Thermostat And Housing - Chevrolet 1988 Light Duty Truck Repair Manual

Figure 3 9 —C hecking the Valve Seals
• Insert the valves into the proper ports.
3. Valve spring shims (if used).
4. Valve springs (20) with dam pers (240).
5. S hields (18).
6. Rotators (17).
7. O-ring seals (16) and valve keys (15).
• C om press the valve sp rin g , using J-8062
(figure 35). Com press the spring enough so
the lower valve stem groove can be clearly
seen.
• Push a new O-ring seal onto the valve stem.
The seal is to be installed on the stem 's lower
groove. Make sure the seal is flat and not
twisted.
• Apply grease to the area of the upper valve
stem groove. Assem ble the two valve keys,
using the grease to hold the keys in place.
Make sure the keys seat p ro p e rly in the
groove.
• Release the com pressor tool. Make sure the
valve keys stay in place.
• Repeat the preceding steps on the rem aining
valves.
• Check each valve stem seal, using J-23738-A
(figure 39). Place the adapter cup over the
s h ie ld (18). O p e ra te th e v a c u u m
O bserve the vacuum pum p gage. No air
should be able to leak past the seal. If the
O-ring seal will not hold a vacuum , it may have
been damaged or im properly installed.
I
1
A. G rind out th is portion.
Figure 40 — Scale for Checking Valve Spring
t j j M easu re (F ig u re s 3 4 , 4 0 , and 41)
• Valve spring installed height of each valve spring.
1. Use a narrow, thin scale. A cutaway scale (figure 40)
may be helpful.
2. Measure from the valve shim or spring seat to the
top of the shield (18) (figure 41).
3. If this measurem ent exceeds the figure given in
" S pecifications," install valve spring seat shim s of
s u ffic ie n t th ic k n e s s (b e tw e e n th e s p rin g
cylinder head) to give the desired m easurement.
B-05247
NEVER shim the spring so as to give an installed
height under the specified figure.

THERMOSTAT AND HOUSING

The therm ostat is located in a housing bolted to the
front of the cylinder head (figure 4).
Therm ostats consist of a restriction valve controlled by
a therm ostatic elem ent. The restriction valve cracks or
just starts to open at a predeterm ined tem perature and
continues to open as the engine coolant tem perature
increases. To assure proper cooling and engine warm-up
it is im portant that the correct therm ostat be used. Refer
to the p ro pe r Truck S ervice M anual for the co rrect
therm ostat application.
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4.8 LITER L6 6A4-21
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4
3
2
Installed Height
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B-05248
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