How to change lawn mower oil — UK DIY guide
Engine oil is the single most important maintenance item on a petrol mower — and the easiest DIY job. Twenty minutes once a year keeps Briggs, Honda, Stiga and Kawasaki engines running for their full design life. Here is the UK guide for every brand.
When does mower oil need changing?
Once a season, typically at the end of mowing (October-November) so the engine sits over winter with fresh oil.
Or every 25 hours of running time for serious mowers (any Briggs or Honda doing commercial work).
Or any time the oil looks black or smells burnt. Healthy oil is clean amber-to-light-brown; black oil holds combustion byproducts and acids.
What oil to use
SAE 30 is the universal lawn mower oil — works in any 4-stroke walk-behind petrol mower from Briggs, Honda, Stiga, Kawasaki, or Kohler.
10W-30 is a multigrade alternative — also fine in any of the above, slightly easier cold-starting.
15W-40 is for Kubota and other diesel ride-ons only — wrong for petrol mowers.
Capacity: typically 0.5-0.7 litres for walk-behind petrol, 1.5-2.2 litres for petrol ride-ons. Check the dipstick or manual.
1. Run the engine to warm the oil
Run the mower for 3-5 minutes. Warm oil flows out faster and carries more contaminants with it.
Do not run it hot — just warm. The mower must be cool enough to handle safely.
Disconnect the spark plug after warm-up. Non-negotiable safety step.
2. Drain the old oil
Method 1: tilt the mower with the carburettor side up and pour out through the oil filler. Works for any walk-behind without a drain plug.
Method 2 (Briggs, Honda walk-behind): use the drain plug if fitted — typically a bolt on the lower engine casing. Position a tray underneath, undo the plug, let it drain for 5 minutes.
Method 3 (ride-ons): drain plug always fitted, usually underneath the engine sump. Some ride-ons also have a side drain for easier access. Refer to the manual.
Dispose of old oil safely — sealed container, take to your council recycling centre (free service at most UK centres).
3. Replace the oil filter (ride-ons only)
Walk-behind mowers do not have oil filters — splash lubrication only.
Ride-ons with pressure lubrication (Kubota, Kawasaki FS/FX, Briggs Vanguard) have a spin-on oil filter. Change at every oil change.
Use an oil filter wrench to remove. Smear new oil on the new filter's gasket before fitting. Hand-tight only — never spanner-tight (cracks the filter housing).
4. Refill with fresh oil
Pour slowly through the oil filler. Do not overfill — too much oil causes smoking and gasket leaks.
Use the dipstick (most engines have one) — fill to the upper mark, not above.
Re-check the level after pouring. Oil settles into the sump over a minute — top up if needed.
5. Run and check
Reconnect the spark plug, start the engine, run for 30 seconds. Check for any oil leaks from the drain plug or filter (ride-ons).
Recheck the dipstick after stopping the engine. Top up to the upper mark if needed.
Update the service record — a written log of oil-change dates adds £50+ to mower resale value.
FAQs
Can I use car engine oil in my mower?
Yes — SAE 30 or 10W-30 car oil works in any 4-stroke mower engine. Avoid 5W-30 (too thin for mower air-cooling), 20W-50 (too thick for cold starts), or any "high-mileage" car oil with detergent additives. Generic SAE 30 from any motor factor is the right choice.
How much does dealer oil change cost?
£35-£60 at a UK garden machinery dealer for a walk-behind mower. £80-£130 for a ride-on. DIY is £6-£15 in parts and 20 minutes — substantial saving over the mower's life.
What if I overfill?
Drain back to the upper dipstick mark using a small syringe (£3 from any pharmacy) through the filler hole. Overfilled engines push oil past the rings into the cylinder, causing smoke at start-up.
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