Here is a subject that is sure to ignite discussion amongst many Kubota tractor owners. If you shed park your Kubota in sub zero temperatures you might be tempted to use some other kind of starting fluid to get your Kubota tractor firing. Every now and then we hear the question, “Is it OK to use starting fluid on my Kubota tractor?” The simple answer is no!
What is Starting Fluid?
Starting fluids are comprised of volatile hydrocarbons, heptane, butane, hexane and a mixture of up to 60% diethyl ether. Ether is clear, colorless liquid that has a low autoignition temperature – handy when the engine you are attempting to use it on it cold. The temperature at which ether auto ignites is 360 Fahrenheit or 182 Celsius. Ether also has a high cetane number, a measure of fuel ignition delay – ether has a high index and so the delay from fuel injection to fuel combustion is shorter. Finally, ether has no lubricating properties like normal diesel fuel does, making it harder on gaskets and seals. Starting fluid is widely available at any automotive supply chain and typically costs $4-5 per spray-can sized can.
How a Diesel Engine Fires
When we take a closer look at the basic mechanical principles of a diesel engine it become easier to understand why reaching for the starter fluid when you are having a tough time getting your Kubota to start is not a good idea.
In any diesel engine, only air is introduced to the combustion chamber. The compressing of this air raises the cylinder temperature to over 1000 degrees F (550 Celsius). At this precise moment, the tip of the injector opens and diesel fuel, also under pressure, is injected into the top of the combustion chamber. The extreme heat then ignites the atomized diesel fuel, firing the piston downward supplying power to the crankshaft.
Your Kubota’s diesel engine produces between 412 and 470 psi of compression. The air sucked into the engine on the upstroke is squeezed at a 19:1 ratio. Depending on the engine model, the tips of the injectors will open between 1700-3400 psi. These are high compression numbers! Your Kubota’s engine is pressure ignited and built to operate within its design limitations of 470 psi of compression. When we introduce an unregulated fuel source, like starting fluid, into the combustion chamber, the compression is much more volatile and can exceed specification – in short, that fluid can grenade the engine.
The Effects of Starting Fluid
The only way to get starter fluid into the engine of your fuel injected Kubota tractor is through the air box. When you spray starting fluid into the air box of the engine, it replaces a certain volume of air with a highly explosive and volatile fuel.
Once the engine is cranked over it quickly begins to compress the air and starting fluid now inside the combustion chamber. As the piston begins to move upwards compression increases and cylinder temperature begins to climb. However, since starting fluid will ignite at a lower temperature 360 F (182 C) versus the diesel fuel at 1000 F (550 C) a flame inside the combustion chamber occurs ahead of the injectors opening to deliver their fuel.
Kubota fuel injection pumps are designed to begin delivery to the injector at 14-22 degrees Before Top Dead Center (BTDC), depending on the specific engine model. This means that as the piston in still traveling upwards, a flame has already started inside the combustion chamber! Spray some diesel fuel into this flame ball and add a little more compression and you can see where this is going. BANG!
With starting fluid displacing the air, ignition now occurs explosively, uncontrollably and with such force that the upper limits of compression pressure are well exceeded. Never, ever use starting fluid on a diesel engine with glow plugs! KA-BLOOMIE!! Kubota tractors all have glow plugs!
Kubota Technical Service Bulletin SB78-38
In 1978 Kubota issued a service bulletin covering the use of ether or starting aids in their engines.
10 Quick Cold Weather Starting Tips
- Have a good strong battery with 850-1000CCA (cold cranking amps).
- Use a magnetic block heater if your Kubota does not have a water jacket heater to keep the engine block, oil pan and oil warm.
- Crank over the engine for 15-30 seconds with the cylinder head decompression knob pulled out to circulate warm engine oil to the upper parts of the engine.
- Glow the glow plugs for the appropriate time as dictated by the outside ambient temperature. Below zero give them 60 seconds of preheat. Over-glowing does not hurt.
- Service your tractor regularly, change filters and fluids.
- If the engines begins to fire and is running a little lumpy, quickly turn the key backwards to reactivate the glow plugs and bring the temperature of the combustion temperature back up.
- Set a trouble light on top of the engine for an hour or so to warm up a frozen engine. Place it by the air plenum and injector lines but do not leave it unattended or overnight.
- Remove the battery and bring it inside the house if necessary. A warm battery will crank your Kubota over like a hot day in July!
- Park in a heated garage if possible, if not, even an unheated shed offers a degree of protection.
- Make sure the fuel in the tank is fresh, number 2 diesel. If you store your own fuel, make sure it has been treated with an extender and it does not hurt to use a little cetane booster.
Service Department Vic