Resolving a Cylinder Head Crack and Fuel Contamination in a Land Rover Discovery Sport

Land Rover Discovery Sport Ingenium Cylinder Head Crack & Coolant Loss Repair

The owner of this Discovery Sport arrived after searching Google for: “Discovery Sport white smoke from exhaust, rough idle, losing coolant – head gasket?”

The vehicle’s specific problem was a combination of combustion and fuel system issues: visible white smoke from the exhaust with a sweet smell (coolant), a misfire causing a rough idle and hesitation, and a slow but consistent loss of coolant from the expansion tank. The owner’s primary concern was diagnosing the exact cause amidst conflicting online advice about head gaskets, EGR coolers, and injector seals, and ensuring a repair that would last.

Our Diagnostic Process: Finding the Root Cause in the Land Rover Discovery Sport

The symptoms suggested coolant entering the combustion process. We needed to identify the entry point: head gasket, cracked head, or another component.

1. Combustion Leak Test (Primary Diagnosis): With the engine warm, we used a Block Tester (chemical test) on the coolant expansion tank. The fluid rapidly changed from blue to yellow, confirming the presence of combustion gases in the coolant—definitive proof of an internal breach.
2. Cylinder Power Balance & Leak-Down Test: Using the Land Rover SDD (Pathfinder) diagnostic system, we ran a power balance test. It identified a significant misfire on cylinder 2. A follow-up cylinder leak-down test with the engine pressurised in cylinder 2 showed over 40% leakage, with the air audibly escaping into the coolant expansion tank, pinpointing cylinder 2 as the failure point.
3. Fuel Contamination Check: Given the diesel engine and potential for multiple failures, we also tested for fuel dilution. Smelling the coolant revealed a faint hint of diesel, not just exhaust gas. This critical clue pointed towards a potential additional failure of the fuel injector seal or copper washer on the same cylinder, allowing fuel pressure to leak into the coolant jacket.
4. Borescope Inspection: We removed the glow plug from cylinder 2 and inserted a borescope. While visualising the piston crown was difficult, no obvious catastrophic damage was seen, suggesting a crack or gasket failure rather than a holed piston.

The Critical Factor Often Overlooked

A standard repair for a confirmed combustion leak in a diesel Ingenium is to replace the cylinder head gasket. However, if the root cause is a hairline crack in the cylinder head casting—common between the valve seat and coolant passage in these engines—or a failed fuel injector seal, simply replacing the gasket will result in immediate or rapid re-failure. The new gasket cannot seal a crack, and a leaking injector seal will continue to pressurise the coolant with fuel.

The Root Cause Explained

In this case, the root cause was likely a dual-path failure initiated by thermal stress. The primary failure was a hairline thermal crack in the cylinder head, most likely running from the exhaust valve seat of cylinder 2 into an adjacent coolant passage. This crack allowed combustion gases to blast into the coolant (causing pressurisation, coolant loss, and white smoke) and coolant to seep into the cylinder (causing the misfire). Additionally, the extreme heat cycles likely degraded the fuel injector copper seal/washer on the same cylinder, creating a secondary leak path for diesel fuel into the coolant. In simple terms, imagine a coffee mug (the cylinder head) with a tiny crack. Hot coffee (combustion gases) leaks out, and if you also overfill it, pressure forces coffee through the crack. The heat also weakens the mug's handle (injector seal), causing another leak.

Our Repair Strategy: The Most Comprehensive Solution for Long-Term Reliability

Faced with a confirmed internal breach on a specific cylinder, the repair paths are:

1. In-Situ Head Gasket Replacement: Replacing the gasket without removing the cylinder head for testing.
   • Potential Outcome: The fastest, lowest-parts-cost option. May work if the gasket is the only failure.
   • Long-Term Consideration: Extremely high risk. If the head is cracked or warped, the repair will fail almost immediately, requiring complete disassembly again, doubling the labour cost for the customer. It also ignores the injector seal clue.
2. Cylinder Head Reconditioning & Systemic Seal Replacement (Our Chosen Strategy): Removing the cylinder head, sending it for professional crack testing and machining, and replacing the gasket, all fuel injector seals, and related components as a system.
   • Why This Was the Most Comprehensive Choice: This is the only method that provides diagnostic certainty and addresses all likely failure points. Pressure testing the head confirms or rules out a crack. Machining ensures perfect flatness. Replacing all injector seals prevents a future leak on another cylinder. This approach transforms a guess into a guaranteed, engineered repair.

Our Detailed Repair Procedure:

• Engine Strip & Head Removal: We carefully removed the intake, exhaust, high-pressure fuel lines, and timing system to access the cylinder head. The head was lifted and sent to our specialist machine shop.
• Machine Shop Forensic Analysis: The shop performed:
  • Pressure Testing: The head was pressurised underwater, revealing a fine crack emanating from the exhaust valve seat of cylinder 2. This confirmed the core failure.
  • Crack Repair via Welding: Where possible, the crack was repaired using specialised TIG welding techniques for aluminium.
  • Surface Skimming: The mating surface was precision-milled to restore perfect flatness.
  • Valve & Seat Reconditioning: The valves were lapped, and seats were checked.
• Precision Reassembly with System-Wide Parts: The head was returned perfectly clean. We installed:
  • A new Genuine Land Rover Multi-Layer Steel (MLS) cylinder head gasket.
  • A complete new set of Land Rover fuel injector seal kits (including copper washers and O-rings) for all four injectors.
  • New Land Rover cylinder head bolts (critical torque-to-yield components).
  • A new thermostat housing and coolant temperature sensor.
  • A full timing chain kit was fitted as best practice with the engine disassembled.
• Post-Repair Protocol: The cylinder head was torqued in the correct multi-stage sequence. The fuel system was primed. The cooling system was vacuum-bled. Finally, the engine management software was reprogrammed to reset adaptations and recalibrate fuel trims.

Results & "Before/After" Proof

• Coolant Loss: Zero coolant loss over multiple heat cycles and hundreds of miles of driving.
• Exhaust Smoke: The white smoke was completely eliminated. Exhaust cleared to normal.
• Engine Smoothness: The rough idle and misfire were resolved. The engine ran smoothly at all RPMs.
• Fault Codes: All related fault codes (misfire, coolant temperature plausibility) were permanently cleared.

Summary:

• Core Problem: Internal coolant leak and fuel contamination due to a cracked cylinder head and failing fuel injector seal(s).
• Solution: Cylinder head removal, professional crack testing, welding, machining, and reassembly with a new MLS gasket, full set of injector seals, and timing components.
• Outcome: A mechanically restored cylinder head, a sealed fuel system, and a stable cooling system, restoring full engine performance and reliability.