably fair to assume (because the crankcase is a violently mixed system) that the gas that leaves the crankcase into the PCV system is in vapour-liquid equilibrium with the liquid phase (so it will contain some fuel, some water and a teeny weeny bit of lube). Changing the engine conditions (eg higher oil temp, higher blow-by rate & temp) will shift the equilibrium point to favour more fuel/water/oil being transferred. The problem with engines from a chemical engineer's perspective, is that there is no reflux stage. If there was, it would be much easier to rid the oil of fuel & water and keep lube oil out of the PCV system and creating subsequent downstream problems such as inlet valve and combustion chamber deposits.



Yes, it really is like distillation and yes, oil leaving the crankcase through the PCV system does end up getting burnt and going down the exhaust pipe (although these days, because the exhaust passes through the cat, you don't see the tell-tale puff of blue smoke that you used to see in the old days).

The PCV system was always designed to route condensed water and fuel back to the combustion chambers but these days, with oils being thinner & lighter, sumps bring smaller and engines running both looser and hotter (creating hotter blow-by and more of it) you see more oil being routed through the PCV. It's the lightest fractions of the oil than preferentially evaporate into the blow-by and this usually means the lightest parts of the lightest base oil (the 'front-end' of the oil in oil-speak). Additives tend to be relatively heavy and tend to stay in the sump.

This is often seen on the industry standard Sequence IIIG engine test. This test runs the oil at 150C for 100 hours with the engine at full pelt. In theory the test is supposed to test for viscosity increase as a result of oil oxidation. However part (sometimes ALL!) of the rise in oil viscosity is due to oil distillation.

The language is a bit impenetrable but here is one of Oronite's oil formulators talking about both the Sequence IIIG and the new IIIG test that will replace it in GF-6. He talks about oil concentration (distillation) and its impact on viscosity increase.

https://youtu.be/gdmC9nPBMEw

 

[kschachn]

Thanks for the explanation.

 

[carock]

1. Fix the cause of fuel dilution? 5% seems very high, certainly out of my limited experience range.
2. Change oil to different brand?
3. Add TC-W3 marine outboard oil to gasoline? This has worked to solve oil consumption problems, maybe it will work for fuel dilution.

 

[Danh]

Originally Posted By: carock
1. Fix the cause of fuel dilution? 5% seems very high, certainly out of my limited experience range.
2. Change oil to different brand?
3. Add TC-W3 marine outboard oil to gasoline? This has worked to solve oil consumption problems, maybe it will work for fuel dilution.


Thanks for the interest. My dealer can't find anything wrong, even after discussing possible causes with Honda's tech department. Honda is being enigmatic not saying if: a) thIs is normal/typical/as designed/harmless or b) this is not typical but we can't figure out what's wrong or c) we have no faith in the UOAs that show the fuel dilution. So, barring driveability symptoms or something catastrophic, I may be on my own.

Don't know that changing the oil brand would make a difference. It wouldn't change the amount of fuel entering the oil and it seems my Mobil1 is producing decent wear numbers despite the dilution.

I'll probably try a dose of Techron to see if it helps, but it seems unlikely fuel system deposits would be an issue after 15,000 miles, all on Top Tier fuel.