Editing Head gasket

Head gaskets provide the critical seal between the engine block and the cylinder head. They seal all of the combustion chambers, and prevent coolant and engine oil from leaking into the cylinders.

==Different types of head gaskets==
Copper and brass were originally used as head gaskets, followed by asbestos gaskets in the 1950's, and composite metal and impregnated fiber or graphite composites in the 1980's. In the 1990's the Multi-Layer-Steel gasket (MLS) came into widespread use. Most new engines today are designed with MLS gaskets.

In MLS gaskets, multiple thin layers of cold-rolled steel are coated with a very thin layer of elastomeric material. The elastomer "micro-seals" the surface imperfections in the metal, and resists gases, oils, coolants, and high combustion temperatures.

==Aluminum cylinder heads==
Though aluminum is lighter than cast iron, it expands faster. This quicker cycle of expansion and contraction stresses head gaskets. To handle this, a non-stick coating is often applied to the gasket, like Teflon or molybdenum.

With iron heads, a product can be applied for the opposite effect. Silicone, Viton, or other fuoroelastomer sealants are applied to '''increase''' the pressure between the iron heads and the iron block.

==Symptoms of a blown head gasket==
Some of the symptoms below may also indicate a cracked cylinder head.

*Foaming or bubbling coolant. Indicates head gasket has failed between a cylinder and a passage in the water jacket.
*Rapid pressure buildup in cooling system, before engine is warm. Or, cooling system appears to be malfunctioning.
*Radiator frequently gets low on water (it could be being discharged through the tailpipe).
*White smoke in exhaust, or sweet smelling exhaust.
*"Milkshake" oil, caused by coolant in oil.
*Oil in coolant, causing foaming in coolant.
*Oil or coolant leaking from cylinder head.
*Low cylinder pressure.
*Milky-gray ring around the oil cap. It's a coolant deposit.
*Drops of coolant coming out of the tail pipe.
*When the heater is turned on, it smells like coolant. ''(confirm)''
*Spark plugs with coolant deposits. ''(confirm this, and add info if possible)''
*Sound of air rushing or whistling coming from cylinder head. You can also listen with a stethoscope.
*Two adjacent cylinders with low but equal pressure. Indicates head gasket failure between the two cylinders.
*Car misfires or runs rough at low speeds, due to antifreeze in the combustion chamber. '''(confirm)'''

==Head gasket repair additives==
Engine additives that claim to repair questionable head gaskets are ill-advised, and, if used, should only be considered a temporary fix.

==Head gasket test kits==
Chemical test kits that test the coolant system for combustion by products. A blown gasket can thus be indicated by a color change in the test solution.

==Damage caused by a blown head gasket==
Time is of the essence when replacing a blown head gasket. If the car overheats, it can warp the cylinder head, especially if it's aluminum. If it warps too much, it will have to be discarded.

==Reasons why head gaskets fail==
*Overheating, possibly from a blown hose, water pump, or thermostat.
*Engine pre-ignition or detonation.
*Improperly torqued cylinder head.
*Faulty cylinder head bolts.
*Some blocks are more prone to head gasket failure, because the bolt positioning applies uneven pressure

==Compression testing==
*If a compression test shows two cylinders with equal but low compression, then that may indicate a blown head gasket, with a leak between those two cylinders.

==When replacing a blown head gasket==
*Check to make sure the heads and block are straight. If they're warped, you could easily end up with another blown head gasket. This can be done with a straight edge and a feeler gauge. This is also a good time to check for cracks.
*Prep the surface (more info on this). Mating surfaces should be smooth, clean, and dry.
*Chase the bolt and stud holes. Clean with compressed air.
*Pre-fit the head gasket.
*Don't use sealant unless the manufacturer explicitly specifies it.
*Follow specific torque settings and bolt-tightening sequence perfectly.
*Replace both at the same time, even if only one has blown.

==Suppliers of head gaskets==
*Fel-Pro
*Mopar Performance Gaskets (check)
*[http://www.bestgasket.com/ Best Gasket] -- Head gaskets for 1930's - 1960's American automobiles.

==References==
*[http://en.wikipedia.org/wiki/Head_gasket Head gasket] -- Wikipedia
*[http://www.allpar.com/eek/headgasket.html Replacing Chrysler, Dodge, or Plymouth head gaskets] -- Allpar.com
*[http://www.partstrain.com/ShopByDepartment/Head_Gasket Head Gasket] -- Partstrain.com
*[http://www.dupontelastomers.com/Applications/Automotive/head.asp Head Gaskets] -- DuPontElastomers.com
*[http://www.mobiloil.com/USA-English/MotorOil/Car_Care/DIY/Head_Gasket_Basics.aspx Head Gasket Basics] -- MobilOil.com
*[http://www.econofix.com/head.html Cylinder Head and Head Gasket Repairs] -- Econofix.com
*[http://wiki.answers.com/Q/FAQ/522 Head Gaskets and Valve Covers Q&A] -- Wiki.Answers.com