Are 2-3 MPG Gains Valid from Synthetics?

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Aug 11, 2004
Chicago area
I hear on this and other forums about people changing from dino engine and tranny oils to synthetics and reporting 2-3 MPG increases, or even more. Often, this is with the synths. having similar viscosities. I don't think Mfrs. would pass this up, and not put full synthetics in all the cars they make, if this could be true. It seems that they spend millions to get a few tenths of a percent increase. The only mileage/power gains I have really felt or measured were when going to a thinner viscosity [concerning lubes]. What do you guys objectively conclude?
I don't have a reference handy, but I recall numbers in the 1-2% range. However, 1-2% different from what? I can easily accept that there is a 2% range in difference in mileage from one end of the spectrum to the other. I can also accept that mineral oils tend to fall on one end of that spectrum and synthetics on the other end. However, I find it difficult to accept the no mineral oils are on the high mileage end and that no synthetics are on the low mileage end of that spectrum.
In cooler weather, and under little load, the oil in the diffs will never really warm up much. Diff temp guages on heavy duty trucks show that. Even a manual tranny might take a while to warm up. Considering how thick gear oil is below full operating temperature, I could definitely believe a noticeable increase in fuel economy by switching to synthetic. A lot of new vehicles with gear oil use synthetic 75W-90 now. I don't think synthetic engine oil could make a difference in fuel economy, unless it was a thinner grade in very cold weather. They pass the same "energy conserving" tests as the dinos.
I would agree with 1-3% range if ALL fluids are changed over. So if you got 30 MPG before, you would get 30.3-30.9 MPG after. Well within any real world variance, so IMHO I don't think you can show significance to any increase in MPG seen. 2-3 MPG from synthetic I don't buy.
I switched my 01 Tacoma to all Amsoil (oil, gear, ATF)and did not see any noticeable change in mpg. I am very happy with the Amsoil but can't say it helped with fuel economy.
I have a very difficult time believing that synthetics would have that much effect. However, when I changed over, I got several mpg increase. It was on a fairly new car, though, so I attribute it to more fully being run-in (some people refer to this condition as is the same thing to me). PLUS, I started using Fuel Power. PLUS, it got, even though I was now running the AC, less dense warm air combined with a possible change-over in fuel composition, combined with all the above, and I saw mpg go from 33 to 37.6 mpg on the same long trip with the cruise control set. Then, there are the variables of the way you car is sitting when filled up, as well as the temperature at fill up and the flow rate of the pump, not to mention the depth at which the nozzle protrudes into the filler hole. Oh, and wind direction/speed. Take my original 37.6 mpg trip. I got 37.6 mpg on the return trip. Sounds fairly accurate, doesn't it? Still, it wasn't scientifically done, so I cannot argue that it is factual. Very nice coincidence, for sure. Again, just because mpg changes when you change one variable, it doesn't mean it wasn't some other variable(s) causing (or at least contributing) to the change.
I've switched on and off synthetics for years. At most, I've seen is a 0.5 mpg difference over quite a few runs on the same stretch of highway that I frequent. Even then, the difference is almost certainly the actual viscosity difference. Most notable difference is viscosity.My previous vehicle was a 2001 F150, spec'ed for 5w-20. After break-in I ran some mileage numbers, trying to only base the differences on crankcase oils. This meant the same stretch of highway (round trip), same approximate ambient temperature and same gas station (which is subjective). Same time of day and traffic considerations were also mimicked. In my underpowered 1/2 ton, the 5w-20 gave me 1.5 mpg better consistently over the same brand (Motorcraft) 5w-30. But my little V6 was louder with the 5w-20. Hence, back to the more accessible 5w-30.
I think there's a lot of anectdotal evidence, but little in the way of repeateble, controlled studies. A few years ago, Trucks! TV put Royal purple fluids into a truck and claimed something like 8 hp, something like a 3 or 4% power increase. If that's the result of reduced friction, then I'd imagine it would affect MPG. But in this month's Popular Hot Rodding, they actually lost about a half-horsepower or so (I'll have to check the article when I get home) when they swithced from factory-fill to Redline lubes. At least so far as dyno testing goes, I think there are too many variables that affect the results. I do find it hard to believe that there's a significant difference in lubes, with the exception of viscosity as noted above.
My thought is that the mileage improvements are anecdotal. You'd really need to measure this over a very large number of tanks of gas in the same exact conditions, with the same exact driving patterns. It's pretty hard to do, but not impossible. It would likely take a long time before you could really establish a trend that was reliable. The trucks TV 8hp gain is hard to argue with however.
My experience is that when I switched from Castrol Syntec to Mobil 1 EP, I gained .5 to 1 MPG. My oil change also occurred (sp?) as the temps were getting warmer and the fuel was switching. My opinion would be that unless you had some way to accurately (and consistantly)measure MPG, then it's all in your head.
Originally posted by Jim 5: The trucks TV 8hp gain is hard to argue with however.
Yes, but since the dyno runs were at least an hour apart (they ran the car on the rollers for 30 minutes each to get fluid temps up), changes in atmospheric conditions alone could skew the results.
In the winter you will get a large gain from going to a synthetic gear oil in the differentials for sure. Dino is only good to -35c or so. The synthetics are good to -50c.
Doesn't have to be synthetic. Havoline Energy 5W30 dino gave 6% better economy in independent tests. Redline gear oils improve economy as well. Subaru dealer does not believe the fuel figures I tell them our Outback gets. Oils is oils to them.
2-3% gain most propable, to many factors involved. that being sai think using Chevron-Texaco w/Techron has even MORE noticable MPG_+ effects.
Redline claims to reduce friction. Some dino tests have confirmed it. I bet it is because of the gobs of moly in it. However, you only lose a few percent through your differential, and a few percent from your tranny. So, by putting in a better oil you might reduce the friction losses which were 3%, down to 2.5%. I dont think there is any way that you can get more than 1% total by using a better oil. 2-3MPG would be 10% improvement. Where are you going to recover 10% from?!?! [I dont know]
The only thing that has ever really made an impact on engine performance for any of my cars was the gas I used. I think gasoline has more of an impact on performance. AS far as mpg goes, I think you'll see some small differences but only if you factor in all the other variables and somehow make sure they are the same when you calculate it.
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