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MotorVac, A Teeth-Cleaning For Your Car

by Tim Considine

"The Tune-up of the Nineties," is what the literature claimed. It was said to clean enough carbon deposits and other contaminants from an engine to improve fuel economy, ease cold-starting, promote a smoother idle, quicker acceleration, and increase power. All this while lowering exhaust emissions. Pretty strong claims. Strong enough to arouse a good bit of skepticism from one whoís experienced any number of snake oil salesmen over the years. The product is usually some magic elixir which, when added to the gas tank, is supposed to miraculously cure whatever ails an engine. You know, do damn near everything but lower your cholesterol. Baloney. This one, however, wasnít an additive. Called MotorVac, it was a procedure that sounded pretty logical, and importantly, the results of which could immediately be measured. That got our attention.

The fact is that even a one-year old carís engine has accumulated carbon deposits, gum, varnishes, dirt and other contaminants that build up in the air intake, fuel delivery system, combustion chamber, and exhaust system. Yes, modern engine computers monitor and adjust for some of these changes, but in time, as these systems get further and further from original spec, inevitably, engine efficiency suffers. The way we usually experience this is subtle at first. Perhaps the car is a little harder to start when cold, or the idle is a bit lumpy, or the engine occasionally stalls, or gas mileage begins to edge downward. It is most likely a combination of the above. Left unaided, these symptoms get worse as the miles pile up. Acceleration suffers, power is down generally, and the engine is no longer smooth. A major contributor is incomplete combustion, which means along with the symptoms we notice, is one we frequently donít - increased tailpipe emissions. An inefficient motor pumps significantly larger amounts of Hydrocarbons, Carbon Dioxide, and Carbon Monoxide out the tailpipe. In California, where Smog-Check II, a stringent new smog certification standard, has been adopted, some drivers have been unpleasantly surprised to find their year-old cars need substantial "fixing" in order to be certified.

As a matter of course, contaminated spark plugs are cleaned or replaced and engine computer sensors and functions checked to improve performance and bring tailpipe emissions in line. All well and good. But it stands to reason that maximum performance and fuel economy simply cannot be achieved if problem-causing sludge and deposits are in the fuel delivery system, not to mention the combustion chamber and exhaust system. These contaminants can be removed in two ways; by a time-consuming - and costly - teardown or by introducing some cleaning detergent. Hereís a rule of thumb. If itís added to the gas tank, itíll do a great job - of cleaning the gas tank. The trouble is, whatever sludge and deposits are dislodged from the tank usually just end up clogging the fuel delivery system, which can be thought of as a series of progressively finer filters on the way to the intake valves. Pack up any of those filters along the way and there are further problems.

Another strategy for cleaning the fuel system is to introduce a fuel injection cleaner directly into the fuel line feeding the injectors of a running engine from a pressurized can. These are available to professional and do-it-yourself mechanics at most autoparts stores. Again, the downside is that contaminants may be just moved farther on, clogging up fine injector filters or, should they survive combustion, even oxygen sensors or catalytic converters in the exhaust system. What piqued our curiosity about MotorVac - enough so to test it out on our own family car, a 1990 Mitsubishi Galant - was that while it, too, relied on a detergent introduced to the fuel delivery system for cleansing, the manner in which it was accomplished was both novel and comprehensive.

First of all, one doesnít just tip a can of detergent in the tank and drive off. MotorVac is a multi- step procedure that requires about an hour to complete. It can be administered only by a trained mechanic using a specially instrumented 3 1/2 foot tall 12-volt powered machine on casters. It is distributed in the U.S. by, among others, the well-known Snap-On Tool company. To establish a baseline for comparison in at least one area, that of tailpipe emissions, immediately before testing, we had the Mitsubishiís exhaust analyzed for Hydrocarbons (HC), Carbon Dioxide (CO2), and Carbon Monoxide (CO), pollutants emitted from all internal combustion engines. The results were both surprising and somewhat disappointing - for test purposes. The truth is, our Mitsu was quite "clean." Certainly, well within Smog-Check II-mandated specs in all four areas. Regardless, we pressed on, though it was clear that we werenít going to see any dramatic gains in terms of tailpipe emissions.

For the initial "diagnostic" phase, the MotorVac technician popped our hood and connected one line from the machine, by means of a "T", into the fuel line, between the fuel pump and the injectors. In this configuration, the engine was started and allowed to idle. We were told that about a quart of fuel would be drawn into the machine and mixed with the special MotorVac detergent for later use. With gauges on the machine, fuel pressure, the pressure regulator, and fuel volume were checked and compared with manufacturerís spec. At the same time, virtually every component in the entire fuel system was checked for leakage. The engine was then switched off and the technician performed a "leak-down" test - a tip-off to whether there was enough fuel pressure retained to ensure cold starting. Our car happened to pass each of these tests, but obviously, had it not, any number of specific problems would easily have been discovered. This first phase took only a couple of minutes to complete. So far, so good.

