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How to Test Engine Compression

compression test

How to Test Engine Compression

Testing engine compression in the AMSOIL mechanical lab.

Engine compression = engine power.

A simple equation even we non-engineers can understand. Compression refers to the pressure your engine generates inside the cylinders while it’s running. How much pressure the engine produces and how well it converts that pressure into usable work influence your engine’s efficiency and power.

How it all works and how wear and deposits can erode compression (i.e. horsepower) over time are interesting topics you can read more about here. But today, we’re talking about how to test engine compression.

For this example, I used my 1998 Toyota Corolla. Don’t laugh. I paid cash for it and it runs as smooth as a sewing machine. I also sought the help of Pat Burgraff, one of the techs in our Mechanical Lab. Pat knows his way around an engine.

#1 Ensure the vehicle won’t start when you crank it over

Testing compression requires you to crank the engine several revolutions, and you don’t want it to fire in the process. Remove the fuel-pump and fuel-injection fuses so you’re not dumping gas into the cylinders each time you crank the engine. Then, disconnect the coil packs. Bear in mind the process for your vehicle may be different from the images here.

Disconnect power from the coil packs.

#2 Pull the spark plugs

Label the plug wires so you return them to the correct positions. Otherwise, your vehicle won’t start when you’re done. Thread the compression gauge into a spark plug opening. Take care not to cross-thread it. You can get a compression tester for less than $50 at most auto parts stores.

#3 Crank the engine

Have a helper crank the engine 5-10 times, or until the needle on the compression gauge stops ratcheting up. Note the psi and move to the next cylinder.

Thread the compression gauge into a spark-plug hole.

Crank the engine until the gauge stops ratcheting up.

What’s considered normal compression?

Here’s where things grow murky. “Good” compression depends on the engine. Unfortunately, engines don’t come with their proper compression stamped on the outside. But a good rule of thumb says that each cylinder in a mechanically sound engine should have compression of 130 psi or higher. While I’ve seen some people claim 100 psi is sufficient, the gearheads and other sources I’ve consulted consider that too low.

In addition, you want consistency from one reading to the next. Again, a good rule of thumb is no more than 10 percent variation between any of the cylinders. That’s not to say 15 or 20 percent variation in one cylinder means your engine is junk. But a good, healthy engine should demonstrate minimal variation.

My trusty Corolla nailed the test, making between 165-175 psi in each cylinder.

If one cylinder has low compression, try pouring about a teaspoon of oil into the spark-plug hole and retesting. If compression increases, it’s likely the rings are stuck or worn. The oil acts as a seal and helps close the gap between the rings and the cylinder wall through which the cylinder is losing pressure.

If that doesn’t work, it’s possible the valves or valve seals are worn.

If you suspect stuck rings, try an engine flush designed to clean deposits, such as AMSOIL Engine and Transmission Flush. You can also try a fuel additive that cleans pistons, like AMSOIL P.i.

Word to the wise: you may illuminate your check engine light performing this test, as I did. It went off by itself after driving a few miles, though.

McDonalds or KFC: Should I Run Vegetable Oil in my Diesel?

French fries oil fuel

McDonalds or KFC: Should I Run Vegetable Oil in my Diesel?

Can Your Motor Oil Handle the Seven Responsibilities of a Lubricant?

Spring Oil Change

Can Your Motor Oil Handle the Seven Responsibilities of a Lubricant?

Most motorists understand the primary functions of motor oil: reduce friction and wear. However, motor oil and other lubricants must do more to protect your vehicles and equipment. With engines and equipment becoming more powerful and sophisticated, it takes a properly formulated, well-balanced lubricant to carry out these seven critical functions.


• Minimize Friction

Lubricants reduce contact between components, minimizing friction and wear.

• Clean

Lubricants maintain internal cleanliness by suspending contaminants within the fluid or by preventing the contaminants from adhering to components. Base oils possess a varying degree of solvency that assists in maintaining internal cleanliness. Solvency is the ability of a fluid to dissolve a solid, liquid or gas. While the solvency of the oil is important, detergents and dispersants play a key role. Detergents are additives that prevent contaminants from adhering to components, especially hot components such as pistons or piston rings. Dispersants are additives that keep contaminants suspended in the fluid. Dispersants act as a solvent, helping the oil maintain cleanliness and prevent sludge formation.

• Cool

Reducing friction minimizes heat in moving parts, which lowers the overall operating temperature of the equipment. Lubricants also absorb heat from contact surface areas and transport it to a location to be safely dispersed, such as the oil sump. Heat-transfer ability tends to be a trait of the base oil’s thickness – lighter oils tend to transfer heat more readily.

• Seal

Lubricants act as a dynamic seal in locations like piston rings and cylinder contact areas to prevent contamination.

• Dampen Shock

A lubricant can cushion the blow of mechanical shock. A highly functional lubricant film can resist rupture and absorb and disperse these energy spikes over a broad contact area. As the mechanical shock to components is dampened, wear and damaging forces are minimized, extending the component’s overall operating life.

• Protect

A lubricant must have the ability to prevent or minimize internal component corrosion. Lubricants accomplish this either by chemically neutralizing corrosive products or by forming a barrier between the components and the corrosive material.

• Transfer Energy

Because lubricants are incompressible, they can act as an energy-transfer medium, such as in hydraulic equipment or valve lifters in an automotive engine.

