Five free practice questions on lubrication and cooling systems: content area D of the ASE A9 Light Vehicle Diesel Engines test, 6 of its 50 scored questions (12%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A light-duty diesel has a top-mounted cartridge oil filter housing. When the cap and old element are lifted out, the oil left in the housing drains down into the oil pan by itself. What makes this happen?
- The housing drain valve that opens on removal
- The filter bypass valve opening without the element
- The anti-drainback valve opening once the cap is off
- The pressure regulator valve venting the housing
Show the answer
A. Correct. Top-mounted cartridge housings of this kind have a drain valve or standpipe port that stays shut while the element and cap are installed and opens as they are lifted out, so the housing empties into the pan instead of spilling. On designs where the element itself closes the drain, a missing or wrong element can leave it open with the engine running, so the element the manufacturer specifies is always fitted.
Why not the others
B. The bypass valve lets oil flow around a plugged element into the engine while it runs; it does not empty the housing into the pan with the engine stopped. The draining comes from the housing's drain valve, which opens as the element and cap come out.
C. An anti-drainback valve does the opposite job: it keeps oil from draining out of the filter and passages when the engine stops, so oil pressure builds quickly at start-up. The housing empties through a drain valve that opens as the element and cap come out.
D. The pressure regulator only relieves oil when the pump is running and gallery pressure reaches its setting. With the engine off there is no pressure for it to relieve; the housing drains through its own drain valve.
ID A9-D-006 · Task A9-D-3 (ASE task list)
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A plate-type engine oil cooler has been removed from a light-duty diesel because oil has been showing up in the coolant. Which of these checks shows whether the cooler leaks between its oil and coolant passages?
- Flush its oil side with solvent and inspect the output
- Pressurize its oil side with air in a water tank
- Run a chemical combustion leak test on the coolant
- Measure the pressure drop across its oil side at full flow
Show the answer
B. Correct. With the oil ports plugged and regulated air at the pressure the manufacturer specifies applied to the oil side, any leak through the plates shows as bubbles from the coolant passages while the cooler is submerged. A leaking cooler is replaced, and the cooling system is flushed of the oil it picked up.
Why not the others
A. Flushing cleans sludge or debris out of the oil passages but proves nothing about a leak between the two sides. A leak test needs pressure on one side while the other side is watched for bubbles.
C. A combustion leak test detects exhaust gas in the coolant, which points at a head gasket or cracked head, not at oil crossing from an oil cooler. With the cooler removed, pressurizing its oil side under water answers the question directly.
D. Pressure drop at a given flow shows how restricted the passages are, not whether oil crosses into the coolant side. An internal leak is found by pressurizing one side and watching the other for bubbles.
ID A9-D-008 · Task A9-D-4 (ASE task list)
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The owner's manual of an older light-duty diesel pickup calls for SAE 15W-40 oil meeting API CJ-4. The shop stocks SAE 15W-40 licensed to API CK-4. What can the technician tell the owner?
- Only an oil still licensed to CJ-4 may be used
- CK-4 is approved only for 2017 and newer engines
- Any newer diesel category, FA-4 included, may be used
- CK-4 can be used where CJ-4 is called for
Show the answer
D. Correct. API describes CK-4 oils as exceeding the performance criteria of CJ-4, CI-4 PLUS, CI-4 and CH-4 and able to lubricate engines that call for those categories, so a 15W-40 CK-4 meets the manual's requirement. The viscosity grade the manufacturer lists still has to match.
Why not the others
A. Insisting on a CJ-4 license is not needed: API describes CK-4 oils as exceeding the performance criteria of CJ-4 and able to lubricate engines that call for it. The 15W-40 CK-4 on the shelf meets the manual's requirement.
B. CK-4 was written for engines built to the 2017 on-highway standards and for previous model-year diesel engines as well, so its use is not limited to newer engines. It can be used where CJ-4 is called for.
C. FA-4 is the exception: API states that FA-4 oils are not interchangeable or backward compatible with CK-4, CJ-4 and the older categories, so FA-4 goes only into engines whose manufacturer approves it. CK-4 is the category that can replace CJ-4.
ID A9-D-011 · Task A9-D-6 (ASE task list)
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A light-duty diesel's thermostat is a full-blocking type, with a second, smaller valve on its stem below the main valve. What does this second valve do once the thermostat is fully open?
