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How To Fix A Blown Head Gasket

An engine block and pistons minus the cylinder head

The words “blown head gasket” strike fear into the heart of almost any vehicle owner. While not as horrifying as “blown engine”, a blown head gasket typically means a very expensive repair bill is about to come your way. It might even be the deciding factor as to whether you keep a vehicle or simply buy another one. But a failed cylinder head gasket doesn’t have to mean the end of the road for your trusty ride. Let’s look at what a head gasket repair takes.

What Exactly Went Wrong?

A head gasket doesn’t actually blow up, but rather it is no longer able to seal the cylinder head to the engine block. The engine block needs to pass vital fluids like oil and coolant into the cylinder head. The cylinder head needs to be sealed to the engine block to provide the cap for the cylinders and create the combustion chamber itself. If the cylinder head gasket fails to keep everything in their designated place, it is considered compromised. Normally a cylinder head gasket failure means that combustion chamber gasses are being pushed into the cooling system via the joint where the cylinder head meets the engine block. But it also means a failure where the engine coolant enters the oiling system via the same area. Oil and water mixing in the engine is very bad and can wipe out bearings in no time.

How To Test For A Bad Head Gasket

Leak Detector Kit / Engine Block Test

The best course of action to verify if a head gasket is truly leaking is to use a leak detector kit. A typical blown head gasket test kit includes a special test chamber and test fluid. The test chamber holds the special test fluid that changes color if combustion gasses are detected. Remove the radiator cap and insert the tapered end of the test chamber into the radiator opening. Start the car and let it warm up. If combustion gasses are leaking through the cylinder head gasket and into the cooling system, bubbles will enter the test chamber and change the color of the test fluid.

To test for coolant in the oil simply remove the oil dipstick and look at the end. If it looks like chocolate milk, you have a problem. If you don’t have a dipstick you will need to drain the oil into a pan to look at it.

How To Fix A Blown Head Gasket

Let’s just go ahead and get this out of the way. Replacing a failed cylinder head gasket is not a quick repair and will require disassembling the engine down to the engine block. Whether you decide to DIY or let your local NAPA Auto Care handle the job (and it will indeed be quite a job) you need to be prepared. There will also be several “might as well” items that you will want to do while you are in there. Might as well do the timing belt/chain guides, water pump, or anything else that is questionable that lives deep in the engine. Got a V6 or a V8? Might as well do both sides even if only one cylinder head gasket is leaking. At this point you may consider getting a complete cylinder head gasket set that has all the bits you will need for the job.

Now that we set the expectations, let’s take a look at the general steps required to fix a blown head gasket. For a complicated repair like this we suggest taking lots of photos to reference later when it is time to reassemble.

  1. Drain the cooling system via the petcock at the bottom of the radiator. Make sure to capture all the coolant in a drain pan and dispose of it properly following local laws.
  2. Disconnect the battery to prevent any accidental shocks or sparks.
  3. Remove the air intake and intake manifold. There will likely be lots of hoses and wires connected, so make sure to make note of each one and where they go. The fuel system will also likely need to be disconnected.
  4. Remove the exhaust manifold. Depending on the amount of room in the engine bay it may be possible to only remove the bolts connecting the exhaust manifold to the cylinder head. Either way the exhaust manifold must be disconnected from the cylinder head.
  5. Depending on your engine you will likely need to remove the engine driven accessories from the front of the engine. It is common for these to be bolted to the cylinder head, so they have to be disconnected.
  6. Depending on your engine you may have to remove the timing cover. Again, this is usually bolted to the cylinder head.
  7. Removing the actual cylinder head.
    1. If you have an engine with the camshaft located inside the engine block, you can likely now remove the cylinder head bolts and lift the cylinder head off the engine block. Be careful as it will be very heavy.
    2. If you have an engine with the camshaft(s) located inside the cylinder heads, you will need to remove the timing belt/chain. You will want to consult a repair manual for the correct way to set the engine rotation to prevent any piston/valve damage later. Once the timing belt/chain is removed you should be able to remove the cylinder head bolts and lift the cylinder head off the engine block. Again, be careful as it will be heavy
  8. With the cylinder head removed you will need to have it checked by a professional for any damage or warping. You can then decide to reuse your original cylinder head, have it rebuilt, or replace it with a new (or remanufactured) unit. Remove the cylinder head gasket but do not discard it yet. It is wise to compare the new gasket with the old one before putting things back together.
  9. The engine block deck will need to be carefully cleaned for the best possible seal.

Reassembly is typically the reverse of the removal but with a few extra steps.

  1. Refer to a repair manual for the exact method of reinstalling the cylinder head, especially for engines with the camshaft inside the cylinder head. The timing belt/chain must be reinstalled perfectly or else serious engine damage will likely occur.
  2. Cylinder head bolts must be tightened in the exact specified factory sequence and torque to the correct amount. You may or may not be able to reuse the original cylinder head bolts depending on the engine design, as some are “torque-to-yield” and will have been stretched.
  3. Once everything is back together, refill fluids and check for leaks.

You can now see why this is typically a major repair job regardless of who does the wrenching. When you see a quote for how much to fix a blown head gasket, think about the entire process involved.

Is There A Quick Head Gasket Fix?

While a traditional head gasket replacement is the best method for a repair, there is an alternative. You may be wondering how to fix a blown head gasket without replacing it. Years ago some very creative scientists developed stop leak products that are designed to re-seal a leaking head gasket. While they may vary in their packaging or chemistry, most of these products are designed to be added to the cooling system. Each product is different and it is very important to read the instructions in full before using any of them. Some may be able to be added directly to the cooling system with no other steps, while others may require flushing and filling the cooling system. They are also only designed to fix a head gasket leak where gasses from the combustion chamber are entering the cooling system. If your oil looks like a chocolate milkshake or there is coolant in the oil, stop leak won’t help you. Head gasket stop leak can’t fix major leaks like those found on early Cadillac Northstar V8 engines (which actually strip the cylinder head bolt hole threads). If the cylinder head has warped or otherwise separated from the engine block, stop leak may not work.

A leaking cylinder head gasket doesn’t have to mean the end of your vehicle’s days on the open road. But it also can’t be ignored. Letting a head gasket leak continue will eventually destroy your engine, there is no question. So give your repair options careful consideration, especially if you had planned on keeping the vehicle for a long time. A vehicle in otherwise great shape may very well be worth repairing for many more miles of service. Check out all the engine parts available on NAPAonline or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on what causes a blown head gasket, chat with a knowledgeable expert at your local NAPA Auto Parts  store.

Photo courtesy Flickr.

Brian Medford View All

With an automotive writing career spanning over two decades, Brian has a passion for sharing the automotive lifestyle. An avid DIYer he can usually be found working on one of his many project cars. His current collection includes a 1969 Olds Delta 88 convertible, BMW E46 sedan, and a slant-6 powered 1975 Plymouth Duster.

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