heating DATSUN 210 1979 Service Manual

Condition

ENGINE
POWER
NOT

UP

TO
NORMAL

Low

compmsion

Ignition
system
out
of

order

Fuel

system
out
of

order

Air
intake

system
out

of

order

Emission
control

Overheating

J

f
H
r

Overcooling
Engine
liune
up

Probable
cause

Malfunction
of
throttle
valve
switch
and

linkage
FU

models

Incorrect

ignition
timing

Damaged

spark
plugs

Wom
distributor

points

Malfunction
of

T
C
S

cMalfunction
of
S
D
V

Milfunction
of
choke

system

Clogged
fuel

pipe
or

floating
valve

Dirty
or

clogged
fuel
filter

Fuel

pump
will
not
work

properly

Clogged
carb

retor

jets

Clogged
air
cleaner

Air

aling
from
manifold

g
sket
r

carburetor

gasket

Malfunction
of
E

G
R
valve

Stick
E

F
E
valve
shaft

Insufficient
coolant

Loose
fan
bel

Wom
or
oiled
fan
belt

Inoperative
therinostat

Wom
ater

pu
p

Clogged
or
leaky
radiator

Wom
radiator
filler

ca

Air
in

cooling
ystein

Improper
engine
oil

grade

Incorrect

ignition
timing

Clogged
carburetor

lean
miiture

Inoperative
thermostat

1

ET
19
Corrective
action

Check
throttle
valve
switch
and

linkage

Adjusi
i
r

replace
if

necessary

Previously
m
entioned

Adjust

Clean

adjust
or

replace
plugs

Dress
or

replace
points
Also
check

condenser

Check
and

correct

Check
and

replace

Adjust

Clean

Replace

Repair
or

replace

t
J
Disassemble
and
clean

Replace
element

Replace

gasket

Check
and

replace

Repair

Replenish

Adjust
fan
belt

Replace

Replace

Repl
ce

Flush

repair
or

replace

ReplaCe

Retightin
e
ch

part
of

cooling
system

Replace
with

proper
grade
oil

Adjust

Overhaui
carburetor

Replace

VALVE

GUIDE

Measure
the

clearance
between

valve

guide
and
valve

stern
If

the

clearance
exceeds
the

specified
limit

replace
the
worn

parts
or
both
valve

and
valve

guide
In
this

case
it
is

essential
to
determine
if
such
a
clear

ance
has

been
caused

by
a
worn
or

bent
valve
stem

or

by
a
worn
valve

guide

Determining
clearance

Precise
measurement
of
clearance

between
valve

stem
and

valve

guide

needs
the

aid
of
a
micrometer

and
a

telescope
hole

gauge
By
using
these

gauges
check
the
diameter
of
valve

stem
in

three

places
top
center
and

bottom

EM030

Fig
EM
22

Checking
Valve
Stem

Diameter

Insert

telescope
hole

gauge
in

valve

guide
bore

measuring
at
center

Subtract
the

highest
reading
of

valve
stem
diameter
from
valve

guide

bore
to
obtain
the
stem
to

guide

clearance

As

an

expedient
a
valve
is

pushed

in

valve

guide
and
moved
to
the

right

and
left
If
its

tip
deflects

beyond
the

specified
limit
there
it
will
be
known

that
the
clearance
between
stem
and

guide
exceeds
the
maximum
limit

Max
allowabl

deflection

0
2

mm
0
008
in

Max
tolerance

Stem
to

guide
clearance

0
1

mm
10
004
in

ote
Valve
sbould
be
moved
in

paraIlel
with
rocker
ann
General

ly
a

large
amount
of
wear
occurs
in

this
direction
Engine
Mechanical

Max
deflection
limit

Unit

mm
in

EM467

Mea6uring
Clearance

between
Valve
Stem

and
Valve
Guide
Fig
EM
23

Replacement
of
valve

julde

I
To
remove
old

guides
use
a
drift

and

a

pie
and
drive
them
out
of

rocker

cover
side
toward
combustion

chamber

Heating
cylinder
head
to
I

SO

to
200
C
302
to
392
F
will
facili

tate

operation

T11033000

EM468

1
II

Fig
EM

24

Driving
Valve
Guide
out

of

Cylinder
Head

2

Ream
cylinder
head
valve

guide

hole

using
Reamer
STlI081000

12
2

mrn
0
