Engine Knocking After Oil Change – Why?

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Post-oil-change engine noise diagnosis

A New Knock After Service Can Signal Low Oil, Lost Pressure or the Wrong Oil Filter

A deep knocking sound that begins immediately after an oil change should not be dismissed as the engine “getting used to” fresh oil. Shut the engine off, check the oil level and inspect the filter, drain plug and ground for leakage before running it again.

Common service-related causes include too little oil, too much oil, the wrong viscosity or specification, an incorrect or defective filter, a filter seal problem, delayed oil-pressure buildup, or an installation leak. The oil change may also be coincidental with valve-train, timing-chain, bearing, injector, accessory or exhaust noise that was already developing.

Red oil-pressure warning Switch off immediately and do not keep restarting.
First physical check Verify the oil level correctly on level ground.
First service checks Confirm oil grade, quantity, filter number, seal and leakage.
Deep persistent knock Tow the vehicle for oil-pressure and mechanical testing.
What to do right now Use the noise helper Check the likely causes
Stop and protect the engine Do not rev or road-test a new persistent knock while hoping that oil pressure will eventually improve.
Verify every service item Check the oil level, specification, quantity, filter application, filter seal, drain plug and visible leakage.
Measure rather than guess If the basics are correct, test actual oil pressure and identify the sound before replacing parts.
Do not continue running the engine

Engine Knocking Warning Signs That Require Immediate Shutdown

Lubrication emergency

Red oil-pressure warning

Switch off the engine immediately. A correct oil level does not prove that oil pressure or oil flow is adequate.

Bearing-risk sound

Deep rhythmic knock

A heavy knock that follows engine speed can indicate serious crankshaft, connecting-rod or lubrication trouble.

Rapid oil loss

Growing puddle or oil spray

A loose filter, double gasket, damaged housing or drain-plug problem can empty the engine quickly.

Mechanical distress

Noise worsens with RPM

Do not rev the engine to identify a knock when the sound becomes louder, faster or more forceful as speed increases.

Combustion or oil issue

Heavy smoke or severe misfire

Oil overfill, oil ingestion, contamination or another fault may be affecting combustion.

Uncertain startup noise

Rattle repeats at every start

Repeated startup rattle can indicate filter drain-back, tensioner, valve-train or oil-pressure buildup trouble.

Do not assume that a red oil-pressure warning means only “add oil.” It can indicate insufficient pressure caused by a low level, leak, wrong filter, blocked flow path, pump fault, pickup problem, aerated oil or internal engine damage.
Interactive post-service diagnosis

Engine Noise After Oil Change Helper

Select the closest sound, duration and dashboard condition. The result suggests the safest first action—not a final mechanical diagnosis.

Describe what happened after the oil change

Keep the engine off while entering the details when the sound is deep, persistent or accompanied by an oil-pressure warning.

Recommended next action

    Ten practical post-service answers

    Engine Knocking After an Oil Change: Quick Answers

    Is knocking normal after an oil change? A persistent metallic knock is not normal. A momentary light startup tick may occur on some engines, but it should not continue, worsen or trigger an oil-pressure warning.
    What should I check first? Switch off the engine, check the oil level correctly and inspect the filter and drain-plug areas for fresh leakage.
    Can too little oil cause knocking? Yes. Insufficient oil quantity can reduce the supply available to the pump and lubricated engine components.
    Can too much oil cause noise? Severe overfill can aerate the oil, disturb lubrication and cause smoke, rough running, leakage or abnormal mechanical sounds.
    Can the wrong viscosity cause ticking? Using an unapproved viscosity or oil specification can alter cold flow, hot protection and operation of oil-pressure-dependent components.
    Can a wrong oil filter cause knocking? An incorrect filter may have unsuitable dimensions, flow characteristics, bypass settings, sealing design or drain-back control for the engine.
    Should I rev the engine to circulate oil? No. Keep engine speed low and shut down for persistent noise or a pressure warning. Revving increases load before the cause is known.
    Will fresh oil clean sludge and cause noise? Do not assume new oil harmlessly “cleaned something loose.” A new knock still requires checks for level, pressure, filter, specification and mechanical wear.
    Can the oil change be a coincidence? Yes. Injector noise, worn bearings, valve clearance, timing parts, accessories, exhaust shields or detonation may begin around the same time.
    When should the car be towed? Tow it for a red oil-pressure warning, deep persistent knock, rapid leak, empty dipstick, heavy smoke or worsening noise with RPM.
    Protect the engine before diagnosing

