Coolant Loss and White Haze on a Euro 6 Tractor
A 2019 Euro 6 6x2 tractor unit with 312,000 km reports coolant loss of about 1.5 L/100 km and a sweet-smelling white haze from the exhaust at idle. There is no external coolant leak, the oil level is slightly high, and the expansion tank cap has been replaced once. A pressure test at 1.4 bar drops to 0.9 bar in 10 minutes. When the EGR cooler coolant circuit is isolated, the system holds 1.4 bar for the same period. A combustion-gas test on the coolant is positive. The intake pipe downstream of the EGR valve contains a pale emulsion. The driver has a 250 km loaded run booked tomorrow and asks whether he can 'just top it up and go'.
1. Interpret the test results and identify the most likely failure.
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The pressure test shows a real internal leak: the complete system cannot hold 1.4 bar. When the EGR cooler coolant circuit is isolated, the system holds pressure, which localises the leak to the cooler or its circuit. A positive combustion-gas test supports exhaust gas entering the coolant. The pale emulsion in the intake downstream of the EGR valve shows coolant has crossed into the intake path.
The most likely failure is an internal crack or seal failure in the EGR cooler, allowing coolant into the intake and exhaust gas into the cooling system. A head gasket failure would not normally stop leaking when the EGR cooler is isolated. The slightly high oil level may indicate coolant contamination or simply overfilling; that must be checked before running the engine. The correct conclusion is an EGR cooler internal leak, pending removal and bench testing.
2. Set out the repair and post-repair verification, including the risks of continuing to run the vehicle.
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Continuing to run the vehicle risks coolant ingestion into the cylinders, which can cause hydrolock, bent connecting rods, cylinder wash, and aftertreatment damage. It can also cause overheating and further contamination. 'Topping it up' is not acceptable.
Repair should include replacing or rebuilding the EGR cooler, flushing the cooling system, cleaning the intake and EGR passages, and changing the oil and filter if contamination is confirmed. Before attempting to start, check that no liquid coolant is trapped in the intake or cylinders; rotate the engine by hand if practical. After repair, pressure-test the complete system, run the engine to operating temperature, check for white haze and coolant loss, repeat the combustion-gas test, and verify intake cleanliness. A loaded road test should confirm no fault codes and stable coolant level. Document the repair and the oil sample result.