This is my first Instructable... Please comment below if it needs further editing. Videos can be seen by opening the video URL in your media viewer.
Here's my experience with replacing a new head gasket on my '91 Civic. But first, some background:
This is a great car! It ain't pretty but it gets almost 40mpg on a good day. About a year ago, it failed to pass several emissions tests. My mechanic told me that the pistons needed new rings. Because the engine would be in pieces, and because of the expense and effort invested already, I agreed to have the water pump, timing belt, and head gasket replaced. Afterwards, the car passed emissions with flying colors and ran very well until recently.
Several weeks ago, the engine began to overheat erratically. After googling the problem, I personally replaced, in ascending order of expense, the radiator cap, the thermostat, and eventually, the radiator, which was very old. Because the problem was intermittent, it seemed that each part replacement solved the problem. I hoped it wasn't the water pump because I knew that would be a huge pain to replace.
In the end, some white smoke and serious engine vibrations told me that it was not the water pump but some cylinder/coolant related problem. I was afraid that it was a cracked cylinder which would have meant replacing the engine block, which didn't seem worth the expense on a 16 year old car with 174,000 miles on it. So, I went into the engine bay prepared for the worst. What follows is my experience and illustrates why your trusted mechanic can't always be trusted....