Five free practice questions on hydraulic systems: block J of the Red Seal 310T Truck and Coach Technician exam, about 8 of its 135 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A dump truck's hoist will not raise at all, the PTO indicator shows engaged, and the pump is turning. The technician hears oil flowing but sees no pressure on a gauge at the pump outlet. What is the most likely cause?
- The tires are low on pressure.
- A stuck-open relief or neutral spool.
- The box is overloaded and too heavy.
- The cab is tilted forward.
Show the answer
B. Correct. A turning pump with flow but no pressure is oil going straight back to tank: a relief valve stuck open by debris, a control valve spool that is not shifting (linkage, or a solenoid not commanded), or a failed pump that moves oil but cannot build pressure. The RSOS lists fail to raise or lower among symptoms and relief valves, control valves and pumps among components; with the gauge in place the technician operates the control and checks whether pressure builds against the relief setting, then isolates the relief valve and the spool.
Why not the others
A. Tire pressure is unrelated to hoist pressure.
C. An overloaded box would build pressure to the relief setting; no pressure at all means the oil is not being contained.
D. Cab position has nothing to do with the hoist circuit.
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A technician is replacing a burst hydraulic hose on a dump truck. Which practices apply to the replacement?
- Use any hose that fits the fitting.
- Skip the leak test to save time.
- Match rating; route clear; leak-test.
- Twist the hose tight to take up slack.
Show the answer
C. Correct. The replacement hose must match the original's pressure rating, size, length and fitting type (the RSOS requires the technician to identify pressure limits of hoses and fittings); it is installed without twist (a twisted hose fails early under pressure cycling), with enough slack for movement, routed and clamped clear of heat, sharp edges and moving parts, and the system is then cycled and inspected for leaks. Hoses, fittings and seals are listed among components replaced, and the repair is verified and documented.
Why not the others
A. Hose rating and construction must match; a lower-rated hose bursts.
B. Verification is required; a leaking new hose is an injection hazard.
D. Twist shortens hose life dramatically under pressure.
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While inspecting a snowplow truck's hydraulic system, the technician feels a hot spot on the return line near the control valve, while the rest of the system is warm. What does this indicate?
- Low oil level.
- Normal; the valve is always hottest.
- Relief dumping or internal bypass.
- The wrong plow blade.
Show the answer
C. Correct. A localized hot spot is where pressure is being converted to heat: oil passing over a relief valve that is opening too early or continuously, a control valve spool leaking internally, or a restriction in that line. The RSOS lists feeling for hot spots among hydraulic sensory inspections and relief valves and control valves among components; the finding directs the pressure and flow tests to that valve. Left alone, the heat degrades the oil and seals throughout the system.
Why not the others
A. Low level causes aeration and pump noise, not a localized hot spot at a valve.
B. A system's temperature should be fairly uniform; a distinctly hot spot is a fault indicator.
D. The blade has nothing to do with the hydraulic temperature.
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A refuse truck's compactor cycles slowly and the hydraulic oil runs very hot, and the filter's restriction gauge reads in the bypass zone. What is the most likely cause?
- The wrong hydraulic oil colour.
- A plugged, bypassing filter.
- Too much oil in the reservoir.
- A worn PTO.
Show the answer
B. Correct. A restriction gauge in bypass means the filter element is loaded and oil is being forced around it unfiltered; the pressure drop across the loaded element becomes heat, and a restricted suction or pressure-line filter also cuts the flow reaching the actuators, slowing the cycle. The RSOS lists slow operation among symptoms, restriction among tests, restriction gauges among tools and filters among consumables; the filter is replaced and the reason it loaded so fast (a failing pump or cylinder, or a missed service) is found with an oil sample, then cycle time is re-measured.
Why not the others
A. Colour is irrelevant.
C. An overfull reservoir does not restrict flow or heat the oil.
D. A worn PTO slips or grinds; it does not put the filter gauge into bypass.
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A vocational truck's hydraulic system works but the oil smells burnt and has darkened, and the customer reports the system has been running hot for weeks. What does the technician conclude about the oil and the system?
- Increase the relief pressure.
- Switch to engine oil.
- Oxidized oil; find the heat source first.
- Top up and continue; oil darkens normally.
Show the answer
C. Correct. Burnt-smelling, darkened oil has been overheated and oxidized; its additives are depleted and it will varnish valves and harden seals. The RSOS lists smelling for burnt oil among sensory inspections and requires failure analysis to determine the root cause: a relief valve dumping continuously, a restricted cooler or filter, a bypassing cylinder or an undersized reservoir. The cause is repaired, the system flushed and refilled with the specified oil, and the filters replaced; otherwise the new oil burns the same way.
Why not the others
A. Raising relief pressure increases heat and load; it is the opposite of a fix.
B. Engine oil is not the specified hydraulic fluid and does not fix the overheating.
D. Darkening with a burnt smell is oxidation from overheating, not normal ageing.
02Answer key
| Question | Answer | Sub-task |
|---|---|---|
| Q1 | B | Diagnoses hydraulic systems |
| Q2 | C | Repairs hydraulic systems |
| Q3 | C | Services hydraulic systems |
| Q4 | B | Diagnoses hydraulic systems |
| Q5 | C | Diagnoses hydraulic systems |
03What block J covers
This block covers hydraulic systems on vocational trucks, such as dump hoists, lift gates, snowplows, refuse compactors, cement mixers, aerial lifts and mobile cranes. It includes pumps and PTO drives, reservoirs and inlet screens, filters, relief and control valves, cylinders, hoses and fittings, electronic solenoid controls, oil sampling, and pressure, flow and cycle time testing.
The Red Seal Occupational Standard names this block “Services, diagnoses and repairs hydraulic systems”. It carries 5.9% of the exam, about 8 of the 135 questions, split across one task. The share column is each task's weight within the block, as the standard publishes it.
| Task and its sub-tasks | Share of block |
|---|---|
| Services, diagnoses and repairs hydraulic systems Services hydraulic systems; Diagnoses hydraulic systems; Repairs hydraulic systems | 100% |
04What the questions turn on
Support it, then relieve it
A raised dump box or boom is held by a mechanical prop or stand, never by hydraulic pressure alone. Trapped pressure is then relieved through the controls before any fitting is cracked, because a fluid jet can inject through skin.
Foamy oil or clear oil
Foamy oil with a noisy pump is aeration: air drawn in through a loose suction fitting, a pump shaft seal or a low reservoir level. A sharp rattle with clear oil is cavitation from a restricted inlet, such as a plugged screen.
Slow only under load
A worn pump delivers close to rated flow at low pressure but leaks internally as pressure rises, so a loaded lift is slow while an empty one looks normal. A flow test at rated pressure separates the pump from a low relief setting.
Flush after a pump failure
A failed pump sheds metal through the whole system. Flush the reservoir, lines, cylinders and cooler, replace the filters, and find the contamination or inlet restriction that caused the failure, or the new pump fails the same way.
05The other blocks
The 310T exam has 11 blocks. Each has its own page of free questions:
The 310T Truck and Coach Technician practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.