MPG vs UOA

[Truck-Guy]

I have to admit, I have not done a UOA in awhile, but I have my own personal system, not nearly as scientific.

I pay pretty close attention to MPG and often reset the trip computer on certain sections of my commute. I do understand many variables affect MPG, but what I have consistently found on a few of my vehicles is the tendency to start taking a hit around 4 - 5k miles. Probably mostly related to dilution. During my own personal test I maintain the same variable as best I can, same stretch of highway, speed, temps are hit and miss of course, and using the same fuel / octane. This is one reason why I don’t tend to do longer OCI’s. Thoughts?

 

[kschachn]

I can't figure out what you're asking.

Many variables in determining fuel consumption in everyday driving. You cannot control variables such that you get consistent results to isolate one variable. It's impossible, plus the energy content of the fuel varies even at the same gas station irrespective of summer or winter blends.

 

[Truck-Guy]

I can't figure out what you're asking.

Many variables in determining fuel consumption in everyday driving. You cannot control variables such that you get consistent results to isolate one variable. It's impossible, plus the energy content of the fuel varies even at the same gas station irrespective of summer or winter blends.

I don’t totally agree if I see a trend. I notice a consistent drop in MPG at about this mileage in the oil.

 

[kschachn]

Noticing something is the easy part, ascribing it to one isolated variable is far more difficult. You don't need to agree but there are tens of uncontrolled variables in everyday driving that are significant. Oil viscosity differences are there but they are only isolated in a laboratory that controls all other variables to an extent that the oil isn't in the noise. Besides, fuel thinning of the oil would result in a lower viscosity that will ever so slightly decrease fuel consumption. But trying to isolate this is far into the noise of everyday driving.

 

[ATex7239]

Things like weather, wind speed and direction, tire pressure, seasonal fuel blend changes, road and traffic conditions just to name a few will affect MPG way more than “dirty” oil likely ever could.

 

[Truck-Guy]

Things like weather, wind speed and direction, tire pressure, seasonal fuel blend changes, road and traffic conditions just to name a few will affect MPG way more than “dirty” oil likely ever could.

Fuel dilution is a number one cause of oil breakdown, particularly and direct injected engines, I would think with the degradation of the additives this would play a role in MPG reduction. I agree in general that there are a lot of variables with MPG. It’s just hard for me to disregard the trend that I see and I put a good amount of mileage on my vehicles. Especially, if it’s a consistent reduction. Never an increase.

 

[kschachn]

Fuel dilution is a number one cause of oil breakdown, particularly and direct injected engines, I would think with the degradation of the additives this would play a role in MPG reduction. I agree in general that there are a lot of variables with MPG. It’s just hard for me to disregard the trend that I see and I put a good amount of mileage on my vehicles. Especially, if it’s a consistent reduction. Never an increase.

It is? Breakdown how? What kind of breakdown are you taking about?

And what kind of additive degradation, and which additives?

 

[ATex7239]

Fuel dilution is a number one cause of oil breakdown, particularly and direct injected engines, I would think with the degradation of the additives this would play a role in MPG reduction. I agree in general that there are a lot of variables with MPG. It’s just hard for me to disregard the trend that I see and I put a good amount of mileage on my vehicles. Especially, if it’s a consistent reduction. Never an increase.

Without a UOA though how can you even begin to try to determine the impact of dilution over time? You’d have to at least measure it periodically to try to correlate the two. You’re seeing the MPG change, fine. But you’re just guessing at the reason for it cause you aren’t measuring anything else.

 

[nicholas]

I have to admit, I have not done a UOA in awhile, but I have my own personal system, not nearly as scientific.

I pay pretty close attention to MPG and often reset the trip computer on certain sections of my commute. I do understand many variables affect MPG, but what I have consistently found on a few of my vehicles is the tendency to start taking a hit around 4 - 5k miles. Probably mostly related to dilution. During my own personal test I maintain the same variable as best I can, same stretch of highway, speed, temps are hit and miss of course, and using the same fuel / octane. This is one reason why I don’t tend to do longer OCI’s. Thoughts?

