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)
A pull-type clutch has no free travel left at the pedal. What is the likely result if the truck keeps running this way?
- The clutch slips and the release bearing wears quickly
- The clutch brake engages on every gear change
- The clutch will not release at the bottom of pedal travel
- The transmission input shaft stops turning at idle
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A. The clutch slips and the release bearing wears quickly
Free travel shows there is clearance in the release mechanism. With none left, the release bearing is loaded all the time and the pressure plate cannot clamp fully, so the clutch slips and overheats. Failure to release is the result of too much free travel, not too little.
Reference: ASE T3 Drive Train task list, clutch (adjustment)
Four 12-volt batteries rated 950 CCA each are connected in parallel. What is the battery bank's rating?
- 48 volts, 950 CCA
- 12 volts, 3,800 CCA
- 12 volts, 950 CCA
- 24 volts, 1,900 CCA
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B. 12 volts, 3,800 CCA
Parallel connection keeps voltage at 12 volts and adds the cranking capacities: 4 x 950 = 3,800 CCA. The 48 volt answer would be all four in series.
Reference: ASE T6 Electrical/Electronic Systems task list, battery (series and parallel connection)