head gasket

[HeWhoKillz]

I was wondering if anyone could explain to me what a head gasket is, does, and how it can keep a car from running if it is "blown". Where is it located? Whats it look like? Its not the same as a valve over gasket is it? Even if it is, how can it stop a car from running? Is it easy or difficult to replace? How? Sorry alot of questions.

[Gearhead202]

Are you looking for where it is on a specific vehicle because it varries greatly on how difficult it is to replace depending on the vehicle.

[HeWhoKillz]

Its on a 92 saturn. I think its an ion. I also have a corolla that I'm still learning on but the saturn is the one "blown" with a head gasket.

[Andydg]

It's the gasket between the block and the head. When you blow one coolant can mix with oil it also helps to ensure proper cylinder compression.

[HeWhoKillz]

Originally Posted by Andydg

It's the gasket between the block and the head. When you blow one coolant can mix with oil it also helps to ensure proper cylinder compression.

Is that the same thing as a valve cover gasket? The thing that looks like a stencil of the piston holes from atop? Sorry, I'm trying to learn. If not, how does a blown one stop a ccar fron running?

[KiwiBacon]

Originally Posted by HeWhoKillz

Is that the same thing as a valve cover gasket? The thing that looks like a stencil of the piston holes from atop? Sorry, I'm trying to learn. If not, how does a blown one stop a ccar fron running?

Your description of "a stencil of the piston holes" does fit with a head gasket.

It seals the head (contains the valves, sparkplugs etc) with the block (which has the cylinder holes and pistons).

The rocker cover gasket goes on top of the head, between the head and the rocker cover. It is only really to keep oil in and dust out.

[2turboimports]

Originally Posted by HeWhoKillz

How does a blown one stop a ccar fron running?

Some or all of the clyinders will have little to no compression. Coolant will mix with the oil causing it to foam up, which is extremely bad for parts that need to be lubricated. The engine will overheat and in extreme cases can cause the block/heads to warp or crack.

[UncleBob]

head gaskets fail in multiple ways.

The primary goal of a head gasket is to keep three different elements seperate from each other, and also keep those three elements from escaping from their confined area.

The three elements are combustion chamber gases/pressure. coolant. And oil.

The combustion chamber pressures are much higher than any of the other pressures. so usually if something is going to leak, it will leak from there, to somewhere else. For example, leaking combustion into the coolant system. This will over-pressurize the coolant system, causing the coolant to get pushed out of the system into the overflow bottle.

Its pretty rare for combustion pressure to push into the oiling system, simply because oil doesn't eat at the gasket like coolant does. Coolant creates electrolysis and can become corrosive if neglected.

The other issue is when oil or coolant leaks externally. IE, when coolant or oil starts leaking past the gasket and to the outside of the engine. Some engines are very prone to this, such as 2.0L dodge engines (neon) or Subaru's (all of them, just about)....just 2 examples.

There is one other way they can fail, and that is the gasket can fail between two cylinders. This will create a leak from one cylinder to the other, and since two cylinders are never at compression stroke at the same time, this creates a very large compression leak when it happens. Chrysler 2.2/2.5's seemed prone to this

Severe overheating can cause head gaskets to leak, but its not really the head gaskets fault. The engine can get so hot that the head warps which creates paths for intermingling of elements

Its actually pretty rare for coolant to get into the oil via a head gasket. That is much more likely to be either a leaking oil cooler in a radiator, or a leaking intake manifold on a V-config motor.

One side note on Saturns. They come from the factory with a coolant "conditioner" that can create a mayo-like residue in the coolant surge tank. Sometimes this....substance is misdiagnosed as a bad headgasket.