2015 YAMAHA YZ250F engine coolant

CYLINDER HEAD
5-18
EAS1SM5215
CYLINDER HEAD
Removing the cylinder head
Order Part name Q’ty Remarks
Seat Refer to “GENERAL CHASSIS” on page 4-1.
Side cover (left/right) Refer to “GENERAL CHASSIS” on page 4-1.
Air scoop (left / right) Refer to “GENERAL CHASSIS” on page 4-1.
Fuel tank Refer to “FUEL TANK” on page 7-1.
Exhaust pipe and silencer Refer to “ENGINE REMOVAL” on page 5-1.
Radiator hose Disconnect.
Coolant temperature sensor coupler Disconnect.
Throttle body Refer to “THROTTLE BODY” on page 7-5.
Camshaft Refer to “CAMSHAFT” on page 5-11.
Upper engine bracket Refer to “ENGINE REMOVAL” on page 5-1.
1 Bolt (cylinder head) 2
2 Bolt (cylinder head) 4
3 Cylinder head 1
4 Cylinder head gasket 1
6
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
33 Nm (3.3 mkgf, 24 ftIbf)T.R
.
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.

CLUTCH
5-37
Removing the right crankcase cover
Order Part name Q’ty Remarks
Right engine guard Refer to “ENGINE REMOVAL” on page 5-1.
Engine oilDrain.
Refer to “CHANGING THE ENGINE OIL” on
page 3-15.
CoolantDrain.
Refer to “CHANGING THE COOLANT” on
page 3-8.
Brake pedal Refer to “ENGINE REMOVAL” on page 5-1.
Clutch cover Refer to “CLUTCH” on page 5-35.
1 Oil filter element cover 1
2 Oil filter element 1
3 Radiator pipe 2 1
4 Kickstarter lever 1
5 Right crankcase cover 1
6 Gaskets 1
7 Dowel pin 2
8Collar 1
For installation, reverse the removal proce-
dure.
T.R.
LS
New
New
67
2
5
4
1
7 8
New
3
LS
New
New
LS
NewNew
LT
LS

RADIATOR
6-1
EAS1SM5296
TIP
This section is intended for those who have basic knowledge and skill concerning the servicing of
Yamaha motorcycles (e.g., Yamaha dealers, service engineers, etc.). Those who have little knowl-
edge and skill concerning servicing are requested not to undertake inspection, adjustment, disas-
sembly, or reassembly only by reference to this manual. It may lead to servicing trouble and
mechanical damage.
EAS1SM5297
RADIATOR
Removing the radiator
Order Part name Q’ty Remarks
CoolantDrain.
Refer to “CHANGING THE COOLANT” on
page 3-8.
Seat Refer to “GENERAL CHASSIS” on page 4-1.
Side cover (left/right) Refer to “GENERAL CHASSIS” on page 4-1.
Air scoop (left / right) Refer to “GENERAL CHASSIS” on page 4-1.
Fuel tank Refer to “FUEL TANK” on page 7-1.
Air filter case Refer to “THROTTLE BODY” on page 7-5.
1 Radiator guard 2
2 Radiator hose clamp 8 Loosen.
11
12
New
New
New
LS
LS

WATER PUMP
6-4
EAS1SM5300
WATER PUMP
Removing the water pump
Order Part name Q’ty Remarks
CoolantDrain.
Refer to “CHANGING THE COOLANT” on
page 3-8.
Engine oilDrain.
Refer to “CHANGING THE ENGINE OIL” on
page 3-15.
Right crankcase cover Refer to “CLUTCH” on page 5-35.
1 Water pump housing 1
2 Dowel pin 2
3Gasket 1
4Washer 2
5Collar 1
6Gear 1
7Pin 1
8 Impeller shaft assembly 1
9 Oil seal 1
9
8
2
2
3
1
10
6
7
5
4
4
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
New
New
New
E
11
New
E
LS
LS

WATER PUMP
6-6
EAS1SM5301REMOVING THE OIL SEAL
TIP
• Remove the oil seal when the coolant level
changes frequently more than usual, coolant
has discolored, or engine oil has become
milky.
• Do not use the removed oil seal.
1. Remove:
• Oil seals “1”
EAS1SM5302CHECKING THE WATER PUMP
1. Check:
• Water pump housing cover
• Impeller shaft
Cracks/damage/wear  Replace.
EAS1SM5303CHECKING THE BEARING
1. Check:
• Bearing
Rotate the inner race with your finger.
Rough spot/seizure  Replace.
EAS1SM5304INSTALLING THE OIL SEAL
1. Install:
• Oil seals “1”
TIP
• Apply the lithium soap base grease on the oil
seal lip.
• Install the oil seal with its manufacture’s
marks or numbers facing the right crankcase
cover “2”.2. Install:
• Bearing “1”
TIP
Install the bearing by pressing its outer race
parallel.
EAS1SM5305ASSEMBLING THE WATER PUMP
1. Install:
• Impeller shaft assembly “1”
• Washer “2”
•Pin “3”
• Gear “4”
• Collar “5”
• Circlip “6”
TIP
• Take care so that the oil seal lip is not dam-
aged or the spring does not slip off its posi-
tion.
• When installing the impeller shaft, apply the
engine oil to the oil seal lip, the bearing, and
the impeller shaft.
1 1
New
1 1New
New
LS
LS
New
1
2
52346
New
E

