What Are Valve Seals?

Inside an engine, valves are the gatekeepers. Intake valves let in air (or a mix of air and fuel), while exhaust valves let out the spent gases. Each cylinder usually has one or two of each type.

Valve stem seals, made from tough rubber, are small but mighty—about the size of a fingertip. Their main gigs are:

• Keeping pressure from escaping.
• Preventing oil from sneaking into the combustion chamber through the cylinder head.

What Are Piston Rings?

Pistons move up and down in the engine cylinders, and each one is surrounded by piston rings. Most pistons sport three rings: the top two seal the compression in the combustion chamber, while the bottom one acts as an oil seal.

Piston rings have a few key jobs:

• Keeping pressure contained in the chamber.
• Stopping oil from splashing in and getting burned.
• Stabilizing the piston during its up-and-down dance.
• Helping manage temperature by spreading heat from the piston to the cylinder walls.

Symptoms of Bad Valve Seals and Piston Rings

When valve seals and piston rings start to fail, they can’t do their job of keeping pressure in and oil out. So, it’s no surprise that the signs will be all about compression and oil issues. Here’s what to watch for:

• Increased Oil Consumption: If oil starts making its way into the combustion chamber, it’s going to burn up, leading to higher oil consumption. Look for:
• Gray or blue smoke puffing from the exhaust. That’s the oil burning.
• Low oil pressure warning lights.
• Coolant overheating on the temperature gauge.
• Low oil levels on the dipstick or sensor.
• Reduced Engine Power: When the seals or rings are shot, pressure leaks out. This means less oomph when the spark plug ignites the air-fuel mix. Signs include:
• Sluggish acceleration.
• Struggling to hit higher speeds.
• Rough idling.
• Stalling or shaking from an unbalanced engine.

How to Tell if It’s Piston Rings or Valve Seals

Spotting oil on the spark plug? That’s a telltale sign of bad valve seals. Piston rings tend to fail more often than valve seals, so if a pressure test fails, it’s likely the rings that are the problem.

If the pressure test leaks slowly, it’s probably the valve seals at fault. A mechanic can confirm this by removing the cylinder head to check things out.

Replacement Costs for Valve Seals and Piston Rings

If the valve seals are good but the cylinder isn’t holding pressure, an engine rebuild might be in the cards. A blown head gasket is often the first thing a mechanic will check.

For those who aren’t car-savvy, this isn’t a DIY job. The only way to know for sure if the piston rings are the issue is to tear down the engine.

Rebuilding an engine isn’t cheap—expect to shell out at least $3,000. If it’s a larger or rare engine, the costs can skyrocket.

Replacing valve seals involves removing the cylinder head and other components, and this can run between $1,000 and $1,500.