Compression Test

[qube 3570]

Does anyone have any recommendations on where/who to do this? 

Do I need to take the car to a workshop is or there a mobile mechanic to run this test?

 

Thanks!

[Mr Vapour 76]

or you could do it your self with some very basic tools. 

If you can change spark plugs then you can do a compression test. 

the only extra thing you would need is the compression tester. 

 

Edited August 3, 2017 by Mr Vapour

[zero 1162]

Yea, easy to do yourself, and you could proboably buy a cheap compression tester for similar to having a mechanic do it for you.

[Mad_Max 231]

23 minutes ago, zero said:

Yea, easy to do yourself, and you could proboably buy a cheap compression tester for similar to having a mechanic do it for you.

I paid about $30 for a kit on TradeMe with all the fittings you'll need to test most cars and it seems pretty accurate. Most important though, you need to know what to look for and how to test it. Should always do the test on a warm motor whenever possible, and you're looking for more than about a 5 to 10% variance across the cylinders, don't get too hung up on overall numbers (unless they are really low across the board).

If you have a cylinder or two that are lower, drop about half a tablespoon of fresh oil down the plug hole of the offending cylinders, crank the motor over a couple of times then retest. If the compression rises on them, you have an issue with the lower end (block or piston rings) causing the lower compression, if it stays pretty much the same the issue lies in the top (head, gasket, valves etc). 

[zero 1162]

Yes, and make sure you have the throttle open when testing.

[Mad_Max 231]

3 hours ago, zero said:

Yes, and make sure you have the throttle open when testing.

I've never been told that one before, is there a theory behind it? Just asking out of curiosity, not a criticism.

[zero 1162]

1 hour ago, Mad_Max said:

I've never been told that one before, is there a theory behind it? Just asking out of curiosity, not a criticism.

It maximizes the test and delivers a higher figure.

[hotwire 352]

2 hours ago, Mad_Max said:

I've never been told that one before, is there a theory behind it? Just asking out of curiosity, not a criticism.

As above. Wide open throttle gets maximum air into the cylinder to give maximum volume to compress & get the reading,

If throttle is closed then minimal air volume will get into the cylinder to be compressed. Means there will be a lower reading but also due to the lower compression - it does not put the sealing components (valves, rings etc) under maximum load to highlight a problem.