SERVICE MANUAL NUMBER 26
CLOSED COOLED MODELS
3.
4.
Put enough coolant into hose to fill the center 4 or 5 inches (10-13 cm) of the “U.”
Observe the “U” while the engine is running.
a. During Idle and Warm-Up: Some coolant and/or air will leave the reservoir.
b. During Cruising Speed (2500-3500 rpm): Coolant and/or air leaving the reservoir
should stop after approximately five minutes running at a given rpm. A leaking head
gasket will produce air bubbling through the “U,” going to the coolant recovery bottle.
The frequency and size of the bubbles will depend on the size of the leak.
c. At Higher Speeds (4000+ rpm): Normal operation is the same as described in “b”
above. A failed head gasket will cause the bubbles to come faster and may be
accompanied by violent, intermittent bursts of coolant.
It is important not to confuse normal warm-up expansion with a failed head gasket. Normal
warm-up produces an intermittent flow of coolant which will stop within approximately five
minutes at a given rpm. A head gasket leak will not stop because the one thing that marks
a failed head gasket is the continued passage of air. This may be accompanied by violent,
intermittent bursts of coolant leaving the reservoir. If coolant continues to flow (not in violent,
intermittent bursts) from the reservoir at cruising speed, something else besides the head
gasket is causing the engine to overheat.
Testing Heat Exchanger
FOR INTERNAL LEAK: An internal leak will cause coolant to go into the seawater circuit
when pressure is put on the closed cooling circuit.
1.
Remove a seawater hose from the exchanger. Do not drain the exchanger.
Pressurize the closed cooling circuit to 14-20 psi (97-138 kPa) with a radiator tester.
If seawater begins to flow from the nipple there is a leak.
2.
3.
FOR BLOCKAGE:
IMPORTANT: Seawater flows THROUGH the tubes in the exchanger. Closed cooling
coolant flows AROUND the tubes.
1.
Remove end caps and inspect for any blockage in the seawater circuit (broken impeller
blades, weeds, etc.).
2.
Remove closed cooling circuit hoses and inspect the tubes just inside the nipples.
Because the complete exchanger cannot be inspected, the heat exchanger should be
replaced if blockage is suspected.
Testing Pressure Cap
Pressure cap is designed to maintain a pressure of approximately its rated capacity (refer
to “Specifications”) in closed cooling section once engine has attained operating tempera-
ture. Cap should be cleaned, inspected and pressure-tested at regular tune-up intervals or
whenever cap is suspected of maintaining improper pressure as follows:
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.
1.
Carefully remove pressure cap from reservoir or heat exchanger.
2.
Wash cap with clean water to remove any deposits or debris from sealing surfaces.
Index
90-861329--1
MARCH 1999
Page 6B-7
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 181 CID |
| Model Year | 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
(6 votes, average: 5 out of 5)
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