1999 SUBARU LEGACY overheating

TROUBLE PROBLEM PARTS, ETC. POSSIBLE CAUSE RANK
4) Engine stalls after initial
combustion.Fuel injection system A
IIntake systemILoosened or cracked intake uct B
ILoosened or cracked PCV hose C
ILoosened or cracked vacuum hose C
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDirty air cleaner element C
IFuel lineIClogged fuel line C
ILack of or insufficient fuel B
IBeltIDefective B
IDefective timing B
ICompressionIIncorrect valve clearance C
ILoosened spark plugs or defective gasket C
ILoosened cylinder head bolts or defective gasket C
IImproper valve seating C
IDefective valve stem C
IWorn or broken valve spring B
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing B
IImproper engine oil (low viscosity) B
2. Rough idle and engine stall Fuel injection system A
IIntake systemILoosened or cracked intake duct A
ILoosened or cracked PCV hose A
ILoosened or cracked vacuum hose A
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDefective PCV valve C
ILoosened oil filter cap B
IDirty air cleaner element C
IFuel lineIDefective fuel pump and relay C
IClogged fuel line C
ILack of or insufficient fuel B
IBeltIDefective timing C
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket B
ILoosened cylinder head bolts or defective gasket B
IImproper valve seating B
IDefective valve stem C
IWorn or broken valve spring B
IWorn or stuck piston rings, cylinder and piston B
IIncorrect valve timing A
IImproper engine oil (low viscosity) B
ILubrication systemIIncorrect oil pressure B
IDefective rocker cover gasket C
ICooling systemIOverheating C
IOthersIMalfunction of evaporative emission control system A
IStuck or damaged throttle valve B
IAccelerator cable out of adjustment C
74
2-3a[K100]DIAGNOSTICS
1. Engine Trouble in General

TROUBLE PROBLEM PARTS, ETC. POSSIBLE CAUSE RANK
3. Low output, hesitation and
poor accelerationIFuel injection system A
IIntake systemILoosened or cracked intake duct A
ILoosened or cracked PCV hose A
ILoosened or cracked vacuum hose B
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDefective PCV valve B
ILoosened oil filter cap B
IDirty air cleaner element A
IFuel lineIDefective fuel pump and relay B
IClogged fuel line B
ILack of or insufficient fuel C
IBeltIDefective timing B
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket B
ILoosened cylinder head bolts or defective gasket B
IImproper valve seating B
IDefective valve stem C
IWorn or broken valve spring B
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing A
IImproper engine oil (low viscosity) B
ILubrication systemIIncorrect oil pressure B
ICooling systemIOverheating C
IOver cooling C
IOthersIMalfunction of evaporative emission control system A
4. SurgingIFuel injection system A
IIntake systemILoosened or cracked intake duct A
ILoosened or cracked PCV hose A
ILoosened or cracked vacuum hose A
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDefective PCV valve B
ILoosened oil filter cap B
IDirty air cleaner element B
IFuel lineIDefective fuel pump and relay B
IClogged fuel line B
ILack of or insufficient fuel C
IBeltIDefective timing B
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket C
ILoosened cylinder head bolts or defective gasket C
IImproper valve seating C
IDefective valve stem C
IWorn or broken valve spring C
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing A
IImproper engine oil (low viscosity) B
ICooling systemIOverheating B
IOthersIMalfunction of evaporative emission control system C
75
[K100]2-3aDIAGNOSTICS
1. Engine Trouble in General