    What to Do Immediately When Knocking Starts After an Oil Change

    Release the accelerator and stop safely. Do not continue driving under load while listening for whether the knock becomes worse.
    Switch off the engine. Avoid repeated starts when the sound is deep, persistent or accompanied by a warning.
    Record the dashboard warning. Photograph any oil-pressure, oil-level, check-engine or service message before switching the ignition fully off.
    Look beneath the vehicle. Check for a fresh puddle or trail without crawling under an unsupported car.
    Inspect the engine compartment. Look for oil around the filler cap, dipstick tube, filter housing and visible engine surfaces.
    Check the oil level correctly. Park on level ground and use the exact waiting and dipstick or electronic-gauge procedure in the owner’s manual.
    Compare the oil level with the approved range. Below MIN, above MAX and a dry dipstick require different corrections; none should be ignored.
    Check the service invoice or oil container. Confirm the SAE viscosity, API, ILSAC, ACEA or manufacturer approval and the quantity installed.
    Verify the oil-filter part number. Confirm it against the exact model year, engine, market and filter-housing design.
    Check whether the old filter gasket was removed. A double gasket on a spin-on filter can cause rapid oil loss after startup.
    Inspect the cartridge-filter O-ring position. The O-ring must be the correct size and installed in the specified groove rather than on the cap threads or another ledge.
    Do not tighten components blindly. An overtightened filter cap or drain plug can crack housings, distort seals or strip threads.
    Correct a confirmed low or high level. Use only the approved oil, add or remove small amounts and repeat the level check.
    Restart only when no shutdown warning is present. Keep the engine at idle and stop immediately if the noise or oil-pressure warning continues.
    Arrange an actual oil-pressure test when needed. A mechanical pressure gauge can distinguish a sensor concern from real lubrication-system failure.
    Do not crawl underneath to inspect the filter or drain plug unless the vehicle is supported by approved ramps or properly rated jack stands. Never trust the jack alone.
    Service-related causes ranked by urgency

    Why an Engine May Knock After Fresh Oil and a New Filter

    Possible cause
    What may have happened
    Clues
    Best next action
    Oil level too low
    Too little oil was added, the wrong refill capacity was used or oil leaked out.
    Dipstick below MIN, dry dipstick, pressure warning, leak or increasing mechanical noise
    Switch off, correct the level only after locating any rapid leak and verify oil pressure.
    Oil level too high
    Too much oil was installed or the old oil did not drain completely.
    Reading above MAX, foamy oil, smoke, rough running or new leaks
    Remove the excess before normal engine operation.
    Incorrect oil viscosity
    An oil thicker or thinner than the approved grade was used.
    Noise begins only when cold or hot, invoice shows wrong SAE grade
    Replace it with oil meeting the exact manufacturer viscosity and approval.
    Oil lacks the required approval
    The viscosity looks correct but the oil does not meet the required API, ILSAC, ACEA or OEM specification.
    Container or invoice does not list the required approval
    Drain and refill with the exact approved oil and a correct filter.
    Wrong oil filter
    The filter may not match the engine’s sealing, flow, bypass or anti-drainback requirements.
    Noise began immediately after service, incorrect part number or repeated startup rattle
    Replace with the exact manufacturer-approved application and inspect pressure.
    Defective or damaged filter
    A damaged element, seal, valve or housing may restrict flow or leak.
    Pressure warning, filter-area leak, crushed filter or noise that disappears after filter replacement
    Keep the engine off and replace the filter after inspecting the mounting surface.
    Double filter gasket
    The old spin-on gasket remained on the engine and the new gasket was installed over it.
    Sudden large leak at startup, oil sprayed near filter
    Shut down immediately, remove both gaskets and inspect before refilling.
    Incorrect cartridge O-ring placement
    The O-ring was installed in the wrong groove, twisted, cut or reused.
    Leak around filter cap, low level or oil-pressure concern
    Install the correct new O-ring in the specified location and torque the cap properly.
    Delayed pressure buildup after filter replacement
    The filter housing must refill after the oil change.
    Only a very brief light tick during the first startup, no warning and no repeat
    Verify the exact filter and level; investigate any noise that lasts, repeats or becomes heavy.
    Drain-plug or oil-pan leak
    Wrong washer, damaged threads, incorrect torque or cracked pan allows oil loss.
    Fresh drip beneath pan and falling dipstick level
    Repair the sealing joint rather than overtightening it.
    Overfilled or aerated oil
    Rotating parts may churn a severely high oil level and mix air into it.
    Foam, smoke, roughness, pressure fluctuation or leakage
    Remove excess and inspect for continuing symptoms.
    Pre-existing engine wear
    Rod, main, piston, valve-train or timing wear may have become noticeable around the service date.
    Correct oil, correct filter, normal pressure but persistent localized noise
    Use sound localization, oil inspection and mechanical testing.
    Identify the sound before naming the failure

