importwarrior Posted September 20, 2014 Report Share Posted September 20, 2014 (edited) If compression test results are with in spec per service manual. Can the head still be cracked and leak water and not cause lowCompression test results? ? ? Edited September 20, 2014 by importwarrior Link to comment Share on other sites More sharing options...
ucw458 Posted September 20, 2014 Report Share Posted September 20, 2014 My instincts say yes it could affect the results. But I can't be 100% sure since I have never had a cracked head to test. You can hook an air compressor to each cyl and pressurize them one by one. With the rad cap off you will see bubbles if the pressure is leaking into the cooling system through a HG or crack. If you don't see bubbles then you're probably good. Link to comment Share on other sites More sharing options...
STARION_NORTH Posted September 20, 2014 Report Share Posted September 20, 2014 Are you doing the compression test with the engine hot? A crack might not show up cold. Link to comment Share on other sites More sharing options...
Walker Posted September 20, 2014 Report Share Posted September 20, 2014 i'm not a car mechanic so i cannot say with any certainty.....but i do know physics and temperature..... it's conceivable to me that a crack may or may not leak depending on it's current temp due to expansion and contraction of the metal as it heats/cools if you originally did a compression test with a cold engine....then maybe try a new test with an engine up to operating temp.......or vice versa Link to comment Share on other sites More sharing options...
importwarrior Posted September 21, 2014 Author Report Share Posted September 21, 2014 Thanks for the help. i believe the head is cracked and as you guys mention TEMP.the temp is seems to change the cars performance as it warms up. it starts to smoke morre when it is hot. i will have to repeat the test when hot. Thanks again. Link to comment Share on other sites More sharing options...
StarquestRescue Posted September 21, 2014 Report Share Posted September 21, 2014 A compression check is unlikely to show a cracked head. This is why you must put the compressed air in the cylinders and put your ear to the open radiator cap to listen for the gurgling. Like wise a compression check may not show a cracked ring land as the bad cylinder may only be down 5-10 psi. But the bad cylinder would show more leak down on a leak down tester and maybe a louder hissing from the removed oil cap in that cylinder. Sadly it is possible to have multiply problems at the same time. A cylinder consuming water will often show a white residue on the plug. And coolant would be disappearing from the radiator. Link to comment Share on other sites More sharing options...
importwarrior Posted September 21, 2014 Author Report Share Posted September 21, 2014 Thank you for the information Link to comment Share on other sites More sharing options...
techboy Posted September 30, 2014 Report Share Posted September 30, 2014 After doing some of the things listed above .... If you have a hunch as to what cylinder it is you can let the car sit overnight, pull the spark plug wire (leave the plug in) and crank the car over. If you have a bad enough coolant leak it will splash coolant up on the bottom of your plug. This is where your smoke comes from when you drive. If you don't know what cylinder you can also perform this test on each plug one at a time. DISCLAIMER: If your leak is only happening when the motor is hot you may not get results. Link to comment Share on other sites More sharing options...
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