Cylinder Head And Cylinder Block Leak Test Procedure - Mack E7 Service Manual

5-101.bk Page 13 Friday, March 17, 2006 11:05 AM
Cylinder Head and Cylinder Block
Leak Test Procedure
Verify suspected leaks in the cylinder heads or
cylinder block by pressure testing before deciding
to replace the cylinder head or block. Do not use
magnaflux inspections alone as replacement
criteria.
Before proceeding with the following tests, make
sure leakage is not from the oil cooler or air
compressor. Watch for small bubbles indicating
minor leaks that can develop into more severe
leaks during engine operation.
To prevent unnecessary engine disassembly,
perform the simpler checks first.
CYLINDER HEAD AND HEAD GASKET
CHECK — IN CHASSIS
1. Look for coolant stains around the 3/4-inch
NPT pipe plugs on top of the cylinder heads.
Check plug torque. Plug torque specification
is 28 lb-ft (38 N•m). Refer to Figure 9-3.
Figure 9-3 — Cylinder Head Pipe Plugs (3/4-Inch NPT)
2. Before removing thermostat, drain coolant
from the cooling system until coolant level is
below the thermostat housing.
3. Remove the thermostat and leave the
thermostat housing open. Install a short
section of hose, approximately 6–8 inches
(152–203 mm) long, on thermostat housing.
Add enough coolant to fill the thermostat
housing.
4. Remove fan belts from the water pump.
200 TROUBLESHOOTING
CYLINDER HEAD FUEL PASSAGES LEAK
CHECK — IN CHASSIS
The symptoms of coolant-in-fuel are a loss of
coolant with no apparent external leak, together
with one or more of the following: coolant in fuel
tank, coolant in fuel filter or yellow fuel out of fuel
return line.
5. Start engine and run at 1000 rpm.
6. Observe coolant in the thermostat housing
for air bubbles. This indicates combustion
pressurization of the cooling system and
possible cylinder head gasket failure. Air
bubbles may also indicate leakage from the
cylinder head or oil passage.
7. Apply a soap-and-water solution between
two cylinder heads to check for external
combustion leakage.
1. Disconnect the return fuel inter-connecting
tube between the front and rear cylinder
heads. Run a line from each cylinder head
into a container.
2. Pressurize the cooling system with a
maximum of 15 psi (103 kPa) air pressure
and look for coolant coming out of a fuel
return line.
3. An alternative method is to disconnect the
fuel return line at the front of the front
cylinder head. Introduce a maximum air
pressure of 25 psi (172 kPa) to the fitting in
the cylinder head. Then look for air bubbles
in the coolant.
4. After determining which cylinder head is
suspected of leaking, remove the nozzles
from that cylinder head and pressurize the
cooling system with a maximum of 15 psi
(103 kPa). Look into each nozzle sleeve
bore for signs of coolant leakage.
5. A cracked or leaking nozzle sleeve should
be replaced as an on-engine repair using the
procedures described in the ENGINE
DISASSEMBLY section. If replacing the
nozzle sleeve(s) and the re-pressure test
shows that the problem still exists, the
cylinder head(s) should be replaced.
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