Compression tester with the motor working?

$pider · 03-21-2005, 08:29 AM

Is that safe for my motor to do a compression just by removing a spark plug and let the motor run... than run to 3000 rpm

cause it seems that the headgasket is bad from 3000 to cutoff..

Let me know please...

Last month i was able to run up to 5000 rpm before the temperature drop... now it's 3000... so i can't go real fast now

$pider · 03-21-2005, 12:13 PM

with the motor working but when the motor is running
will it be safe ?
It's like removing spark wire when the cars is running nope ?

510&SE-R · 03-22-2005, 12:25 AM

If your headgasket is bad it will leak when you do a compression test at 300RPM provided by the starter. You do not do compression tests by deadheading a cylinder and letting the engine get all Subaruistic sounding.

If its bad, its bad all around, not just at certain RPM.

SHAWNATGERBROCK · 03-22-2005, 01:49 AM

You cannot check a blown headgasket with a compression test anyways , unless its blown between 2 cylinders, then you would have 2 dead cylinders, you will need to do a leak down test to properly test for a BHG !!

510&SE-R · 03-22-2005, 02:42 AM

I had a Z22E with a blown gasket, it was blown into a coolant port, and it did read ultra low compression on that cylinder. Under 30PSI.

$pider · 03-22-2005, 02:51 PM

compression is real fine on all cylinders .. 150 on all (when hot)

the motor takes more oil and coolant than before...
and the motor goes wrong when i run over 3000 rpm... not on idle so i have to check compression when he's over 3000.. else the motor is fine.

What can i do

nissanboi · 03-22-2005, 04:17 PM

one thing to do is look at your oil when you change it and see if there is antifreeze in it or if it smells like gas, second make sure your plugs dont look oil soaked or smell like oil that will be another way to tell a bhg in addition to what everyone else is saying to do good luck

SHAWNATGERBROCK · 03-22-2005, 07:38 PM

Quote:

Originally Posted by $pider

compression is real fine on all cylinders .. 150 on all (when hot)

the motor takes more oil and coolant than before...
and the motor goes wrong when i run over 3000 rpm... not on idle so i have to check compression when he's over 3000.. else the motor is fine.

What can i do

Didnt I just answer that ?? You have to do a Leak down test , that will tell you if you have a BHG and what cylinder !!

SHAWNATGERBROCK · 03-22-2005, 07:42 PM

Quote:

Originally Posted by 510&SE-R

I had a Z22E with a blown gasket, it was blown into a coolant port, and it did read ultra low compression on that cylinder. Under 30PSI.

Yea, if its really blown it wil show low comp. but that will not say for sure that the BHG is the reason for the low comp.A leakdown test will show for sure it is a BHG, also alot of coolant in the cylinder can wash the rings and cause low compression ...