    Ticking, Rattling, Pinging and Knocking Sound Differences

    Light ticking A fast, higher-pitched sound from the top of the engine may involve valve-train parts, injectors, low oil pressure, incorrect viscosity or normal component operation. Compare it with the pre-service sound.
    Startup rattle A brief chain-like rattle may involve an oil-pressure-fed timing tensioner, filter drain-back, variable-valve-timing hardware or pre-existing timing wear.
    Deep knocking A dull metallic thud from the lower engine that follows RPM is more concerning for bearing, crankshaft, connecting-rod or severe lubrication trouble.
    Piston slap A hollow cold-engine sound may decrease as the engine warms. It may be unrelated to the oil change but should be inspected when newly severe.
    Detonation or pinging A metallic rattle mainly under acceleration can be combustion knock related to fuel quality, ignition, deposits, temperature or engine-management problems—not necessarily oil pressure.
    Injector clicking Direct-injection systems can make a rapid clicking sound during normal operation. Compare all cylinders and the vehicle’s established normal sound.
    Accessory knock A pulley, tensioner, alternator, compressor or belt can create a noise that seems internal. Do not reach near moving belts while the engine runs.
    Exhaust or shield rattle A loose underbody shield, oil-change access panel or exhaust heat shield may rattle after service and imitate internal engine noise.
    Phone recordings help with comparison but not final diagnosis. Record cold startup, warm idle and a safe light-RPM condition only when no shutdown warning or deep knock is present.
    Quantity errors are common after service

    How to Check Whether the Engine Was Underfilled or Overfilled

    Find the vehicle’s approved checking conditions. The manual may require a cold check or a warm engine followed by a specific waiting period.
    Park on level ground. A sloped driveway can create a false high or low reading.
    Switch off the engine. Wait for oil to drain from the upper engine into the sump.
    Wipe and reinsert the dipstick fully. Read both sides and repeat when the oil is smeared up the stick.
    Use the electronic procedure when there is no dipstick. Meet the required temperature, parking, ignition and driving conditions.
    Compare with the marked range. The oil should be within the manufacturer-approved area and should not exceed the upper mark.
    Do not rely only on listed capacity. Oil capacity is often a drain-and-refill reference; the final level remains the control.
    Correct gradually. Add or extract a small amount, wait and recheck instead of moving from overfill to underfill.

    Signs of possible underfill

    • Dipstick below MIN or dry
    • Oil-pressure warning
    • Valve-train ticking or deep knock
    • Fresh leak beneath the vehicle
    • Quantity added was below specification
    • Filter or drain plug is leaking

    Signs of possible overfill

    • Dipstick clearly above MAX
    • High oil-level warning
    • Foam or bubbles in the oil
    • Blue smoke or rough running
    • New seal or gasket leakage
    • Quantity added exceeded the reference
    Viscosity is only part of oil selection

    How the Wrong Engine Oil Can Affect Noise

    Cold flow

    Oil is too thick when cold

    Oil that is not approved for the temperature or engine may circulate more slowly during startup and delay operation of pressure-fed valve-train or timing components.

    Hot protection

    Oil is too thin when hot

    An unapproved low-viscosity oil can alter hot oil pressure and protection in an engine designed for another grade.

    Specification mismatch

    Correct SAE number, wrong approval

    Two oils with the same viscosity may differ in additive chemistry and manufacturer approvals required for timing, turbocharger or emissions-system durability.

    Additive issue

    Unapproved aftermarket additive

    Additional viscosity modifiers, cleaners or treatments may alter oil behavior and may not be recommended by the vehicle manufacturer.

