We always replace both head gaskets. If one is leaking due to corrosion, mainly from old coolant that has become acidic, it is just a matter of time before the second one starts leaking too. Your customer is not going to be pleased with you for trying to save a few bucks now, then having to do the job over a second time later. That is like buying one new sock to replace the old one with a hole in it.
If the leak does not seal itself when the engine is off, you can find the leaking cylinder with a "cylinder leakage test". That involves forcing compressed air into the cylinder, through a tester that regulates that air pressure to around 30 psi. The piston must be at TDC on the compression stroke. The gauge on the tester will show the percent leakage, and you can listen in four places to identify the cause of excessive leakage. With a leaking head gasket, you will see bubbles in the radiator. For a leaking intake valve, you will hear hissing at the throttle body. For a leaking exhaust valve, you will hear hissing at the tail pipe. If the piston rings aren't sealing well, you'll hear hissing at the oil cap or dipstick tube.
Friday, December 23rd, 2016 AT 5:19 PM