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Symptoms
Losing coolant
What causes it depends on the engine. 40 documented failures on 22 engines list this among their signs. Pick your engine for the causes ranked, how to tell them apart and the usual fix.
7.3 Power Stroke (1994.5-2003)
1 known cause: Water pump wear
6.0 Power Stroke (2003-2007)
5 known causes, most widespread: EGR cooler failure
6.4 Power Stroke (2008-2010)
3 known causes, most widespread: EGR cooler failure -> #8 hydrolock
6.7 Power Stroke (2011-present)
2 known causes, most widespread: Dual-circuit cooling system leaks (radiator / crossover tube / degas bottle / water pump)
5.9 Cummins (1994-2007)
2 known causes, most widespread: 53-block casting crack (24v ISB)
6.7 Cummins 2007-2018
3 known causes, most widespread: Water pump failure
6.7 Cummins 2019+
2 known causes, most widespread: EGR cooler failure (2019+ 6.7)
Ram 1500 EcoDiesel (2014-2019)
2 known causes, most widespread: EGR cooler cracking and coolant loss (recall 19V-757)
Duramax LB7-LMM (2001-2010)
2 known causes, most widespread: EGR cooler clogging / failure (LB7-LMM)
Duramax LML (2011-2016)
2 known causes, most widespread: Cooling system wear: water pump, fan clutch, oil cooler (LML)
Duramax L5P (2017-present)
1 known cause: Cooling system wear: water pump, hoses, thermostat (towing duty)
Duramax 3.0 (LM2/LZ0)
2 known causes, most widespread: EGR system failures: valve, cooler, wiring (derate-prone)
3.2 Power Stroke (Transit)
2 known causes, most widespread: EGR cooler failure: overheating and coolant loss (three Ford field actions)
Sprinter 2.1 (OM651)
1 known cause: EGR system: coking and cooler coolant leak
6.2 Boss (gas)
1 known cause: Cooling service (water pump / thermostat / degas)
7.3 Godzilla (gas)
1 known cause: Cooling service (water pump / thermostat / degas)
3.5 EcoBoost (gas)
2 known causes, most widespread: Internal water pump: coolant loss and coolant-into-oil risk
Transit V6 (gas)
1 known cause: Cooling service: thermostat/housing and hoses
6.4 HEMI (gas)
1 known cause: Cooling service (water pump / thermostat)
ProMaster 3.6 (gas)
2 known causes, most widespread: Plastic oil filter/coolant housing-adapter leak (the signature Pentastar leak)
GM 6.0 L96 (gas)
1 known cause: Cooling system wear: water pump, fan clutch, thermostat (L96)
GM 6.6 L8T (gas)
1 known cause: Cooling system wear: water pump, hoses, thermostat (towing duty)
Built from the failure-mode records on this site: a failure is listed when its own symptom list describes this sign. Engines not shown have no documented failure with it in our records. How we tier and source facts.