TROUBLE PROBLEM PARTS, ETC. POSSIBLE CAUSE RANK
5. Engine does not return to
idle.Fuel injection system A
IIntake systemILoosened or cracked vacuum hose A
IOthersIStuck or damaged throttle valve A
IAccelerator cable out of adjustment B
6. Dieseling (Run-on)IFuel injection system A
ICooling systemIOverheating B
IOthersIMalfunction of evaporative emission control system B
7. After burning in exhaust
systemIFuel injection system A
IIntake systemILoosened or cracked intake duct C
ILoosened or cracked PCV hose C
ILoosened or cracked vacuum hose B
IDefective PCV valve B
ILoosened oil filter cap C
IBeltIDefective timing B
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket C
ILoosened cylinder head bolts or defective gasket C
IImproper valve seating B
IDefective valve stem C
IWorn or broken valve spring C
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing A
ILubrication systemIIncorrect oil pressure C
ICooling systemIOver cooling C
IOthersIMalfunction of evaporative emission control system C
8. KnockingIFuel injection system A
IIntake systemILoosened oil filter cap B
IBeltIDefective timing B
ICompressionIIncorrect valve clearance C
IIncorrect valve timing B
ICooling systemIOverheating A
9. Excessive engine oil con-
sumptionIIntake systemILoosened or cracked PCV hose A
IDefective PCV valve B
ILoosened oil filter cap C
ICompressionIDefective valve stem A
IWorn or stuck piston rings, cylinder and piston A
ILubrication systemILoosened oil pump attaching bolts and defective
gasketB
IDefective oil filter seal B
IDefective crankshaft oil seal B
IDefective rocker cover gasket B
ILoosened oil drain plug or defective gasket B
ILoosened oil pan fitting bolts or defective oil pan B
76
2-3a[K100]DIAGNOSTICS
1. Engine Trouble in General

TROUBLE PROBLEM PARTS, ETC. POSSIBLE CAUSE RANK
4) Engine stalls after initial
combustion.IFuel injection system A
IIntake systemILoosened or cracked intake duct B
ILoosened or cracked PCV hose C
ILoosened or cracked vacuum hose C
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDirty air cleaner element C
IFuel lineIClogged fuel line C
ILack of or insufficient fuel B
IBeltIDefective B
IDefective timing B
ICompressionIIncorrect valve clearance C
ILoosened spark plugs or defective gasket C
ILoosened cylinder head bolts or defective gasket C
IImproper valve seating C
IDefective valve stem C
IWorn or broken valve spring B
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing B
IImproper engine oil (low viscosity) B
2. Rough idle and engine
stallIFuel injection system A
IIntake systemILoosened or cracked intake duct A
ILoosened or cracked PCV hose A
ILoosened or cracked vacuum hose A
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDefective PCV valve C
ILoosened oil filler cap B
IDirty air cleaner element C
IFuel lineIDefective fuel pump and relay C
IClogged fuel line C
ILack of/or insufficient fuel B
IBeltIDefective timing C
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket B
ILoosened cylinder head bolts or defective gasket B
IImproper valve seating B
IDefective valve stem C
IWorn or broken valve spring B
IWorn or stuck piston rings, cylinder and piston B
IIncorrect valve timing A
IImproper engine oil (low viscosity) B
ILubrication systemIIncorrect oil pressure B
IDefective rocker cover gasket C
ICooling systemIOverheating C
IOthersIMalfunction of evaporative emission control system A
IStuck or damaged throttle valve B
IAccelerator cable out of adjustment C
72
2-3b[K100]DIAGNOSTICS
1. Engine Trouble in General

TROUBLE PROBLEM PARTS, ETC. POSSIBLE CAUSE RANK
3. Low output, hesitation
and poor accelerationIFuel injection system A
IIntake systemILoosened or cracked intake duct A
ILoosened or cracked PCV hose A
ILoosened or cracked vacuum hose B
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDefective PCV valve B
ILoosened oil filler cap B
IDirty air cleaner element A
IFuel lineIDefective fuel pump and relay B
IClogged fuel line B
ILack of/or insufficient fuel C
IBeltIDefective timing B
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket B
ILoosened cylinder head bolts or defective gasket B
IImproper valve seating B
IDefective valve stem C
IWorn or broken valve spring B
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing A
IImproper engine oil (low viscosity) B
ILubrication systemIIncorrect oil pressure B
ICooling systemIOverheating C
IOver cooling C
IOthersIMalfunction of evaporative emission control system A
4. SurgingIFuel injection system A
IIntake systemILoosened or cracked intake duct A
ILoosened or cracked PCV hose A
ILoosened or cracked vacuum hose A
IDefective intake manifold gasket B
IDefective throttle body gasket B
IDefective PCV valve B
ILoosened oil filler cap B
IDirty air cleaner element B
IFuel lineIDefective fuel pump and relay B
IClogged fuel line B
ILack of/or insufficient fuel C
IBeltIDefective timing B
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket C
ILoosened cylinder head bolts or defective gasket C
IImproper valve seating C
IDefective valve stem C
IWorn or broken valve spring C
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing A
IImproper engine oil (low viscosity) B
ICooling systemIOverheating B
IOthersIMalfunction of evaporative emission control system C
73
[K100]2-3bDIAGNOSTICS
1. Engine Trouble in General

