A Bobcat 328 running hot under load usually points to one of four problems: a clogged or damaged radiator, a failing thermostat, low coolant, or an engine oil level that has dropped below the minimum mark.
The 328 is a compact excavator built to work hard, but it pulls heat from the engine through the cooling system the same way any machine does. When the temperature gauge climbs into the red zone only when you are digging or moving material—not at idle—the issue is almost always one of those four things, and you can check three of them yourself in under an hour with basic tools.
The reason it matters: running hot damages the engine. Seals fail faster, metal expands unevenly, and the hydraulic fluid that powers your boom and bucket loses its ability to do its job. Catching the problem early means a $50 radiator flush instead of a $3,000 engine rebuild.
Key Takeaways
- Check your coolant level first with the engine cold—low coolant is the fastest fix and the most common cause of overheating under load.
- A clogged radiator restricts water flow and causes heat buildup only when the engine is working hard; cleaning the fins and core from the outside often solves it.
- The thermostat can fail in a way that lets coolant bypass the radiator instead of flowing through it, and replacement takes about two hours on a 328.
- Engine oil that drops below the minimum line reduces cooling efficiency because oil carries heat away from the engine block; check the dipstick with the machine level and the engine off.
- If you have checked all four and the machine still runs hot, the water pump may be failing or the head gasket may be leaking, and those require a mechanic.
Check coolant level and condition first
The coolant reservoir on a Bobcat 328 sits on the right side of the engine compartment. Let the machine sit for at least 30 minutes after shutdown so the coolant cools enough to handle safely—pressurized hot coolant can spray out and cause burns. The cap itself is usually under pressure, so open it slowly by turning it a quarter turn, letting steam escape, then unscrewing it fully.
The coolant should reach the "full" line on the side of the reservoir, or come to within an inch of the cap opening if there is no line marked. If it is low, top it off with the coolant type specified in your operator manual—mixing types can cause sludge buildup. Bobcat machines typically use a long-life ethylene glycol coolant, often green or orange depending on the year.
While the cap is off, look at the coolant color. Rust-colored or cloudy coolant means the system has corrosion inside, and you should plan a full flush. Coolant that smells sweet but also smells like fuel suggests a head gasket leak, which is a bigger problem. If the level was low and the coolant looks clean, top it off, run the machine under load for 20 minutes, and check again—if it drops, you have a leak somewhere in the hoses or block.
Inspect the radiator for blockage and damage
The radiator on a 328 sits in front of the engine and has thin aluminum fins that cool the hot water flowing through the core inside. Dirt, dust, and plant material pack into those fins and act like insulation, trapping heat instead of releasing it. This happens slowly, so you may not notice until the machine is working hard and the engine cannot shed heat fast enough.
With the engine off and cool, look at the radiator from the front. If you cannot see through the fins to the core behind them, it is clogged. Use compressed air at 40 to 60 PSI and blow from the engine side toward the front, pushing the debris out. Do not use a pressure washer—the force can bend the fins and make the problem worse. If compressed air does not clear it, a soft brush or old toothbrush can help loosen stubborn buildup, then blow again.
Check the radiator for leaks or damage while you are looking at it. Small weeping leaks around the seams may not show much fluid on the ground but will cause the coolant level to drop over days or weeks. If you see cracks in the aluminum or holes, the radiator will need replacement. A used radiator from a salvage yard costs $200 to $400; a new one runs $600 to $900 depending on the supplier.
Test the thermostat by watching coolant flow
The thermostat is a valve inside the engine that opens when coolant reaches a certain temperature, letting it flow through the radiator to cool down. If the thermostat gets stuck closed, coolant never reaches the radiator and the engine temperature climbs. If it gets stuck open, coolant flows through the radiator all the time and the engine may run cold even under load—but this is less common and usually not the "runs hot" problem.
A straightforward test: with the engine cold, locate the upper radiator hose where it connects to the engine. Start the machine and let it idle. Feel the hose gently after a minute or two—it should stay cool at first. As the engine warms up, the hose should become hot to the touch within 3 to 5 minutes. If the hose stays cold for 10 minutes or more, the thermostat is likely stuck closed and coolant is not flowing through the radiator.