FUEL INJECTION SYSTEM
8-11
1. Crankshaft position sensor
2. AC magneto
3. Rectifier/regulator
4. Joint connector
5. Condenser
7. Engine stop switch
8. Neutral switch
9. ECU
12.Fuel injector
13.Fuel pump
14.Intake air temperature sensor
15.Coolant temperature sensor
16.Throttle position sensor
17.Intake air pressure sensor

FUEL INJECTION SYSTEM
8-20
TIP
Make sure that the machine is completely cold before checking the coolant temperature sensor.
Fault code 21
Symptom Coolant temperature sensor: open or short circuit detected.
Fail-safe systemAble to start engine
Able to drive vehicle
Diagnostic code No.06
Diagnostic tool displayDisplays the coolant temperature.
ProcedureCompare the actually measured coolant temperature with the
Yamaha diagnostic tool display value.
Or-
derProbable cause of malfunc-
tion and checkMaintenance job Reinstatement method
1 Connection of coolant tem-
perature sensor coupler.
Check the locking condition
of the coupler.
Disconnect the coupler, and
check the pins (for bent or
broken terminals and locking
condition of the pins).Improperly connected 
Connect the coupler secure-
ly, or repair/replace the wire
harness.Turn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
2 Connection of wire harness
ECU coupler.
Check the locking condition
of the coupler.
Disconnect the coupler, and
check the pins (for bent or
broken terminals and locking
condition of the pins).Improperly connected 
Connect the coupler secure-
ly, or repair/replace the wire
harness.Turn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
3 Wire harness continuity. Open or short circuit  Re-
place the wire harness.
Between coolant temperature
sensor coupler and ECU cou-
pler.
green/white–green/white
black/blue–black/blueTurn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
4 Mounted condition of coolant
temperature sensor.
Check for looseness or
pinching.
Check the mounted condition
for correctness.Improperly mounted sensor
 Remount or replace the
sensor.Turn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
5 Defective coolant tempera-
ture sensor.Execute the diagnostic mode.
(Code No. 06)
When the machine is cold,
displayed temperature is
close to the ambient temper-
ature.
Improper display  Replace
the coolant temperature sen-
sor.Turn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
6 Faulty ECU Replace the ECU.

TROUBLESHOOTING
9-2
3. Ignition system
• Faulty ECU
• Faulty crankshaft position sensor
• Broken generator rotor woodruff key
EAS1SM5355POOR MEDIUM-AND-HIGH-SPEED PER-
FORMANCE
Refer to “STARTING FAILURES” on page 9-1.
Engine
1. Air filter
• Clogged air filter element
Fuel system
1. Fuel pump
• Faulty fuel pump
2. Throttle body
• Defective throttle body
3. ECU
• Faulty ECU
EAS1SM5356FAULTY GEAR SHIFTING
Shifting is difficult
Refer to “CLUTCH” on page 5-35.
EAS1SM5357SHIFT PEDAL DOES NOT MOVE
Shift shaft
• Bent shift shaft
Shift drum and shift forks
• Foreign object in a shift drum groove
• Seized shift fork
• Bent shift fork guide bar
Transmission
• Seized transmission gear
• Foreign object between transmission gears
• Improperly assembled transmission
EAS1SM5358JUMPS OUT OF GEAR
Shift shaft
• Incorrect shift pedal position
• Improperly returned stopper lever
Shift forks
• Worn shift fork
Shift drum
• Incorrect axial play
• Worn shift drum groove
Transmission
• Worn gear dog
EAS1SM5359FAULTY CLUTCH
Clutch slips
1. Clutch
• Improperly assembled clutch
• Loose or fatigued clutch spring
• Worn friction plate
• Worn clutch plate
2. Engine oil
• Incorrect oil level
• Incorrect oil viscosity (low)
• Deteriorated oil
Clutch drags
1. Clutch
• Unevenly tensioned clutch springs
• Warped pressure plate
• Bent clutch plate
• Swollen friction plate
• Bent clutch push rod
• Damaged clutch boss
• Burnt primary driven gear bushing
2. Engine oil
• Incorrect oil level
• Incorrect oil viscosity (high)
• Deteriorated oil
EAS1SM5360OVERHEATING
Engine
1. Cylinder head and piston
• Heavy carbon buildup
• Clogged coolant passages
2. Engine oil
• Incorrect oil level
• Incorrect oil viscosity
• Inferior oil quality
Cooling system
1. Coolant
• Low coolant level
2. Radiator
• Damaged or leaking radiator
• Faulty radiator cap
• Bent or damaged radiator fin
3. Water pump
• Damaged or faulty water pump
• Damaged hose
• Improperly connected hose
• Damaged pipe
• Improperly connected pipe