Head Gasket Failure

Symptoms

• External coolant weeping or visible deposits/residue running down the side of the block, particularly below the exhaust ports [3, 11].
• Actual coolant droplets found on the crossmember below cylinder 3 and 5 exhaust ports [11].
• Gradual coolant loss requiring periodic top-offs (e.g., adding coolant 3 times over 30,000 miles) [11].
• Cooling system pressurizes under boost — a latex glove placed over the coolant reservoir inflates when the engine is put under load [7].
• Coolant leaking into one or more cylinders, visible via borescope through the injector holes after the cooling system is held under pressure [1].
• Possible steam disruption of oil film on cylinder walls, associated rattling, or piston damage if coolant intrusion is severe [5].
• Blue/crusty residue build-up on coolant hoses near the leak area [11].

Causes

• Gasket material failure at the sealing surface between the cylinder head and block, which may worsen progressively until coolant enters cylinders [0, 1].
• Warped or damaged cylinder head sealing surface — the aluminum head is susceptible to distortion, and even minor surface grooves or wear marks are unlikely to seal properly long-term [13].
• Cracked cylinder head — one fleet specialist reports this is the actual cause 4 out of 5 times rather than the gasket itself [6].
• Cracked block — listed as a less common but possible source of the same symptoms [6].
• Previous inadequate repair — head gasket replacements that do not fully correct the underlying surface condition or use the wrong parts can result in recurring leaks [7].

Diagnosis

• Perform a visual inspection of the block flanks for coolant deposits, white residue, or staining below the exhaust ports — progressive worsening of these deposits is a strong indicator [3, 11].
• Pressurize the cooling system with a pressure tester and hold pressure for at least 30 seconds; a drop in pressure confirms a leak somewhere in the system [9].
• Conduct the 'latex glove test': place a glove over the coolant reservoir filler neck with the engine under load (drive mode, foot on brake, engine revved to build boost) — inflation of the glove indicates combustion gases pressurizing the cooling system [7].
• Pull the injectors, pressurize the cooling system, and insert a borescope down the injector holes after letting it sit pressurized for 12 hours — coolant pooling in a cylinder will be clearly visible [1].
• Note that the standard exhaust gas (combustion gas) dye test does NOT reliably work on diesel engines — do not use a negative result to rule out head gasket failure [8].
• Have a machine shop pressure-test the bare cylinder head to distinguish a failed gasket from a cracked head — these require different repair paths [6].
• Check for metal particulate in the oil (e.g., oil smear under magnification) if coolant intrusion and cylinder damage are suspected [5].

Repair

Head gasket replacement on the T1N is a significant engine-off job that requires cylinder head removal, surface inspection, and machining assessment. The cylinder head is made of aluminum alloy and must not be machined beyond tolerance — if warped beyond limits or cracked, the head must be replaced entirely [12]. Because the head cannot be skimmed and the underlying cause (cracked head vs. failed gasket) must be confirmed before reassembly, most experienced T1N owners send this job to a shop [2]. Attempting the repair with owner-supplied parts shifts liability away from the shop, so weigh that risk carefully [2].

Parts

Plain part names — affiliate links and pricing are coming in a later update.

• Head gasket set (shop-supplied recommended — do not supply your own to avoid voiding shop warranty) [2]
• Cylinder head bolts — measure existing bolts and replace any exceeding 104 mm length [12]
• Replacement cylinder head if cracked or warped beyond tolerance (AMC heads with valves and springs are one known supplier option at ~$2,000) [6]

Related forum threads

• 19 ↳$11,000 Mechanics Bill for 2005... Advice?
• 19 ↳Head gasket?? Common issue?
• 19 ↳Melted piston, injector failure?
• 19 ↳Rapid Coolant Loss -- Please Help Identify the Issue!
• 19 ↳Coolant usage and pressure in system.

From the manuals

• Workshop manual (2004–2006)

  "The cap is satisfactory when the pressure holds steady. It is also good if it holds pressure within the 124-145 kPa (18-21 psi) range for 30 seconds or more. If the pointer drops quickly, replace the cap. CAUTION: Radiator pressure testing tools are very sensitive to small air leaks, which will not cause cooling system problems. A pressure cap that does not have a history of coolant loss should not be replaced just because it leaks slowly when tested with this tool. Add water to tool. Turn tool upside down and recheck pressure cap to confirm that cap needs replacement. WATER PUMP REMOVAL WARNI"

• Workshop manual (2004–2006)

  "(1) Seat and retain bottom portion of the air cleaner housing into the bushings on the inner fender (Fig. 11). (2) Install the air intake hose to the air cleaner housing the align and install it in the inner fender and wheel housing liner (Fig. 11). (3) Install air cleaner element (Fig. 11). Fig. 10 AIR CLEANER ELEMENT 1 - AIR CLEANER HOUSING COVER 2 - AIR FLOW SENSOR 3 - AIR CLEANER ELEMENT 4 - AIR CLEANER HOUSING Fig. 11 AIR CLEANER HOUSING 1 - AIR FLOW SENSOR 2 - GASKET 3 - AIR INTAKE HOSE 4 - AIR CLEANER HOUSING 5 - AIR CLEANER ELEMENT 6 - AIR INTAKE PRESSURE SENSOR 7 - AIR CLEANER HOUSING"

• Workshop manual (2000–2003)

  "(7) Remove the engine mount nuts and remove the mount (Fig. 46) INSTALLATION (1) Position the engine mount into the stop plate (Fig. 46) (2) Position the engine mount into position and tighten the retaining nuts to 45 N·m (33 lbs. ft.) (Fig. 46) (3) Lower the vehicle. (4) Lower the engine on to the engine mounts until they contact (Fig. 46) (5) Hand tighten the engine support to engine mount bolt (Fig. 46). (6) Lower the engine on to the engine mount and tighten bolt to 83 N·m (61 lbs.ft.) (Fig. 46) Fig. 45 LEFT ENGINE MOUNT 1 - NUT 2 - WASHER 3 - STOP PLATE 4 - ENGINE MOUNT 5 - ENGINE SUPPORT"

• Workshop manual (2004–2006)

  "OPERATION Intake air is drawn through the air cleaner and into the turbocharger compressor housing. Pressurized air from the turbocharger then flows forward through the charge air cooler located in front of the radiator. From the charge air cooler the air flows back into the intake manifold. DIAGNOSIS AND TESTING- CHARGEAIR COOLER SYSTEM - LEAKS NOTE: Slight engine oil pooling in the charge air inlet hose IS NOT premature turbocharger failure. Slight pooling is the normal result of the breather system. Test the air breather tube for normal operation by referring to the appropriate diagnostic m"

Sources