low compression is #3 cylinder

2008 MAZDA CX7
130,000 MILES • 6 CYL • AUTOMATIC
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DEECHANCE
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Why would my vehicle have extremely low compression?
May 11, 2018 at 8:43 AM
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SQM
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Hello,

There could be number reasons why the compression is low.
It could be for worn piston ring, damaged valve springs, leaking valves, blow head gasket, worn cam shaft etc.
What is the compression you are getting for the #3 cylinder?

The minimum compression should be 130 PSI for this engine with the typical compression being 185 PSI.

https://www.2carpros.com/articles/how-to-test-engine-compression

You can do a quick test to see if you have worn piston rings. On the low cylinder, pour in about a tablespoon of engine oil, thru the spark plug hole. Then check the compression. If the compression rises, then you have faulty pistons rings and the reason for the low compression.

If you have a blown head gasket it is likely that you will have coolant in the engine oil also it will produce white smoke out of the tailpipe.

Best course of action would be to check different items to find out what is the reason for the low compression.

Let me know what you find out on the piston ring test.


Thank you.
Oct 9, 2021 at 9:46 PM