Here is a close up view of the problem.

To the left side of the pic, in the narrow band between #2 cylinder and #1 cylinder, we see the telltale dark and discolored surface of the cylinder head where the head gasket failed. Combustion gases passed between the two cylinders, causing a loss of power.

Between #2 and #3 cylinders, the failure is not quite so obvious; but the damage being done is as bad as, if not worse than, the damage being done between #1 and #2. The discoloration evidences a gasket failure allowing coolant to pass into the two cylinders. The coolant passing into the two cylinders will cause a misfire in both cylinders; and as the coolant is lost, the engine will overheat.

In the engine that this head came from, the complaint was that the engine started to run near the red of the temp gauge. When the hood was opened, coolant was leaking out the side of the head gasket. After adding some coolant, the car was driven home before the engine quit running.

Head problems and head gasket problems can be categorized into three general categories:

#1...the engine overheated; the head gasket then failed...

#2...the head gasket failed; then the engine overheated...

#3...the head gasket failed; the power decrease was noticed; the engine was shut down before overheating occurred...[a rare sequence of events. for sure]


In category #1, the cause is or becomes apparent during examination and diagnosis: a loss or lack of coolant; or a loss of cooling capability: loose fan belt; bad fan clutch; crudded up radiator either internally or clogged fins externally...

The second catagory is not so easily explained. The cause of the head gasket failure may be masked by the effects resulting from the overheating.

In the third category, it might be easier to see the failed head gasket per se; but the real cause is still often missed or misdiagnosed.

The head we are looking at here fell into the second category: when the overheating was noticed, the head gasket was already leaking.


In a category 1 failure, the engine overheating causes the cylinder head to warp. The resulting warp of the head reduces the clamping forces on the head gasket to keep it sandwiched between the cylinder head and the block. Combustion gases, under high pressure, force their way past the gasket, destroying the gasket material beyond the fire-ring; thereby enlarging the gap, and allowing a passage for the coolant to escape.

This is the most common cause of head gasket failures; especially on engines with aluminum cylinder heads. The ususal suspects:
...radiator clogged internally, impairing coolant flow...
...radiator clogged internally by deposit coating, impairing heat transfer...
...radiator clogged externally: debris on the front face of the radiator core [the side you don't see]
...incorrect antifreeze/water mixture ratio. for best heat transfer, a 50/50 mix is recommended.
...low coolant level; from either a slow leak, or a sudden loss, ie a burst hose...

Cooling fan problems can also contribute to the problem: reduced heat transfer from the radiator to the passing air because there is not enough air being drawn through the radiator.


In a category 2 failure, the head gasket failure causes the coolant loss and the subsequent overheating.

In a category 3 failure, the head gasket failure was detected before further major damage resulted.

In category 1, other things cause the head gasket to fail.

But WHY the head gasket failure in the second and third categories?


HMMMMM....lots of reasons are given:

....weak head bolts
....too much boost
....excessive RPMs
....'head gaskets just do that!'
....'the engine is tired'
....'normal with that many miles on it: it was about time for it to let go'
....'aluminum heads always lose their gasket after a while'


Some of the above reasons have validity; some are based on misconceptions; some are based on mis-diagnosis and faulty analysis. We will be looking at most of these reasons, to examine the validity.