(Updated on August 25, 2021)
Combustion engines work best when the correct amount of fuel and air are mixed in the combustion chamber with a well-timed spark and a good seal. It’s important that these gases enter and leave the combustion chamber at the right time.
Valves open and close each combustion chamber, allowing air to enter before combustion and exit after combustion. Valve seals keep the valves working well and keep the correct amount of oil in the combustion chamber.
Each seal is constructed out of a highly durable rubber material. However, this material may get worn out over time which results in the valve guide seals going bad.
What Are Valve Guide Seals?
Valve guide seals are also known as valve seals, valve stem seals, or valve stem oil seals. They work to keep the valve cover lubrication oil out of the combustion chamber, to lubricate the valve, and to align the valve correctly.
Valves do the important job of opening and closing the intake and exhaust chambers in the engine at the proper time. This timing is controlled by the lobes of the camshaft.
Camshaft lobes are oblong in shape. When the camshafts spin, the longer side of the camshaft pushes the valve open, allowing air to flow into or out of the combustion chamber.
Valve movement is coordinated with the timing of piston movement using a timing belt or timing chain.
The valve stems are the long, skinny part of the valve. The little flat disk at the end (called the head) seals the combustion chamber when the valve is closed. Each combustion chamber cylinder has at least one intake and exhaust valve.
Oil circulates just above the valve to lubricate the camshafts, and this excess oil needs to be prevented from entering the combustion chamber. This is one job of the valve guide seal. The guide seal also guides the valve into the valve seat in the cylinder head to keep the valve stems in proper alignment.
Top 7 Bad Valve Guide Seals Symptoms
If you have bad valve guide seals, you will probably notice several things, most of which are related to exhaust. It’s important to understand the symptoms so you can take proper action after you come across them. Here are some of the most common signs of faulty valve guide seals.
1) Lots of Exhaust Smoke
Vehicles often have a tiny bit of white vapor that comes out the tailpipe upon startup, but if it persists, the valve seals may have deteriorated. This causes oil to leak into the combustion chamber and burn creating a blue or sometimes white smoke.
This smoke will likely show up while the vehicle idles and upon acceleration. If the vehicle runs for a long time, the smoke may ease up and go away as the engine components heat up and expand.
2) Excessive Oil Use
As you’d expect, a vehicle with damaged or worn out valve guide seals will end up using more oil than it normally uses as it leaks by the seals. Check your oil level regularly with a dipstick so you will be able to detect this symptom early on.
If there are no other obvious oil leaks and your engine compression is normal, then your problem may be the guide seals.
3) Engine Braking
Engine braking is when you use engine vacuum instead of the brakes to slow down the car. This can be done by letting off the throttle and downshifting so that the engine RPM increases. The increased engine speed and lower gearing creates more engine vacuum and resistance to forward motion, slowing the vehicle.
While engine braking on a hill, you are not applying pressure to the accelerator. When the vehicle is nose-down like this, oil collects around the front of the cylinder head near the valve seals.
When you eventually need to apply the gas pedal again, the car nose will tilt up and pour the oil that had collected at the front of the head over the valve seals. All that oil will be sucked into the combustion chamber if there’s a bad seal. It will then burn up, creating a large cloud of smoke out of the exhaust.
4) Smoke After Idling
Your car spends a while idling in stop and go traffic, or when waiting a long time at a stop light or stop sign.
During this time, oil can accumulate around the valve seal and get sucked into the combustion chamber when you accelerate, creating a cloud of blue or white smoke out of your tailpipe.
5) Cold Engine Test
It is easier to identify a bad valve seal when the engine is cold. If you’ve left your car outside overnight or longer, you’ll have a cold engine when you try and start the car. There should normally be a little bit of oil sitting on top of the valve seal because it thickens at lower temperatures.
A bad valve guide seal will also have a tiny gap in it after it’s been in the cold for a while. This means that when you start a cold engine, that little bit of oil gets sucked through the seal gap into the combustion chamber. The result will be a cloud of blue-white smoke coming out of the tailpipe when you first start the car.
6) Low Power
Misfires and sluggish acceleration may be a problem with worn valve seals, as the oil burns up and leaves ash on the spark plugs and inside the combustion chamber. Check the spark plugs for spark plug fouling.
A compression test on a vehicle with a bad valve guide seal may show unusually high compression – if you see low compression along with these other symptoms, it may be a bad piston ring or a leaky head gasket instead.
7) Ticking Noises from the Engine
When the car starts, misaligned parts or excess play between components in the engine may clack against one another and cause a ticking noise.
Since the valve guide seal lubricates and aligns the parts of the valve correctly, a bad valve seal may cause a valve to be out of alignment or insufficiently lubricated.
Valve Guide Seals Replacement Cost
The cost of replacing your valve guide seals will vary according to the make and model of your vehicle. The good news is the cost of the parts for valve guide seals is between $30 to $100 on average.
The bad news is that you are looking at about 2 to 4 hours of labor if you take your vehicle to a mechanic. It takes quite a bit of work and time to get that deep into the engine.
Since the average mechanic will charge about $60 to $100 per hour, you are looking at about $120 to $400 just for the labor costs. Therefore, the total average price you can expect to pay is between $150 and $500.