The head gasket and valve cover gasket are both located on the upper part of the engine and both play similar roles in sealing different parts of the cylinder head. So, if there is an oil leak coming from the top of the engine, how can you tell if it is the head gasket or the valve cover gasket that is leaking?
In general, if there is an oil leak that is coming from the top of the engine, then it is more than likely caused by a leaking valve cover gasket. Whereas a leaking head gasket will cause a substantial coolant leak around the top of the engine or mixing of oil and coolant internally within the engine.
A failed head gasket usually causes problems like an overheating engine, loss of engine power, lots of white smoke from the exhaust, and a significant loss of engine coolant or engine oil, or both. A leaking valve cover gasket is less serious and usually only results in the loss of engine oil but doesn’t seriously affect the engine performance.
What is the difference between a head gasket and valve cover gasket leak?
A head gasket leak is caused by a failure of the cylinder head gasket that allows coolant and engine to mix and leak into one or more engine cylinders. A leaky valve cover gasket is a failure of the valve cover gasket that allows engine oil to escape out of the engine from the top of the cylinder head.
The cylinder head gasket is located between the engine block and cylinder head and seals the combustion chambers whilst separating the coolant and lubrication channels so that they don’t mix or leak into the engine cylinders. The head gasket must withstand very high temperatures and high pressures.
A head gasket cover is located at the very top of the engine and is there to seal the valve cover onto the top of the engine. It stops oil from leaking out of the cylinder head and operates under fairly low pressure. On older vehicles, the valve cover gasket is often referred to as the rocker cover.
What is the difference between a head gasket and valve cover gasket?
The cylinder head gasket and valve cover gasket are both located near the top of the engine, but they have very different jobs, are made from different materials and their replacement cost varies greatly.
Here are a few of the differences between a head gasket and a valve cover gasket.
- The valve cover gasket (rocker cover gasket) on modern engines is a simple gasket, usually made from silicone rubber but sometimes the older cork type gasket is still used.
- A cylinder head gasket is more complicated and usually consists of a number of thin steel layers that are bonded together. The layers can also be made from copper or grpahite, but steel is the most common material used. The outer layers of the head gasket are usually coated in a rubberized material known as Viton that enhances the seal with the engine block and cylinder head.
2. Fitting location within the engine
- The valve cover seal is located on top of the cylinder head and as the name suggests, seals the valve cover onto the engine. It is a thin gasket that runs around the outer edge of the under side of the valve cover.
- The cylinder head gasket is sandwiched between the cylinder head and the engine block. It is a large, flat gasket that covers the top of the engine block with cutouts for the cylinders and various oil and coolant channels.
- The valve cover gasket should last many years and at least 100,000 miles, but due to their design and rubber material, it’s not uncommon for them to harden and crack over time.
- A cylinder head gasket is in theory designed to last the life time of the car. Modern, steel layered head gaskets are very resilient and should never fail unless the engine is continuously running hot or the cylinder head cracks or warps.
4. Replacement difficulty and Cost
- The valve cover gasket is not too difficult to replace, and usually depends on how many ignition coils and other wiring or hoses that need to be removed first. A replacement valve cover gasket can cost from $50 to $150 to buy, and between $150 and $400 to replace by a mechanic.
- A cylinder head gasket replacement is a complicated and expensive job. It involves removing a lot of parts including the cylinder head. It’s usually only performed by a qualified mechanic and can cost anywhere from $1,500 to $2,500 in labor and parts.
What are the symptoms of a blown valve cover gasket versus symptoms of a blown head gasket?
The symptoms of a blown valve gasket and a blown head gasket are very different and have a different impact on the engine and the associated repair costs.
|Symptoms Of Blown Valve Cover Gasket||Symptoms of A Blown Head Gasket|
|1. Low engine oil – Oil leaking from a valve cover gasket will lead to a drop in engine oil levels||1. Low Coolant Levels – If the head gasket is leaking then it’s almost certain that coolant is being lost by mixing into the engine oil and into the combustion chambers.|
|2. Smell of burning oil – Oil that leaks from the valve cover gasket can drip down the side of the engine onto the hot exhaust where it burns||2. White Smoke From The Exhaust. If coolant is finding its way into the engine cylinders, then it will be burnt off and this will create continuous white smoke from the exhaust.|
|3. Dried oil residue around the valve cover – Oil that leaks from the valve cover will often settle around the top of the engine and dry out, leaving a flaky, dirty residue.||3. Brown milkshake Engine Oil. When the head gasket blows, coolant will mix with the engine oil, making a thick milkshake-like mixture|
|4. Oil around the spark plugs – If enough oil leaks from the valve cover then it can find its way down around the top of the spark plugs||4. Engine overheating. If there is a rapid loss of coolant as a result of the head gasket blowing then this can result in an overheating engine.|
What next – how to check if it is a head gasket or valve cover gasket leak
It’s very easy to tell the difference between a head gasket and a valve cover leak gasket. If the engine is running fine but there is oil leaking from the top of the engine, then it may be a valve cover leak. Here is how you check for a head gasket leak versus a valve cover gasket leak.
