11-14-2025, 04:44 PM
The Bobcat S150 and Its Cooling System Design
The Bobcat S150 skid steer loader was introduced in the early 2000s as part of Bobcat’s mid-frame lineup, offering a rated operating capacity of 1,500 lbs and powered by a 2.0L Kubota V2203 diesel engine. Designed for versatility in construction, landscaping, and agriculture, the S150 featured a compact cooling system optimized for tight engine compartments and variable operating conditions.
The cooling system uses a pressurized radiator, thermostat-regulated flow, and a coolant reservoir. The factory fill typically includes a propylene glycol-based coolant, chosen for its lower toxicity and environmental friendliness compared to ethylene glycol.
When and Why to Change the Coolant
Coolant should be changed every 1,000 hours or every two years, whichever comes first. Over time, coolant degrades due to thermal cycling, oxidation, and contamination. Old coolant can lose its anti-corrosion properties, leading to scale buildup, cavitation, and eventual failure of water pumps or cylinder liners.
In one case, an S150 with 930 hours had not yet had its coolant changed. The owner had completed the 1,000-hour service but skipped the coolant, prompting questions about whether a simple drain and refill would suffice or if a full flush was necessary.
Drain vs. Flush Decision
A drain and refill is usually sufficient if:
The Bobcat S150 originally used purple propylene glycol coolant, which is less toxic and biodegradable. Switching to ethylene glycol requires a complete flush, as mixing the two can cause gel formation and blockages.
Recommendations:
Changing the coolant in a Bobcat S150 is a straightforward but essential task. For most machines with clean coolant history, a drain and refill using compatible propylene glycol is sufficient. A full flush is only necessary when contamination or coolant mixing is suspected. By following best practices and using the correct fluid, operators can ensure long-term cooling performance and protect engine components from premature wear.
The Bobcat S150 skid steer loader was introduced in the early 2000s as part of Bobcat’s mid-frame lineup, offering a rated operating capacity of 1,500 lbs and powered by a 2.0L Kubota V2203 diesel engine. Designed for versatility in construction, landscaping, and agriculture, the S150 featured a compact cooling system optimized for tight engine compartments and variable operating conditions.
The cooling system uses a pressurized radiator, thermostat-regulated flow, and a coolant reservoir. The factory fill typically includes a propylene glycol-based coolant, chosen for its lower toxicity and environmental friendliness compared to ethylene glycol.
When and Why to Change the Coolant
Coolant should be changed every 1,000 hours or every two years, whichever comes first. Over time, coolant degrades due to thermal cycling, oxidation, and contamination. Old coolant can lose its anti-corrosion properties, leading to scale buildup, cavitation, and eventual failure of water pumps or cylinder liners.
In one case, an S150 with 930 hours had not yet had its coolant changed. The owner had completed the 1,000-hour service but skipped the coolant, prompting questions about whether a simple drain and refill would suffice or if a full flush was necessary.
Drain vs. Flush Decision
A drain and refill is usually sufficient if:
- The coolant is still clean and free of debris
- No mixing of incompatible coolant types has occurred
- The machine has been regularly maintained
- The coolant is discolored, sludgy, or contains particulates
- Previous owners may have mixed ethylene and propylene glycol
- The machine has overheated or sat unused for extended periods
- Drain the old coolant completely
- Fill with distilled water and run the engine until warm
- Drain again and repeat until water runs clear
- Refill with compatible coolant
The Bobcat S150 originally used purple propylene glycol coolant, which is less toxic and biodegradable. Switching to ethylene glycol requires a complete flush, as mixing the two can cause gel formation and blockages.
Recommendations:
- Stick with Bobcat-branded propylene glycol or equivalent
- Use pre-mixed 50/50 coolant to avoid dilution errors
- Avoid universal coolants unless compatibility is confirmed
- Use a clean catch pan to inspect drained coolant for metal or oil contamination
- Replace the radiator cap if it shows signs of wear or corrosion
- Inspect hoses and clamps for leaks or soft spots
- Bleed air from the system after refill to prevent hot spots
Changing the coolant in a Bobcat S150 is a straightforward but essential task. For most machines with clean coolant history, a drain and refill using compatible propylene glycol is sufficient. A full flush is only necessary when contamination or coolant mixing is suspected. By following best practices and using the correct fluid, operators can ensure long-term cooling performance and protect engine components from premature wear.