You would think with dilution that your mpgs would go up.....?

 

[BMWTurboDzl]

I have to admit, I have not done a UOA in awhile, but I have my own personal system, not nearly as scientific.

I pay pretty close attention to MPG and often reset the trip computer on certain sections of my commute. I do understand many variables affect MPG, but what I have consistently found on a few of my vehicles is the tendency to start taking a hit around 4 - 5k miles. Probably mostly related to dilution. ....

Fuel dilution would reduce the viscosity so your mpgs would increase.

 

[Titan]

Fuel dilution is a number one cause of oil breakdown, particularly and direct injected engines, I would think with the degradation of the additives this would play a role in MPG reduction. I agree in general that there are a lot of variables with MPG. It’s just hard for me to disregard the trend that I see and I put a good amount of mileage on my vehicles. Especially, if it’s a consistent reduction. Never an increase.

Look at the viscosity decreases in oil subjected to dilution with Fuel. Viscosity decreases. Decreased viscosity would theoretically increase MPG, although miniscule to the point it requires very controlled lab-like environments to do so.

 

[Truck-Guy]

You guys make some interesting points and I agree this is not scientific whatsoever, but the trend that I noticed is consistent in my experience. Speaking with a tribologist who has his own UOA company I am 100% in agreement with him. He consistently claims that fuel dilution destroys the anti-wear additives and highly recommends frequent changes. Of course, the amount of fuel in the oil depends on the engine and type of driving. I do a lot of short trips and this heat cycle / style of driving is prone for this.

As far as viscosity, not sure what to say about this but my own personal data supports the opposite. Mileage goes consistently down as the oil ages and looses a lot of its ZDDP. I can’t ignore the data I collect on multiple vehicles. My mileage has never increased with “dirty” oil in my vehicles.

 

[kschachn]

You guys make some interesting points and I agree this is not scientific whatsoever, but the trend that I noticed is consistent in my experience. Speaking with a tribologist who has his own UOA company I am 100% in agreement with him. He consistently claims that fuel dilution destroys the anti-wear additives and highly recommends frequent changes. Of course, the amount of fuel in the oil depends on the engine and type of driving. I do a lot of short trips and this heat cycle / style of driving is prone for this.

As far as viscosity, not sure what to say about this but my own personal data supports the opposite. Mileage goes consistently down as the oil ages and looses a lot of its ZDDP. I can’t ignore the data I collect on multiple vehicles. Mileage never increased with “dirty” oil in my vehicles.

Who is this? Anti-wear is somewhat different than what you're claiming here.

And your data showing an MPG increase with fuel dilution (which you don't even know is happening) is faulty. No oil "looses a lot of its" ZDDP. No matter how you slice this you will never, ever see a fuel consumption difference in everyday driving from whatever effect this guy is claiming. Who is this person and where have you spoken to him? I could make a guess based on YouTube personalities but you apparently know him.

 

[Titan]

As far as viscosity, not sure what to say about this but my own personal data supports the opposite. Mileage goes consistently down as the oil ages and looses a lot of its ZDDP. I can’t ignore the data I collect on multiple vehicles. My mileage has never increased with “dirty” oil in my vehicles.

As a kid in the early 1980's I had a Tercel with a tiny 4 cylinder engine. I always tracked and GRAPHED MPG! I was surprised when I noticed my graph-paper generated MPG line always ticked slightly DOWN whenever I changed the oil. Like you, I expected MPG would go up...new oil and new lubrication made sense to me. I passed it off thinking that increased idling to check the oil filter for leaks, etc., was the reason for the MPG drop with new oil. Now, 40 years later, perhaps that slight downturn with new oil was real. Maybe the oil was shearing somewhat, so the viscosity was dropping as it was used, therefore perhaps the MPG really was better with older oil. In reality, it could have been coincidence or any of MANY other reasons. You'd need a lab environment to prove a MPG difference between old and new oil, if there is any.