- Check the oil and coolant levels. Start by checking the engine oil and coolant levels to see if they are leaking. If they need topping up, then it may point to a leak. Try topping as necessary and run the engine. A coolant leak internally will cause the coolant levels to drop fairly fast without any signs of a coolant leaking onto the ground or out of the engine. Oil will leak more slowly from a leaking valve cover and it may take a few weeks for a significant amount disappear.
- Check around the top of the engine for signs of an oil leak. If you suspect oil is leaking from the valve cover then check around the top of the engine where the valve cover joins the top of the cylinder head. Look for signs of dried out oil or fresh oil if the engine has been running. Remove the ignition coils from each spark plug in turn and check for pooled oil in the spark plug wells.
- Look for white smoke from the exhaust. A very common sign of a leaking head gasket is continuous white smoke from the exhaust when driving. This is caused by coolant burning withing the combustion chambers. If the engine is cold you may see some white smoke, but this should go away when the engine warms up if it is not caused by the cylinder head gasket failure or a crack in the cylinder head.
- Check the condition of the engine oil. Another tell tale sign of a leaking head gasket is coolant in the engine oil. This will usually cause the engine oil to look milky in texture and will usually be light brown in color. You can check the condition of the engine oil by removing the filler cap or by checking the dipstick. To confirm that the engine oil is contaminated you may need to drain the oil completly from the engine.
- Check for burning smells when the engine is running. Another classic sign of an engine oil leak is a burning smell when the engine is running. This is caused by engine oil leaking onto the exhaust manifold, or other hot parts of the engine and exhaust. If you can find the source of the burning smell, you may be able to trace it back to the source of the leak.
- Check the engine compression. To fully confirm a failed head gasket, you need to check the compression of each cylinder. Most modern petrol engines should have a pressure reading of over 100PSI with a less than 10% difference in compression between cylinders (20% is acceptable if it’s a high mileage vehicle). If one or more of the cylinders has a low pressure reading then there is a compression leak and it may need to be further invesitgated by removing the cylinder head to inspect the cylinder head gasket.
1. Can you drive with a valve cover gasket leak?
Yes, it is possible to drive your car if it has a valve cover gasket leak, as long as you are sure that the leak is not too bad. If there is a lot of oil leaking from the valve cover then it’s not advisable to drive the car (and it may not be safe to do so either). Be sure to check the engine oil level if you need to continue driving and also make sure that there isn’t a lot of oil pooling on hot engine parts that may cause a fire.
Depending on the type of engine in your vehicle, a valve cover gasket leak may also cause a vacuum leak that will lead to a reduction in engine power and a rough idle. An unrepaired valve cover leak can also lead to contaminated spark plugs and damage to the ignition coils if they become soaked in engine oil.
2. Do you need to remove spark plugs to replace the valve cover?
Yes, in general, it is best practice to remove the ignition coils (or coil pack) along with the spark plugs when replacing the valve cover. It’s not always necessary to remove the spark plugs to get the valve cover off, but it is usually easier in practice.
Some valve covers extend into the spark plug wells and you will need to remove the spark plugs before removing this type of valve cover. If the valve cover gasket has blown and oil has leaked onto the spark plugs then be sure to clean off any excess oil and debris before removing the spark plugs.
3. What causes a valve cover gasket to leak?
Valve cover gaskets commonly leak when they crack and shrink because of age. As they are made from rubber, they will harden and stiffen over time becasue of the heat from the engine. This makes them more susceptible to leaking because of their reduced flexibility as they age.
It’s also possible for a valve cover gasket to leak because of a cracked or warped valve cover. Plastic valve covers can become misshapen and lose, causing a gap to form along the seal with the cylinder head. This can damage the gasket allowing oil to escape.