480
in

dia
at
room

tempera

ture

3

Carefully
press
service

Valve

guide

into

cylinder
head

guide
hole
It
will

fit

smoothly
after

heating
cylinder

head
to
ISO
to
200
302
to
392

F

4
Ream

bore
with
valve

guide
press

ed

in

using
Reamer
STll0320000
8

mm
0
31
in
dia

Reaming
bore

8
000

to
8
015

mm

0
3150
to
0
3156
in

EM
6
EM470

Fig
EM
25

Reaming
Valve
Guide

5

Correct
va1ve
seat
surface
with

new
valve

guide
as
the
axis

VALVE
SEAT

Check

valve
seat
for
evidence
of

pitting
at
valve

contact
surface

and

reface
or

replace
if
worn

excessively

Valve
seat
insert

of
0
5

mm
0
020

in
oversize

is
available
for
service

Refaclng
valve
seat

When
width
of
valve
seat
is

wide
or

narrow

beyond

specifications
it

should
be
refaced
with
valve
seat
with

cutter
or

grinding
stone

iIT11670000

EM411

Fig
EM
26

Refacing
Valve

Seat
with

Valve

Seat
Cutter

Replaclna
valve
seat
Insert

I

Old
insert
can
be

removed

by

boring
out
until
it

collapses
Machine

depth
stopper
should
be
set
So
that

boring
cannot
continue

beyond
the

bottom
face
of
the
insert
recess
in

cylinderhead

2
Machine

cylinder
head
recess
in

concentric
circles
to
valve

guide
center

so
that
insert
will
have
correct
fit

3
Ream

cylinder
head
recess
at

room

temperature

4
Heat

cylinder
head
to

tempera

ture
of
150
to
200

C
302
to
3920F

Condition

Waterpurnp

knocking

II
Othw

mllChani

troubl

Stuck

valve

Seized
valve

seat

Excessively
wom

cylinder
and

piston
Engine
Mechanical

Probab
Ie
cause

Improper
shaft
end

play

Broken

impeller

Improper
valve
clearance

Insufficient
clearance
between
valve
stem
and

guide

Weakened
or
broken
valve

pring

Biting
or

damage
of
valve
stem

Poor
fuel

quality

Il1
prop
r
valve
clearance

Weakened
valve

pring

Thin
valve
head

edge

Narrow
valve

seat

Overheating

Over

speeding

Sticked
valve

guide

Shortage

ofengine
oil

Dirty
engine
oil

Poor
oil

quality

Overheat

Wrong
assembly
of

piston
with

connecting
rod

Improper
piston
ring
clearance

Dirty
air
cleaner

Too
rich
mixture

Engine
over
run

Stuck
choke
valve

Over

choking

EM
32
Corrective

action

Replace

Replace

Adjust

Clean
stem
or
ream
the

guide

Replace

Repil
ce
or
clean

Use

good
fuel

Adjust

Replace

Replace
valve

Reface

Repair
or

replace

Drive
at

proper
speed

Repair

Add
or

replace
oil

Check
oil
level
on

daily
basis

Clean
crankcase

replace
oil
and
re

place
oil
ftIter
element

Use

proper
oil

Repair
or

replace

Repair
or

replace

Adjust

Clean

periodically

Adju
t

Drive

correctly

Clean
and

adjust

Start
in
correct

way

Condition

Loss
of

water

Poor
circulation

Corrosion

Overheating

Over

cooling
Cooling
System

TROUBLE
DIAGNOSES
AND
CORRECTIONS

Probable
cause

Damaged
radiator
seams

Leaks

at
heater
connections

or
plugs

Leak
at

water

temperature
gauge

Loose

joints

Damaged
cylinder
head

gasket

Cracked

cylinder
block

Cracked

cylinder
head

Loose

cylinder
head
bolts

Restriction
in

system

Insufficient
coolant

Inoperative
water

pump

Loose
fan
belt

Inoperative
thermostat

Excessive

impurity
in
water

Infrequent
flushing
and

draining
of

system

Inoperative
thermostat

Radiator
fin
choked
with
mud
chaff
etc

Incorrect

ignition
and
valve

timing

Dirty
oil
and

sludge
in

engine

Inoperative
water

pump

Inoperative
torque
coupling
or

tem

coupling

Loose
fan
belt

Restricted
radiator

Inaccurate

temperature
