A construction machine usually gives warning before it breaks down: an unusual noise, smoke of a different colour from the exhaust, a new stain under the machine, a delay you can feel in the controls. An operator who notices these signs early catches the fault while it is small; one who ignores them usually meets the same fault later, in a bigger form.
This guide is not a repair manual but an awareness guide. It explains what the symptoms you hear, see, smell and feel may mean, and gives an urgency level for each: those that call for an immediate stop, those to look at at the end of the day, and those that can be dealt with at the next service.
Symptoms alone don’t give a definite diagnosis; the same noise or smoke can have more than one cause. The aim is to ask the right question and give the service team the right information.
Three levels of urgency
Try to place every symptom in one of the following three levels:
- Stop immediately: Carrying on could cause serious damage or injury. Bring the machine safely to a stop, lower the equipment to the ground and switch off the engine.
- Check at the end of the day: The machine can keep working, but the symptom must be watched; check it when the job is finished and make a note.
- Deal with it at the service: Not urgent, but it must be mentioned to the service team at the next scheduled service.
Whenever you are unsure, choose the level above. Brushing off a symptom with “let’s wait and see” is usually the most expensive option.
The basis for catching symptoms: the five-minute walk-round
To notice symptoms, you first need to know what the machine is like when everything is normal. Every morning before starting the engine, take a five-minute walk around the machine: look underneath it and at the parking spot, inspect the hoses and cylinder rods, look for trapped stones or broken parts in the tracks and rollers, and check the engine oil, hydraulic oil and coolant levels. When you turn on the ignition, check that the warning lights come on, and that they go out once the engine starts. This routine lets you catch most of the symptoms described below before the machine even starts work.
Seven situations where you must stop immediately
- The oil pressure warning light is on. The engine may be running without oil; even a few minutes can cause serious damage.
- Overheating warning or steam from the engine. Stop work immediately and follow the overheating instructions in the operator’s manual; some engines call for a brief cool-down at idle without load, and for the engine to be stopped at once if there is steam or coolant loss. Never open the radiator cap while it is hot; pressurised hot coolant causes serious burns.
- A sudden, loud metallic noise. A new, harsh knocking from the engine, slew system or travel drive.
- Oil spraying from a hose. High-pressure hydraulic oil can penetrate the skin; don’t go near the leak with your hands.
- A smell of burning plastic or smoke from cables. There is a risk of an electrical fire; switch off the battery isolator and keep a fire extinguisher ready.
- Movement contrary to the controls or loss of control. The equipment lowers by itself or the machine moves in an unintended direction.
- A fuel leak near hot surfaces. Fuel dripping onto the exhaust or engine block can ignite.
In any of these situations, the cause must be found before the machine is restarted. Often the best course is to leave the machine where it is and talk to the service team.
What does the colour of the exhaust smoke tell you?
A diesel engine’s exhaust is the most visible clue to what is happening inside the engine. When judging the smoke, take the engine’s temperature and load into account too:
| Smoke | Possible meaning | Urgency |
|---|---|---|
| Black, increasing under load | Too little air for the fuel: blocked air filter, overloading, injector problem | Check at the end of the day; check the air filter first |
| White, briefly at a cold start | Condensation and incompletely burnt fuel in a cold engine; usually normal if it disappears as the engine warms up | Monitor |
| White, continuing after the engine has warmed up | Coolant may be getting into the combustion chamber, or there may be a fuel system problem | Stop immediately if the coolant level is dropping |
| Blue-grey | Engine oil burning: worn piston rings or valve stem seals, overfilled oil | Deal with it at the service; measure oil consumption |
| No smoke, but low power | A problem with the fuel supply, a blocked filter or on the hydraulic side | Check at the end of the day |
White smoke for a few minutes on a cold morning and thick black smoke at full load do not mean the same thing. With black smoke, the first and cheapest item to check is the air filter. To keep track of oil consumption, measure the engine oil level every day under the same conditions and write it down. We explain general care habits for diesel engines in our Kubota diesel engine maintenance guide.
Noises: engine, hydraulics and undercarriage
Get to know your machine’s normal sound; a new noise is usually the first sign of a new problem. Common noises and their possible meanings are:
- A whine or whistle from the hydraulic pump: This can mean the pump is struggling because of a low hydraulic oil level, a blocked suction filter or very cold oil. Check the oil level first.
- A squeal when you hold a function at the end of its travel: This is the relief valve opening when the cylinder reaches the end of its stroke. It is normal if brief, but continuing to hold the lever in that position heats up the oil. If you hear this sound before the end of the stroke, consult the service team.
- Belt squeal: A loose or worn belt; especially noticeable at a cold start or under load.
- Engine speed hunting up and down at idle: This may be air getting into the fuel system or a fuel filter starting to clog; check the water separator and the filter.
- A regular knock from the engine: This may come from the injection system, valve clearance or an internal part; if the noise gets louder, stop the machine.
