What can you learn from a COLD engine compression test.

[32251]

When you come across a motor that is not in running condition, but will turn over, can you get an idea of what kind of shape the cylinders are in by doing a cold engine compression test?? All the info I have seen says to test the engine after it has warmed up.

What will be the major difference in the readings between a cold and a warmed up motor??

Surely a test on a cold motor would be better than no test at all....????

 

[Frank Acampora]

Re: What can you learn from a COLD engine compression test.

When buying an unknown engine not running for any reason, the first test I do is to put my thumb over the plug holes and turn over the engine by hand. If any cylinder does not blow my thumb off the hole, it has no compression and the engine needs a rebuild. If all cylinders blow my thumb off the holes, then I know I have something with which to work. This basic test is good for any engine although I only mess with outboards.

This separates the engine into junker and non-junker class and price.

NOW, a compression test will tell me the basic overall condition of the engine, and whether I will need to put time and money into it.

Compression along with the overall external condition of the engine will fairly accurately tell how well the engine will run and how much service life it will give. Lots of corrosion on the outside means that even if it is sound mechanically inside, sooner or later, components will need to be replaced.

I always assume that all normal maintenance parts (Pump impeller, lower oil, fuel lines and pump diaphragm, etc.) will need to be replaced, even if assured by the owner that they were "JUST PUT IN"

 

[coolguy147]

Re: What can you learn from a COLD engine compression test.

i wouldnt use the thumb rule just get a comprsssion tester and use it the right way

 

[5150abf]

Re: What can you learn from a COLD engine compression test.

Last time I did mine it was@105 cold and then I warmed it up and got @145 so on a cold motor you will still want at least 90-100.

It really isn't much different and actually I think a better reading on the health of the motor as you are getting a base reading and it cnaonly go up from there and yes cold is better than none.

 

[tashasdaddy]

Re: What can you learn from a COLD engine compression test.

you learn if you have a viable base, with which to work. the test has to be done properly, to get accurate readings. >>>>> http://forums.iboats.com/showthread.php?t=299680