- Closes the bypass so coolant goes to the radiator
- Opens the bypass so the engine can warm up faster
- Bleeds trapped air past the thermostat flange
- Throttles radiator flow to hold temperature
Show the answer
A. Correct. While the thermostat is closed, coolant circulates through the bypass inside the engine; as the pellet pushes the main valve open, the lower valve moves onto the bypass port and shuts it. All of the pump's flow then passes through the radiator, which gives the most cooling at high load.
Why not the others
B. This reverses the valve's action. The bypass is open while the thermostat is closed, to circulate coolant through the engine during warm-up; the lower valve closes it as the thermostat opens fully.
C. Bleeding air is the job of the small air-bleed (jiggle) valve in the thermostat flange. The lower valve on the stem seals the bypass passage once the thermostat is fully open.
D. Metering flow to the radiator is the main valve's job as the pellet expands and contracts. The second valve closes the bypass when the main valve is fully open so all the coolant goes through the radiator.
ID A9-D-016 · Task A9-D-9 (ASE task list)
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When the coolant is changed on a light-duty diesel, the manufacturer's procedure removes the engine block's drain plugs as well as opening the radiator drain. Why?
- To let air in so the radiator empties
- Coolant stays in the block otherwise
- To vent pressure before the cap opens
- To flush scale out of the water pump
Show the answer
B. Correct. The radiator drain empties the radiator and whatever can run back to it, but the block's water jackets hold coolant below the passages that lead there, so draining the radiator alone leaves much of the old coolant in the engine. Removing the block drains empties it, so the new coolant is not mixed with the old.
Why not the others
A. Air comes in through the opened filler or surge tank cap, which lets the radiator drain freely. The block drains are low points that let out coolant the radiator drain cannot reach.
C. Pressure is relieved by letting the engine cool and opening the cap slowly; opening a drain on a hot, pressurized system would spray hot coolant. The block drains are opened on a cooled engine to empty what the radiator drain leaves behind.
D. The block drains sit low in the water jackets, not at the water pump, and draining does not remove scale; a cleaner and flush do that. The plugs come out because coolant stays in the block when only the radiator is drained.
ID A9-D-018 · Task A9-D-10 (ASE task list) · NHTSA
02Answer key
| Question | Answer |
|---|---|
| Q1 | A |
| Q2 | B |
| Q3 | D |
| Q4 | A |
| Q5 | B |
03What area D covers
This content area covers the oil and coolant systems of a light-duty diesel: oil pressure readings and the sensors behind them, oil pumps and pickup screens, regulator, bypass and drain valves, oil coolers, turbocharger oil and coolant lines, oil category and viscosity, belts, pulleys and tensioners, coolant temperature and level sensors, thermostats, draining, filling and bleeding, water pumps, radiators and caps, and fans and fan clutches.
The ASE test specification calls this content area “Lubrication and Cooling Systems Diagnosis and Repair”. It carries 6 of the 50 scored questions, 12% of the test.
- Confirm oil pressure and temperature and their sensors
- Inspect oil pumps, screens, regulators and bypass valves
- Test oil coolers and the turbocharger oil supply
- Choose oil by API category and SAE grade
- Check belts, tensioners and pulley alignment
- Test coolant sensors, thermostats and bypasses
- Drain, refill and bleed air from the cooling system
- Inspect water pumps, radiators, caps, fans and clutches
04What the questions turn on
Prove the pressure with a gauge
A mechanical gauge separates a real pressure problem from a reading fault. Good pressure at the gallery but 0 psi at the sensor port means the passage to the port is blocked. A signal pulled near 0 or 5 volts sets a circuit DTC.
An oil grade has two ratings
The W number of an SAE grade rates the oil cold and the second number rates its viscosity hot. A 20 grade in place of a specified 40 runs thin and lowers oil pressure, and the oil chart sets each grade's temperature range.
Slow warm-up, no fault
A diesel idling unloaded in deep cold can lose heat about as fast as it makes it. A cold upper hose, normal highway temperature and a matching infrared reading clear the thermostat and the ECT sensor. A full-blocking thermostat shuts the bypass as it opens.
Air works out over heat cycles
Draining the radiator alone leaves old coolant in the block's water jackets, so the block drains come out too. After a refill, trapped air reaches the surge tank over several heat cycles, and the level is rechecked until it stops dropping.
05The other content areas
The A9 test has six content areas. Each has its own page of free questions:
The ASE A9 Light Vehicle Diesel Engines practice test 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.
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