- Important clarification up front
- Most Hino FG17 / FG19 trucks use diesel engines; diesels do not have spark plugs — they have glow plugs. The procedure below is for replacing glow plugs. If your truck actually has a gasoline engine with spark plugs, the mechanical steps are similar but you will use a spark-plug socket, check/adjust gap, and use spark-plug specific parts.

- Safety first (must-follow)
- Wear safety goggles and gloves.
- Work on a cool engine — allow it to cool fully to avoid burns.
- Disconnect the negative battery terminal before touching electrical connectors or heaters.
- Keep a fire extinguisher nearby when using penetrating oil or working around fuel systems.

- Tools you need (detailed descriptions and how to use each)
- Ratchet handle (1/2" or 3/8" drive depending on sockets)
- Purpose: turn sockets to loosen/tighten fasteners.
- How to use: attach correct drive socket, set direction lever to loosen/tighten, keep steady pressure; avoid sudden jerks.
- Socket set (shallow and deep; metric set including common sizes)
- Purpose: fit and turn nuts/bolts and glow plug sockets.
- How to use: pick the tight-fitting socket; use deep sockets for recessed glow plugs; avoid worn sockets to prevent rounding bolts.
- Glow-plug deep socket (typically 8, 10, or 12 mm inner diameter depending on plug; sometimes a specially shaped socket is required)
- Purpose: specifically fits the hex portion of glow plugs and reaches down into the cylinder head.
- How to use: use the exact size; a magnet or magnetic insert helps remove the plug; if glow plugs have long shaft/insulator you may need a deep socket.
- Extensions (3–6", 10–12" extensions) and universal joint (swivel)
- Purpose: reach glow plugs in tight/recessed positions.
- How to use: attach between ratchet and socket to access angled/blocked plugs.
- Torque wrench (click-type, appropriate range e.g., 5–100 Nm)
- Purpose: tighten glow plugs to correct torque without over-tightening.
- How to use: set target torque, tighten slowly until click; avoid using torque wrench as breaker bar.
- Combination wrenches (metric)
- Purpose: access nuts/bolts where sockets can't fit.
- How to use: match wrench size to nut, pull rather than push for control.
- Long-nose pliers or boot-puller
- Purpose: pull electrical connector boots off glow plugs without damaging them.
- How to use: grip the connector body (not the wires) and wiggle gently while pulling.
- Flat-head screwdriver and small trim tools
- Purpose: pry off clips, hose clamps, or covers.
- How to use: use gently to avoid breaking plastic clips.
- Penetrating oil (e.g., PB Blaster, CRC)
- Purpose: loosen seized/stuck glow plugs before removal.
- How to use: spray around base of plug, wait 10–30 minutes, repeat if needed.
- Wire brush and shop rags
- Purpose: clean around glow plug bore and connector contacts.
- How to use: clean carefully to keep debris out of intake ports.
- Anti-seize compound (high temp)
- Purpose: prevent glow plug threads from seizing in the head.
- How to use: apply a very light smear on threads only (do not contaminate the tip).
- Dielectric grease
- Purpose: protect electrical connectors from moisture and corrosion.
- How to use: put a small dab on connector terminals before reconnecting.
- Multimeter (digital)
- Purpose: test glow plug resistance/current draw and check harness voltage.
- How to use: set to ohms to test resistance; set to volts to check supply (12 V) at the connector during preheat.
- 12V test lead / jumper wire (with inline fuse or test light)
- Purpose: bench-test a glow plug or check that the relay supplies 12 V.
- How to use: briefly apply 12 V to glow plug to see if it heats; use fused lead to avoid short circuits.
- Penetrating heat source / heat gun (optional, used cautiously)
- Purpose: help break seized plugs by expanding surrounding metal.
- How to use: heat around the plug (not the plug tip) for short bursts; avoid damaging nearby components and do not use open flame near fuel.
- Extractor / easy-out & thread repair kit (helicoil / insert) — extra, only if glow plug breaks or threads are damaged
- Purpose: remove broken glow plug fragments and repair threads.
- Why required: seized or snapped glow plugs need extraction; thread repair needed when internal threads are stripped.
- How to use: specialist tool use — if you need these, consider professional help.
- Service manual or repair manual for FG17 / FG19 (paper or PDF)
- Purpose: for exact glow plug size, torque specs, wiring diagrams, removal sequence.
- How to use: consult for model-specific values and diagrams.

- Parts you will need (what to replace and why)
- Glow plugs — correct OEM or equivalent part for your engine
- Why replace: worn or failed glow plugs cause hard cold starts, white smoke, rough idle when cold.
- Recommendation: replace all glow plugs in the engine at once if one has failed or if vehicle has high hours — uneven performance happens if plugs vary in condition.
- Glow plug harness / lead connectors (inspect; replace if corroded/cracked)
- Why replace: damaged harness can prevent plugs from receiving voltage even if plugs are fine.
- Glow plug relay / preheat relay (test and replace if not supplying 12V when commanded)
- Why replace: relay failure is a common cause of no preheat light / no heating.
- Intake manifold gasket or EGR gaskets (only if you must remove the manifold to access plugs)
- Why replace: gaskets should be replaced whenever removed to prevent leaks.
- Thread repair kit / helicoil (only if threads stripped)
- Why replace/repair: damaged threads prevent proper seating/torque of new plugs; helicoil or insert restores threads.
- Anti-seize & dielectric grease (consumables)
- Why: protect threads and connectors.