Then the technician reconfigured connections between the machine and the Mitsubishiís fuel system. Essentially, two closed loops were formed using flexible hoses and metal adapters. The first just sealed off the gas tank by connecting the pressure side of the fuel line to the return side. This way the fuel pump could function normally, pumping fuel right back into the tank. Nothing else had to be disconnected. Two lines from the machine were connected to the engineís fuel lines, one on the pressure side, the other, on the return side. Now the engine was isolated, itís fuel system linked only to the machine, which began the "cleaning" phase by pumping a mixture of fuel and MotorVacís own detergent formula into this loop.

In this configuration, with the engine switched off, virtually every component in the fuel delivery system was flushed and/or soaked by the fuel/detergent mixture pumped into it, then back into the machine. There, any varnish, sludge, or other deposits were removed before the mixture was recirculated. Next, the technician sprayed the inside of the air intake plenum using a spray bottle with a long extension. This was to wash off any oil vapor residue from the PCV valve and other fine dirt that had collected there. Then, still connected to the machine, the motor was started. For the next half-hour, the fuel injectors, valves, combustion chamber, oxygen sensor, and even the catalytic converter were washed with the steam of MotorVacís non-burning detergent. And that was it. The technician simply disconnected the flexible hoses and reconnected the fuel system. All that was left before measuring exhaust emissions again was to steam or burn off any remaining sludge in the exhaust system with a five- or ten-minute drive. Forewarned by the mechanic, we were not alarmed by the white steam cloud that followed us at first. In this short drive, we thought the Mitsu felt quite smooth, and quite lively.

As had been expected, the already clean Mitsubishiís tailpipe emissions were little changed, though the print-out did show a slight decrease in Hydrocarbons or unburned raw fuel emitted, six parts per million as compared to 11 parts per million. Not a significant change, but in the right direction. The real change became evident when we drove the car in the days following its MotorVac treatment.

Without question, our Mitsubishi definitely cold-started easier. It also ran smoother and was more responsive to throttle, most notably, on acceleration. On the whole, the engine did seem to have more power. These changes were independently noted by my wife, the carís regular driver. She also thought gas mileage might be better, though unfortunately, there were no recent mileage figures with which to compare it. Regardless, we were impressed, but wanting still more data, made arrangements to put another car through the MotorVac treatment, this time at a regular service station rather than the factory.

Our next door neighbor and friend drives a Volvo wagon with more than 127,000 miles on the odometer,. A perfect candidate, we thought. Unfortunately, our friend had recently had his Volvo tuned to pass Smog Check II, so he, too, saw only a slight improvement in tailpipe emissions. But with his well- seasoned Volvo, the performance gains were even more dramatic than ours in the relatively low-mileage Mitsubishi. He came back raving about his "new" car and how much smoother and more powerful it was. Interestingly, enough gunk and contaminants were removed from his fuel injection system to make the engineís idle speed considerably higher afterwards. When it was adjusted back down, he said the engine was so smooth and quiet, he hardly knew it was running.

Similar results were achieved by a colleague of ours who tested an older muscle car, albeit another surprisingly "clean" example emissions-wise. After comparing notes, we were both impressed. And, though it had not be proved with our particular cars, neither of us doubted the findings of a six-vehicle test of the MotorVac system by California Environmental Engineering, an independent emissions laboratory certified by the California Air Resources Board (ARB) and the U.S. Environmental Protection Agency (EPA). Using an emission testing procedure developed by the ARB and EPA known as the Federal Test Procedure (FTB), in the six vehicles that received the MotorVac service, Hydrocarbon emissions were reduced by an average of 16.8%, Carbon Monoxide emissions, by an average of 14.5%. Interestingly, the report found that MotorVac service had the greatest effect on cold-start emissions, reducing the unburned Hydrocarbons emitted for the first 2 1/2 minutes after starting a car - and before a catalytic converter muffler can heat up and work properly. In converter-equipped cars, about 75% of the total pollutants emitted during the FTB are produced during that short time period. Obviously, this is a significant emissions reduction.

Will a MotorVac service ensure your vehicle will pass a smog test? No, not if thereís some problem other than fuel delivery system and combustion chamber contaminants, but the diagnostics alone will likely point to those problems. In smog-choked cities in China, though, where some 700 MotorVac units have been in use for three years, any vehicle that fails a smog test must undergo MotorVac servicing. The Israeli Army services all its diesel vehicles with MotorVac, not only to reduce tailpipe emissions, but to maintain performance.

Our conclusion? MotorVac is no cure-all, no panacea that will suddenly transform a vehicle into something it wasnít. What it will do - and did in every case we knew of - was restore performance, restore smoothness, and restore efficiency. Like a professional teeth cleaning, itís the kind of thing that should be done every year or so, particularly if your driving consists mostly of short, low-speed runs, as is typical in cities. Interestingly, the cost of a MotorVac service can vary anywhere from $50 to $150 (the Chevron station where my neighbor took his Volvo charges $140), so it might serve one to shop around. But the bottom line is, it works. And if thereís a better or, for that matter, cheaper way to thoroughly clean and maintain a carís critically important fuel delivery system, we donít know about it.

Copyright Tim Considine, 1996