    Mixed oils

    Unknown leftover lubricant

    Small residual amounts are normal during service, but topping with an unknown or incompatible product makes diagnosis less certain.

    Wrong engine lookup

    Same model, different requirement

    A vehicle nameplate may cover several engines, model years and markets with different viscosities and approvals.

    Official guidance: Vehicle manufacturers direct owners to use the oil type, viscosity and certification specified for the exact engine. Insufficient, deteriorated or unsuitable oil can affect engine performance, longevity and lubrication.

    Find the manufacturer-recommended engine oil
    The filter is part of the lubrication circuit

    Oil Filter Problems That Can Cause Noise After Service

    Filter problem
    Possible effect
    What to inspect
    Incorrect filter part number
    Improper sealing, flow, bypass behavior or anti-drainback operation
    Exact model year, engine, filter dimensions and manufacturer application listing
    Old spin-on gasket left behind
    Rapid leakage between two gaskets
    Filter mounting surface and removed filter gasket
    Filter installed loose
    Oil leakage and possible pressure loss
    Filter instructions, gasket contact and installation turn amount
    Filter overtightened
    Damaged gasket, housing, threads or difficult future removal
    Distortion, cracked cap and installation specification
    Cartridge O-ring in wrong groove
    External leakage or poor cap sealing
    O-ring size, groove, twisting and cap torque
    Old cartridge O-ring reused
    Leakage as the old seal hardens or flattens
    New filter kit contents and old O-ring removal
    Filter internally damaged
    Possible flow restriction or bypass operation
    Crushed housing, torn element, manufacturing defect or transport damage
    Unsuitable anti-drainback valve
    Oil drains from an elevated filter housing and startup pressure takes longer to rebuild
    Correct filter design and whether the noise returns after every parked start
    Incorrect filter cap insert or cage
    Cartridge element may not seat or control flow correctly
    Missing center tube, standpipe, spring or housing component
    If oil is spraying or pouring from the filter, switch off immediately. Do not tighten a hot operating filter by hand or reach near belts and fans.
    Brief does not automatically mean harmless

    Is a Short Tick After the First Startup Normal?

    After the old filter is removed, part of the lubrication circuit may need to refill during the first startup. Some engines may produce a very brief light tick while pressure builds. That possibility does not make every post-service noise normal.

    Lower concern

    Momentary light tick once

    The sound disappears almost immediately, does not return, the pressure warning clears normally, the level is correct and no leak appears.

    Needs inspection

    Rattle repeats after parking

    Repeated startup noise can point to filter drain-back, tensioner wear, oil viscosity or pressure buildup concerns.

    Stop immediately

    Deep or continuing knock

    A heavy sound, warning light, worsening noise or knock that continues at idle is not an acceptable filter-refill event.

    There is no universal safe number of seconds. Some manufacturer oil-change procedures specify that the oil-pressure warning should clear within only a few seconds, but the exact requirement is vehicle-specific.
    Tests that turn guesses into evidence

    What a Mechanic Should Check When the Basics Look Correct

    Confirm the installed oil and filter. Compare the invoice, oil container and filter number with the VIN-specific manufacturer specification.
    Measure actual oil pressure. Use a suitable mechanical gauge at the manufacturer-defined test port and compare cold idle, warm idle and specified RPM results.
    Inspect the removed filter. Check for collapse, missing seals, wrong element size, debris or an incorrect bypass design.
    Cut the filter open when internal wear is suspected. A trained technician can inspect the media for metallic particles without contaminating the evidence.
    Inspect the drained oil. Look for metallic glitter, bearing material, fuel odor, coolant contamination, foam or an unexpectedly low quantity.
    Localize the sound. Use professional listening equipment to compare the valve cover, timing cover, block, oil pan, injectors, accessories and transmission area.
    Scan diagnostic trouble codes. Look for misfire, variable-valve-timing, camshaft timing, oil-pressure, knock-sensor or fuel-system evidence.
    Check timing-chain and tensioner operation. Pressure-fed tensioners can rattle when oil supply is delayed or internal wear is present.
    Check valve clearance and valve-train components. Mechanical lash, collapsed adjusters or worn cam components can create a top-end tick.
    Inspect crankcase ventilation. A blocked or incorrectly connected PCV system can affect pressure, oil movement and leakage.
    Separate accessory noise from internal knock. Use safe professional procedures to inspect pulleys, tensioners, the alternator, compressor and flywheel area.
    Evaluate internal bearing condition. Persistent lower-engine knock with low pressure or metal in the filter may require oil-pan removal and bearing inspection.
    Replacing the oil-pressure sensor alone is not a pressure test. Verify actual pressure before assuming the warning or noise is only electrical.
    Decide whether to drive or tow

    Can You Drive With Engine Knocking After an Oil Change?

