Home » Mowers » S Series Riding Lawn Mowers » S120 Oil-Change Masterclass: Let’s Do It Right

S Series Riding Lawn Mowers

S120 Oil-Change Masterclass: Let’s Do It Right

Jordan

May 3, 2026

0 Views 36 comments

Why Doing the Oil Change Right Matters

Routine oil changes are one of the simplest, most effective ways we can protect the longevity and performance of our John Deere S120 rear-engine rider. When we do the job properly—safety first, correct tools and parts, proper disposal—we avoid costly repairs and keep cutting smooth and reliable.

This guide is a confident, step-by-step masterclass for homeowners who maintain their own mowers. We’ll walk through Safety First, tools and workspace setup, draining oil and replacing the filter, choosing the right oil and filter, refilling and start-up checks, and maintenance planning, troubleshooting, and responsible disposal. Clear instructions, practical tips, and approachable explanations make this something we can do together with confidence and a smile today.

We always treat an oil change as a small project that can go sideways quickly if we skip basic safety. A few deliberate preparations keep us safe, protect the mower, and make the whole job faster.

Pre-job machine steps

Before we touch tools, we take these concrete actions:

These steps cut the common risks—unexpected rollaway, hot-oil burns, and accidental starts.

Personal protective equipment

We protect our hands, eyes, and skin:

I once loosened a stubborn filter and got a surprise spatter—eye protection paid off that time.

Safe handling of hot oil

Hot oil can scald and flare. We let the engine cool, then handle slowly: open the oil cap to relieve pressure, pour slowly, and always angle the drain pan to avoid sudden splashes. Use heat-resistant gloves if we must work sooner.

Workspace and spill control

Choose flat, well-lit ground—avoid wet grass or a slope. Position a low-sided steel or polymer drain pan (2–4 qt capacity) directly under the drain point, and lay oil-absorbent pads (SpillTech, Oil-Dri) nearby to catch drips. Keep a roll of shop towels and a leak-proof sealable container on hand for used oil transfer.

Fire and emergency preparedness

We keep a small ABC dry-chemical extinguisher within reach (2A:10B:C is a good minimum). Have a phone on hand and know the nearest water source or cleanup materials. These small precautions are what separate a smooth oil change from a messy emergency.

Essential tools and materials

We gather everything before we start—nothing slows us down like hunting for a socket while oil drips. Common items we use:

Workspace organization tips

We set the stage like a small assembly line:

Verifying oil viscosity and filter part numbers

We never guess. To confirm supplies:

With tools sorted and the right oil and filter confirmed, we’re ready to move into the hands-on steps: draining old oil and replacing the filter.

Warm the engine and secure the mower

We run the engine 2–4 minutes to warm the oil—warmed oil flows faster and carries sludge out with it. Then we stop the engine, remove the key or disconnect the spark-plug lead, set the parking brake, and place wheel chocks. Gloves and eye protection stay on—hot surfaces and surprises happen fast.

Locate the drain point and position the pan

We find the drain plug and filter (consult the manual or engine label). We position an appropriately sized drain pan under the plug and leave room for filter drain—some filters will dump oil when removed. We open the oil-fill cap to vent the crankcase; that speeds drainage and prevents glugging.

Remove the drain plug and allow a full drain

We use the correct socket, seating it fully to avoid rounding the plug. Turn slowly to break it loose—hot oil may splash. Once removed, we let the oil flow freely into the pan; this can take several minutes. We never tip the mower to force drainage; that risks fuel and oil mixing and makes a mess.

Remove and replace the oil filter

We place the pan under the filter before loosening. For spin‑on filters:

We inspect the filter mounting surface and remove any old gasket material. We lightly oil the new filter’s rubber gasket with clean engine oil—this ensures a good seal and makes later removal easier. Thread the new filter by hand until the gasket contacts the base, then tighten according to the manufacturer: typically hand-tight plus 3/4 turn. If a torque spec is provided, use it.

Clean, inspect, and reinstall the drain plug

We wipe the plug and threads clean, replace the crush washer or gasket if recommended, and reinstall. Follow the manual torque spec for the plug; if unknown, snug with a wrench—avoid over-tightening (which can strip threads). Use a torque wrench where possible.

Photographic checks and troubleshooting

We photograph the drain plug threads and filter sealing surface before final assembly—these pictures save hours at parts counters. If flow is slow, we check that the fill cap is open and wait longer; if the plug or filter is stuck, we apply penetrating oil, let it soak, then use the correct wrench or a strap/cap tool. For rounded heads, an extractor or professional help is safer than brute force. For spills, use absorbent pads or kitty litter and collect residues for proper disposal.

With the old oil drained and a fresh filter in place, we’re ready to choose the correct oil and perform the refill and level checks next.

Picking viscosity and oil type

The first rule: follow the S120 owner’s manual. In practice, many S120s run well on SAE 30 in consistently warm climates and 10W‑30 multigrade where cold starts or variable temps occur. We choose:

How to read labels (quick)

Look for:

A label tells us performance limits at low/high temps and whether it’s suitable for lawn‑tractor/engine use.

Oil capacity and topping off

Find the exact capacity and filler location in the owner’s manual or on the engine decal. When refilling:

Filter selection: OEM vs aftermarket

Good filters trap contaminants and protect oil flow. We weigh pros and cons:

Change intervals and when to shorten them

Typical guidance: change oil and filter every 50 hours or once per season under normal use. In severe conditions—heavy dust, long continuous mowing, wet/dirty storage, or commercial use—move to every 25 hours or more often. Switching to synthetic may extend intervals (always confirm with the manual).

We keep the manual’s capacity and filter part numbers handy (owner’s booklet, engine decal, or John Deere parts website) so replacement shopping is straightforward. Next, we’ll refill and verify levels carefully before the first run.

Refill the crankcase — steady hands, good funnel

We pour the oil slowly to avoid aeration and spills. Use a long‑neck funnel (e.g., Hopkins FloTool or Lisle 17981) or a graduated pour spout so we can control flow and see how much we add. Our practical routine:

Dipstick sequence for an accurate reading

Accurate oil reading depends on sequence and level ground:

First start and immediate leak check

We start the engine for 30–60 seconds to circulate oil and pressurize seals.

Quick post‑service checks while things are accessible

With the engine safe and still warm, we inspect:

Post‑service checklist

Quick corrective steps

We’re now set to move into planning future maintenance, troubleshooting rarer issues, and disposing of used oil responsibly.

Routine planning and recordkeeping

Good maintenance is mostly about habits. We keep a simple log (notebook, phone note, or sticker under the seat) with:

We build oil changes into a seasonal checklist: pre-season tune-up (oil, filter, spark plug), midsummer check, end-of-season winterizing (stabilize fuel, final oil change if storing). A simple calendar reminder every 50 hours or annually keeps us ahead of wear.

Common issues and troubleshooting (fast fixes)

Safe, legal disposal and storage

Small habits—consistent logs, prompt fixes, and responsible recycling—add up to longer engine life and fewer surprises. Next, we’ll wrap up with a short ready‑to‑go checklist so we can get started.

Ready to Get Started

Armed with safety practices, the right tools, and clear step-by-step know-how, we can confidently perform an oil change on our John Deere S120 and keep it running smoothly. Routine service saves time and money, and builds our confidence working on the machine.

Always follow the owner’s manual for model-specific capacities, torque specs, and intervals. If we encounter problems beyond routine maintenance, we should contact a John Deere dealer or a qualified technician. Now let’s get the S120 cared for—steady, safe, and done right. We’ll enjoy smoother mowing seasons and greater machine longevity when we stay consistent.