Head gasket sealer, also known as engine block sealer, reinforces or acts as a substitute for the gasket that sits between the cylinder head and engine block of an automobile.
That gasket has an important job. It maintains the crucial compression in a car's engine and also protects against coolant and oil leaks that can destroy the cylinders. However, it’s a part that gets little thought as part of typical automotive repairs—until there’s an issue.
Sure signs there may be a head gasket leak, cracked engine block, or other issues include an engine that easily overheats, misfires, or causes a stream of white exhaust. You may also notice the vehicle absorbing coolant, meaning that it’s disappearing with no apparent leak.
If you’re constantly adding coolant, consider an issue with your head gasket. Milky-looking oil is another indicator.
If your vehicle has a head gasket leak for any reason, it might be time to figure out how to use a head gasket sealer before bigger, and more expensive, issues arise.
Do Head Gasket Sealants Really Work?
It’s a fair question and the answer is: not always. For minor leaks, it’s a great solution. In a pinch, if you’re away from access to proper mechanical repair, it can save your engine. Mechanics themselves recommend it to those who don't want to replace head gaskets or even the entire engine.
However, engine block sealers should always be considered a somewhat temporary solution. It should not be considered or used as a permanent fix, at least if you plan to drive the car for the long term.
Some people report sealant only holds a few months. Others have noted that while it improves performance, you may notice your car running a little hotter while idling than it normally would, although well below a level of concern.
In either case, you’ll need to get the problem addressed properly in the short or long term.
Even so, using a head gasket sealant is much cheaper and faster than replacing expensive parts and can be an effective way to block cracks and stop up leaks where otherwise extremely costly repairs would be needed.
In many situations, the cost of replacing the head gasket is more than the value of the car. It can run several thousand dollars to get the repair.
If the car is only worth a few thousand dollars, using an engine block sealer can buy you more time to save up for another vehicle and squeeze any remaining life out of the vehicle.
Overall, use an engine block sealer as a temporary but effective and cheap fix until you can have a professional take a look at and repair your car, or find an alternative mode of transportation.
How Head Gasket Sealer Stops Leaks
First, it’s important to understand the job a head gasket performs. The cylinder head is a massive chunk of metal that encases the cylinders in your engine. It makes up a large amount of the engine mass.
You may have more than one cylinder head. If you can see a removed cylinder head, you can see the cylinders inside the casing. A four-cylinder car, or a ‘four banger,’ will have four cylinders inside the head. An eight-cylinder car will likely have two cylinder heads containing four cylinders each.
On the flush surface where the cylinder head mounts to the engine are a series of holes surrounding the valves in the cylinders. These holes are coolant jackets where coolant comes through the engine to cool moving parts.
On a side note, you may hear coolant called antifreeze or radiator fluid.
The flat surface of the cylinder head meets the engine head. Between those two spaces is where the head gasket rests. Each gasket aligns with the coolant jackets to allow coolant to flow through while sealing any other leaks between the cylinder head and the engine head.
If any part of the gasket is damaged, it can allow the coolant to enter the combustion chamber or allow the combustion gasses to seep into the coolant chamber.
Either scenario can lead to overheating, thick exhaust, and misfires. Basically, it can result in a very rough-running engine.
The head gasket also serves the purpose of keeping coolant from getting into the cylinder where combustion is taking place. Similarly, it keeps emissions from the combustion chamber from entering the coolant jackets.
Head gasket sealer's main ingredient is sodium silicate, which is liquid glass. After checking if the car engine is fully cooled, the product is pumped through the coolant system, starting in the radiator and coating the entire system.
As the engine heats up, the heat from the exhaust gasses evaporates the liquid, leaving the glass inside all the small cracks in the head gasket.
How to Diagnose Head Gasket Issues
For starters, evaluate whether using a head gasket sealer is the right course of action. One of the common signs of head gasket damage is your car consuming a lot of coolant.
There are many reasons the coolant can be disappearing. However, it’s not always because of an issue with the head gasket.
For example, you could have a crack in your coolant reservoir. Or, you could have a leak from a hose. To avoid falsely blaming your head gasket for missing coolant, see if you can find any leaks or other causes for the coolant levels dropping.
To do this, make sure your engine is thoroughly warmed up. This pressurizes the system, making leaks more obvious. Open the hood and thoroughly inspect coolant hoses, the water pump, and the radiator, watching for leaks. Also look beneath the car for dripping coolant.
If, however, you’re losing coolant and can’t see anyplace it’s leaking and you’re having issues with poor engine performance, it’s likely time to try the engine block sealer.
Another piece of evidence can come from your oil reservoir. An ineffective gasket will allow flow into your oil, changing the color and consistency. To test it, pull your oil dipstick out of the engine. If the oil is creamy or milky looking, you likely have a head gasket issue.