TROUBLE PROBLEM PARTS, ETC. POSSIBLE CAUSE RANK
5. Engine does not return
to idle.IFuel injection system A
IIntake systemILoosened or cracked vacuum hose A
IOthersIStuck or damaged throttle valve A
IAccelerator cable out of adjustment B
6. Dieseling (Run-on)IFuel injection system A
ICooling systemIOverheating B
IOthersIAccelerator cable out of adjustment B
7. After burning in exhaust
systemIFuel injection system A
IIntake systemILoosened or cracked intake duct C
ILoosened or cracked PCV hose C
ILoosened or cracked vacuum hose B
IDefective PCV valve B
ILoosened oil filler cap C
IBeltIDefective timing B
ICompressionIIncorrect valve clearance B
ILoosened spark plugs or defective gasket C
ILoosened cylinder head bolts or defective gasket C
IImproper valve seating B
IDefective valve stem C
IWorn or broken valve spring C
IWorn or stuck piston rings, cylinder and piston C
IIncorrect valve timing A
ILubrication systemIIncorrect oil pressure C
ICooling systemIOver cooling C
IOthersIMalfunction of evaporative emission control system C
8. KnockingIFuel injection system A
IIntake systemILoosened oil filler cap B
IBeltIDefective timing B
ICompressionIIncorrect valve clearance C
IIncorrect valve timing B
ICooling systemIOverheating A
9. Excessive engine oil
consumptionIIntake systemILoosened or cracked PCV hose A
IDefective PCV valve B
ILoosened oil filler cap C
ICompressionIDefective valve stem A
IWorn or stuck piston rings, cylinder and piston A
ILubrication systemILoosened oil pump attaching bolts and defective gasket B
IDefective oil filter seal B
IDefective crankshaft oil seal B
IDefective rocker cover gasket B
ILoosened oil drain plug or defective gasket B
ILoosened oil pan fitting bolts or defective oil pan B
74
2-3b[K100]DIAGNOSTICS
1. Engine Trouble in General

E: INSPECTION
Check electrodes and inner and outer porcelain of
plugs, noting the type of deposits and the degree
of electrode erosion.
G6M0086
1) Normal
Brown to grayish-tan deposits and slight electrode
wear indicate correct spark plug heat range.
G6M0087
2) Carbon fouled
Dry fluffy carbon deposits on insulator and elec-
trode are mostly caused by slow speed driving in
city, weak ignition, too rich fuel mixture, dirty air
cleaner, etc.
It is advisable to replace with plugs having hotter
heat range.
G6M0088
3) Oil fouled
Wet black deposits show excessive oil entrance
into combustion chamber through worn rings and
pistons or excessive clearance between valve
guides and stems. If same condition remains after
repair, use a hotter plug.
G6M0089
4) Overheating
White or light gray insulator with black or gray
brown spots and bluish burnt electrodes indicate
engine overheating. Moreover, the appearance
results from incorrect ignition timing, loose spark
plugs, wrong selection of fuel, hotter range plug,
etc. It is advisable to replace with plugs having
colder heat range.
G6M0090
33
[W3E0]6-1SERVICE PROCEDURE
3. Spark Plug