Pros: Keeps the valve clean, makes things quiet and smooth, improves gas mileage. Pays for itself?
Cons: Not cheap, an expensive hassle to meet all requirements for the 150,000 guarantee.
I'm as skeptical as anybody. I've tried and rejected many "miracle" products for different uses, occasionally finding one that really worked as claimed. One or two of these products are now invaluable to me, among dozens that were a waste of time and money, and that caused all sorts of trouble.
If only one of the engine treatment products we see advertised really worked, how great it would be! The well-known advice of nearly every qualified mechanic in the world to avoid all "snake oil" is probably nearly always true -- but what if there's a genuine exception? One of my friends mentioned Slick 50 to me, but I was dubious after checking it out.
After seeing the infamous infomercials for ProLong, I called their Technical Assistance line. They said that the different versions (for the engine, transmission, and fuel) used the same active ingredient(s), but different "carriers" (or fillers) tailored to the various mechanical systems. They had a commercial version of the product for industrial use in any application. It contained just the active material with no carriers. After weeks of research, I couldn't find any dealers selling it, so I eventually tried the retail ProLong kit (my first infomercial product ever, but I bought it in a store).
ProLong seemed subjectively to make things quieter and smoother in the engine and manual transmission of the brand-new 2000 Suzuki Esteem I had bought. I did not notice any improvement in gas mileage. Then, Consumer Reports came out with their article debunking ProLong. They had burned up several engines after treating them with ProLong, draining the oil, and driving the cars (as shown in the infomercial). I saw that the FTC was going after makers of oil additives (including ProLong).
Later, I saw the ZMax infomercial, and decided I may as well try it, too. Despite my use of ProLong, my Suzuki Esteem was getting poor mileage (about 24 mpg) in the 700 miles/month of nothing but pure stop-and-go city driving to which I was subjecting it, and it was starting to idle roughly with only 3,000 miles on the odometer.
I called ZMax's Tech Help line and found out that all of their different products (for engine, transmission, and fuel) were exactly the same, had no carriers, and were just packaged differently. By the way, they are actually all the same color. I read about the histories of Linkite and AvBlend, and the effectiveness of ZMax in cleaning the valves of piston aircraft engines. I changed the engine and transmission oil in my Suzuki Esteem, adding ZMax as recommended, and also put in in the gas tank.
My gas mileage improved to around 27 mpg, and the engine of my Suzuki started idling much more smoothly. ZMax appeared to be reducing carbon deposits as claimed. I decided to use it when I felt like it, instead of replacing it every 6 months and dealing with the hassle of documenting everything for the warranty. It isn't cheap, after all (even though the savings in gas seemed to be paying for the ZMax). I read about the increased corrosion issue in lab tests of non-hardened bearings, but I didn't think it was going to be a problem in my car.
When the Suzuki was a year and a half old and had 8,500 miles, I traded it in on a new 2002 Toyota Corolla LE with manual transmission. My in-city mileage was only about 23 mpg. Though I have now read recommendations to wait until 5,000 miles to change to synthetic engine and transmission oil, I made this switch at 2,000 miles in the Corolla LE (adding ZMax to the engine, transmission, and fuel tank at that time).
With the combined change to all-synthetic oil plus ZMax, my Corolla LE immediately bacame quieter and smoother, and I was happy. My city gas mileage improved to about 26 mpg. After a period of uninterrupted stop-and-go city driving, the Corolla LE began to idle roughly, as had the Suzuki. I put a round of ZMax in the gas, and it smoothed right out. I could hear the engine sing, with less friction in the top end, and less noise when I wound it up. ZMax seems to be at its very best in the fuel system as a valve cleaner.
I read on the Web that Toyota was going to come out with a new sports-model Corolla, the XRS. After waiting patiently for a year, I just had to have it. Despite the financial imprudence of the decision, I traded in my 2002 Corolla LE with 23,000 miles for a 2005 Corolla XRS (which is now pushing 4,000 on the odometer). I have driven this fun-to-drive car out of town much more than I did the previous 2 cars, and it hasn't yet developed a rough idle.
However, I found myself wishing for that sense of smoothness in the top end that I had felt before, so I put a reduced dose of ZMax in my gas tank while I wait for the 5,000 mile mark. I am not here to advocate using products differently than their instructions advise, but using less than the recommended amount of ZMax doesn't seem likely to me to hurt anything.
I immediately noticed the increased smoothness of the engine, although I haven't driven far enough or done a complete enough treatment to evaluate my gas mileage in the XRS -- which has been around 22 mpg in town (made worse by the fact that this newfangled wonder runs its air conditioner whenever the defroster is on). So far, I have logged around 37 mpg in pure freeway driving (with no ZMax).
Reverse is next to the 1st and 2nd gears in the 6-speed manual transmission of the Corolla XRS, and it's all too easy to hit reverse when you wanted 1st... Ouch! It's an old reflex -- all the way left and up when you want to get moving. So, when I ground the gears into reverse by accident, I immediately replaced my factory transmission oil with Valvoline 75W/90 (at 867 miles). The transmission felt slicker with the only the Valvoline gear oil than it had with the factory fill.
It happened again last week at about 3800 miles. Grrr! This is the Achilles heel of this car, no doubt about it. I changed the transmission oil again, still using regular Valvoline gear oil instead of synthetic because I haven't hit the magic 5,000 mile mark. I put 1 oz. of ZMax in there because I just couldn't stand to wait any longer. (The normal dose for the transmission is 4 oz.) I noticed the increased smoothness and quietness of the transmission immediately. It's like floating on air.
I am sold on ZMax.