gauge

Impurity
in
water

Inoperative
thermostat

Inaccurate

temperature
gauge

CO
7
Corrective
action

Repair

Repair

Tighten

Tighten

Replace

Check

engine
oil
for

contamination
and
reml

as

necessary

Replace

Check

engine
oil
in

crankcase
for

mixing

with
water

by
pulling
oil

level

gauge

Replace

Tighten

Check
hoses
for

crimps
and
clear
the

system

of
rust
and

sludge
by
flushing
radiator

Replenish

Replace

Adjust

Replace

Use
soft
clean
water
rain

water
is
satis

factory

Cooling
system
should
be
drained
and
flush

ed

thoroughly
at
least
twice
a

year

Permanent
antifreeze

Ethylene
glycol
base

can
be

used

throughout
the

seasons
of
the

year
and

change

periodically
at

intervals

recommended

Replace

Clean
out
air

passage
thoroughly
by
using
air

pressure
from

engine
side
of
radiator

Adjust

Refill

Replace

Replace

Adjust

Flush

radiator

Replace

Use
soft
dean
water

Replace

Replace

Emission
Control

System

EARLY
FUEL
EVAPORATIVE
E
FE

SYSTEM

DESCRIPTION

@
jl
D

W

o

0
0
UL
@

1

Intake
manifold

9
Screw

2

Stove

gasket
10

Thermostat

spring

3
Mar
fold
stove
11

Heat
control
valve

4
Heat
shield

plate
12
Control

valve
shaft

5

Snap
ring
13
Exhaust

manifold

6

Countczwcight
14

Cap

7

Key
15

Bushing

8

Stopper
pin
16

Coil
spring

The

early
fuel

evaporative
system
is

provided
with
a
chamber
above
a

manifold
stove
mounted
between
the

intake
and
exhaust

manifolds

During

engine
warming
up
air

fuel
mixture
in

the
carburetor
is

heated
in

the
cham

ber

by
exhaust

gas
This
reuslts
in

improved
evaporation
of
atomized
fuel

droplets
in

the
mixture

and
in

smaller

content
of

hydrocarbons

HC
in
the

exhaust

gas

especially
in
cold
weather

operation

OPERATION

The

counterweight
rotates
counter

clockwise
and

stops
at

the

stopper
pin

mounted
on

the
exhaust
manifold

while
the

engine

temperature
is
low

With
this
condition

the
heat
control

valve
is
in

the

fully
closed

position

obstructing
the
flow

of
exhaust

gas
As

engine

temperature
goes

up
and
the

ambient

temperature
becomes

high

enough
to
actuate

the
thermostat

spring
the

counterweight

begins
to
j

@

l

7

1
1

5

If

@

I

Exhaust
gas
flows

valve
dosed

valve

opened

EC247

Fig
EC

8
Early
Fuel

Eaaporatiae
E
F
E

System

rotate
clockwise
and

again
comes
into

contact

with
the

stopper
pin
With
this

condition
the

heat
control
valve
is
in
the

full

open
position
and
exhaust

gas

passes
through
the

exhaust
manifold

without

heating
the
manifold
stove

REMOVAL
AND
INSTALLATION

1

Snap
ring

2
Lock
bolt

3

Key

4

Counterweight

5
Thermosta
t

spring

6
Coil

spring

7

Heat
controlvalve

EC913
8
Valve
shaft

Fig
EC

9
KF
E

Sy
tem
Component

EC

8

following
functions
without

affecting

the

effectiveness
of
the

exhaust
emis

sion
control

system

Minimizes
exhaust

gas
tempera

ture
rise

2
Minimizes

horsepower
losses
reo

sulting
from
air

injection
into
the

exhaust

system

3

Protects

pump
from
excessive

back

pressure

To
carburetor

air
cleaner

Secondary

ir

Not
actuated

To
carburetor

air
cleaner
J

l
Secondary

sir

Actuated

EC294

Fig
EC
18
Air

Pump
Relief
Valve

c
A
C
valve

Californiamodels

The
C
A
C
valve

controls
the

quantity
of

secondary
air
fed
from
the

air

pump
according
to
the
load
condi

tion
and
it

discharges
the

secondary

air
into
the

atmosphere
to

prevent

overheating
of

the

