Viscosity after fuel contamination?

[Eiron]

OK, I've been wondering about these questions for a while, & the posts in my last question beg me to finally ask: 1) What percentage of fuel creates x change in viscosity? 2) At what percentage value can you first detect any viscosity change? 3) At what point does fuel contamination negatively affect engine oil lubricity? 4) What percentage value is so great that you wouldn't want to use the oil any longer? 5) Can viscosity actually increase by way of fuel contamination?

 

[sbc350gearhead]

Can I add a question? Are the effects of fuel contamination the same, regardless of base oil?

 

[labman]

I don't have any real numbers. You may want to look at your own UOA's or ones posted here. Fuel will reduce the viscosity very quickly. Gasoline is largely chemically the same as dino, and will lubricate, but has very poor film strength. Second post. Like dissolves like. The more like, the faster the viscosity will go down. The ester based synthetics should be slightly more resistant to dilution. Diesel being thicker than gasoline will not thin oils as quickly. Getting much of either in any oil will dramatically reduce the viscosity.

 

[Eiron]

sbc, No problem adding questions, thanks! labman, I agree, but how quickly? How much does each 1% affect the oil? Or each 0.5%? (Sorry, I know you don't have the numbers.) My own UOA is of no help, because the lab doesn't even begin listing fuel until 4%. The lab says lubricity's not affected before then, but folks here have said that's rediculous. The trouble is, nobody's providing any data. Thanks for the help!

 

[Patman]

Here is some interesting data from two of my UOAs. Both were using Schaeffer Supreme 10w30, but the first one was during the winter with 1% fuel, the second one was during the spring/summer, with 0% fuel: 4400 miles, 1% fuel, oxidation 51%, viscosity of 10.1 cst 4800 miles, 0% fuel, oxidation 46%, viscosity of 10.3 cst I figured 1% fuel would have a higher thinning rate here. I'm pretty sure both intervals were with oil from the same case too, so they should've been the same batch number, and the same starting viscosity.

 

[MolaKule]

"1) What percentage of fuel creates x change in viscosity? I would say that you would have to have approx. 10% fuel dilution before you saw any viscosity reduction. "2) At what percentage value can you first detect any viscosity change?" Between 5% and 10%. "3) At what point does fuel contamination negatively affect engine oil lubricity?" Anything over 10%, when you see viscosity decrease since lubricity is reduced. "4) What percentage value is so great that you wouldn't want to use the oil any longer?" > = 25% "5) Can viscosity actually increase by way of fuel contamination?" If fuel burns only partially soot will form and viscosity will increase.

 

[MolaKule]

A 2 cSt reduction in a 40 weight oil orginally at 17 cSt still gives you a 40 weight oil even at 15 cSt. Now if you're at 14 cSt and you go to 12 cSt, then yes there would be a one SAE weight grade reduction. I would say that much depends on the oil formulation. [ September 03, 2003, 04:13 PM: Message edited by: MolaKule ]

 

[pinoy99]

Just trying to apply this case to my situation;so, in general <=2% of fuel dilution for a 30 - 40 weight oil used for 3.5 - 5k miles is not a major concern then?

 

[Robbie Alexander]

quote:

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Originally posted by Eiron: OK, I've been wondering about these questions for a while, & the posts in my last question beg me to finally ask: ---- Me too: ---- ---- 1) What percentage of fuel creates x change in viscosity? -- I donno, but on one car I had a problem with some computer chip or relay, I don't recall but I had a rough time for a few months with it stalling and not starting and spent around 5,000 in repairs and tows... All during this time I had problems with Fuel Dillution, and I think if my poor memory serves me, I saw some change either 1 or 1.5% and it went as high as I think 6 or 8% where they warned me I think after 2% but told me since the usual limit was 2 and I was having problems, that I shouldn't worry about any Real problems til I think they said 4-5% but not to push it, anyhow it(FD) jumped so fast between ???--donno 2.5-> 7.5 -8 in about ???-500-1000 miles, the new oil change was I think just under 2% and it rose high to 5-6% in something like 1200 miles (this was with oil I was doing 16-20K before), anyway, the details are fuzzy, but I had a lot of problems with it til they fixed it, and a few weeks later my wife total-ed it |-] Somewhere in there a mechanic told me it could explode, I don't know if he was serious or not. ---- 2) At what percentage value can you first detect any viscosity change? I would guess around 1%, and I suppose this is the importance of regular oil testing-to know and to have the potential to save on repairs. ---- 3) At what point does fuel contamination negatively affect engine oil lubricity? I would guess again at 2%+ ---- 4) What percentage value is so great that you wouldn't want to use the oil any longer? I would guess 4% with problems you are trying to fix and 2% when you have no known problems. --- 5) Can viscosity actually increase by way of fuel contamination?

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???? donno, didn't pay close enough attention. This is what oil testing is about; detecting minor problems (usually before you know they are present) and correcting them before they become costly failures. Only through TREND oil analysis can this be done, and it takes a series of runs, say 3 or 4 in order to have something to look at.

 

[MolaKule]

pinoy, Correct. I don't think it's that great of an issue at your levels.

 

[friendly_jacek]

Hi, I my experience, 4% fuel produced almost 2 cst decrease (SAE40 --> high SAE30).

 

[Eiron]

Thanks guys! I figgerd there was somebody among us who could lay out the data, & was hoping this post would catch their eye. To MolaKule: The info you've provided is exactly what I was looking for. The ability of motor oil to sustain such a high level of fuel contamination really surprises me. I was guessing it to be more than commonly worried about, but not anything to that extent! This definitely relaxes my "worry-quotient" when contemplating my own (future) UOAs.

 

[Robbie Alexander]

quote:

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Originally posted by MolaKule: "4) What percentage value is so great that you wouldn't want to use the oil any longer?" > = 25%

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What? greater than 25%... Is that what you mean 25%? Is this for Gasoline only? do you know what is it for diesel? How on earth is the oil going to function properly, wouldn't it be too thin?