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Problem: Engine overheats - general
Possible Cause Solution
Low raw water flow: See below.
Check coolant level: Top up.
Pressure cap loose: Tighten correctly or replace.
Switch sender faulty: Replace.
Insufficient restrictions in pipe to calorifier: Clamp off pipe to confirm.
High exhaust back pressure: Must not exceed the information given in ‘exhaust back
pressure’ in the installation section.
Keel cooler insufficient size: Contact boat builder.
Problem: Engine overheats - heat exchanger cooled
The most common cause of overheating is insufficient seawater flow due to a blocked intake. If this happens first clear
the debris, causing the blockage. If the problem is not cured then check the system for sea water flow which should
be 18 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/minute. Repeat twice and take an average. If the flow rate is noticeably less than the 18 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 located and removed.
(d) Check flow again as in (a).
*NB: 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 gases.
Problem: Engine overheats - keel cooled
Commonly overheating is caused by:
(a) Not fully venting the engine cooling system of air. It is necessary to remove all air from the cooling system -
including the “skin” tanks and (if fitted) the Calorifier and associated piping.
(b) Incorrectly sized “skin” tanks that have been sized for ‘usual’ canal use (rather than maximum engine output
that can sometimes be required) on fast flowing rivers. An additional “skin” tank may need to be fitted; please refer
to our website: Inland waterways - Guidelines: keel cooling tank sizes.
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