A truck is losing coolant with no external leaks, and white steam with a sweet smell comes from the exhaust. The oil is clean. Which component is the most likely cause?
- A leaking charge air cooler
- A leaking EGR cooler
- A stuck wastegate actuator
- A plugged fuel-water separator
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B. A leaking EGR cooler
The EGR cooler passes exhaust gas through a coolant-filled core; when the core cracks, coolant enters the gas stream and leaves as steam. A charge air cooler carries only air, so it cannot lose coolant.
Reference: ASE T2 Diesel Engines task list, exhaust aftertreatment (EGR cooler diagnosis)
The safety (pressure relief) valve on the supply reservoir is normally set to open at about what pressure?
- 150 psi
- 60 psi
- 100 psi
- 250 psi
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A. 150 psi
The relief valve protects the system if the governor fails to unload the compressor and is typically set at 150 psi, above the normal cut-out range of about 120 to 135 psi. A setting of 100 psi would be below cut-in and would vent constantly.
Reference: ASE T4 Brakes task list, air supply and service systems (safety valve)
Two tires are being matched as a dual pair. What is the generally accepted maximum difference in their overall diameters?
- 1/2 inch
- 1 inch
- 2 inches
- 1/4 inch
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D. 1/4 inch
Duals should be within 1/4 inch in diameter (about 3/4 inch in circumference). A larger mismatch makes the bigger tire carry more load and the smaller one scrub, overheating both.
Reference: TMC recommended practice for dual tire matching; ASE T5 Suspension and Steering task list (wheels and tires)