Suzuki DF300B, DF325A and DF350A Service Guide: Oil, Filter, Gear Oil, Plugs and Intervals

This is the routine service for the Suzuki DF300B, DF325A and DF350A, written by the Boat Max Online service team from Suzuki's owner's manual for these motors and the Suzuki 4-stroke maintenance manual. It covers the 20-hour first service, the annual 100-hour service and the items that come due at 200 and 300 hours, with the capacities, part numbers and torques you need to do the job with the right parts.

Models covered: DF300B, DF325A, DF350A, DF300BMD, DF350AMD. If you are not sure which family your motor belongs to, the model code is on the clamp-bracket plate.

Parts and specifications

Everything on the annual list ships together in the DF300B/350A oil change kit (ECSTAR 10W-40 in the right quantity, the filter, gear oil and drain gaskets); the DF300B/350A 100-hour kit is the same idea for the 100-hour service. Plugs are on the Suzuki spark plug page by model and year, and the 300-hour maintenance kit is listed by part number.

Suzuki's schedule marks some items with an asterisk, meaning it recommends an authorized dealer or qualified mechanic: the oil filter, the 400-hour fuel filter replacement, idle speed, valve clearance, the water pump and impeller, fasteners, the thermostat, internal anodes. Engine oil, gear oil, spark plugs, fuel line, external anodes, lubrication, the battery, the low-pressure fuel filter inspection are unmarked, and the manual says you may service them yourself if you have mechanical experience. This guide follows that split: it gives the full procedure for the owner items and tells you what the dealer items are and when they fall due.

When each service is due

• 20 hours or 1 month (first service): engine oil, oil filter and gear oil replaced; fuel filter, idle speed, anodes, bonding wires, battery, lubrication points, propeller nut and pin, and all fasteners inspected. This is the big one; it is not the 10-hour end of break-in.
• Every 100 hours or 12 months: engine oil and gear oil replaced; plugs, thermostat, anodes, fuel filter, fuel line, battery, lubrication, prop nut and fasteners inspected.
• Every 200 hours or 12 months: oil filter replaced; water pump and impeller and idle speed inspected. Valve clearance has a single inspection on the larger motors' schedule (the DF115A/140A manual puts it at 300 hours).
• Every 300 hours or 36 months: water pump impeller replaced (the maintenance kit service).
• Longer intervals: low-pressure fuel filter replaced every 400 hours or 2 years; boat-mounted water-separating filter element every 12 months.
• The full schedule with every line item is in the Suzuki maintenance schedule explained.

Engine oil change, Suzuki's way

1. Run the engine a few minutes so the oil is warm and drains fully, then shut it off. Suzuki's manual cautions that the drain plug can be hot enough to burn: let it cool enough to touch before you loosen it.
2. Put the motor in the vertical position and remove the motor cover. Remove the oil filler cap.
3. Put a drain pan under the engine oil drain plug, remove the plug and its gasket, and let the oil drain completely.
4. Fit the drain plug with a new gasket and tighten it to 13 N·m. Suzuki is explicit that a used gasket can leak and damage the engine; a spare comes in the tool bag.
5. Replacing the filter (every 200 hours or 12 months, and at the 20-hour first service; Suzuki lists it as a dealer item, and this is what the job is): unscrew the old 16510-96J11 spin-on filter into the pan, wipe the mounting face, put a film of fresh oil on the new filter's gasket, spin it on until the gasket seats, then tighten to 14 N·m.
6. Fill with about 8.5 L (8.98 US qt) of SAE 10W-40 if you changed the filter, or 8 L (8.45 US qt) if you did not, through the filler. Wait a minute, then check the dipstick with the motor vertical and top up to the upper mark; do not fill past it.
7. Refit the filler cap, run the engine in the water or on a flushing attachment (never dry) for a couple of minutes, shut down, let it cool, and recheck the level and the drain plug for weeps before the cover goes back on.

Gear oil change

1. The 3.2 L dual-prop gearcase has two procedures by year: 2018–2022 motors are filled trimmed up 4 degrees from horizontal; 2023-and-newer motors are drained in full trim-up with the water filters removed, then filled upright through the drain hole until oil exits the adjustment hole. Follow the manual page for your year. The same rules apply as on every Suzuki: drain plug out first, new gaskets, recheck the level after 10 minutes.

More detail and photos: changing lower unit gear lube on a Suzuki.

The rest of the 100-hour list

• Spark plugs: remove, read the electrodes (tan is normal, black is rich or oil, white is lean or hot), check the gap, and replace if worn. Torque to the figure in the table on a clean dry thread.
• Thermostat: inspect; replace if corroded, sticking or slow to open in a hot-water test. Part numbers and temperatures are in the thermostat lookup.
• Low-pressure fuel filter: inspect (replace every 400 hours or 2 years). Fuel line and breather: inspect for cracks and hardening.
• Anodes: inspect the external anodes (internal anodes are a dealer check); replace any that are two-thirds gone, never paint them, and clean them with a wire brush to remove any coating.
• Lubrication: grease the throttle and shift linkages, tilt and swivel pivots, clamp screws and the propeller shaft with Suzuki water-resistant grease.
• Propeller nut and cotter pin: inspect; use a new cotter pin whenever the prop comes off. Check all bolts and nuts for tightness.
• Battery: check the terminals, hold-down and charge. Minimum spec is in the table above.

At 200 hours

• Engine oil filter: replace.
• Water pump and impeller: inspect. The impeller is replaced every 300 hours or 36 months.
• Idle speed: inspect (dealer item). Valve clearance is a single dealer inspection on this family's schedule.

Notes specific to this family

• The dual-prop gearcase holds 3.2 L and the procedure changed by year: 2018–2022 motors are filled trimmed up 4 degrees from horizontal; 2023-and-newer motors (including the BMD/AMD) are drained in full trim-up after removing the port and starboard water filters, then placed upright and filled through the drain hole until oil exits the adjustment hole (plugs 9–11 N·m, recheck after 10 minutes). Follow the manual page for your year rather than the small-motor procedure.
• Because there are two propellers, Suzuki inspects the propeller nut, pin and the front propeller nut stopper at 20 hours and every 100 hours.
• The 2018 DF350A used thermostat 17670-98L00 (53–57 °C); 2019-and-newer DF300B/325A/350A use 17670-98L20 (58–62 °C). Maintenance kits: 17400-98875 for 2018–2022, 17400-87840 for 2023-and-newer including the BMD/AMD.

After every saltwater outing

Flush the cooling passages with fresh water: a few minutes on muffs, or about five minutes through the flush port on models that have one, and check that the tell-tale stream is strong before every trip. How to flush with muffs.

Reference charts for every Suzuki family: oil capacity, spark plugs, gear oil, batteries, maintenance kits. Questions about a motor built near a changeover year? Send us the serial number.

Sources: the Suzuki owner's manual for this model family and the Suzuki 4-Stroke Outboard Maintenance Manual (Feb 2025). Capacities, part numbers and torques are Suzuki's published figures. Always fill to the dipstick mark and confirm part numbers against your serial number.