Testing Closed Cooling
System
3. Clean inside of filler neck to remove any deposits
or debris. Examine lower inside sealing surface
for nicks or other damage. Surface must be per-
fectly smooth to achieve a good seal between it
and rubber seal on cap. Also check locking cams
on sides of filler neck to be sure that they are not
bent or damaged. If locking cams are bent or
damaged, pressure cap will not hold the proper
pressure.
Testing Coolant for Alkalinity
!
WARNING
Allow engine to cool before removing pressure
cap as sudden loss of pressure could cause hot
coolant to boil and discharge violently. After en-
gine has cooled, turn cap 1/4 turn to allow any
pressure to escape slowly, then push down and
turn cap all the way off.
4. Adjust coolant level in fresh water section to 1 in.
(25 mm) below filler neck.
5.
Attach an automotive-type cooling system
pressure tester to filler neck and pressurize
closed cooling section to amount specified in
following chart, based on pressure cap rating for
your engine.
Coolant in fresh water section should be changed ev-
ery two years and should be checked for alkalinity at
least once between change intervals. To check cool-
ant for alkalinity, proceed as follows:
Amount of Pressure
Applied to Closed
Cooling System
Pressure Cap Rating
PSI (110 kPa)
1.
2.
3.
4.
Obtain pink litmus paper from a local supplier
(drug store, pet shop, etc.).
16
20 PSI (138 kPa)
Remove pressure cap from heat exchanger and
insert one end of litmus paper into coolant.
6. Observe gauge reading for approximately two
minutes; pressure should not drop during this
time. If pressure drops, proceed with the follow-
ing steps until leakage is found.
If pink litmus paper turns blue, coolant is alka-
line and need not be replaced.
7.
While maintaining specified pressure on closed
cooling section, visually inspect external portion
of cooling system (hoses, gaskets, drain plugs,
petcocks, core plugs, circulating pump seal, etc.)
for leakage. Also listen closely for bubbling or
hissing, as they usually are a sure indication of a
leak.
If pink litmus paper remains pink, coolant is
not alkaline and MUST BE REPLACED, as ex-
plained under “Changing Coolant.”
Pressure Testing System
8.
Refer to “Testing Heat Exchanger” in this section
and test as outlined.
!
WARNING
Allow engine to cool before removing pressure
cap. Sudden loss of pressure could cause hot
coolant to boil and discharge violently. After en-
gine has cooled, turn cap 1/4 turn to allow any
pressure to escape slowly, then push down and
turn cap all the way off.
9. If no leakage could be found in above steps, en-
gine is leaking internally, and it probably is due to
one or more of the following: (1) loose cylinder
head bolts or damaged gasket, (2) loose intake
manifold bolts or damaged gasket, (3) loose ex-
haust elbow or distribution block retaining nuts or
damaged gasket, (4) cracked or porous cylinder
head or block, or (5) cracked or porous exhaust
manifold. Proceed as follows until location of in-
ternal leak is found.
If coolant section of closed cooling system is sus-
pected of leaking or not holding sufficient pressure,
and no visible signs of leakage can be found, perform
the following test:
a. Start engine. Re-pressurize system to pre-
viously specified amount and observe pres-
sure gauge on tester. If needle in gauge vi-
brates, compression or combustion is leaking
into closed cooling section from a leak in the
combustion chamber. Exact cylinders, where
leakage is taking place, sometimes can be
found by removing spark plug wires (one at a
time) while observing pressure gauge. Vibra-
1.
Remove pressure cap from heat exchanger or
reservoir.
2.
Clean, inspect and pressure test pressure cap,
as outlined under “Testing Pressure Cap,” to
eliminate the possibility that cap is not maintain-
ing proper pressure in system and is causing
coolant to boil over.
Index
6B-4 - CLOSED COOLING SYSTEMS
90-823224--2 796
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1993, 1994, 1995, 1996, 1997 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
(4 votes, average: 4.5 out of 5)
Marine readers have rated 1993 1997 Mercury-MerCruiser GM V8 454 CID 7.4L and 502 CID 8.2L Marine Engines Service Manual Number 16 4.5 out of 5.0 based on 4 product reviews. Hugely helpful service manual! Perfect. Thank you!
Manuals are all Important for Technician
This book is invaluable if you do your own repairs. Great book.
Could not find a copy until a search brought me here.
Excellent print.
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