valve seals

Bad Valve Seal Symptoms, Information & Replacement Cost

In Engine by Magnus Sellén2 Comments

valve sealsA vehicle has around 30,000 working parts both big and small.

With so many parts it should not be surprising that some parts wear out over time and need replacement. The highest concentration of wear in a vehicle is in its engine. Since the engine heats up and creates a lot of pressure, some components are bound to lose integrity.

Valve seals are one such component that can be adversely affected by the heat and pressure of an engine.

The Function of a Valve Seal

A valve is responsible for regulating the amount of fuel and air that goes into an engine’s combustion chamber. Since the combustion chamber is pressurized, its contents look for an escape route after every cycle. It is possible for the combustion gases to leak into the valves and get mixed up with fuel. To stop that from happening valve sleeves are put in place. Furthermore, it is also possible for the engine oil circulating through the system to get sucked in the valve chamber.

To prevent that from happening valve seals are used to shut off the passage of oil. Valve seals are made of high-quality hardened rubber which maintains the pressure in the combustion chamber and prevents foreign objects from entering into the system. Over time these seals deteriorate and your engine starts to feel the effects. As a driver, you should be aware of when that happens. Fortunately, there are some signs that can help you detect valve seal failure.

Symptoms of a Valve Seal Failure

1. Residual Oil on the Engine

valve seal replacementValve seal failure is easy to catch if you are starting a cold engine. If you are starting your car after a long period of time, take a look under the valve cover and in top of the engine’s head. There should be residual oil over there that must have come over there because of a leaking valve seal. Furthermore, on a cold engine start, you will see a cloud of thick white smoke coming out of your car’s exhaust, that largely means your engine’s valve seals have been compromised.

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However, you need to look under the hood and under the valve cover to notice any change. Some people are not aware or simply too lazy to do the work themselves and end up reducing the life of their car.

2. Rough Idling

A failing valve seal will be easily noticeable when your car is idling. When the car is stationary, the high amounts of vacuum from the intake manifold closes the throttle shut which results in the oil getting sucked in at the valve’s stem. As soon as you accelerate, this oil seeps into the combustion chamber because the valve seals are failing and it burns which results in white smoke emitting from the exhaust.

Keep in mind that this only happens in city driving or when you are stopping and moving rigorously as you would while stuck in traffic. During highway cruising such white smoke goes away.

3. Downhill Braking

When your foot is off the throttle, the intake manifold creates a vacuum that sucks in the oil as mentioned before but that effect is helped by the downhill position of the car that facilitates the movement of oil towards the front of the engine. As a result, there is more oil gathered at the top front of the engine and in the absence of a good valve seal this oil leaks into the combustion chamber as soon as you accelerate. Once again smoke will emit from the exhaust signaling towards a valve seal failure.

4. Bad Oil Consumption

We know about the role of engine oil in an engine. It helps lubricate the mechanical components to allow them to run smoothly. As such engine oil circulates inside the engine continuously. If there is a leak somewhere, in this case, a valve seal failure, the amount of engine oil in circulation will be reduced. This will keep on happening until the oil levels have depleted. You would find yourself going for an oil change frequently.

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You would also see that the oil gets black and dirty sooner since it burns up. As soon as you face this problem, book an appointment with a mechanic and get the valve seals checked. You using up ten minutes of your time at the earliest would save you from wasting time frequently for an oil change.

5. Too Much Smoke From Exhaust

Initially, when the valve seals start to deteriorate the smoke would emit in small quantities and then disappear. However, once the problem starts to get worse the smoke will get worse. You will notice that the white smoke lasts longer than before and it doesn’t go away even when you are cruising at fast speeds.

When this happens you should not waste a moment and go to the mechanic directly. The mechanic will have a clear idea of what to do. He will change the valve seals for you so you could keep on driving safely.

6. Loss in Acceleration

Faulty valve seals will reduce the pressure in the combustion chamber which would directly result in less power created by the engine. Your car will lose acceleration which could prove to be dangerous if you are driving on a highway. Fortunately, a loss in acceleration is immediately discernible so you are not oblivious to the damage.

Valve Seal Replacement Cost

Valve seals are made of rubber so they do not cost a lot of money. Furthermore, they do not break frequently so you don’t have to worry about getting them changed every now and then. Depending on your car a new valve seal replacement could cost you from $40 to $150 for the product.

However, the bad news is that a valve seal replacement takes a lot of time. You are looking at around 3-4 hours of labor work and we know that the labor costs of a mechanic are not cheap. A professional mechanic would easily charge you $100 or more per hour for the replacement. So, you could expect to pay around $300-$400 for a simple valve seal replacement.

  1. Can you please provide a comment and/or a best-guess cause of the following complaint: Smoke at cold start (white-blue) that occurs approximately every second or third day. Smoke lasts approximately 5 minutes. Compression test gives good numbers for all 4 cylinders. (Vehicle is a 1999 Honda CR-v – 2.0 motor). Engine runs fine – no misses, idles fine, good acceleration and no random ‘noises’. Oil consumption is minimal – approximately a litre between regular oil change schedules. Use synthetic oil. IF it has worn valve seals, could you provide an approximation of # of hours to replace them…??? Any help is much appreciated – I’m retired pensioner, so $$ are no longer as plentiful … 🙂 – …. thanks for any help!

    1. depending on the type of engine, should take no longer than 2-3 hours with the proper equipment (VALVE SPRING COMPRESSOR). i had to create my own, using a 12” 1k working load clamp, which i applied to a windowed 4” pvc pipe. wear goggles for your safety! keepers are hard to keep!

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