    Level 1: One brief tick Noise occurred only once, disappeared immediately, oil level and pressure indication are normal, and no leak is present.
    Level 2: Repeated light rattle Do not ignore it. Verify oil and filter details and arrange prompt inspection before extended driving.
    Level 3: Continuous knock Avoid driving. Keep the engine off and arrange oil-pressure and sound diagnosis.
    Level 4: Warning or rapid leak Do not restart. Tow the vehicle to prevent possible engine destruction or fire.
    Condition
    Driving recommendation
    Immediate action
    One momentary light tick, no repeat
    Monitor carefully
    Verify oil level, filter application and absence of leaks.
    Tick or rattle repeats every cold start
    Limit driving
    Check filter drain-back, oil specification, tensioner and actual pressure.
    Deep knock continues at idle
    Do not drive
    Switch off and arrange towing or mobile diagnosis.
    Oil-pressure warning remains on
    Do not drive or continue idling
    Stop immediately and test the lubrication system.
    Oil below MIN but no rapid leak
    Do not drive until corrected
    Add the exact approved oil gradually, then investigate why it was low.
    Oil clearly above MAX
    Avoid normal driving
    Remove excess oil and recheck before operating.
    Fresh oil pouring from filter or plug
    Do not restart
    Contain the spill and repair the installation.
    Knock only under acceleration
    Avoid heavy load
    Check fuel quality, detonation, ignition and engine-management causes as well as oil service details.
    Protect your repair evidence

    What to Do if a Repair Shop Performed the Oil Change

    Document before returning

    • Photograph the oil level.
    • Record the dashboard warning.
    • Video the sound only when safe.
    • Photograph oil on the ground.
    • Keep the invoice and filter label.
    • Record mileage and time since service.
    • Note whether the engine was cold or warm.
    • Do not erase diagnostic codes.

    Ask the shop to verify

    • Exact oil viscosity and approval
    • Actual quantity installed
    • Correct filter part number
    • Old filter gasket removal
    • Cartridge O-ring placement
    • Drain-plug washer and torque
    • Measured mechanical oil pressure
    • Metal in the filter or drained oil
    Useful wording: “The engine developed a new [tick/rattle/deep knock] immediately after the oil change. Please verify the exact oil and filter, measure mechanical oil pressure and preserve the removed filter and drained oil for inspection.”
    Do not drive back to the shop with a red oil-pressure warning or deep continuous knock. Ask the shop or roadside service to arrange towing.
    The timing may be misleading

    When the Oil Change Did Not Actually Cause the Knock

    Worn connecting-rod or main bearing

    Existing clearance or damage may become noticeable at the same time as service, especially if the engine already had low pressure or metal contamination.

    Valve clearance or lash adjuster

    A top-end tick may be caused by mechanical clearance, a worn adjuster or oil passage concerns unrelated to filter installation.

    Timing chain or tensioner

    A worn chain guide or tensioner can create startup rattle that becomes more noticeable over time.

    Direct injector noise

    High-pressure fuel injectors and pumps can make sharp regular sounds that may be normal for the engine.

    Detonation under load

    Pinging during acceleration can be related to fuel octane, ignition timing, overheating, carbon deposits or sensor problems.

    Loose underbody panel

    A service panel, shield or fastener disturbed during the oil change can rattle against the body or exhaust.

    Belt tensioner or pulley

    An accessory bearing may knock or click in rhythm with engine speed.

    Flywheel or flexplate

    Cracks or loose fasteners near the engine-transmission joint can imitate lower-engine knock.

    Engine mount or exhaust contact

    Movement during acceleration can allow metal parts to touch and create a dull knock.

    Coincidental does not mean harmless. Once the oil level, specification, filter and pressure are confirmed, persistent noise still deserves proper mechanical diagnosis.
    Avoid preventable engine damage

    Mistakes to Avoid When the Engine Knocks After Service

    Revving to make the noise disappear

    Higher RPM increases load and can worsen damage when oil pressure or bearing lubrication is inadequate.