 

[TurboZedd-R]

I can't figure out what you're asking.

Many variables in determining fuel consumption in everyday driving. You cannot control variables such that you get consistent results to isolate one variable. It's impossible, plus the energy content of the fuel varies even at the same gas station irrespective of summer or winter blends.

So we don't know if fuel dilution hurts or helps mpg. Hypothesis: fuel dilution decreases mpg. Run test methods and reject or fail to reject. Can't say for sure until research is found or conducted.

 

[MolaKule]

...Speaking with a tribologist who has his own UOA company I am 100% in agreement with him. He consistently claims that fuel dilution destroys the anti-wear additives and highly recommends frequent changes. Of course, the amount of fuel in the oil depends on the engine and type of driving. I do a lot of short trips and this heat cycle / style of driving is prone for this.

What is this tribological mechanism that destroys organo-metallic compounds?

 

[Truck-Guy]

Lake Speed Jr specifically said the levels of ZDDP in M1 euro 40 weight is why the oil maintains rather good efficiency and MPG properties, but he also says this oil is prone for LSPI.

 

[Truck-Guy]

Interesting video as well

 

[IndyIan]

I would th

I have to admit, I have not done a UOA in awhile, but I have my own personal system, not nearly as scientific.

I pay pretty close attention to MPG and often reset the trip computer on certain sections of my commute. I do understand many variables affect MPG, but what I have consistently found on a few of my vehicles is the tendency to start taking a hit around 4 - 5k miles. Probably mostly related to dilution. During my own personal test I maintain the same variable as best I can, same stretch of highway, speed, temps are hit and miss of course, and using the same fuel / octane. This is one reason why I don’t tend to do longer OCI’s. Thoughts?

Well the 4-5k mile mark is a good time to change oil in any case.
My limited understanding would say oil viscosity would decrease from new(from dilution and shearing) and mileage would go up slightly, unless the oil is getting so thin the motor is going from fluid film lubrication to mixed or boundary lubrication, which then I suspect creates more heat and friction in the bearings. https://www.machinerylubrication.com/Read/28766/what-is-lubrication#:~:text=There are three different types,oils to protect against wear.
Assuming the oil always stays in fluid film mode, then eventually the oil begins to thicken up as it ages/oxidizes which would increase viscosity and create more waste heat/friction in the motor.
I doubt you are getting to the point of the oil increasing its viscosity in 4-5k miles so I think your decreasing mileage is just chance, but a 4-5k change is probably good if you are using 20 weight oil anyways, IMHO.

 

[Truck-Guy]

I would th

Well the 4-5k mile mark is a good time to change oil in any case.
My limited understanding would say oil viscosity would decrease from new(from dilution and shearing) and mileage would go up slightly, unless the oil is getting so thin the motor is going from fluid film lubrication to mixed or boundary lubrication, which then I suspect creates more heat and friction in the bearings. https://www.machinerylubrication.com/Read/28766/what-is-lubrication#:~:text=There are three different types,oils to protect against wear.
Assuming the oil always stays in fluid film mode, then eventually the oil begins to thicken up as it ages/oxidizes which would increase viscosity and create more waste heat/friction in the motor.
I doubt you are getting to the point of the oil increasing its viscosity in 4-5k miles so I think your decreasing mileage is just chance, but a 4-5k change is probably good if you are using 20 weight oil anyways, IMHO.

I agree with what you saying to a point, but my theory on why mileage decreases is full dilution. If ZDDP contributes to maintaining this film and it’s been shown time and time again fuel dilution, particularly in DI engines, destroys these additives, it’s only logical to see a decrease in mileage. I don’t t know, but LSJ consistently beats a drum about NOT doing long OCi’s, he has his own oil analysis company, I kind of trust what he is saying. ZDDP has more of an affect on mileage than viscosity. This is on 40 weight / 2023 F150 5.0 / 3.73. 28.4 MPG is fantastic for a full size truck. I also run Ceratec, but this is a different topic I don’t care about debating.