WATER DAMAGE TO AUTOMOTIVE ENGINES:
Charles C. Roberts, Jr., Ph.D., P.E.
A specific type of
automotive engine damage occurs when water enters the engine and is compressed
in one or more cylinders. Figure 1
illustrates the damage sequence often called hydrostatic lock. The left drawing
in Figure 1 shows water entering a typical automotive engine cylinder during
the intake stroke. Water, unlike the fuel/air mixture, is incompressible and
during the compression stroke, locks the piston in place as shown in the drawing
at the right of Figure 1. This condition
tends to overload the connecting rod, causing a bending failure of the rod and
severe engine damage. A common way for water to enter the engine is driving
through water sufficiently deep to allow injecting into the air intake system
of the vehicle, such as crossing flooded roads.
Figure 2 shows a failed
connecting rod that sustained hydrostatic lock. After stalling in a flooded
street, the vehicle operator started the engine, which suddenly failed. In this
case, the connecting rod bending failure resulted in a fracture through the
cross-section of the connecting rod. Figure 3 is a view of a connecting rod
that sustained a hydrostatic lock bending failure without a fracture.
Figure 4 shows an
engine that operated poorly after the owner drove through a flooded
street. The lower piston in the photo
(red arrow) should be at the same height as the upper piston (green arrow), but
is not. The lower piston is displaced downward relative to the upper piston,
suggesting that the connecting rod is shorter or bent as a result of
hydrostatic lock brought on by water ingestion into the engine.
Other evidence of
water ingestion into the engine may exist in the form of mud and water debris
patterns. Figure 5 shows a water damaged air filter, which is often damp and
crumbles when handled. Water marks on upholstery and carpeting in the occupant
compartment are additional clues that corroborate the assessment that water may
have entered the engine. Finally, an oil analysis2 may add further
information regarding the condition of the engine. If wear metal analysis
yields evidence of long term related engine damage, then it is possible that the
engine failure was not related to hydrostatic lock, absent any other evidence
as exemplified in Figures 2 through 5. It should be noted that some engine failure
modes such as connecting rod bearing wear-out2 can cause connecting
rod failure, which is not related to hydrostatic lock.