This is utter nonsense and the conclusions you draw from your theory are unwarranted to say the least.
How about answering @MolaKule to start?
MPG vs UOA
- Thread starter Truck-Guy
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How about answering @MolaKule to start?
Patman
Staff member
There is no evidence that excess fuel in the oil depletes the anti wear package otherwise we would be seeing this show up in the UOAs. The oil formulators are well aware of the potential presence of fuel getting into the oil and making sure that the final product they put out will still provide excellent wear protection regardless
Could be possible that excessive fuel dilution could effect the AF/AW additives and the existing tribofilm which could increase the friction in parts in mixed and boundry lubrication. As the friction goes up, the fuel mileage goes down. Just a big reduction in oil viscosity due to high fuel dilution can cause more friction between moving parts. I'd expect an engine with high fuel dilution to have more friction, more wear and worse fuel mileage.
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It's been discussed here before that new oil can possibly strip the existing AF/AW tribofilm from the previous oil run. That could increase friction until a new full tribofilm is built back up from the new oil.
Lots of moving parts in an engine are always in some level of mixed and/or boundry lubrication. If the friction level increases in those components due to whatever reason, then the engine is going to get less fuel mileage with all other factors held constant.
What in a UOA would indicate there was any effect on the AW/AF package from whatever could effect it in actual use of the oil in the engine? Time to search for any controlled studies on the effect of fuel dilution on the overall friction level in a running engine.
"Engine oil contamination with fuel, fuel dilution, can cause a reduction in viscosity which could potentially lead to the crankshaft bearing failure in car engines. It can also reduce the effectiveness of lubricant additives in forming low friction and durable protective films in piston rings and cams. "
Exactly.
Enough increased friction to produce the claimed observable change in MPG would be highly detrimental to the engine. That's a large increase in friction.
No laboratory study anywhere supports such a large increase in friction from fuel dilution, especially one that massively overwhelms the lowered viscosity of the oil. This entire thread has no reference whatsoever.
This. Not YouTube videos and wholly uncontrolled MPG readouts.
I have watched a number of video from LSJ with UOA’s and Dyno’s looking at wear numbers and how viscosity affects this. The guy formulates his own oils, I’ll trust his opinion over keyboard warriors, no offense. Again, he clearly states the number 1 factor in oil degradation is dilution.
Does he also quantify how this supposed degradation affects fuel economy? Because that's what your whole post is predicated upon.
"Wear numbers" from a spectrographic analysis aren't cutting it in this instance.
"Oil degradation" is not equivalent to "increased friction". Perhaps you over-estimate the MPG effects of Anti-wear, Anti-friction additives in virgin oil compared to a fuel-diluted (and therefore lower-viscosity) oil. I've turned over by hand countless engines...and there is oh-so-little "friction" to overcome. I think Viscosity has a greater effect on power loss than friction. A Centistoke is a TINY value, and the difference between a 20 weight and a 50 weight in centistokes at operating temperatures is not enough to show a significant difference in MPG except in VERY sensitive lab-based tests. Where the lighter-weight oils provide better MPG (and it isn't very much, 1-2% at best in lab tests) is during short-tripping, where the engine is often cold so it is thick then...and it's the lower viscosity of the lighter-weight oils that provides the tiny increase in MPG...not the anti-friction additives. That's why the MPG improvement in the lighter oils shows up in short-tripping and not at a constant hot-temp operation. The difference is viscosity at startup with light-weight oil compared to heavier oil is in the Hundreds (or perhaps Thousands) of centistokes, whereas the difference between the viscosity at temp between a 20 and a 50 weight oil is less than 10 centistokes. Anti-friction additives provide benefits much more like the difference in cSt of 20 vs 50 weights in hot oil than the difference in cSt between 20 vs 50 weights in cold oil.
I saw a distinct increase of 1.5-2 MPG average (ie, taking into account the "noise" in the data) on my Tacoma after the engine was fully broken-in. Some of that could have also been switching from a conventional to a full synthetic oil after break-in. So apparently the higher running friction was the cause of the lower fuel mileage because that truck was driven back and forth to work 95% of the time over the same 50 mile per day route, so it had a pretty consistent driving style. The engine didn't destroy itself during break-in and came out doing a consistent increase in MPG after full break-in.
What was the OP's claim in fuel mileage difference? I don't recall seeing exact numbers.
You'd have to know what level of friction change accounts for what change in MPG on each specific engine. Might be a study or two out there on some testing like that.
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Do you have these data to be able to plot up? So every time you do an oil chnage, you mpgs, tracked, drop at about 4K miles and this repeats over and over?
If you look at the left graph on page 14 in the study linked below, you can see the effect of decreased or increased engine friction on fuel consumption. That graph can be used in two ways ... the effect from increased asperity friction or effect from decreased asperity friction. If someone is already using a low viscosity oil and then it becomes excessively fuel diluted, then that's going to increase the asperity friction the most. The graph shows the effect of friction on fuel consumption, and the highest friction example shows ~5% change in fuel consumption. Could be worst than that if things are really out of control in terms of oil viscosity and fuel dilution. The study shows that the impact is greater at low engine speeds, because MOFT is also a function of the speed of moving parts along with the viscosity of the oil film between them. You can download the PDF of the study below.
So we also know that "degradation of the additives" by fuel dilution, especially ZDDP, causes this magnitude of friction increase? OP also doesn't even know if he has a dilution problem nor the extent if he does.
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Yes. obviously more investigation would have to be done by the OP to try and determine the change in fuel mileage. If it's a repeating phenomena, then there's a reason (or reasons) why. An appropriate UOA would help to determine if the oil is fuel diluted and/or if the viscosity is way down for some reason - maybe that engine shears oil down too. Obviously, the more the viscosity decreases from more fuel dilution and/or whatever other reasons, the more potential friction there could be going on. More friction means more wear and less fuel mileage.
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