How Engine Wear & Deposits Kill Horsepower

Most people equate engine wear and deposits with a sudden, catastrophic engine failure that leaves you stranded alongside the road. In reality, wear and deposits are more likely to erode engine power and efficiency over time. Here’s how it works and what you can do about it.

Engine compression = power

For your engine to produce maximum power, the combustion chamber must seal completely during the compression and combustion strokes. Wear and deposits can prevent the valves or piston rings from sealing, allowing pressurized gases to escape the combustion chamber and take potential engine power with them.

To illustrate, imagine using a hydraulic floor jack. Pumping the handle will raise the vehicle as long as the release valve is tightly seated and doesn’t leak. A poorly sealed release valve, however, allows pressure to escape, causing the vehicle to sink to the ground no matter how much you pump the jack handle.

The same principle applies inside your engine. If some of the pressure created during the compression and combustion strokes is lost due to valves and piston rings that don’t seal completely, the engine will create less power.

how wear and deposits kill horsepower

Wear & deposits reduce compression

Over time, deposits or valve wear can prevent the valves from closing completely, interfering with a good seal. Wear can also interfere with proper valve operation, disrupting optimum fuel/air flow.

piston ring against cylinder wall
If the piston rings do not seal tightly against the cylinder wall, pressurized combustion gases can escape past the rings and enter the crankcase, taking potential power with it.

Worn or stuck piston rings produce the same effect. The rings are designed to move freely in their grooves and press tightly against the cylinder wall. They should form a seal that prevents fuel/air from escaping. Ring wear can interfere with formation of a tight seal. Likewise, deposit buildup can cause the rings to stick in their grooves, also preventing a good seal. As a result, some fuel/air escapes the combustion chamber during compression, reducing power. On the combustion stroke, pressurized gases can blow by the rings and travel down the cylinder wall and into the oil sump, taking potential power with them. This is what’s meant when someone says an engine has lost compression.

(Check out our 5 Ways to Boost Horsepower for Under $500)

AMSOIL Signature Series helps prevent the problem

AMSOIL Signature Series Synthetic Motor Oil provides…

  • 75% more engine protection against horsepower loss and wear*
  • 62% cleaner pistons than required by the proposed industry standard**

Its outstanding performance helps prevent deposits and wear that rob engines of horsepower, helping preserve that like-new feeling you crave when driving.

To prove it, we installed Signature Series 5W-30 Synthetic Motor Oil in a Ford F-150 with a new 3.5L Ecoboost engine to test its ability to protect turbocharged direct-injection (TDGI) engines from torque and horsepower loss during extended drain intervals up to 25,000 miles. Power sweeps were done at the beginning and end of the test to evaluate horsepower and torque retention. As the video shows, Signature Series helped maintain engine performance throughout the 100,000 mile test.


*Based on independent testing of AMSOIL Signature Series 0W-20, in ASTM D6891 as required by the API SN specification.

**Based on proposed ILSAC GF-5 Plus specification.

Updated. Originally published: October 25, 2017


  1. Other than idling 15 minutes with Amsoil Engine and Transmission Flush, drain, and adding Amsoil 5W-30 Signature Series into my 200k miles 2000 Volvo S80 2.9L non-turbo WORN engine with sludge, what else can I do to further reduce friction in the engine?

    Do you also recommend that I do a flush and oil change at least 3 times after every 3000 miles?

    1. Steve,

      Please call AMSOIL Technical Services at 715-399-TECH and they can answer all your questions about your Volvo at once.



    1. Hi George,

      Use SABER Professional Synthetic 2-Stroke Oil for your chainsaw, string trimmer, leaf blower and other handheld equipment. Use HP Marine Synthetic 2-Stroke Oil in your marine motors. Use INTERCEPTOR Synthetic 2-Stoke Oil in your snowmobile. If you’re into racing or modified engines, use DOMINATOR Synthetic 2-Stroke Race Oil. And, if you want a less-expensive, good all-around two-stroke oil for your outboards or sleds, we offer Synthetic 2-Stroke Injector Oil.

      When in doubt, contact your local independent AMSOIL Dealer and he or she will be glad to help you.

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