My Petrol Lawnmower is blowing white/grey/blue smoke

If your petrol lawnmower is producing white, grey, or blue smoke from the exhaust, it is often caused by engine oil entering areas where it should not normally be present.

In many cases, the issue is temporary and can be resolved with a few simple checks.

Table of Contents

1. Common Causes of White, Grey, or Blue Smoke
2. Check the Engine Oil Level
3. Has the Lawnmower Been Tilted?
4. Allow Excess Oil to Burn Off
5. Check the Air Filter
6. Sponge Air Filter
7. Cartridge (Paper) Air Filter

Common Causes of White, Grey, or Blue Smoke

White, grey, or blue smoke is commonly caused by:

• Overfilled engine oil
• Oil spilled onto the engine or exhaust during maintenance
• The lawnmower being tilted incorrectly
• Oil entering the air filter housing
• A dirty or oil-soaked air filter

These issues can cause oil to burn during operation, resulting in visible smoke from the exhaust.

Check the Engine Oil Level

Before starting the engine, check the oil level.

Step 1 – Locate the Dipstick

Remove the oil filler cap and dipstick.

Step 2 – Check the Oil Level

Ensure the oil level is between the minimum and maximum marks on the dipstick.

For most petrol lawnmowers, the recommended oil is SAE 30 or an equivalent oil specified in the user manual.

Step 3 – Correct Any Overfilling

If the oil level is above the maximum mark, remove the excess oil before operating the machine.

Excessive oil can be forced into the combustion chamber or air intake system, causing smoke.

Has the Lawnmower Been Tilted?

If the lawnmower has recently been tipped onto its side, oil may have entered the exhaust, cylinder, or air filter housing.

This is one of the most common causes of temporary smoke.

Typical situations include:

• Cleaning underneath the mower deck
• Transporting the mower
• Performing maintenance

If this has occurred, the smoke will often clear after a short period of normal operation.

Allow Excess Oil to Burn Off

If the oil level is correct and the mower has been tilted recently:

Step 1

Start the engine in a safe, well-ventilated outdoor area.

Step 2

Allow the engine to run normally.

Step 3

Monitor the exhaust smoke.

As any excess oil burns away, the amount of smoke should gradually reduce and eventually stop.

Note: This process may take several minutes depending on how much oil has entered the exhaust or intake system.

Check the Air Filter

Oil contamination can sometimes affect the air filter, particularly if the mower has been tilted.

Remove the air filter cover and inspect the filter element.

Sponge Air Filter

A clean sponge air filter is generally yellow or grey in colour.

Cleaning a Sponge Filter

1. Remove the filter.
2. Wash it using warm soapy water.
3. Rinse thoroughly.
4. Allow it to air dry completely before refitting.

Do not reinstall a wet filter.

Cartridge (Paper) Air Filter

A clean paper air filter is usually white or off-white in colour.

Paper filters cannot be effectively cleaned.

If the filter is:

• Dirty
• Damaged
• Oil-soaked

It should be replaced.