    Adding oil without checking the level

    A correctly filled or already overfilled engine can become severely overfilled.

    Assuming the warning is only a sensor

    Confirm actual pressure before replacing the sender and continuing to run the engine.

    Installing a thicker oil as a repair

    A heavier unapproved grade may mask sound without fixing worn bearings, low pressure or restricted flow.

    Changing only the filter repeatedly

    If pressure remains low, the pump, pickup, passages or internal clearances may need testing.

    Overtightening a leaking filter or plug

    More force can damage seals, housings or oil-pan threads.

    Using an additive to quiet the knock

    An additive cannot repair a loose filter, low level, failed bearing or damaged timing component.

    Discarding the removed filter

    The filter can contain valuable evidence of metal, collapse, wrong fitment or seal failure.

    Driving because the shop is nearby

    A severe lubrication fault can damage the engine before a short destination is reached.

    Working under a jack-only vehicle

    Use approved ramps or stands on firm, level ground before inspecting the filter or drain plug.

    Post-oil-change knocking FAQs

    Frequently Asked Questions

    Why is my engine knocking immediately after an oil change?

    Possible causes include an incorrect oil level, wrong viscosity or specification, wrong or defective filter, filter-seal leak, drain-plug leak, delayed oil-pressure buildup or a pre-existing mechanical fault that became noticeable at the same time.

    Is engine knocking normal after changing the oil filter?

    A momentary light tick during the first startup may occur while the filter housing refills on some engines. A deep knock, repeated startup rattle, continuing noise or oil-pressure warning is not normal and requires inspection.

    Can low engine oil cause knocking after an oil change?

    Yes. Underfilling or a service-related leak can reduce available oil and lead to low pressure, valve-train noise or serious bearing knock. Switch off the engine and check the level and leaks.

    Can overfilled engine oil cause knocking?

    Severe overfill can allow rotating parts to aerate the oil, which can disturb lubrication and cause pressure problems, smoke, rough operation, leakage or abnormal sounds.

    Can the wrong oil viscosity make an engine noisy?

    Yes. An unapproved viscosity can affect cold flow, hot oil pressure and operation of timing or valve-train components. Use the exact viscosity and manufacturer approval listed for the engine.

    Can the wrong oil filter cause low oil pressure?

    An incorrect or defective filter may have unsuitable flow, bypass, sealing or anti-drainback characteristics. Verify the exact filter application and test actual oil pressure when a warning or persistent noise occurs.

    Should I rev the engine after an oil change to build pressure?

    No. Start at idle and shut the engine off for a persistent oil-pressure warning or abnormal knock. Revving increases engine load before the lubrication system has been verified.

    Can fresh oil make worn bearings knock?

    Fresh oil does not normally create bearing wear instantly, but incorrect viscosity or an existing worn bearing can make noise noticeable after service. Confirm the oil and filter, then measure oil pressure and inspect for metal.

    When should I tow a knocking engine after an oil change?

    Tow the vehicle when the knock is deep or continuous, the red oil-pressure warning appears, oil is pouring out, the dipstick is dry, smoke is heavy or the noise worsens with RPM.

    What should a mechanic test for post-oil-change knocking?

    The mechanic should verify the oil and filter, measure mechanical oil pressure, inspect the removed filter and drained oil for metal, scan diagnostic codes and localize the sound to the valve train, timing system, bearings, accessories or exhaust.

    Official manufacturer references

    Official Sources Used for This Engine Noise Guide

    Oil-pressure timing, refill capacities, filter installation and approved oil specifications vary by engine, model year and market. Use the owner’s manual for the exact vehicle as the final authority.

    How to use the sources: Confirm the exact vehicle and engine, check the approved oil and filter, follow the manufacturer’s level-check procedure and use its low-oil-pressure warning instructions rather than a generic time allowance.

    Find an exact vehicle owner’s manual

    Last official-source review: July 26, 2026.

    Independent automotive information: EngineOiil-Capacity.com is an independent informational website and is not a vehicle manufacturer, dealership, oil company, filter manufacturer or repair facility. A deep or persistent engine knock can indicate severe lubrication or mechanical damage. Switch off immediately for a red oil-pressure warning, rapid oil loss, heavy smoke, a dry dipstick or worsening metallic knock. Never work beneath a vehicle supported only by a jack.