Engines – Keep Cool…Don’t Overheat

Tips to avoid overheating
By John Alker      
Westerly Fulmar,  Blue Star

We have a 1984 Westerly Konsort with Bukh DV24 engine with direct sea water cooling. The engine was installed by the previous owner in 1999.

We have had one minor overheating issue about 10 years ago (cause, see later).  So we take certain actions as described below, to avoid overheating and which may be applicable to your boat.  It is reported that a significant number of engine breakdowns are attributed to overheating from one cause or another.

We had only owned Blue Star for a year when there were cooling water supply issues.  This seemed to be caused by the in-line basket strainer.  It may have had a poorly sealing lid, wrapping it in cling film overcame the issue temporarily.  We very quickly dispensed with the strainer and fitted an in-line filter just after the intake sea cock (See photo1 and 2) which is easy to clean, the line goes straight from this inlet to the water pump. (photo 3)

Photo 1,  Photo 2 and Photo 3

The water coolant circuit

The pump impellor is inspected a couple of times a season and replaced at least every 2 years (depends on usage).  If the engine is unused for long periods (e.g. winter lay-up) it is best to remove the impellor. In addition, when it has been unused and therefore in a fixed distorted position it pays to immerse it in boiling water, this can relieve any distortions set in.  Obviously inspect each blade for cracks.

Just after the water pump there is a T diverter pipe (see photo 4).  The water flow is governed by the thermostat calling for cooling water to engine or to bypass.  When motoring hard on one occasion our engine overheat warming came on, but at lower revs all was OK.  On removal and inspection, the pipe section was reduced by around 50% by scale, salt and calcareous deposit.  The pipe was removed and cleared. We now do this routinely every 2 years, but timing will depend on usage.  This pipe is a fiddle to remove and fix.  Ensure a good gasket is used; a leaking gasket will promote deposits. An Allen key cut down makes removing the screws easier.  We have considered replacing the bolts with cross head screws so a screwdriver can get in more easily.

Photo 4

Photo 5

Thermostat (see photo 5)

Every 2 years we remove the top housing and clean out both sections.  The operating part (photo6) is descaled, use kettle descaler).  After cleaning it is tested by immersing in a pan of water and warming up to observe it operating (worth maintaining as genuine Bukh thermostats are £100+ for the inner bit!).

Engine flushing

We flush through with fresh water for a minimum of 10 minutes each year.  I have not used flushing agents, but I would only use a proprietary one (not “just some acid”).  For direct sea water cooled engines there are flushing cleaners that you can just run into the engine and then leave to rest for a while before flushing out.  Do get the engine to running temperature before flushing.  It is a bit trickier to do long circulatory flushing with direct cooled engine.  It is important after flushing, especially with acidic material, to check the engine anode state afterwards, if possible, it is better to remove the anode while flushing.

Keep cool!