Lesson 5/Learning Event 2
All leaks must be corrected even though they may appear as no more than a stain spot where leakage has
evaporated. A leaking drain cock or pipe plug that cannot be tightened should be replaced. Leaking expansion
plugs must be replaced. If tightening gasketed joints will not correct leaks, replace the gaskets.
Since you cannot see internal coolant leaks in an engine, you must detect these leaks by looking for their results
instead of the actual leak. Coolant leaking into the crankcase can often be detected by checking the level and
condition of the engine oil. Any large leaks will raise the oil level a noticeable amount. Also, if the engine has
been operated recently, any coolant in the crankcase will be mixed with the engine oil. Coolant mixed with oil
will cause the oil to have a milky color.
On the other hand, if the engine has not been operated for some time, the coolant and oil in the crankcase will
separate. The coolant, being heavier than oil, will settle to the bottom of the oil pan. Therefore, to check for
coolant in the crankcase when the engine is cold, slowly remove the oil drain plug and watch for any coolant.
The results of coolant leaks into a combustion chamber will depend on the size of the leak. A liquid, such as
engine coolant, cannot be compressed at ordinary pressure. Therefore, if the leak is large, enough coolant will
leak into the combustion chamber to lock the engine as the piston comes up on the compression stroke. When
an engine is locked up by any kind of liquid in the combustion chamber, it is referred to as a "hydrostatic lock."
If an engine will not crank and a hydrostatic lock is suspected, remove the spark plugs and then attempt to
crank the engine. Any liquid that is trapped in a combustion chamber will be forced out of the spark plug hole,
relieving the hydrostatic lock. The cause of the engine lockup should be corrected before the engine is