I'm now using Marvel Mystery Oil in the gas, carefully mixed at 4 oz per 10 gallons.

Now here's the test I conducted. About the time I got my Jeep 4 months ago I became interested in MMO due to good reviews here and elsewhere, so I started sporadically adding a little to gas now and then. Over time it became my perception that the fuel gauge went down faster without Marvel in the tank, so I started adding it consistently. I then decided I needed to do a more controlled test to see if I was wasting my money or not. Here's what I did.

With MMO added to the gas, I ran three complete tanks of fuel. My routine is very consistent and is a mixture of city and highway commute driving. I refueled at that exact same Phillips 66 station, used the exact same pump, and filled the tank on the lowest flow setting and removed the nozzle as soon as it clicked off the first time, no top offs. I considered this the best way I would be able to get a consistent fill without variation. It has been beastly hot this whole period so AC use has also been consistent, as well as tire pressures monitored. All calculations were done using the trip odometer and actual fuel used.

All three tanks with MMO netted 18.1 to 18.3 mpg. This is for my 04 Grand Cherokee 4.0 I-6 4wd.

I then refilled the exact same way and ran a tank without MMO. I got 15.96 mpg. Nothing changed that I know of than the MMO being excluded.

I didn't consider a single tank a conclusive sample so I ran another. That netted me 15.56 mpg. I wonder if a little MMO was still in the system the first time, as I dropped another .4 mpg on the second tank without it.

At that point I'd seen enough so I refilled and added MMO. Here's the real sweet part, a full 20 gallon fill of gas only takes 8 oz of MMO which costs a whopping $1.33. At + 2.5 mpg on 20 gallons thats another 50 miles, or $10.22 worth of gas in these parts, so even after deducting the MMO I pocket almost $9 a tank. I'll take that deal anyday!

Why does it work? I'm not really sure, MMO claims it improves combustion and lubricates the fuel system. My suspicion is that it's helping overcome that [censored] ethonal the govt is making them put in my gas. Note: MMO recommends 4 oz to 10 gallons and more is NOT better, in fact I plan to experiment with a little less on down the road.

I don't know if it will work for you but it is for me and I'm now introducing it into my other vehicles. No I don't work for MMO or anything like that, I'm just trying to help my fellow BITOG'ers save a buck. I know a lot of you are already using MMO, but those are my results as best as I can document them.

Nice report, several members have noticed increased mpg with MMO in the gas as well. We have a fair amount of people who hate MMO and will pick your test results apart,so be prepared. I use the product and think it is well worth it. Let us know how changing the MMO dose effects your mpg.

Excellent write up! I love MMO.

Nice job. You did everything right as far as filling up, etc. Nice results that you got.

An exact same route is really what you need to test mpg. I've tested various products and have kept detailed mpg. The only downside is that my job is a courier. As such, my "commute" is always variable. I have however found that MMO increases my mpg over 5,000 mile mpg records.

I tried MMO in my '00 E430 twice, first it was 4oz per 10 gallons then 2oz per 10 gallons. Both times the engine felt sluggish in city and highway. I tried MMO because of positive posts like yours, MMO works well in some fuel systems and didn't work too well in some other fuel systems. But, I had better result using MMO in engine, the engine seems to run smoother.

Thanks for posting.

We have used MMO @ the rate of around 4 oz in our last 3 vehicles with good results too.

Wal-Mart here sells the gallon jug but it is not kept where the smaller bottles are and comes in a different colored container.

One must hunt around for it.

I use the stuff too for the mower fuel as it also acts as a fuel stabilizer.

We still have a few stations here that sell 100% gasoline or that is what the signs say but they have become far and few between.

I'm doing the same thing since I found out about MMO on here. I'm keeping track of my MPG but not paying attention to details like you are (I do top-off my tank, fueling with lowest setting, etc) but I am keeping tire pressure constant.

My 2 fill ups before finding out about MMO, I was getting 31.7 mpg and 33.7 mpg. ( I drive a 2002 Toyota Celica GT, 1.8L). the 2 times I did use MMO in the tank, I got a respectable 35.7 and 35.8 mpg. All of the above is driving 80% highway, 20% city.

It seems to work for me also and I'm a believer too!

I also posted this on Jeepforum for my Jeep brothers, and here was a very interesting response posted there. Makes sense to me.

OP:

You are correct in stating that ethanol blends are an issue with today's fuels. Adding ethanol effectively strips any of the lubricating properties that fuels may have (remember leaded fuel? Yep, added for lubricity). Add to the fact that ethanol wicks moisture from the atomosphere and you can quickly see where this is going.

Unfortunately the issue is only going to get worse in the coming years, with the EPA recently clearing (IIRC) 2001 and newer vehicles for use with E15 blended fuels (15% Ethanol, 85% dino fuel). With this new blend, it is going to be increasingly important to use fuel driers in the winter and during long term storage of fuel, as water in the tank will be more prevalent.

I've seen the same effect on my Buick. I'll get about 2-3 mpg better on MMO than without. 29 mpg with MMO, 26 mpg without.

Picked up about 1mpg in my 1987 Jeep 4.0 using MMO. Low 17's to
low 18's. Same route, very consistent on the throttle.
Wife's 2004 Honda did the same. This is over one month's time,
filling up at 1/2 empty.

Good stuff.

Not to throw science into this discussion but that is a 17%+ increase in efficiency. You are obviously missing something in this experiment or purposely driving different to skew the numbers. There is no logical justification for that kind of increase.

Had a cold,loud lifter/rocker? tick in my 2006 vette at around 25k. Yes, nothing but Mobil 1 by about half of the OLM. Half a pint of MMO added to crankcase. In less then 500 miles of normal driving it went away. Changed oil/filter and still ok.

Good job on the tests and tracking the results. I use MMO too, and I always get a consistent 1 to 2 more MPG with it than I do without it. Glad to know the MMO is working so well for you.

I've been using MMO for awhile in my truck's gas and never saw any mpg improvement. I add it for it's properties as an upper cylinder and fuel system lube, cleaner, and stabilizer.

All the people who had success with MMO must be wrong. LOL