What causes bonnet gaskets to leak?

Since bonnet gaskets tend to leak over time, many different causes can significantly contribute to the deterioration of the quality of bonnet gasket construction. Most of these are at least partially related to vehicle maintenance.

Overheating
Overheating is a major cause of bonnet gasket leaks. Every vehicle's engine is designed to run at a specific temperature.
When this predefined value is exceeded, such as when an engine overheats, the gasket of any engine is subjected to thermal stress, which increases the likelihood of rupture and bursting.
Overheating is not only harmful to valve cover gaskets, but it can also jeopardize the durability of other critical seals, including the engine's cylinder head gasket.
Several blown gaskets on an engine are not uncommon when the engine is overheated.

Irregular oil changes
Irregular engine maintenance can be a major cause of early valve cover gasket damage. Regularly changed engine oil contains a variety of compounds that help prevent gasket damage.
Over time, these compounds degrade, causing your engine's valve cover gaskets to wear and deteriorate even more. This often happens when regular maintenance tasks are neglected over time.

Loose or over-tightened valve cover bolts
In addition, recently replaced valve cover gaskets will often begin to leak shortly after installation if the engine's valve cover bolts are not properly tightened.
Excessive torque on the bonnet bolts may result in incorrect gasket installation or squeezed gasket edges. In addition, improper tightening of such bolts will often prevent an adequate seal from forming between the cylinder head and valve cover surfaces of the engine.

How do I repair a leaking valve cover gasket?

Failure to repair a leaking bonnet gasket can result in serious damage. Don't worry. If you have some mechanical skills and are planning a DIY task, we'll discuss how to replace a leaking bonnet gasket. Let's outline a quick fix for replacing the bonnet gasket.

Step 1: Remove the hood
First, remove your hood. Many engines use a full-coverage plastic top. Their plastic hood should be removed to allow full access to your valve cover.

Step 2: Uninstall the assembly
Continue removing components. With all electrical components and emission control tubes removed, the valve cover can usually be used on a four-cylinder engine. There may be any blocked gas pedal connections, in which case you will have to loosen them.
You may or may not be able to remove the intake manifold from a six- or eight-cylinder engine. Depending on the leaking valve cover gasket, this assembly will need to be removed.

Step 3: Remove the bolts and valve cover
After accessing the valve cover, unscrew the valve cover nut or bolt and remove the valve cover. Next, the sealing surface of the bonnet will be tested with a straightedge to ensure it is flat, usable, and secure.

Step 4: Clean the bonnet
Clean the valve cover using a gasket scraper, making sure to remove any gasket dirt from the surface. Clean the cylinder head thoroughly and check for any remaining gasket debris. Spray the surface with brake cleaner to make it clean and free of grease residue.

Step 5: Gasket Installation
It is time to install the replacement gaskets. A new head gasket and any necessary rubber grommets should be installed. If any spark plug tube seals need to be replaced, these should also be replaced.
In some cases, you can apply an oil-resistant vulcanizing or RTV sealant to different parts of the sealing surface to provide a secure, efficient, and airtight seal.
Next, place and secure the valve cover. It is good if you use a calibrated inch-pound torque wrench to properly measure the tightness of the bolts. Then reinstall all remaining components in the proper locations.

Step 6: Test
After setup is complete, test run your engine and check for leaks.

Bonnet Gasket Life

Bonnet gasket life depends heavily on a number of circumstances. These considerations include the manufacturer of the engine, the driver's driving pattern, and the schedule for routine maintenance.
Specific aftermarket gaskets are stronger than others, resulting in longer service life. In addition, valve cover gaskets in well-maintained vehicles are almost always more durable than those in poorly managed vehicles.
In addition, gaskets in engines that are rarely driven by cars are more likely to fail early because they harden and dry out.
However, on average, people can expect their engine's valve cover gaskets to survive between 50,000 and 80,000 miles without incident. In some cases, these types of gaskets can last even longer.

Things to remember after replacing a valve cover gasket

The following are some of the best things to consider when replacing a leaking bonnet gasket:

Some gaskets are easy to replace
The mechanical components of an automobile engine are usually more durable than the gaskets used to seal the engine. Many gaskets, including bonnet gaskets, are very easy to replace.

Reject "stop leak" products
Avoid any "stop leak" products you may encounter regarding your engine oil. In principle, they may seem beneficial, but they often cause more trouble than they are worth.
Most of these chemical solutions are not even defined or allowed by the vehicle manufacturer. So, leave them alone, as they tend to cause more problems while increasing repair costs.

Leak testing
Often, if the car is old enough to suffer from valve cover leaks, more leaks are almost inevitable. Therefore, you will benefit from requesting a leak check from a mechanic you trust. If other leaks exist, what is the point of fixing them?

Checking other rubber parts
Sometimes your positive crankcase vent valve (or PCV valve) will fit into a rubber gasket located in one of the valve covers.
You may have a leak with an old and cracked rubber grommet. After accessing the valve cover, inspect these components and repair as needed.

Can you drive a car with a leaking valve cover?

Driving a car that suffers from a valve cover leak will only spill a small amount of oil or oil dripping onto the driveway rather than into hot engine parts and can be driven safely in the short term.
While running with any oil leaks is discouraged, it is acceptable if no other transportation is available. Bonnet gaskets can sometimes leak enough oil to drip onto a scorching hot exhaust manifold.
The smell of burning oil or whitish smoke emanating from the exhaust manifold indicates a serious leak. In this case, do not drive the car until the leaking valve cover gasket is repaired.
However, when you are forced to drive your car with a leaking valve cover gasket, you must be aware of the accompanying short-term engine effects.

Oil leaks can affect engine performance
Oil system leaks can affect engine performance. Engine oil is used to lubricate moving parts such as pistons. During steep climbs, you may need to upshift to accommodate the loss of power. This can be difficult if you need to shift into a lower gear on steep climbs, such as when pulling onto a highway.

Oil is important to protect your engine
Oil is also important to prevent engine rust. When driving through standing water during rainfall, metal parts can corrode and seize up completely if there is no oil left or enough oil to protect them.

Bonnet Gasket Replacement Costs

The typical cost of a valve cover gasket replacement is approximately $100 to $350. The cost of these components is typically about $30 to $50, while the labor cost is about $70 to $300.
That said, some vehicles have bonnet gaskets that cost more than $100, and labor costs can be much higher due to the complexity of the engine setup.
However, in most cases, this is a relatively inexpensive component to replace. The cost will depend on the hourly rate of your technician and the quality and quantity of your components.
If you can find an experienced mechanic who charges a lower hourly rate and works quickly, you may be able to save on labor costs.