John Deere 9.0 L Diesel Engines — Remove and Test Thermostats
Maintenance · Cooling system thermostats
For the John Deere 9.0 L Diesel Engines, from the John Deere service manual.
Applies to: John Deere 6090H engine
Before you start
- Do not drain coolant until coolant temperature is below operating temperature. Always loosen cooling system filler cap, radiator cap or drain valve slowly to relieve pressure.
Procedure
- Visually inspect the area around the coolant manifold for leaks; partially drain coolant from the cooling system.
- Remove thermostat cover with gasket.
- Remove thermostats.
- Inspect thermostats for debris or damage.
- Test each thermostat using an approved testing procedure; they should start to open within specification.
- If either thermostat fails to open within this range, replace both thermostats as a set.
Tools required
- thermostat test equipment Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Thermostat 82°C (180°F) — opening temperature 80—84°C (175—182°F)
Full service-parts list: John Deere 6090H engine →
Source: John Deere service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.