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White smoke blowing from your engine’s exhaust is a sign that oil has escaped into the fuel system or fuel has entered the oil compartment.

Want to know how to identify and fix the problems so you can get your lawn mower performing at an optimum level? Keep reading…

In this article, I share some common reasons your John Deere mower engine might be releasing white smoke from its exhaust and simple fixes to help you correct these problems.

Contents show

Reasons Why Your John Deere Blows White Smoke From The Exhaust

White smoke blowing from the exhaust is caused by oil in the gas or gas in the oil. This could be as a result of any of the following:

Blown head gasket
Stuck carburetor float needle
Overfilled oil tank
Damaged cylinder head
Cracked engine block

John Deere Blows White Smoke From Exhaust: Causes, Diagnosis, and Fixes

1. Blown Head Gasket

The most common cause of white smoke blowing from the engine’s exhaust is a blown head gasket. The head gasket is located between the cylinder head and the engine block.

It seals the combustion chamber of the engine allowing the engine to produce enough power while making sure that oil does not leak out into the cylinders, and fuel does not escape from the combustion chamber.

When the gasket blows, it is no longer able to act as a seal, and oil and fuel may begin to leak into different areas, mixing up, and producing white smoke as a result.

Diagnosis: Open up the engine and check the head gasket. If you notice a line of oil around where the two parts are held together, the head gasket is blown.

Fix:

Replace the head gasket with a new one

2. Stuck Float Needle in the Carburetor

The fuel float is the second thing to check after the head gasket. A stuck float needle can be the reason your John Deere blows white smoke from the exhaust.

A float needle regulates the amount of fuel that enters the carburetor. Debris or stale fuel can cause the float needle to get gummed up and stuck in the open position. As a result of this, fuel floods the carburetor and runs freely into different parts of the engine.

Free-flowing fuel can enter the oil tank and mix with the engine oil, causing white smoke to blow out through the exhaust.

Diagnosis:

Inspect the carburetor of the engine for signs of fuel flooding. Excess fuel indicates that the float needle is stuck.
Check the oil compartment using the dipstick. If the oil appears too thin and smells like fuel, it is a sign that fuel has leaked into it as a result of the fuel float being stuck.

Fix:

Drain out the excess fuel from the carburetor
Change the engine oil
Use a carb cleaner to free the stuck float needle
Fit a fuel valve in the fuel line and turn it off whenever the engine is not in use

3. Overfilled Oil Tank

An overfilled oil tank is another common cause of white smoke blowing through the exhaust. Oil will go back into the carburetor compartment and mix with the fuel when it is in excess.

Excess oil may be seeping past the piston rings and into the combustion chamber, where the engine attempts to burn it along with the fuel causing white smoke to blow through the engine’s exhaust.

Diagnosis: Open the oil tank and check the oil level with a dipstick. If it is above the ‘Full’ mark, the oil is in excess.

Fix: Reduce the oil until it is behind the ‘Full’ mark. Normal oil levels should be between the ‘Add’ and ‘Full’ marks.

After reducing the oil, start the engine and allow it to run. This is to allow the oil already inside the combustion chamber to burn completely. The white smoke is the engine burning off the excess oil. It may take about 5 minutes for the smoke to clear completely.

4. Damaged Cylinder Heads

If you have fixed the head gasket, oil level, and float needle of your engine and white smoke continues to blow out of the exhaust, then the cylinder heads of your John Deere might be cracked or damaged.

The cylinder heads control air flow and fuel deployment in and out of the cylinders. It works together with the head gasket to seal the cylinders in the engine.

A cracked cylinder head will allow fuel and oil to overflow into the engine which can cause white smoke to blow out of the exhaust.

Diagnosis: Oil leak may be a sign of a cracked cylinder head. If you notice oil leaking from your mower, the cylinder head may be damaged. Also, check the mower engine for oil stains around the cylinder head.

Fix: Repairing a cracked cylinder head requires professional experience. Take it to a nearby small engine repair shop to be fixed.

5. Cracked Engine Block

The final reason your riding mower blows white smoke from the exhaust might be a cracked engine block.

A cracked engine block is a more serious problem and should be checked after you have exhausted the above options as it is a rare occurrence.

The engine block provides a foundation for the cylinder heads and houses the crankshaft, pistons, and connecting rods.

A cracked engine block can allow oil to leak into the fuel system of the engine causing white smoke to blow through the exhaust.

Diagnosis:

You can spot a crack that is leaking oil through a visual inspection of the engine block
External oil leaks can also be a sign of a cracked engine block

Fix: Contact a small engine technician to mend the crack or replace the engine block.

John Deere Head Gasket Replacement – Step-By-Step Guide

A blown head gasket is a primary reason for white smoke blowing through the exhaust. It is also responsible for other engine problems such as overheating, and engine stalling.

Tools You Need For This Job

Some tools you might need while changing the gasket include:

Work gloves
Screwdriver
Socket wrench
Putty knife
Magnetic plate (to collect the screws)
Clean rag
New head gasket

The following steps will show you how you can replace a blown head gasket in your vehicle’s engine.

Step 1: Allow your engine to cool, lift the engine cover and detach it.

Step 2: Remove the air filter cover and air filter.

Step 3: Use a socket wrench to remove the blower housing mounting bolts, detach the oil drain tube and lift off the blower housing.

Step 4: Remove the exhaust manifold and pull it out from the muffler.

Step 5: Remove the valve cover mounting using a putty knife or flathead screwdriver. A small amount of oil might spill after removing it.

Step 6: Use a screwdriver to remove the screws securing the rocker’s arms.

Step 7: Rotate the arms and remove the pushrods.

Step 8: Remove the cylinder heads.

Step 9: Remove the old gasket attached to the cylinder heads.

Step 10: Clean off any residue from the old gasket with a clean rag before replacing it with a new one.

Step 11: Align the new gasket on the cylinder mounting pins.

Step 12: Reposition the cylinder head and replace the bolts.

Step 13: Return the push rods and reassemble the engine.

Conclusion

Your John Deere might be blowing white smoke from the exhaust as a result of a blown gasket, stuck float needle, overfilled oil tank, damaged cylinder head, or a cracked engine block.

Inspect the parts mentioned in this article and apply the recommended fixes to stop white smoke from blowing through your engine’s exhaust.