catalytic
converter

This
valve
is

operated
by
intake

manifold
vacuum

and
air

pump
dis

charge

pressure
When
intake
manifold

vacuum
is

small
or
in

the

high
load

range
the
No
2
valve

opens
when
it
is

great
or
in

the
low
load

range
the
No

I

valve

opens
If
air

pump
discharge

pressure
is

large
or
the

engine
is

running
at
a

high
speed
the
No
3

valve

opens
admitting
the
air

pump

discharge

pressure
to
the
No
2
dia

phragm
chamber
of
the
C

A
C
valve
mission
Control

System

and

opening
ihe
No
i
valve
At
this

point
the
No
2
valve

serves
as
a

relief

valve

F
111

air
pump
No
3

valve

EC787

Fig
EC
19

C
A
C
Valve

I
Engine
in
low

speed
and

light
load

When
the

engine
is

operating
under

these
conditions
intake
vacuum
is

high
The
No
2
valve
unitized

with

the
No
I

diaphragm
is

lifted

by
the

intake

manifold
vacuum

pushing
up

the
No
I

valve
These
valves
will
then

stop
at
a

position
where
a

balanced

condition
exists
between
air

pump

discharge
pressure
an
d

spring
tension

acting
on
the

No
I

and
No

2
valves

The

No
2

jiaphragm
however
does

not
move
due

to
low

engine
speed
low

air

pump
discharge
pressure
and

spring

tension

acting
on
the
No

3
valve
For

this
reason
these
valves
are

brought
to

a
balanced
condition

To
intake
manifold

t

i

l

3

Spring

4

ValveNo
3

5
Di

phragm
No
I
I

@

6

Spring

7

Valve
No
1

8
Valve
No

2

EC683

Fig
EC

20

Operation
of
C
A
C

Valve

1

2

Engine
in

low

speed
and

heavy
load

EC12
Wheo
the

engine
is

operating
under

these
cooditions

intake
manifold

vacuum
is
low
and

all
valves

are

balanced

t
To

intake

manUol

U

E

ii

ji
j

Ii
5

LL

jj

Ii
JI

l
Jij

ulJC

1t

To

atmosphere
EC685

Fig
EC
21

Operation
of
C
A
C

Valve
2

3

Engine
in

high
speed
and

middle

load

When
the

engine
is

operating
under

these
conditions
intake

manifold

vacuum
lies

midway
between
1

and

2

above
The
No
3
valve

moves
to

the
left

because
of

high
air

pump

discharge
pressure

To

intake
manifold

t

L

J

f
E

bt

I
5

tfi
11

I

LJr

To

tmg
J
j
1

EC
4

Fig
EC
22

Operation

of
C
A
C

Volve
3

REMOVAL
AND

INSTALLATION

Air
pump
air
cleaner

Loosen

nuts

securing
air

pump
air

cleaner
to

bracket
then
detach
air

cleaner
from
bracket

Air
cleaner
filter

and
air
cleaner
lower

body
are
built

into

a
unit
construction

Replace
air

cleaner
filter
and
lower

body
as
an

assembly

INSPECTION

I

Disconnect

high
tension

cables

from

spark
plugs
by
pulling
on

boot

not
on
cable
itself

2

Remove

spark

plugs

3

Check
electrodes
and
inner

and

outer

porcelains
of

plugs
noting
the

type
of

deposits
and
the

degree
of

electrode
erosion

Refer
to

Fig
EE

76

Normal
Brown

to

grayish
Ian
de

posits
and

slighl
electrode
wear

indicate
correct

spark

plug
heat

range

Carbon
fouled

Dry
fluffy
carbon
de

posits
on
the
insulator
and
elec

trode
are

mostly
caused

by
slow

speed
driving
in

city
weak

ignition

too
rich
fuel
mixture

dirty
air

cleaner
etc

H
is
advisable
to

replace
with

plugs

having
hotter
heat

range

Oil
fouled

Wet
black

deposits
show

excessive

oil
entrance
into

comb
us

tion
chamber

through
worn

rings

and

pistons
or
excessive

clearance

between
valve

guides
and
stems
If

the
same
condition
remains
after

repair
use
a
hotter

plug

Overheating
White
or

light
gray
insu

lator
with
black
or

gray
brown

spots
and
bluish
burnt
electrodes