- Clicking from the joints: A sign of play in pins and bushings; you can find the details in our pins, bushings and greasing guide.
- Squeaking or clicking when travelling: This may be a roller running dry, a worn drive sprocket or a slack track; we explain this in detail in our undercarriage guide.
- Grinding or knocking when the upper structure slews: This may be a lack of lubrication or wear in the slew gear.
Noises are hard to describe. If you are going to consult the service team, record the noise on your phone; a short video gives more information than the most detailed description. Film from a safe distance without getting close to moving parts.
Leaks: the colour and consistency of the stain
A new stain where the machine is parked is the cheapest fault warning there is. If you keep the parking spot clean, you will notice a new stain straight away. Dabbing the stain with white paper or a cloth lets you see its colour and consistency better:
- Dark brown or black, slippery: Usually engine oil. Look around the sump, oil filter and gaskets.
- Light-coloured or honey-coloured, slippery: Often hydraulic oil; its colour can vary with the type and age of the oil. Cylinders, hoses and fittings are the first places to look. We explain cylinder leaks in our hydraulic cylinder guide.
- Green, red, pink or blue, watery: Coolant; its colour depends on the antifreeze used. Look around the radiator, coolant hoses and water pump.
- Thin, spreading quickly, with a distinct smell: Diesel fuel. Check the fuel lines, the filter and around the tank; if it is near hot surfaces, stop the machine immediately.
- White-green deposits around the battery: A sign of corrosion and acid fumes; clean the terminals and check the battery case.
When looking for the source of a leak, the engine should be off and cooled down. Don’t feel for a leak on a pressurised hydraulic line with your hand; use a piece of cardboard instead.
Some “leaks” go not outwards but from one system into another. Engine oil on the dipstick that looks light brown, foamy or milky may mean coolant has got into the oil; in that case, don’t run the machine. On machines with a hydraulic oil sight glass, oil that looks cloudy or milky may be a sign that water has got into it. Both are symptoms that call for a word with the service team.
Smells and what you feel from the operator’s seat
Some symptoms reach the operator before any noise or smoke does:
- Smell of burning oil: Oil leaking onto the exhaust or engine, or overheated hydraulic oil.
- Sweet-smelling steam: A coolant leak; keep an eye on the temperature gauge.
- Smell of burning plastic or electrics: Overheating in a cable or electrical component; stop immediately.
- Smell of raw fuel: A leak in the fuel line or filter.
- Slower hydraulic movements: Cold oil, a low level, a blocked filter or an internal leak. If only one function is slow, that points to its cylinder or valve; if all functions are slow, it points to the pump or the oil side.
- Equipment lowering by itself: An internal leak in a cylinder or valve; a direct safety risk.
- Unusual vibration: A problem with the engine mounts, fan, belt or a rotating part.
- Machine pulling to one side: A difference in track tension or a travel motor problem.
In machines with an enclosed cab, such as the R350 with its air-conditioned cab, less of the noise and smells outside reaches the operator. That’s why it is a good habit to open the door or window a few times a day to listen to the machine, and to do the daily walk-round from outside.
Gauges and warning lights
Warning lights are the machine’s own first diagnosis. Because symbols can vary from machine to machine, go through the list in your operator’s manual once and keep a photo of it in the cab. In general:
- Oil pressure light: If it comes on while the engine is running, stop the engine immediately.
- Overheating light: Stop work and cool the engine down as instructed in the manual.
- Charging light: If it doesn’t go out while the engine is running, the charging system may not be working; the battery will run flat after a while.
- Air filter restriction indicator (if fitted): Check or replace the filter.
- Glow plug light: It is normal for it to come on at a cold start; wait for it to go out before cranking.
On most machines it is normal for the oil pressure and charging lights to come on when you turn the ignition on before starting the engine; they should go out once the engine is running. A warning light that never comes on with the ignition on, however, may point to a bulb or circuit fault; in that case, you won’t get that light’s warning.
Recording the symptom: the right information for the service team
Two different people can describe the same symptom very differently. Before contacting the service team, note down the answers to these questions:
- When did the symptom start — suddenly or gradually?
- Does it appear when the engine is cold, when it is hot, or under load?
- In which movement or function does it occur?
- Which warning light came on?
- How many operating hours does the machine have?
- What was done to the machine at the last service or in recent days?
Adding a photo showing the symptom, or a video with sound, to these notes noticeably speeds up the diagnosis. We explain step by step how to prepare a service request in our service request guide.
Summary
- With an oil pressure or overheating warning, a burning smell, spraying oil or loss of control, stop work immediately and shut the machine down safely.
- Judge the smoke colour together with the engine’s temperature and load.
- A new noise or a new stain is the cheapest fault warning there is.
- Look for leaks with cardboard, not your hand; the engine should be off and cold.
- Note the symptom and film a video; the diagnosis will be faster.
If you are unsure about a symptom, you can fill in the service request form or send photos and videos directly to our technical service line on WhatsApp.
