Mercury 8.1S Horizon, Product Applications Manual

Page: 96 / 163

Exhaust System
90-863758060 AUGUST 2006 Page 6A-27
1. After the 15 minute idle preparation, drain the exhaust manifolds of water. If the engine
uses a closed‑cooled system, pinch or plug the hose from the heat exchanger to the
exhaust elbow to prevent coolant from spilling because the heat exchanger is higher.
2. Remove the exhaust elbows.
3. Check for water in the exhaust manifold. Use a flashlight if needed to aid inspection. If
water is found, measure the amount and record. See
Interpreting Results
.
NOTE: A suction device with a rubber hose attached to the end can be used to suck the
water from the manifold and discharge it into a container.
4. Replace the elbows using new gaskets. Refer to the appropriate
Mercury MerCruiser
Service Manual
.
CHECKING BY DRILLING AND TAPPING EXHAUST MANIFOLDS
1. Drill and tap a 1/8 in. NPT hole into the bottom and center of the exhaust manifold
runners for cylinders numbers 4 and 5. Be sure to drill in the area that is not
water‑jacketed.
a
13414
b
13415
a - Number 4 exhaust manifold runner b - Number 5 exhaust manifold runner
2. Insert brass drain plugs into the holes.
Qty. Description Part Number
2 Brass drain plugs 22‑818390
3. Run the engine as outlined in the extended idle test.
4. Drain water from the manifolds into a suitable container. Measure and record the
amount of water using a graduated cylinder. An acceptable amount of condensation
water is 5 ml (0.2 fl. oz.).
5. Replace the manifolds with new manifolds.
INTERPRETING RESULTS
Water vapor is a normal by‑product of the combustion process, so a small amount of water
[5 ml. (0.2 fl oz.)] is acceptable. This condensation has not shown to cause a problem.
Water amounts in excess of this could be an indication of a water intrusion problem that
requires corrective action. Some of the more common causes for this condition are:
• Insufficient exhaust riser height. See
Measuring Exhaust Elbow Height
.
• Improper exhaust hose slope.
• Failure to have at least 457 mm (18 in.) between the exhaust outlet and muffler,
collector, or first angular fitting. See
Exhaust System Design
.
• Missing or mispositioned exhaust resonators. See
Exhaust Resonators
.