CLOSED COOLED (FRESH WATER) MODELS
SERVICE MANUAL NUMBER 23
Pressure Testing System
WARNING
Allow engine to cool before removing pressure cap. Sudden loss of pressure could
cause hot coolant to boil and discharge violently. After engine has cooled, turn cap
1/4
turn to allow any pressure to escape slowly, then push down and turn cap all the
way off.
If coolant section of closed cooling system is suspected of leaking or not holding sufficient
pressure, and no visible signs of leakage can be found, perform the following test:
1.
2.
Remove pressure cap from heat exchanger or reservoir.
Clean, inspect and pressure test pressure cap, as outlined under “Testing Pressure
Cap,” to eliminate the possibility that cap is not maintaining proper pressure in system
and is causing coolant to boil over.
3.
Clean inside of filler neck to remove any deposits or debris. Examine lower inside seal-
ing surface for nicks or other damage. Surface must be perfectly 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.
4.
5.
Adjust coolant level in fresh water section to 1 in. (25 mm) below filler neck.
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.
Amount of Pressure Applied to Closed
Pressure Cap Rating
Cooling System
16
PSI (110 kPa)
20 PSI (138 kPa)
6.
7.
Observe gauge reading for approximately two minutes; pressure should not drop during
this time. If pressure drops, proceed with the following steps until leakage is found.
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
either is usually a sure indication of a leak.
8.
9.
Refer to “Testing Heat Exchanger” in this section and test as outlined.
If no leakage could be found in above steps, engine 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 exhaust elbow or distribu-
tion 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
internal leak is found.
a. Start engine. Re-pressurize system to previously specified amount and observe
pressure gauge on tester. If needle in gauge vibrates, compression or combustion
is leaking into closed cooling section from a leak in the combustion chamber. Exact
cylinders where leakage is taking place, can sometimes be found by removing spark
plug wires (one at a time) while observing pressure gauge. Vibration will decrease
or stop when plug wire is removed from leaking cylinder. Stop engine.
b. Remove spark plugs (one at a time) from cylinders and examine for presence of
coolant. A spark plug that is perfectly clean or milky appearing is a sure indication
of a leak.
Page 6B-6
90-861326--1 MARCH 1999
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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