3 Symptoms of Bad Valve Seals and Piston Rings and Replacement Cost

In this article, we’re going to discuss the symptoms of bad valve seals and piston rings, as well as their basic functions and common replacement costs. Valve seals and piston rings are crucial for your engine to function. If you learn to recognize the warning signs for these components, you’ll be able to replace them before any serious damage is done to your engine.

Functions of Piston Rings

Piston rings are located between the piston and cylinder and provide four different functions:

  1. Compression Seal:  The ring creates a seal, preventing combustion gasses from leaking out of the chamber. Leaks can drastically reduce engine performance.
  2. Heat Transfer:  Every time combustion occurs, the internal temperature of the chamber spikes. These high temperatures can cause serious damage. A piston ring helps transfer this excess heat from the piston head to the cylinder, reducing the risk of heat damage.
  3. Lubrication Control:  A film of oil is necessary to keep the piston lubricated. The piston ring helps regulate the amount of oil that reaches the piston.
  4. Piston Support: The piston works on a crank and could easily bang into the cylinder wall if not for the piston ring’s padded support.

It is important to note that piston rings wear out, which means you’ll have to have them replaced routinely.

Functions of Valve Seals

Valves regulate how much of the fuel mixture enters the cylinder. The valve itself has a seal (and sometimes a protective sleeve) to help prevent leakage of combustion gasses and prevent oil from leaking into the main engine area.

These seals are commonly constructed out of a super strength rubber material and they’re placed into a small collar of the valve stem’s top area. Once these valve seals start to wear out, you’ll begin to notice some major symptoms that are unique to this problem.

Symptoms of Bad Valve Seals and Piston Rings

The symptoms of bad valve seals and piston rings are quite similar. Whenever either fails, the performance of the vehicle will drop,  and other symptoms will manifest. Let’s take a look at some warning signs that these components are going bad:

#1 – Exhaust Smoke

If you notice thick smoke that’s blue-gray or light-gray, this is a good indication your car is burning oil. It’s a sign that oil is leaking into the combustion chamber of your engine.

#2 – Too Much Oil Being Consumed

As mentioned above, if the piston rings are worn out or the valve seal is broken, oil will begin to leak into the combustion chamber. This causes your engine to use up its oil supply much quicker.

#3 – Not Enough Accelerating Power

When there is damage to the piston rings and valve seals, compression will be reduced. This causes you to lose engine power. As a result, you won’t be able to accelerate when you put your foot on the gas pedal.

Although bad valve seals and piston rings have similar symptoms, the time and costs of repairing them are quite different. Learning to pinpoint which one is bad by yourself will help save both time and money when taking it to a mechanic for repair.

You can do a compression test to help pinpoint the problem. Remove the EFI fuse and crank the engine. Then check the results on the compression gauge.

In the event your compression test results appear to be average or higher, the valve seals are likely the problem. However, low compression usually indicates that the piston rings are your problem.

To further confirm worn piston rings are the problem, do a wet compression test. Here you open the spark plug and inject a bit of oil (about a tablespoon) into the cylinder. If the compression increases, your piston rings are bad.

Replacement Cost of Piston Rings

When replacing piston rings, the cost will be determined by several factors. The make and model of your vehicle is one example. You also have to consider the type of engine that’s in your car and its condition. Most mechanics will charge around $1,500 minimum for this task, up to about $2,500.

The reason this replacement job is so expensive is because it can be quite complicated. The engine must be completely disassembled and the cylinders reconditioned. After that, the car is reassembled. Only an experienced mechanic can perform this task efficiently, requiring several hours to do so.

Replacement Cost of Valve Seals

If you have discovered there is damage to your valve seals, then have an auto technician install new oil seals. The cost of this replacement job will be between $900 and $1,800, depending on the make and model of your vehicle. The process of replacing valve seals involves disassembling the entire engine until you can reach the valve spring.

Remove the cylinder head cover, the spark plugs, pushrods, and rocker arms. How long this will take depends primarily on the make and model of your vehicle. Sometimes the technician will have to dismantle and remove the cylinder head, then use a cylinder kit which contains a cylinder head gasket to replace it.



  1. Thank you so much for such a thorough post. It has been my desire lately to educate myself concerning engines. My 1990 Toyota Celica GTS has 200,000 miles. The previous owner did not maintain the engine adequately, so I am reading, studying, troubleshooting, and in most cases, attempting the repairs myself. I look forward to any other articles you may wish to share.

  2. if I used GUNK heavy duty gel degreaser and original engine degreaser in order to clean up inside of the head and didn’t blow it out completely from under the springs because of hard access in Subaru head. Would the degreaser destroy my valve seals as a brake cleaner would do it by drying them out and cracking?