Many cars will show one symptom or another. Some won’t show any. Some will show all. Keep that in mind if you’re not seeing white exhaust or find milky oil in your reservoir.
One more diagnostic test is to test for gasses inside the radiator, or for some vehicles, the reservoir. To do this, use a test kit made up of a blue liquid and a tube with a suction bulb.
Insert the tube into the reservoir or location of the radiator cap. Remove the bulb from the top and add the blue liquid to the fill line. Then pump the bulb, which incorporates air into the mixture.
The liquid measures the gasses moving through and will change color if exhaust gasses are present. If the liquid stays blue and you have no other identifying results, a head gasket leak likely isn’t the problem with your engine performance.
You can also replicate these results with a funnel full of antifreeze inserted into the coolant reservoir or radiator. Start the engine and allow it to warm. If gasses are escaping through the head gasket, you will see bubbles form inside the coolant in the funnel.
How to Use Engine Block Sealer
Once you’ve decided to try a sealer, make sure to read the head gasket sealer instructions for whichever brand you choose. They vary slightly from one another.
Note that some brands don’t mix well with radiator fluid and will require you to drain the fluid before starting. Review your specific product's instructions before starting, and make sure you have extra radiator fluid handy to top off your radiator after finishing with the head gasket sealant.
Step 1 - Locate and Remove the Radiator Cap
You’ll be adding the head gasket sealer directly to the radiator through the opening provided by the removal of the radiator cap.
Make sure the engine is fully cooled before attempting to remove the radiator cap.
Safety Note: Never remove a radiator cap while the engine is still hot, since it can result in burns when the compression releases hot steam and liquids.
The radiator cap will be clearly marked and typically sits near the front of the engine. Some car models don't have a traditional radiator cap, but rather a pressurized overflow coolant tank. Be sure to review your car's owner manual to locate the correct insertion point.
Step 2 - Add Sealant
Ensure you have enough space in your reservoir before adding the head gasket sealer. Use a turkey baster to remove coolant if you need more room.
Following the directions on the bottle, mix your engine block sealer and pour it into the appropriate reservoir. The amount needed will vary depending on how many cylinders your vehicle has.
If you're not sure how many cylinders your car has, always check the owner's manual, as too much or too little block sealer can cause further issues or fail to address the issue at hand.
Top off the reservoir with coolant if necessary. Then replace the radiator or reservoir cap.
Step 3 - Warm the Engine
Once the block sealer is added, turn on the engine and allow it to idle for 15-30 minutes, as directed. Turn the heat inside the car to the maximum setting during this time. Watch the engine heat gauge inside the car to verify it reaches operating temperature.
Step 4 - Cool and Check
Once you’ve run the engine and heating system for the recommended time, turn off the engine and allow it to fully cool. This can take several hours. Check the radiator fluid level and top it off if needed.
Take a short drive to check your car for any signs of a continued head gasket leak. This can include running hot, misfiring, or thick exhaust.
However, you may need to drive the vehicle over the course of a few days for the product to fully work its way through the system. Do this in short windows.
Drive less than 20 minutes or so, then allow the engine to cool and check the coolant level. If after several drives, the coolant is still disappearing, the sealant may not have solved the problem.
Check the system frequently for the first several drives to ensure the product fully patched the system before resuming normal driving habits.
Step 5 - Follow up
Remember to schedule an appointment with your local auto shop to get your car checked out even after using head gasket sealer.
While it can be a great temporary fix, there could be an underlying issue or a long term problem with the car that should be diagnosed to prevent further damage.
Which Head Gasket Sealer Works Best?
The answer to the question, at least in part, is whichever one works best for your needs and your specific automobile make and model. Read the directions to understand each brand's recommendations for choosing the best engine block sealer for your car.
For example, if the directions say the car engine must idle for 30 minutes, but your car is drinking coolant faster than that, choose a different product with a shorter engine run time.
The following options are a great place to start:
K-Seal ST5516 HD Multi-Purpose One Step Permanent Coolant Leak Repair
Bar's Leak HG-1 HEAD SEAL Blown Head Gasket Repair
BlueDevil Pour-N-Go Head Gasket Sealer
Steel Seal Blown Head Gasket Fix Repair Sealer - 6 Cylinder
Can You Use Head Gasket Sealer Twice?
Technically, yes, you can use engine block sealer more than once (although not the same sealer you’ve already put through the engine). It will even carry a high probability of correcting the issue in subsequent uses.
The problem is head gasket sealer is a bit like putting a band-aid on a large wound. It will neither address bigger issues nor offer a permanent repair.
Remember head gasket sealer is intended to offer a quick fix with mostly desirable outcomes in many situations, but it’s still meant to merely hold things together until you can access proper mechanical repair.
If you decide to make the repair yourself, check out How to Repair a Blown Head Gasket.
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