16
Problem: Engine overheats
Possible Cause
Solution
Check coolant level:
Top up.
Insufficient sea water flow:
Clear blocked intake or filter.
Damaged or worn pump
impeller:
Replace.
Blocked tube stack in heat
exchanger:
Remove tube stack and clean – replace ‘O’ rings.
Zinc anode flakes blocking tube
stack:
Remove and clean tube stack as above.
Pressure cap loose:
Replace.
Switch sender faulty:
Replace.
Inlet sea cock is too small:
Replace (see heat exchanger cooled seawater inlet system in
section 3).
High exhaust back pressure:
Must not exceed 3.1" of Hg.
Air locks in cooling pipe work
to keel cooler:
Vent the system and top up coolant.
Keel cooler insufficient size:
Contact boat builder
GENERAL -HEAT EXCHANGE ONLY:
The most common cause of overheating is insufficient
seawater flow due to a blocked intake (weed or a plastic bag!). If this happens then clear the
blockage. If the problem is not cured then check the system for sea water flow which should be
15 litres / minute minimum at 1,500 rpm as follows:
(a) With the boat tied up and out of gear run the engine up to 1500 rpm.
*
Hold a plastic bucket
over the exhaust outlet for 10 seconds and measure the amount of water collected. Multiply this
value by 6 to give the flow in litres/min. Repeat twice and take an average. If the flow rate is
noticably less than the 15 litre per minute minimum at 1,500 rpm, then:
(b) Check impeller in sea water pump - if worn replace.
(c) If impeller has a vane missing then this will be lodged either in the pipe to the heat exchanger
or in the end of the exchanger. This must be removed.
(d) Check flow again as in (a).
*Note:
This operation must only be done in safe conditions, in port and with two assistants.
Working from a rubber dinghy is best. The person holding the bucket should take precautions
against breathing in the exhaust gasses.
Problem: Knocking noise
Possible Cause
Solution
Propshaft touching gearbox
output coupling through split
boss or Type 16 coupling:
Adjust, giving correct clearance (10mm) between gearbox and
propeller shaft
Flexible mount stud touching
engine bed:
Adjust stud to clear
Drive plate broken
Replace / repair
Engine touching engine bed
Re-align engine / modify bed