indicate

engine
overheating
More

over
the

appearance
results
from

incorrect

ignition
timing
loose

spark
plugs
low
fuel

pump
pres

sure

wrong
selection
of
fuel

a

hotter

range
plug
etc

H
is
advisable
to

replace
with

plugs

having
colder
heat

range

4
After

cleaning
dress
electrodes

with
a
smaU
fme
file
to
flatten
the

surfaces
of
both

center
and
side
elec

trodes
in

parallel
Set

spark
plug

gap
to

specification

5

Install

spark

plugs
and

torque

each

plug

6
Connect

spark
plug
wires

CLEANING

AND

REGAP

Clean

spark
plugs
in
a
sand
blast
Engine
Electrical

System

SPARK

PLUG

Conventional

type

Normal

Overheating

Multi

gap
type

Nonnal

Overheating

type
cleaner
Avoid
excessive

blasting

Clean
and
remove
carbon
or
oxide

deposits
but
do
not
wear

away
porce

lain
If

deposits
are
too
stubborn

discard

plugs

After

cleaning
spark

plugs
renew

firing
surface
of
electrodes
with
file

mentioned

above
Then
check

spark

plug
gap
with
wire

feeler

gauge
All

spark
plugs
new
or
used

should
have

the

gap
checked
and
reset

by
bending

ground
electrode

EEOSO

Fig
EE
77
Setting
Spark
Plug
Gap

Except
FU
model

EE
29
Carbon

fouled

EE079

Worn

Carbon

fouled

Worn

EE601

Fig
EE

76

Spark

Plug

EE586

Fig
EE
78

Setting
Spark
Plug

Gap
FU
models

Condition

Clutch

slips

Clutch

drags
Clutch

TROUBLE

DIAGNOSES
AND

CORRECTIONS

Probable

cause
and

testing
Corrective
action

Slipping
of
clutch

may
be
noticeable

when

any
of
the

following
symptoms
is

encountered

during
operation

I
Car
will
not

respond
to

erigine
speed
during
acceleration

2
Insufficient

car

speed

3
Lack
of

power

during
uphill

driving

Some
of
the

above
conditions

may
also
be
attributable
to

engine
problem
First
determine

whether

engine
or
clutch
is

causing
the

problem

If

slipping
clutch
is

left
unheeded
wear

and
or

overheating
will
occur
on
clutch

facing
to
such

an
extent
that
it
is

no

longer
serviceable

TO

TEST
FOR
SLIPPING
CLurCH

proceed
as
follows

During
upgrade
havelling
run

engine
at

about
40
to
50

km
h
25
to
31
MPH

with

gear
shift

lever
in

3rd
speed
position
shift
into

highest

gear
and
t
the
same
time

rev

up
engine
If
clutch

is

slipping
car
willnot

readily
respond
to

depression
of
accelerator

pedal

Clutch

facing
warn

excessively

Oil
or

grease
on
clutch

facing

Warped
clutch

cover
or

pressure
plate
Replace

Replace

Repair
or

replace

Dragging
clu

tch
is

particularly
noticeable

when

shifting

gears
especially
into

low

gear

TO
TEST
FOR

DRAGGING
CLurCH

proceed
as
follows

I
Start

engine

Disengage
clutch
Shift
into

reverse

gear
and
then
into
Neutral

Gradually

increase

engine

speed
and

again
shift
into
reverse

gear
If
clutch
is

dragging
gear
grating

is
heard
when

shifting

gears
from
Neutral
into

Reverse

2

Stop
engine
and
shift

gears
Conduct
this
test
at
each

gear
position

3
In

step
2

gears
are
shifted

smoothly

except
1st

speed
position
at

idling

a
If

dragging
is

encountered

at
the
end
of

shifting
check
condition
of

synchro

mechanism
in

transmission

b
If

dragging
is
encountered
at
the

beginning
of

shifting
proceed
to

step
4

below

4

Push

change
lever
toward
Reverse
ide

depress
pedal
to
check
for
free

travel
of

pedal

a
If

pedal
can
be

depressed
further
check
clutch
for

condition

b
If

pedal
cannot
be

depressed
further

proceed
to

step
5

below

5
Check

clutch