  3. Based on what I have read online, it seems that the piston rings in my car are faulty. I have a 2007 toyota camry and it consumes a lot of oil. Even toyota acknowledged it and have extended their warranty. Unfortunately, the warranty doesn’t apply to me as my car is older than 10 years. I end up adding around 1 quart every 500 miles. Is it ok for me to keep adding oil whenever it is low? I don’t want to spend $2K to fix the problem, as I am only planning on using this car for maybe 2 more years. Could there be any serious damage is I keep adding oil and getting oil changes in regular interval?

    • actually oil will always burn in combustion chamber…and your engine life span will effect in the future, but is okay you can always add the oil and can run the vehicle with smokes blowing from exhaust
      just let you know, between a bad piston ring and valve seal mostly same symptoms, and cost replace valve seal is lower than piston ring.

      • Hi…Thanks for your inputs on this issue. I am also having similar complaints with my 2014 Kia Rondo. It has about 150000 Kms on it and since past one year, it is consuming around 5 Litres of engine oil for every 5000 Kms only as Top Up. On an average, I have to top it up every 800-1000 kms. But there is no blue smoke at all though I have noticed fuel smell inside the car occasionally and a decrease in the engine power lately.

        My service mechanic has advised me to replace the engine as the issues with piston rings and valve seals are beyond repair. The replacement cost is around CAD 6000.
        It would indeed be wonderful if you can guide me on the best path forward as I intend to use this car for another six months to one year.

        1. Can the engine stop running all of a sudden anytime ?
        2. Are there any passenger safety issues if I keep running this car ?
        3. For how long can I keep adding up the oil and using it ?

        Kind Regards

        • 1. possible if you forget to add oil
          2. i think no problem while you car run in the short trip and low speed 40 – 60 km/h
          3. Depend on how often you use the car

  4. In the article you wrote: Exhaust Smoke – If you notice thick smoke that’s a gray or white color, this indicates that your car is burning oil. What about intermittent light blue smoke. Other online info says it’s also a signal that you’re burning oil. What do you say about blue smoke at times but not always?

      • it , they say, chrysler 300 6 cyl , has bad “top and bottom” smoke and loud pings . recommend replacement engine. finding one for less than the rings , very hard. what best idea?

        • My 2010 Toyota Corolla makes has rattling noise and I was told by a mechanic that it was a bent valve however another mechanic friend said that is not because the car runs good plus it just passed the smog check this past month. I bought this car a few weeks ago and I don’t know wether or not last owner maintenance the car or not. What symptoms would my car have it it is a bent valve I don’t count with to much money at this time so i will really appreciate any kind of advice.

  5. My 2.8 diesel engine is not starting after i changed the cylinder head from to new..i have put back everything in place where it is supposed to be..but the engine just turning over and over again but not starting..any idea what it is?

    • some car need to dismantle cylinder head, most car no need (especially 4 cyl car)
      approx: 3 – 8 h
      Most common job to be done:
      -Put piston on TDC
      -remove valve cover
      -remove camshaft
      -remove timing belt / chain
      -put air pressure to cylinder through spark plug hole ( to avoid valve comes down)
      -remove valve spring
      -remove seal
      and then drink coffee (as i did to recharge energy, lol)
      -fix seal
      -fix spring
      -fix camshaft
      -fix timing belt / chain
      -fix valve cover
      and so on….


  7. I just recently changed the piston rings, gasket etc of my Honda car due to the fact that it was emitting white smoke. But after the repair the car is still smoking same whit smoke. My vehicle Mechanics said it should stop soon but I am really worried as to what could be the cause

    • If it’s white smoke and not just due to normal condensation when first warming up the car, it can mean coolant is leaking into your engine. If it’s more of a light gray or light blue smoke, that would indicate oil leaking. If that’s the case, you may still have some residual oil being burned off from the leaking seals or piston rings which should stop soon. But if it doesn’t go away after a couple days you may still have an issue or different issue.

  8. Hi. You note: “In the event your compression test results appear to be average or better, the piston rings are likely the problem. However, below average results prove that the valve seals are your problem.”
    Isn’t that the opposite of what the test means? Smoking with good compression means the rings are in good shape and still maintaining compression, but the seals are worn; while poor compression indicates the rings are shot, and the seals could be either good or bad.

  9. I noticed reduced amount of coolant after a while. My spark plugs gets soaked with oil. Light blue smoke from tail pipe at start up and reduces while in motion. finally shortage of engine oil… Pls what do you think is the problem of my engine

  10. Hmm definitely don’t want to *fill* your cylinder with oil and then immediately do a compression test, as this will hydrolock the engine (worst case scenario) or at least fill your exhaust system with oil (best case scenario).

