5_108.bk Page 36 Thursday, October 4, 2001 11:45 AM
TROUBLESHOOTING CYLINDER HEAD AND CYLINDER BLOCK LEAK TEST PROCEDURES Verify suspected leaks in the cylinder heads or cylinder block by pressure testing before deciding to replace a cylinder head or the block. Do not use magnaflux inspections alone as replacement criteria.
Cylinder Head and Head Gasket Check 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 55 lb-ft (75 N•m). Refer to Figure 11. 11
Before proceeding with the following tests, make sure leakage is not from the oil cooler. 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.
Figure 11 — Cylinder Head Pipe Plugs (3/4-Inch NPT)
Before performing any unnecessary tests, look for stains around the 3/4 inch NPT plugs on the tops of the cylinder heads. Check that the plugs are tightened to 55 lb-ft (75 N•m) torque.
2. Before removing thermostat, drain coolant from the cooling system until coolant level is below the thermostat housing.
Cylinder head pipe plugs have encapsulated epoxy sealant applied to the threads. The epoxy sealant locks the plugs in place after tightening. These plugs will not turn when an attempt is made to tighten them. If a coolant leak is suspected, remove the plug by heating it to approximately 400°F (205°C) using a torch. Before reinstalling the plug, thoroughly clean the threads of the plug and the threads in the cylinder head, using Loctite® Primer T. Reseal the plug threads with Loctite® 277 and reinstall the plug and tighten to 55 lb-ft (75 N•m) torque.
4. Remove fan belts from the water pump.
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. 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 the two cylinder heads to check for external combustion leakage.
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