If the thermostat is stuck, it must be replaced. On a 328, this usually means draining the coolant, removing the thermostat housing (typically held by two or three bolts), taking out the old thermostat, and installing a new one with a fresh gasket. The job takes about two hours if you are comfortable working on engines. A replacement thermostat costs $30 to $60, and a gasket kit is another $10 to $15.
Check engine oil level and condition
Engine oil does more than lubricate moving parts—it also carries heat away from the engine block and toward the pan where it cools. If the oil level drops too low, there is not enough oil to move heat efficiently, and the engine temperature rises. This is especially true under load when the engine is working hard and generating maximum heat.
Park the machine on level ground and let the engine cool for at least 10 minutes. Locate the dipstick, usually a yellow or orange handle on the side of the engine block. Pull it straight out, wipe it clean with a rag, reinsert it fully until it seats, then pull it out again and read the level. The oil should reach the "full" mark or the upper line. If it is below the minimum mark, add the correct oil type and weight for your machine—your operator manual specifies this.
While you have the dipstick out, smell the oil and look at its color. Dark brown or black oil is normal after use. Oil that smells burnt or looks milky (like a coffee with cream) suggests coolant is leaking into the oil, which points to a head gasket problem. If the oil level was low and you have not added any recently, you have a leak—check under the machine for drips and inspect the pan gasket and drain plug for seeping.
When to stop troubleshooting and call a mechanic
If you have checked coolant level and condition, cleaned the radiator fins, tested the thermostat, and verified the oil level, and the machine still runs hot under load, the problem is likely inside the engine. A failing water pump does not circulate coolant efficiently even if the thermostat opens. A head gasket leak allows coolant to escape into the combustion chamber or oil passages, raising temperature and lowering coolant level at the same time.
These repairs require removing the engine or opening the block, which is beyond field troubleshooting. A mechanic with a Bobcat diagnostic scanner can also check for sensor faults—a bad coolant temperature sensor can cause the gauge to read high even if the engine is actually cool, though this is rare. At this point, the cost of a shop visit is worth the certainty of knowing what you are dealing with.
Frequently Asked Questions
Can I run the machine if it is overheating, or will it break when ready?
Running hot for short periods will not destroy the engine when ready, but every minute of overheating shortens its life. Seals dry out, metal warps, and internal corrosion accelerates. If the temperature gauge enters the red zone, shut down and let it cool before continuing. Pushing through overheating to finish a job today can cost you thousands in repairs next month.
What coolant should I use if I do not have the manual?
Bobcat machines built before 2010 typically use a green ethylene glycol coolant; newer machines often use orange long-life coolant. Check the color of the coolant already in the reservoir and match it. If the reservoir is empty or you are unsure, a Bobcat dealer can tell you the correct type for your serial number, or you can post the model and year on a Bobcat forum and get an answer within hours.
Is it safe to drive the machine to a mechanic if it is running hot?
Short distances at low speed are usually okay if you monitor the temperature gauge and stop if it climbs into the red. Highway speeds or long distances will make the problem worse. If the machine is overheating at idle or low load, do not move it—have it towed. If it only overheats under heavy load, you can usually move it slowly to a shop without damage.
Why does the machine run hot only when digging, not when sitting still?
At idle, the engine is not generating much heat and the cooling system has an straightforward time keeping up. Under load, the engine works harder, produces more heat, and the cooling system has to work faster to shed it. If the radiator is partially clogged, the thermostat is sluggish, or the coolant level is low, the system can keep up at idle but fails under load. This is why the problem only shows up when you are working.
How often should I flush the coolant to prevent overheating?
Most manufacturers recommend a coolant flush every two to three years or every 2,000 operating hours, whichever comes first. A Bobcat 328 that works five days a week will hit 2,000 hours in about eight years. If you work the machine year-round, plan a flush every two years. Flushing removes corrosion and sediment that build up inside the block and radiator, keeping the system efficient.