- Quick pre-checks before removal
- Verify type of plug: look at plug top and part number; glow plugs look like long thin rods with electrical terminal; spark plugs have porcelain insulator and are thicker.
- Scan for fault codes (if you have an OBD/diagnostic tool) to check glow plug circuit faults.
- Inspect harness and connector condition visually.

- Replacement procedure (step-by-step, bullets only)
- Disconnect negative battery terminal to eliminate electrical hazards.
- Remove engine covers, air intake hose, and any cosmetic shrouds that block access to the cylinder head and glow plug harness.
- Locate glow plug harness and follow wiring to each glow plug; remove harness clips and carefully unplug the boots from each glow plug by pulling the connector body, not the wires.
- Clean the area around each glow plug with compressed air and a wire brush (or a vacuum) to prevent debris falling into the cylinder when the plug is removed.
- If glow plugs are easily accessible, use the correct-size deep glow-plug socket, extension, and ratchet to break the plug loose — turn counterclockwise gently. If difficult, apply penetrating oil around the base and wait.
- If a plug is seized:
- Apply penetrating oil and wait; try again after tapping the head of the plug lightly with a hammer to help penetration.
- Heat the surrounding metal with a heat gun (small bursts) if needed — be cautious around fuel lines and plastic.
- If the plug still won’t move, do not use excessive force — a snapped plug will require extraction tools or professional help.
- Once loose, remove the glow plug carefully (magnetic socket helps). Inspect the plug tip for carbon build-up, cracking, or ossification.
- Bench-test each removed glow plug with a multimeter (resistance check) or apply fused 12 V briefly to ensure it heats. Typical good glow plugs show low resistance (a few ohms) and will heat quickly; consult the manual for exact resistance values.
- Compare test results; replace any plug that fails open, has very high resistance, or does not heat.
- Clean the glow plug bore threads in the head using a thread chaser if available (do not cross-thread new plugs).
- Lightly coat new glow plug threads with a small amount of high-temp anti-seize (manufacturer guidance varies — some recommend none; check manual). Avoid getting anti-seize on the heating tip.
- Hand-start new glow plug into the bore to ensure correct seating and threads alignment.
- Torque new glow plugs to manufacturer specification with a torque wrench (if you don’t have the exact spec, use a conservative range of 8–12 N·m for small diesel glow plugs — but confirm with the service manual). Do not over-tighten — stripping or snapping is common.
- Apply dielectric grease to the inside of each connector boot, then reconnect the harness carefully to each glow plug.
- Refit any intake parts, hoses, and engine covers you removed. Replace any gaskets if the manifold was removed.
- Reconnect the negative battery terminal.
- Turn the ignition to the preheat position and check that the preheat light/indicator works and that voltage is present at the harness during preheat (use a multimeter).
- Start the engine and let it warm; listen and observe for smoother starting and less white smoke. Re-scan for codes.

- Testing glow plugs and related systems
- Resistance test with multimeter: disconnect plug, measure resistance across the heater tip and body. Compare to spec (few ohms typical).
- Current/voltage testing: check that the relay supplies ~12 V to each plug during preheat; or use a test light to confirm supply. If voltage present but plug fails to heat, plug is bad.
- Relay test: if none of the plugs receive voltage, test/replace preheat relay or check fuses and control wiring.

- Common problems and what extra tools/repairs are required
- Seized or snapped glow plug
- Tools/parts required: extractor/ easy-out, left-hand drill bits, helicoil/thread repair kit; possible machine shop help if plug breaks flush.
- Why: metal corrosion and over-tightening cause seizure; extraction is delicate.
- Stripped threads
- Tools/parts required: thread chaser or helicoil kit; possibly a replacement cylinder head if damage severe.
- Why: cross-threading or snaps require repair before new plugs can be installed.
- Damaged harness or connectors
- Tools/parts required: replacement harness or individual connector terminals, crimp tools, heat-shrink.
- Why: corrosion or broken wires mean voltage never reaches plugs.
- Relay or control module failure
- Tools/parts required: relay replacement and diagnostic tool to confirm.
- Why: electrical control must switch power to plugs during preheat.

- Replacement strategy recommendation
- Best practice: replace all glow plugs at once if one has failed or if truck has high hours; mismatched plug performance causes uneven starting and will quickly lead to more failures.
- Use OEM or high-quality equivalent glow plugs specified for your engine model — cheaper low-quality plugs may fail early.
- Replace any intake manifold gaskets, EGR gaskets, or seals you remove in the process.

- Final checks and tips
- Keep fasteners and small parts organized; mark which hoses come from where.
- Do not overtighten glow plugs — they are fragile and threads in aluminum heads are vulnerable.
- If you encounter a broken plug, stripped thread, or heavy corrosion, stop and consider professional assistance — further force can make repair much more expensive.
- Always consult the Hino workshop manual (model/year/engine-specific) for exact glow plug part numbers, torque specs, and access steps for your FG17 / FG19.

- Quick symptom checklist that indicates glow plug/related replacement likely needed
- Hard cold starts, lots of white exhaust smoke on start, extended cranking in cold weather.
- Preheat light not illuminating or engine control codes indicating heater circuit fault.
- One or more glow plugs test open or show abnormally high resistance.

- Disposal and cleanup
- Dispose of old glow plugs and contaminated rags per local hazardous-waste rules.
- Keep the work area clean and recheck all connectors and hoses before road testing.

End of instructions — follow the model-specific workshop manual for exact sizes, part numbers, and torque values.
rteeqp73

From the Archives: Hino FG Series Old footage of the Hino FG Series truck.

From the Archives: Hino FG Series Old footage of the Hino FG Series truck.

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