Coolant Temperature Sensor Location and Coolant Type

[MikePhua]

Overview of the Cat 301.8 and Perkins Engine
The 2002 Cat 301.8 mini excavator is part of Caterpillar’s early compact‑equipment lineup, powered by a small Perkins diesel engine known for reliability, simplicity, and low fuel consumption. During the early 2000s, Caterpillar sold tens of thousands of compact excavators globally, and many of them used Perkins engines due to their proven performance in harsh climates and municipal operations. These engines rely on a basic electrical system, including a coolant temperature sensor that feeds data to the machine’s gauge cluster.
When the temperature gauge stops working, the most common cause is a failed coolant temperature sensor. Replacing it is straightforward—once the sensor is located.

Locating the Coolant Temperature Sensor
The coolant temperature sensor on the Perkins engine used in the Cat 301.8 is threaded into the engine block or thermostat housing. Because the engine compartment is compact and components are tightly packaged, the sensor can be difficult to spot at first glance.
Terminology Note 
Coolant temperature sensor: A thermistor‑based device that measures engine coolant temperature and sends a signal to the gauge.
Thermostat housing: The metal housing that contains the thermostat and directs coolant flow.
Threaded sender: A screw‑in sensor with an electrical connector on top.
Once located, the sensor can be removed with a standard wrench. The replacement part threads into the same port and reconnects to the existing wiring harness.
The retrieved content confirms that the owner eventually found and replaced the sensor successfully.

Choosing the Correct Coolant Type
After replacing the sensor, the next question was which coolant to use. The operator’s manual only states “extended life coolant,” which can be confusing because extended‑life coolants come in several colors and formulations.
A knowledgeable technician clarified that ELC (Extended Life Coolant) is compatible with most long‑life coolants on the market, with one major exception: Dex‑Cool should be avoided.
Terminology Note 
ELC: Extended Life Coolant, typically red or orange, formulated with organic acid technology (OAT) for long service intervals.
EC‑1: Caterpillar’s specification for extended‑life coolant.
ASTM D4985: An industry standard for heavy‑duty engine coolant performance.
These specifications ensure corrosion protection for aluminum, cast iron, and mixed‑metal cooling systems.

Why Dex‑Cool Should Be Avoided
Dex‑Cool, originally developed for automotive applications, can cause problems in heavy‑equipment cooling systems:

• It may react poorly with certain gasket materials
  
• It can form sludge if mixed with non‑OAT coolants
  
• It is sensitive to air exposure, which can occur in machines with small coolant reservoirs
  

A municipal fleet manager once reported that several Perkins‑powered machines developed gelled coolant after a contractor topped them off with Dex‑Cool. The repair required a full system flush and replacement of several hoses.

Understanding Coolant Color and Compatibility
Coolant color is not a reliable indicator of chemistry. For example:

• Red coolant may be ELC
  
• Orange coolant may be Dex‑Cool or ELC
  
• Yellow coolant may be hybrid OAT
  
• Green coolant may be conventional ethylene glycol
  

Because of this, the safest approach is to:

• Use coolant that meets EC‑1 or ASTM D4985
  
• Avoid mixing coolant types
  
• Flush the system completely if switching formulations
  

A complete flush ensures that old coolant does not contaminate the new mixture, preserving long‑term corrosion protection.

Maintenance Tips for the Cooling System
To keep the Cat 301.8 running reliably:

• Inspect hoses for cracks or swelling
  
• Check coolant level regularly
  
• Replace the thermostat if the engine runs too cool or overheats
  
• Clean the radiator fins to maintain airflow
  
• Use distilled water when mixing coolant
  
• Replace coolant at recommended intervals
  

A well‑maintained cooling system prevents overheating, protects the engine block, and ensures accurate temperature readings.

Historical Context of Perkins Engines in Compact Equipment
Perkins has been a major supplier of small diesel engines since the 1930s. By the early 2000s, Perkins engines powered millions of machines worldwide, including generators, agricultural tractors, and compact excavators. Their engines were known for:

• Mechanical simplicity
  
• Easy field service
  
• Long service life
  
• Global parts availability
  

Caterpillar’s acquisition of Perkins strengthened the integration of these engines into Cat’s compact equipment lineup.

Conclusion
Locating and replacing the coolant temperature sensor on a Cat 301.8 with a Perkins engine is a straightforward task once the sensor is identified. Choosing the correct coolant is equally important. Extended‑life coolant meeting EC‑1 or ASTM D4985 specifications is recommended, while Dex‑Cool should be avoided. With proper coolant selection and routine maintenance, the cooling system will continue to protect the engine and ensure accurate temperature readings for years to come.