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Dr. Gear Head / A sometimes close examination of
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Under the Hood

October 01, 1998

Last month I talked about motor oil and all its slippery details. This month: a critical look at oil additives. You've probably heard dire warnings that when you start your engine you're grinding metal on metal, resulting in about 85% of total engine wear.

First, this kind of wear isn't responsible for engine failures. Second, bearings aren't running dry--oil remains after you've turned off the engine. Finally, the wear that's taking place has far less to do with metal-to-metal contact from lack of oil than with byproducts of combustion. Those acidic gases condense and etch cylinder walls and piston rings. Once oil pressure comes up, which happens quickly in a healthy motor, the problem is taken care of. That's part of the reason it's a good idea to run a cold engine 15 to 30 seconds before driving off.

It's this kind of wear that PTFE (better known as Teflon) additive makers used to claim their products would prevent. However, because PTFE (polytetrafluoroethylene) doesn't bind with metal parts, this kind of wear isn't prevented by the additive.

As I've said before, oil already has its own additives, and nobody aside from the additive makers recommends putting more of anything into your engine.

The base for most additives is 50-weight engine oil. To the base, the company might add PTFE, zinc dialkyldithiophosphate or varying combinations and amounts of what's already in oil. There are also products that are made up primarily of solvents and/or detergents.

PTFE is a popular ingredient for oil additives, and the brands that contain it are among the bestsellers, including the No. 1 additive, Slick 50. Despite its popularity, PTFE is by no means a proven ingredient for use as an engine lubricant. DuPont's fluoropolymers division originally took the stand that PTFE was not useful in internal combustion engines. DuPont went so far as to refuse to sell PTFE to any company that was planning to use it that way. It was sued for restraint of trade and lost. Additive makers also found other sources for the product. DuPont's official stance is now much more neutral. The company has said it has no proof of additive makers' claims and it has no knowledge of any advantage gained from using PTFE in engine oil.

Were that not enough, in July 1996, the Federal Trade Commission accused Quaker State, the maker of Slick 50, of false advertising for making unsubstantiated claims about the additive's ability to reduce wear, cut emissions, increase mileage and boost horsepower. Quaker State and its subsidiaries signed a consent agreement limiting their advertising claims in July of last year. (Keep in mind that a consent agreement is for settling the complaint filed by the FTC and does not constitute an admission of wrongdoing.)

But what's really wrong with PTFE in engine oil?

In a word, it's solid. Sure, it's a very fine powder, but a solid nonetheless. And if PTFE is capable of binding to metal parts under extremes of temperature and pressure, then it's probably really good at collecting in places where temperature and pressure are lower, such as oil passageways. Tests performed by NASA's Lewis Research Center found that PTFE provided no benefit for bearing surfaces. The study also found that in some cases the solid tended to accumulate at inlets, blocking the flow of oil and depriving parts of lubrication.

Another point to keep in mind is that your oil filter's purpose is to take suspended solids out of the oil. Too many solids will clog your filter and cut pressure in the engine. Some additive makers say they use a PTFE that's fine enough for the particles to pass through an oil filter. However, PTFE expands when exposed to heat.

A test by the University of Utah Engineering Experiment Station involving a PTFE additive detected a pressure drop that resulted from possible clogging of the filter. "In addition," the report read, "oil analysis showed that iron contamination doubled after using the treatment, indicating that engine wear didn't go down--it appeared to shoot up."

This test was paid for by Petrolon, the marketers of Slick 50 at the time. It wasn't all bad news; there were some increases in horsepower (5.3% to 8.1%) and mileage (11.8% under a light load and 3.8% under a heavy load). Are those increases worth lower oil pressure and increased wear? I don't think so--there are other ways to get those benefits without the negative effects.

So while it sounds good to coat your engine's parts with Teflon, it doesn't mean the reduction of friction is going to be as effective as a nonstick omelet pan.

Another popular active ingredient in oil additives is zinc phosphate compound. It's not the stuff in cold lozenges but a chemical that is already in motor oil in varying amounts. There are higher amounts of zinc in performance or racing oils because it offers protection against metal-to-metal contact, particularly between cylinder walls and piston rings.

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