ASE A1 Engine RepairLubrication and Cooling SystemsMedium
A technician is performing a cooling system pressure test. The system is pressurized to 15 psi, and after 10 minutes, the pressure has dropped to 10 psi. The technician visually inspects all hoses, the radiator, and the heater core, finding no external leaks. There is no white smoke from the exhaust, and the oil appears clean. Which of the following is the MOST appropriate next step in diagnosing the pressure drop?
- APerform a continuity test on the cooling fan circuit
- BFlush the cooling system
- CCheck for internal leaks using a block tester (combustion leak detector)
- DReplace the radiator cap
Show answer & explanationAnswer & explanation
Correct answer: C. Check for internal leaks using a block tester (combustion leak detector)
A pressure drop without visible external leaks, white smoke, or oil contamination strongly suggests an internal leak that is not yet severe enough to cause obvious external symptoms. A block tester can detect combustion gases in the coolant, indicating a head gasket leak or cracked component.
Why the other options are wrong
- A. A continuity test on the cooling fan circuit is irrelevant to a cooling system pressure drop.
- B. Flushing the cooling system addresses contamination or clogs, not a pressure leak.
- D. While a faulty radiator cap can cause pressure issues, the drop in pressure without other symptoms points to a leak, not just an inability to hold pressure from the cap.
Combustion Leak Detector (Block Tester)
A tool used to detect the presence of combustion gases (CO2) in the engine's cooling system.
- Indicates a head gasket leak, cracked block, or cylinder head.
- Fluid changes color in the presence of CO2.
- Performed by drawing air from the radiator neck through a test fluid.
Memory trick: Pressure drops, but no drips? Look inside!