394411 778199 Thermostat for Johnson Evinrude | JLM Marine

Thermostat 143℉/62℃ for Johnson/Evinrude 2-Stroke Outboard Motors – Fits 65, 85, 100, 115, 135 HP

This precision-engineered thermostat (Vernatherm) is designed for Johnson and Evinrude 2-stroke outboard motors ranging from 65 HP to 135 HP. Operating at 143℉ (62℃), it ensures optimal engine temperature regulation for reliable performance across a wide range of model years and applications.

This aftermarket replacement directly replaces OEM part numbers 394411 and 778199, providing an exact fit for dozens of Johnson/Evinrude cylinder and crankcase assemblies from the mid-1980s through the mid-1990s.

• Operating Temperature: 143℉ / 62℃
• Type: Vernatherm design for precise temperature control
• Compatible with both Johnson and Evinrude 2-stroke outboards

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Johnson/Evinrude owners, here's a guide to help you identify your engine's serial/model: Johnson/Evinrude Serial Number Guide.

Technical Specifications

Package Contents

• 1 × Thermostat (Vernatherm) – 143℉/62℃

Installation Guide

1. Preparation: Allow the engine to cool completely and disconnect the battery to ensure safe working conditions.
2. Access the Thermostat Housing: Remove any cowling or covers obstructing access to the thermostat housing on the cylinder head.
3. Drain Coolant (if applicable): For water-cooled systems, drain a sufficient amount of coolant to prevent spillage when opening the housing.
4. Remove Housing Fasteners: Unscrew the bolts or clamps securing the thermostat housing cover. Keep hardware organized for reassembly.
5. Extract Old Thermostat: Carefully lift out the old thermostat, noting its orientation and position within the housing.
6. Clean Mating Surfaces: Thoroughly clean the housing and cover surfaces, removing old gasket material and debris to ensure a proper seal.
7. Install New Thermostat: Position the new thermostat in the same orientation as the original, ensuring the sensing element faces the correct direction.
8. Apply New Gasket/Sealant: Install a new gasket or apply marine-grade sealant as recommended by your engine manual.
9. Reassemble Housing: Replace the cover and tighten fasteners evenly in a crisscross pattern to the manufacturer's torque specification.
10. Refill Coolant: If coolant was drained, refill to the proper level and bleed air from the system according to service manual instructions.
11. Test Operation: Reconnect the battery, start the engine, and monitor for leaks and proper operating temperature. Check that the thermostat opens at the correct temperature.
12. Final Inspection: After a short test run, re-check all fasteners and inspect for any coolant seepage around the housing.

Troubleshooting & FAQ

How do I confirm this thermostat fits my specific engine?
Cross-reference your engine's model number and year with the compatibility table above. You can also verify the OEM part number (394411 or 778199) in your engine's parts diagram or service manual.

How often should I replace the thermostat?
Thermostats should be inspected annually and replaced every 2–3 years or if you notice overheating, erratic temperature readings, or sluggish warm-up. Regular replacement prevents corrosion buildup and ensures reliable temperature regulation.

What are the signs of a failing thermostat?
Common symptoms include engine overheating, failure to reach normal operating temperature, fluctuating temperature gauge readings, and poor fuel economy. If you observe any of these, test or replace the thermostat promptly.

Does this thermostat come with a gasket or seal?
Package contents vary; refer to the "Package Contents" section above. If a gasket is not included, we recommend purchasing one separately or using marine-grade sealant as specified in your service manual.

Can I install this on both Johnson and Evinrude engines?
Yes, this thermostat is designed to fit both Johnson and Evinrude 2-stroke outboards in the specified HP range and model years, as these brands share many interchangeable components.

Is this an OEM or aftermarket part?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.