Interpreting fuel dilution in UOA

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Will the fuel dilution number in a UOA vary depending on when you take a sample?

For example, taking the sample after weeks of short trips vs taking the sample after a long trip that took place after weeks of short trips.

If so ie if the long trip ends up hiding the fuel dilution, what else in the UOA might show the effects of fuel dilution? Accelerated TBN depletion?
 
It makes if you are going to get a UOA to do it in the middle of a typical drive for you. and not after the one 4 hr highway trip you take once a year.
more fuel means lower flashpoint for sure
 
+1

No matter what, fuel does not make a lubricant better. Any amount is not good. Some might claim that a small amount is acceptable or won't do any harm but I don't think so.

I have an 84 Honda with a lot of miles on it, with a carburetor and have never had any fuel in the oil on a UOA.
 
Originally Posted By: OneEyeJack
+1

No matter what, fuel does not make a lubricant better. Any amount is not good. Some might claim that a small amount is acceptable or won't do any harm but I don't think so.

I have an 84 Honda with a lot of miles on it, with a carburetor and have never had any fuel in the oil on a UOA.



We have ample data posted here in the uoa section that proves some fuel dilution is harmless.

So what you "think" isn't consistent with the data that is posted,and proven.
Unless you have data your thoughts mean nothing
Share them with jack handy,til then unless you can prove your point perhaps keep those thoughts to yourself. It doesn't help anything to post,and believe,stuff that just ain't true.


Yes Benito. You are correct. A ton of short tripping when th oil doesn't maintain operating temp for long means any fuel that passes by the rings cannot evorate,so it will accumulate in the crankcase and results can be skewed by it.
An engine with oil temps at 200f will evaporate gasoline pretty quickly. 20 minutes at those temps can evaporate a lot of fuel as long as the pcv is working properly.
If vented to the atmosphere it may take longer to evaporate
 
Last edited:
Originally Posted By: OneEyeJack
+1

No matter what, fuel does not make a lubricant better. Any amount is not good. Some might claim that a small amount is acceptable or won't do any harm but I don't think so.

I have an 84 Honda with a lot of miles on it, with a carburetor and have never had any fuel in the oil on a UOA.


Wow, no fuel detected in the UOA.
1984 model, high mileage and with a carburetor as well.

Amazing.
 
Originally Posted By: Clevy
Originally Posted By: OneEyeJack
+1

No matter what, fuel does not make a lubricant better. Any amount is not good. Some might claim that a small amount is acceptable or won't do any harm but I don't think so.

I have an 84 Honda with a lot of miles on it, with a carburetor and have never had any fuel in the oil on a UOA.



We have ample data posted here in the uoa section that proves some fuel dilution is harmless.

So what you "think" isn't consistent with the data that is posted,and proven.
Unless you have data your thoughts mean nothing
Share them with jack handy,til then unless you can prove your point perhaps keep those thoughts to yourself. It doesn't help anything to post,and believe,stuff that just ain't true.


Yes Benito. You are correct. A ton of short tripping when th oil doesn't maintain operating temp for long means any fuel that passes by the rings cannot evorate,so it will accumulate in the crankcase and results can be skewed by it.
An engine with oil temps at 200f will evaporate gasoline pretty quickly. 20 minutes at those temps can evaporate a lot of fuel as long as the pcv is working properly.
If vented to the atmosphere it may take longer to evaporate



There is no proof that fuel dilution is harmless even in very small amounts. That would take a lot of testing and some teardowns. And it's not just idle thoughts. Fuel is not a good lubricant.

In my work with emergency power generators fuel and moisture will start evaporating really well at temps of around 140F. Once the oil reaches 200F there will be localized hot spots well above the boiling point of water especially after shutdown and fuel and moisture will evaporate quickly and continue until the oil temp drops below 140F. This we know because of environmental testing done for generators enclosed and isolated in living spaces in severe cold climates.

Gen sets that experience chronic fuel dilution in the range of 1-3% with the same duty cycles as those that do not require more maintenance than those that experience no measurable dilution in our experience. We've never measured higher amounts because we think higher amounts get burned off before we get around to the measurements. We have found that fuel dilution on cold samples to be of little or no value.

No matter what the tolerance factor might be, fuel dilution is not good. Most members here probably never keep a car long enough to wear out an engine. To prediction the effect with a UOA is of little value.
 
This is how I look at fuel dilution, and your point and Clevy's point are not mutually exclusive. There is almost no way to avoid fuel dilution altogether. It may not show up, but it does happen, at least sporadically, in just about every engine. Unless you switch to natural gas or LPG, some (perhaps very tiny) amount of gasoline will get into the oil, along with nasty combustion byproducts.

So, we understand it's pretty hard to avoid, even though it could be all over the map, from high dilution from a GDI type engine or a bad carb, to the best case scenario with the better fuel injection systems out there. We haven't seen anything terribly untoward with GDI fuel dilution, such as a bunch of spun bearings or anything. And we still don't see a lot of engines wearing out prematurely.

That's not to say that OCIs in engines that are bad with fuel dilutions might not have to be shortened, or that we have to watch the shear. Heck, look at how things were with the old F-150 and it dumping fuel in. Towards the end of an OCI, the oil pressure light would come on at hot idle, if using an ILSAC 30 grade.

That's when to worry about fuel dilution. Of course, I, too, probably because of that, get a tad picky and would rather see as close to "no" fuel dilution as humanly possible.
 
Originally Posted By: Benito
Will the fuel dilution number in a UOA vary depending on when you take a sample?

For example, taking the sample after weeks of short trips vs taking the sample after a long trip that took place after weeks of short trips.

If so ie if the long trip ends up hiding the fuel dilution, what else in the UOA might show the effects of fuel dilution? Accelerated TBN depletion?


#1? Definitely.

#2? The truly documented effects of fuel dilution in automobiles is nil. We have tons of vehicles with and without in the UOA section. No real proof it harms anything except your oil's specs.

Almost every car can dump excessive fuel as engine protection if needed. Then there's warm up, trip length, etc. Yet we seldom hear of blown engines or spun bearings, etc...
 
From the UOAs of DI engines observed on this site, I have not seen any increased wear attributed to fuel dilutions of up to 3% or so. We should first review the engine wear values and if that appears excessive then, look to fuel dilution or other problems as the cause. JMO. Ed
 
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