Why You Must Always Replace a Blown Head Gasket

Something’s wrong with your vehicle, it’s just not running right. The temperature is getting high, there’s moisture in the oil, it’s sluggish — so you have it checked out. Turns out, the head gasket is blown and the mechanic down the street wants $3,000 to fix it. But a buddy says that you can buy some "stuff", pour it into your cooling system, and "problem solved." Sounds too good to be true, right? Generally, it is too good to be true.

Quick fix

Here's a rundown on what a head gasket is, what your repair options are, and an explanation as to why the "quick fixes" just don't work.

What’s a Head Gasket Anyways?

Head gasket repair

An engine is made up of a block and cylinder heads — and much more, but externally speaking, these are the two parts. Inside the block is where you’ll find the pistons, camshaft, crankshaft, etc. The cylinder head(s) contain the valvetrain (generally speaking - some designs are different), which move air and fuel into each cylinder and help move exhaust out. In between the block and the cylinder head(s) is where the head gasket is located.

The gasket between the head(s) and the engine block exists because cylinder heads need to be removable. Valves can become damaged for a variety of reasons, and replacing them is much cheaper than replacing an entire block.

But, basically, the only actual job of the head gasket is to seal the area where the cylinder head and block meet. The seal is for three different areas in this location:

  1. The combustion chamber where the air, fuel, spark, and compression take place. Head gaskets must withstand extreme temperatures and high pressures in this area. This is the most common place to have a head gasket failure.
  2. Head gaskets also seal the coolant passages between the block and the head. There isn’t as much pressure here, but engine coolant can sometimes cause corrosion at this point, eventually leading to a leak. This isn’t common if you properly service your cooling system.
  3. The final areas a head gasket seals are the oil passages, another place that’s not under a lot of pressure so it’s rare to have a leak here. However, a poor quality head gasket can start leaking from just about anywhere.

Signs of a Blown Head Gasket

If you’ve already been to a mechanic, and you trust them, it’s still a good idea to know what the symptoms of a blown head gasket are — here’s how you can tell:

  • The engine overheats or exhaust gases are entering your radiator causing constant bubbling.
  • Engine is running very poorly — sluggish, misfiring, etc.
  • There’s coolant in the oil
  • Oil blow-by is coming out of the oil cap or oil seals due to increased pressure in the crankcase
It's important to note that white smoke coming out of the tailpipes is not typically a problem with the cylinder head gasket, but if it's very thick, it may be.

Quick Fixes and Sealers

There’s no magic bullet and no product out there to magically repair a head gasket once it’s gone bad — so if you’re hoping for a quick fix, stop. Using products that advertise as being able to repair a head gasket are not only a waste of money, but they could cause more problems on down the road. These problems include:

  • Blocked coolant passages
  • Clogged radiator tubes
  • Heater core blockages

There are rare cases where using a sealer is the only way to get you home in an emergency, but you’re really just playing with fire at that point. It may even work for a little bit, but expect to pay for it in a week or two.

The only real solution is to replace the head gasket with a genuine GM replacement. Cheap off-brand gaskets are also a bad idea in this case because they need to be a precise thickness and shape to properly seal the three discussed points.

Head gasket block

Replacement at home could be a solution, it really just depends on your skill level and your vehicle. Some GM models have very accessible cylinder heads and you could do the job with minimal mechanical experience — other’s will require removal of the engine to get the heads off. If you do choose to take on gasket replacement yourself:

  1. Be aware that the block and engine surface need to be absolutely spotless for the new gasket to seal properly.
  2. Also, your head(s) may need to be machined, which is another task and needs to be done in a machine shop.
  3. Finally, you have to torque a cylinder head back down in a specific order, so refer to a vehicle specific repair manual before attempting this somewhat daunting task.

Last but not least, remember that you can never reuse a head gasket, so if you torque it down in the wrong order and have to take the head back off, you’ll need to start over with a new gasket.