Engine Compression Test

weak car engine compressionI have a Ford Focus with 135,000 mile son it and was told today that the #2 cylinder has zero compression. Mechanic thinks something internal broken and has suggested we not repair as it probably involves replacing the engine (rebuild would be equally costly.) Any thoughts?


Engine Compression Test

Hey there Nick,

Ya, this is going to be a tough call. I would first get a second opinion from another mechanic, unless you really trust this one and his diagnosis.

If it is just 1 cylinder with no compression, but the other 3 all have normal compression AND there is no knocking noises coming from inside and underneath the engine…..I would pull off the cylinder head and send it to a machine shop for a valve job.

You want a complete valve “grind” or replacement, a magna-flux (checks for cracks) and a resurface of the cylinder head surface done.

You will basically be rebuilding the top half of the engine (although bottom half will still be original)

This will probably cost you about $1500++– once all said and done. There are many parts that have to be removed, so if they need replacing do it then to save money since you already paid the labor.

This is a gamble, there could be something major wrong inside, but if there are no knocking noises and other cylinders have good compression….I would take the gamble if this was my car, or you were my customer.

If this is an older vehicle, either sell it for scrap now or put some money into it and see if you can get a few more years out of it.

I would ask your mechanic about this and how much he will charge to do the labor and if he has a machine shop he uses and recommends.

Reasons for weak engine compression

1. Lack of engine oil changes

2. Severe engine overheating

3. Broken timing belts that bent the valves

4. High mileage – dude buy a new car

Please share this with your friends,
Austin Davis

Posted in: Head Gaskets

3 Comments on "Engine Compression Test"

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  3. Joe Kelemen says:

    I had exactly same thing happen on my 1995 sw2 Saturn and was very confused by 0 compression, always had at least some.I looked with scope to see if there was a hole in piston and all looked good. I found that a small piece of exhaust valve broke off and would have thought it would have had a small amount of compression. I really enjoy your info even though I have worked quite a bit on my own cars. You are very descriptive about various problems and sometimes remind me of things I didn’t know or forgot.

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