control

pedal
height
pedal
free

play
free

travel
withdrawal
lever

play
etc

If

any
abnormal

condition
does
not
exist
and
if

pedal
cannot
be

depressed
further
check

clutch
for

condition

Clutch
disc

runout
or

warped

Wear
or
rust

on
hub

splines
in

clutch

disc

Diaphragm
spring
toe

height
out
of

adjustment
or
toe

tip
worn

Worn

or

improperly
installed

parts
Replace

Clean
and
lubricate

with

grease
or

replace

Adjust
or
replace

Repair
or

replace

CL12

Body
Electrical

System

VENTILATING
AND
HEATING
BI
LEVEL

BI

LEVEL

position

COl
OFF
VENT
B

l
HElT

HOT

Move
the
lever
to
the

desired

temperature

HEATING

HEAT

position

OFF
IINl

COlO
L
HElT

HOT

Move
the
lever
to

the

desired

temperature

DEFROSTING

OFF
VENT
L
HElT

HOT

J
COlf

Move
the
lever
to
the

desired

temperature

RECIRCULATING

OFF

COlOr
VENT
L
HEll

HOT

Move
the
lever

to
the

desired
temperature
RECHEIl

fIN
OfF
1
2
3
Olf

Move
the
lever

to
the

desired
air
flow

I
Olf
RECHll

FIN
OfF
1
2
3

Move
the
lever
to
the

desired
air
flow

OEF

position

Olf
RECHll

fIN
OFH
2
3

Move
the
lever

to
the

desired
air
flow

RECIRC

position

J

1
OEf
RECHEIl

fIN
PfF
I

3

J

Move
the
lever

to
the

desired
air
flow

BE
25
To
defroster
nozzle

ft
To
side

L
defroster

Outside
air

L
c

U

D

l

To
floor

BEl40D

Fig
BE
59

Ventilating
and

Heating
Air
Flow

To
defroster

nozzle

fr

Outside
air
c
t

Ul

B
yO

Toflaor

BE141D

Fig
BE

60

Heating
Air
Flow

To
defroster
nozzle

fr

Outside
air

Ul

@Jtc
Y
D

l

1

BE142D

Fig
BE
61

Defrosting
Air
Flow

To
defroster

nozzle

LJ

Iniideair
c

@

To
floor

BE143D

Fig
BE

62
Recirculating
Air
Flow

Condition

Insufficient

heating

performance

No
heated

air

discharged

Insufficient
air

flow

to

floor

Insufficient

defrosting

performance

Cold
air

discharged

Insufficient
air
flow

to
defroster

Heated
air

discharged

with

lever
in
VENT

Blower

motor
does

not

run

Control
lever

drags

Outside
air
comes
in

with
fan
in
OFF

Noise

frol11
blower

motor
Body
Electrical

System

Probable
cause

Cooling
water

temperature
too

low

Heater
core

plugged

Insufficient

cooling
water

level

Malfunctioning
air
mix
door

Malfunctioning
water

cock

Blower
motor

speed
too

low

Malfunctioning
floor
door

Refer
to
No

heated
air

discharged

Malfunctioning
hoor
door

or
faulty
seal

Defroster
nozzle

plugged

Leak

at
defroster
duct
lo
nozzle
connection

Water
cock
not

operating
properly

Mode
door
not

operating
properly
or

seal

damaged

Fuse
melted

MOlor
wire
connector
disconnected

Faulty
switch

Faulty
motor

Faultyblower
control

amplifier

Inner
wire

rubbing

against
outer
case
end

Control
cable
bent

excessively

Malfunctioniilg
doors
door

levers
etc

Air

intake
door
not

operating

properly

Control

cable
out
of

adjustment

Loose
bolt

in
blower

motor

BE

56
Corrective
action

Check
thermostat

Rep1ace
as
nece

ry

Clean

Rem

Adjust
control
cable

Adjust
control
cable

Check
motor
terminal

voltage

Repair

poor
connection
and

discontinuity

Replace
motor
if

necessary

Replace
blower

control

amplifier
if
neces

sary

Adjust
control
cable

Adjust
control
cable

Clean

Correcl

Adjust
control
cable

Adjust
control
cable

Correct

cause
and

replace

qrrect

Replace

Check
and

correct

Replace

Adjust
control
cable

Correct

Ch

ck
and
COrrect

Repair
or

replace

Adjust
control
cable

Check
and

tighten
loose
bolts