I conducted a test in the spring on a 253 mile road trip taking my daughter to a state competition. This was done in my '97 Nissan Maxima with 4 people plus luggage. All maintenance was up to date (Castrol GTX 5w30 only had 900 miles on it, along with a fresh air filter, new PCV, and throttle body cleaned). Since I routinely run MMO between oil changes, and Techron immediately prior, I assume my injectors and combustion chambers were clean, so any differences couldn't be associated with MMO cleaning anything. Tire pressure was 35 psi all around.
On the way down, I filled up my tank to the first "click" with 89 octane at my local Shell station I normally get gas at, and immediately got on the interstate. We did not use the AC at all, nor have the windows down (it was cool enough in the afternoon to just run the vent). Driving style was conservative, with speed kept at 75mph (cruise control) the entire way. We made one stop for lunch at a quick mart type shop. When we arrived in Baton Rouge, I immediately filled up to the first "click" at the Shell station right next door to our hotel. I averaged 27.22 mpg, with all but 1 mile being interstate.
On the way home, I filled up at the same Baton Rouge Shell station with 89 octane with the very same pump, and again only to the first click. I added 5.25 oz MMO (from an old Lucas UCL bottle I carry filled with MMO). We took the same exact route back home, even stopping at the same quick mart place for lunch. Speed was once again kept at 75mph by cruise control. The car was loaded identically. The only difference with this leg of the trip was that we ran the AC the entire way home. Arriving in my home town, I filled up at the same Shell station I initially got gas at, using the same exact pump, and only to the first click. I got 27.67 mpg.
These were as identical of trips as I could possibly do. Same exact route, time of day, vehicle loading, vehicle speed, and even the same pump at the same gas stations for both legs. The only differences were on the return trip, I added 5.25 oz MMO to my 18.5 gallon tank, and on the return trip we used the AC the entire way (which should have hindered mileage as it usually does in my car). And ambient temp on the way down was in the low 70's, and the way home was the mid 80's. To me, this definitely proves the value in adding the recommended dose of MMO from a fuel efficiency standpoint. It may only appear to be a .47 mpg increase, but keep in mind that was with the added drag of running the AC while the MMO was added. I consistently see almost a 2 mpg decrease in mileage when running the AC, so conservatively I can say I gained atleast 2 mpg with MMO (interstate travel, city could be lower). And considering my buddy gets me quarts of MMO for free, it is definitely worth it. But even if it wasn't free, after seeing this data, I would still run it (it costs about $9.00 for a 1/2 gallon at my local Walmart). If it measurably increases my fuel efficiency, I would think it is also protecting moving parts from wear. So it just makes sense from a maintenance standpoint to use it, too. Maybe someone more knowledgeable than me about engine wear can chime in with their thoughts on it.
Running the numbers, at 27 mpg I would get 499.5 miles on a completely full tank (18.5 gallons). At 25 mpg, only 462.5 miles, for a 37 mile difference. A 5.25 oz dose of MMO would cost about $0.75. At $2.30/gallon for gas, that 37 mile difference would cost me $3.40. So I am saving $2.65 per tankful by using MMO. This is only the savings in gas, and not the savings in wear which I would have no idea how to compute. I doubt the wear difference would even be measurable with an oil analysis, although a good idea may be achieved over the life of 2 identical vehicles.
It would be interesting to be able to perform tests like this for several different additives. It would be very nice to see differences between the different "classes" of additives, like UCL's against just fuel injector cleaners. Unfortunately, due to being a disabled vet, I probably won't be making any long trips in the near future. But when I do make my next one, it will probably be with Lucas UCL, which is another old favorite of mine that "seems" to get me better mileage.
Anyways, those are the results from my real-life test. Hope it helps someone in making an informed decision. And possibly spark some interest in posting similar tests with different additives.
By the way, for those who are itching to know, my daughter took third in the state for her 7th grade report on the battle of Khafji (topic was her choice).
Semper Fi,
Dave