    Also worth noting that these are both jobs that a moderately experienced home mechanic can do with relatively simple tools available at harbor freight or any auto parts store. No need to shell out thousands of dollars fixing it (many cars can get a replacement engine under $2000…my last replacement engine was $100)

    Otherwise, nice guide. Could you explain why good compression indicates bad rings, while bad compression indicates bad valve stem seals? I was thinking it would be the opposite. Replacing the valve stem seals tomorrow either way, and if it’s still smoking after that I’m just gonna pull the engine and overhaul it, but would be nice to learn to positively identify which one was failing so I don’t just resort to buying full gasket sets every time this happens.

  11. Nice expositions there @autotechnician,
    I am from Nigeria and I use a Honda Accord, the old 1990s model. I have two issues with the car. Firstly, I see blueish smoke if the car is parked for 3 days, the smokes stop once the car starts moving.
    Secondly, when I press my brake pedals for long on a slope or a decline, the pedal starts to go down gradually and the car starts sliding forward or backward depending on the position of the car. Please what could be the problem and what should I do?
    Thank you.

    • The blue smoke is likely oil slowly leaking through your valve seals. When your car is sitting, the oil slowly leaks into the combustion chamber. When you start the car, the oil is burned off.
      For the brake issue, check your brake fluid! You probably have a leak somewhere (check the brake master cylinder first). I’d recommend not driving the car until you get the condition fixed.

  12. Just learned my 2005 Freestyle has a bad valve. No compression in #3 cylinder. I’m told $6700 for new engine. I know the car isn’t worth that much, 92000mi (always been serviced regularly), body is in very good condition, no rust. Trying to figure if it is repairable & if so how much it should cost or whether to call the salvage yard. Thanks.

    • Sorry this happened to you. I’d recommend going to a couple independent shops and getting quotes on replacing with a used engine. Used engines for your car will be plentiful (the shop will have connections on getting one) and not too expensive. Obviously labor costs will be high for an engine swap but nowhere near that $6700 number.

  13. Hello Everyone
    I was googling around and this article turned up for my search on top. First of all congrats for that achievement!
    I have ‘1.3L Honda City EXI S 2003’ and from two weeks, my exhaust is smoking light blue on start-up and then I can see high RPM while car is parked (not while running)!
    Don’t have idea if it smokes during drive – tried a few times on high speed but nothing visible during drive?
    While crawling, it jerks like camel if I take-off my feet from accelerator
    Oil consumption is quarter in a month (1,000 km) to top-up before next change [using havoline 20w50]
    no coolant top-up & no engine heating issues
    spark plugs get fouled (dry carbon) in a week same as the exhaust pipe tip
    after drive, when I get out of car, there is petrol like smell
    fuel consumption is down to 11 km per litre within city with A/c
    running condition is normal though, I can do 100-120 km/hr without hesitation
    Garage#1- engine tuning, spark plugs and use Hi-octane to clear.
    found it useless effort!
    Garage#2- guy’s comments match your’s but he has suggested almost everything:
    Piston’s Ring
    Head Gas Kit
    Wall Seal
    Oil Seal
    Timing Seal
    Timing Belt [to be checked]
    Timing Bearing [to be checked]
    Chamber Join
    Oil Filter
    Engine Oil

  14. Thanks very much for these educational tips, they’ve been too helpful. My engine isn’t smoking but loses oil. This’s why I visited your site.

  15. Is anyone out there that can answer my question are the 2003 Honda Civic I took it into this car Doctor plays in Redlands California to have the oil leak fix well I thought it was fixed but a week later or a few days later I started had to put more oil in it now I’m burning 5 quarts a week almost a quarter day driving 60 miles away from work one way at first I thought oil was getting in through the spark plugs but it burning oil you gets really smell it bad I thought if you had bad valve seals it wouldn’t come and go

  16. I have a 97 dodge ram 5.2 that blows white smoke while idling but not while driving even at slow speeds no smoke. I was told it’s the pistons if so it’s not the prettiest and not worth putting a lot of money into. Is there a kind of addictive to stop the leak if that may be the case? Also to say the engine runs fine I haven’t had any other issue except smoke while idling.

    • White smoke is generally only caused by normal condensation burn off when cold or a coolant leak somewhere (check your coolant level). Leaking piston rings would give you more of a grayish or blueish smoke. If you don’t want to put money into it, you could always try something like Lucas Oil Stop Leak to see if it helps.

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