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Tips and Advice on How to Pass a Smog Test

No matter what you do, some cars just won't pass the smog test.

No matter what you do, some cars just won't pass the smog test.

Knowing how to pass a smog test is one of those essential bits of knowledge that every car owner in California should know. But there are a lot of pitfalls involved in passing a smog test. Some people inadvertently shoot themselves in the foot doing things that they'll think should help them pass a smog test but, in fact, cause them to fail.

A Few Misconceptions About Smog Checks

  1. There's nothing I can do to help my car pass. Wrong. There's a lot you can do, which we'll talk about in the next section.
  2. Higher octane fuel will help me pass. The biggest mistake people make is buying more expensive fuel. People often have the misconception that how to pass a smog test is to use premium 91 octane fuel. It seems to make sense, right? More expensive fuel is probably purer, which means it probably burns cleaner and gives off fewer emissions right? Wrong. 91 Octane fuel contains higher amounts of combustible chemicals, which means it's formulated to burn longer, in higher performance engines. If you put it in an engine that's not meant for high performance, the fuel won't completely burn up inside the chamber, meaning that every time a piston fires, a little bit of unburnt fuel will be pushed out of the exhaust, causing much MORE emissions to come out of the engine.

Tips on How to Pass a Smog Test

These tips will not only help vehicles pass a smog test, but run at higher performance and get better gas mileage:

  1. Use low octane fuel. The lower the octane the better. We already discussed above that buying premium fuel can cause you to utterly fail your smog test. Go the other way. If you can find 85 octane fuel, use it. Don't use it permanently—just use it to pass the smog test. What happens is that lower octane fuels burn up faster while still in the combustion chamber, giving your engine the maximum amount of time to incinerate those pesky emissions, before sending them on their way.
  2. Do a tuneup. Cars run inefficiently after awhile because the individual components are either clogged or wearing out. If you clean or change your air filter, get new spark plugs, and get an oil change, you'll notice your car is running at higher peak efficiency.
  3. Use a heavier oil. Vehicles that burn oil have more emissions. Old vehicles are especially notorious for leaking a bit of oil into the combustion chamber. That's why heavier oils were invented, to slow down these little leaks. If you know your engine is burning a little bit of oil, ditch the 5w30 or 10w30 and ask them to put in something like 10w40 or thicker.
  4. Use a fuel injection cleaner a few weeks beforehand -- It's always a good idea for your engine and fuel system to be as clean as possible before you go into a smog station. A few weeks before your trip, pour a bottle of fuel injection cleaner into your gas tank when you go for a fill up at the gas station. This will hopefully take care of some of the gunk and grime clinging to your fuel system.
  5. Use a fuel treatment system. If you're really worried about passing your smog test, buy a fuel treatment system that specializes in lowering emissions. Lucas Fuel Treatment is one such specialized formula that seems to get some great results. I've read a lot of testimonials online and people seem to really like it.
  6. Clean your MAF sensor. The mass air flow sensor (MAF) helps to determine the amount of air to add to the fuel/air mixture. If your MAF sensor is dirty, it can cause the fuel mixture to be too rich in gasoline, which can lead to excess emissions.

Reject This "Tip" on Rubbing Alcohol

While using fuel additives like methanol and ethanol to pass a smog test is illegal, some say that rubbing alcohol (isopropyl alcohol) might be legal, though I wasn't able to find anything definitive on that. In general, adding alcohol to the fuel is risky. It can damage rubber seals that are very difficult to replace, once damaged. Damaged rubber seals within the motor can cause oil leaks into the combustion chamber and other unpleasantness. To be safe—and to make sure you're not breaking the law—I'd say pass on the rubbing alcohol.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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