Lubricants do far more than simply protect against wear. High-quality lubricants – like AMSOIL synthetic lubricants – are formulated to excel in each of these critical areas, ensuring you get the most out of your vehicles and equipment.

Why Jay Leno Is Angry About Ethanol In Gasoline

fight ethanol problems

Why Jay Leno Is Angry About Ethanol In Gasoline

Change is the one constant in life. It’s also difficult, because when there is a change – whether in technology or how we do things – there are often unforeseen consequences.  One of the changes that has been taking place is that since 2005, the U.S. government has mandated that gasoline contain ethanol, most of it derived from corn.  The aim of this policy, among other things, has purportedly been to reduce our nation’s dependence on foreign oil, though it may also be a way to utilize the excess corn of our megafarm corn growers. What this change has done is to set in motion a number of unintended consequences, from its impact on food prices to mechanical issues in our cars and other equipment with engines.

And this latter is what prompted comedian and car collector Jay Leno to write a somewhat impassioned column in Autoweek this month titled, “Can’t We Just Get Rid Of Ethanol?”

Leno argues that this change to ethanol in gasoline has damaging consequences for older cars. The piece begins with a paragraph about the rise in the number of old-car fires lately, stating that the cause is related to the corrosive nature of ethanol when in contact with fuel-pump diaphragms or old rubber hose lines.

Change is a challenge in any field of endeavor, which is why we depend on others to help make us aware of the consequences of change so that worst case scenarios can be avoided. When fuel injectors became the standard in modern engines it was soon learned that deposits on the injector tips needed to be managed. AMSOIL introduced P.i Performance Improver at that time to address this, a much cheaper solution than replacing injectors every time they fouled.

So it is that ethanol in gasoline is now recognized to be a serious issue due to a phenomenon called phase separation. Ethanol is susceptible to water intrusion; when water collects in the gas tank through condensation or other means, the bond between ethanol and gasoline can break because ethanol is hygroscopic (it likes water more than it likes gasoline).

When the ethanol bonds with moisture it sinks to the bottom of the fuel tank, which can create a whole host of problems, including the formation of gums, varnish and other insoluble debris that can plug fuel flow passages and negatively affect engine performance. When this ethanol/water mixture is pulled into the engine, it creates a lean-burn situation that increases combustion chamber temperatures and can lead to engine damage.

Four years ago AMSOIL earned a SEMA New Products award for Quickshot, a gasoline additive developed specifically to address this issue of phase separation. Though initially introduced in a smaller package size for small engines, AMSOIL more recently introduced a quart-sized bottle for automobiles that sitt idle for any length of time.

The more you know, the more you discover how important it is to stay current with the changes occurring all around us, especially when it involves something you’re passionate about like your cars.

What to Do When Your Car is Underwater

Ohio Flood, July '06

What to Do When Your Car is Underwater

Ohio Flood, July '06

 

Hurricane Harvey hit Houston hard.

Tragically, reports say the hurricane claimed the lives of at least 60 people. It has also wrought devastation to countless communities and households.

It seems meaningless by comparison to the lives lost, but some reports say that one million cars were destroyed. Images of submerged vehicles quickly circulated the Twittersphere in Harvey’s wake. Floods of all kinds are merciless and heartbreaking, but especially so on a scale this massive.

I remember when I was growing up in New Jersey we had a torrential rainfall one year and the creek below our next-door neighbor’s house went from five feet wide and one foot deep to 100 yards wide and 10 feet deep, filling the neighbor’s basement with water. When the water receded, the change in the water’s velocity as it went through the house left behind a couple feet of silt in the basement. The appliances were ruined and it was a heckuva mess to clean just this one house. I can’t imagine a whole city being taken out like this.

Or a million cars.

Speaking of which, a dozen years ago I had a friend who dabbled in automobile auctions. He drove to Chicago or Minneapolis, bought a few cars at auction, towed them back north to repair them and finally sold them. On one occasion I was looking at cars with him and I saw a brand-new Jaguar. I had always thought it would be cool to have a Jaguar, and this one was only $100. The reason it was so cheap? It had been underwater. That car had seen its best days.

What to do if your vehicle floods

If you Google this issue, there are several websites with advice on dealing with cars caught in floodwaters. Here are a handful of tips extracted from this Popular Mechanics article.

  1. “How high’s the water, mama?” –Johnny Cash
    First, try to identify the high-water line. Usually there will be leaves, debris or silt that indicates how high up your vehicle the water reached, sort of like a bathtub ring. If the water line goes partway up the windshield, scrap the vehicle.
  2. Disconnect the battery ground strap before tinkering.
  3. Do not start the engine to see if it still runs. As the saying goes, oil and water do not mix. If there is water in the engine and transmission, starting the car will turn that oil/water mix into a gooey mess, thereby making it that much more difficult to clean.
  4. Get as much water out of the vehicle as quickly as you can as soon as you can. The best tool is a wet/dry shop vac. Soak up all you can with towels and run fans to dry the vehicle. Some people recommend baking soda or some other moisture-absorbent product to reduce the chance of mold taking over.
  5. Change the oil, drivetrain fluids and filters. If this is beyond the scope of your auto maintenance skills – yes, the tranny fluid can be a pain – have your car towed to a place where the work can be done for you. That’s why people like me pay for AAA coverage. It’s a lot cheaper than a new car. (Note: Don’t tow the vehicle with the wheels on the ground; that defeats the purpose. Instead, use a flat-bed truck.)

I hope this is helpful. And don’t forget – try to park on high ground.