Thermostat For Honda TRX420 Rancher And TRX500 Fourtrax Foreman 2003 To 2018 Direct Fit Cooling Component

This thermostat is a precise, direct-fit cooling component for Honda ATVs in the TRX420 Rancher and TRX500 Fourtrax Foreman families, spanning model years roughly 2003 through 2018. It ensures the engine reaches and holds the optimal operating temperature by opening at the correct coolant temperature, helping prevent overheating and excessive fan activity in tough trail or farm conditions. A proper thermostat swap restores reliable warmups, steady idle, and consistent cooling under load, reducing the risk of coolant boil and thermal stress on the engine.

Built as a robust aftermarket replacement, this unit is designed to mirror OEM performance with durable construction and reliable operation in dusty, heat-soaked environments. It’s a value-focused upgrade that delivers consistent temperature control across a wide range of Honda TRX420 Rancher and TRX500 Foreman variants, making it a dependable choice for riders who depend on their ATV in demanding conditions. The part number pairing 19300-HN8-003 and 19300-HN8-305 reflects proven OEM references echoed in aftermarket cross-compatibility, ensuring a familiar fit and function for trail, farm, and utility use.

Comprehensive Vehicle Fitment

Product Specifications

OEM & Aftermarket Cross-Reference Information

What's Included

Included in the box:

• Thermostat

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Engineered to drop in with Honda TRX420 Rancher and TRX500 Foreman models for quick, hassle-free service.
• OEM Cross-Reference: Backed by Honda OEM references 19300-HN8-003 and 19300-HN8-305 for confidence in fitment.
• Premium Materials: Built to endure high-heat coolant cycles and dusty, outdoor work environments.
• Performance Restoration: Restores proper temperature regulation, reducing overheating and excessive fan operation.
• Reliability in Harsh Conditions: Suited for trails, fields, and work-sites where engine temps swing quickly.
• Easy Installation: Designed for straightforward replacement with standard coolant-drain and reassembly steps.

Installation Notes:

• Safety first: Disconnect the battery and allow the engine to cool before servicing the cooling system.
• Coolant management: Drain or partially drain coolant from the radiator to relieve pressure before removing the thermostat housing.
• Access & orientation: Remove the thermostat housing and hoses; note the correct orientation of the thermostat before installation.
• Seating surface: Clean all mating surfaces free of old gasket material, corrosion, and debris to ensure a proper seal.
• Seat & seal: Install the thermostat with the correct orientation to align the valve and spring; replace any gasket if included with the kit or use a compatible gasket sealant per OEM guidelines.
• System bleed & test: Refill coolant, bleed air from the system, and start the engine to verify a steady temperature rise and absence of leaks; monitor for proper fan operation at normal operating temperature.

Why Upgrade?

Running a worn or failing thermostat can allow the engine to overheat, shorten warm-up times, and cause erratic cooling fan cycling. Replacing with this unit restores reliable temperature regulation, protecting the engine from heat-induced wear and helping maintain consistent performance in demanding riding or work conditions.