BLOWN HEAD GASKET.......diagnosed and explained

What is a head gasket?

A headgasket is a gasket that sits between the engine block and cylinder head(s) in an internal combustion engine.

Its purpose is to seal the cylinders to ensure maximum compression and avoid leakage of coolant or engine oil into the cylinders; as such, it is the most critical sealing application in any engine, and, as part of the combustion chamber, it shares the same strength requirements as other combustion chamber components.

What causes a blown head gasket?

The most common cause of a blown head gasket is overheating.
You may ask.. "how  can an engine overheat?"
There are many factors that can contribute to overheating such as..

1. Loss of coolant 
2. Faulty thermostat
3. Faulty water pump
4. Blocked radiator
5. Faulty radiator fan

Other causes of head gasket failure 

Design of the engine is often a factor in head gasket failure.  Some vehicles have more problems than others. This is due to engine design limitations. Preventing head gasket and cylinder head problems is always much easier with good cooling system service.  A well maintained cooling system greatly reduces the odds of head gasket and cylinder head problems.

 

Symptoms of a blown head gasket

A blown head gasket may cause a number of different symptoms. Coolant in the engine oil, an engine misfire, oil leaking from the engine or white smoke from the exhaust could all be a symptom.

Head gasket failure types

Compression leaks between cylinders causing misfire or rough idle

 Compression leak to coolant causing high pressure build up in cooling system



The above mentioned are the most common gasket failure types, but there are many more depending upon the circumstances...

Fixing the problem

The cylinder head has been removed, so the next step is the most important! The easiest way would be just to replace the head gasket, but not recommended!!
It's most likely the cylinder head is warped due to high temperatures.

The cylinder head has to be pressure tested for cracks.
A cracked head can give the same symptoms as a blown gasket. In the photo below, the crack is obvious. Often the crack is too small to see with the eye. Though they are small, a crack in a cylinder head will cause serious problems. Cylinder head shops use dye, pressure and other methods to find very small cracks. Sending cylinder heads to a professional, for testing, is a wise precaution.

If no cracks were found, the next process is skimming.

What is cylinder head skimming?

Cylinder head skimming is a way of refacing the mating surface of the head. The method used is sometimes called 'fly cutting' which involves mounting the cylinder head on a milling machine which has a fixed head and a moving table. The milling head has a bespoke attachment with a cutter which spins at around 800 rpm, and the table of the mill moves the cylinder head across the cutter. This is the most accurate way to resurface a head. 

Important facts

1. It is important that we find the cause of overheating. Repairing the cylinder head and installing with a faulty thermostat will only bring us back to another blown head gasket.
2. On certain engines, a thicker head gasket will be needed due to the skimming procedure.
3. In  some rare cases water cooled oil coolers have been known to cause oil and coolant mix up due to corrosion.