Friday, 5 August 2011

The water systems thermostdat

This is the forgotton hero in any engines water system,I almost wrote 'Cooling System' but its almost the complete reverse,here is why.

This applies to both petrol and diesel engines and given you probably drive one or the other check your road car for UNDER HEATING next time you drive,the same with the marine diesel engine of course.

Two stainless thermostadts,the real Perkins Power Part is in the 4108 Perkins engine they fit,these are just spares.One is an 87c and the other 88c temperature setting,I fitted an 82c in the engine when I last had reason to check the cooling system.

The temp setting will be stamped on the unit,often on the lower end,just have a look.

We learn as we go along I like to think and some time after launching,I mentioned to a fellow yachtsman,Peter on the Morgan 31 named Pato, that my engine seemed to run fine at a steady 45c or so. Peter commented right away that a marine diesel should run at around 85c to 90c,thats some fifty percent higher than my engine was running at!

I checked the manual,he was correct,I removed the fresh water heat exchanger and found a very old bellows type thermostadt,which was stuck wide open and doing nothing much.

How many time in the past have I seen a really keen sailor call for the engine to be switched off as soon as we were heading down the Duncan Dock after exiting the Small Craft Basin at the RCYC,Cape Town.
Tradition said that sailing was the thing to do and having an engine on was just not proper.In reality they were just killing their (or the owners) very expensive marine diesel engine.

The cause comes from an engine that may have sat some while,the oil may have absorbed moisture,which then has a tendency to form acids,which in turn attacks the bearings.liners and piston rings,running the engine over a decent period,say at least an hour should burn that acid off,switching off the engine when its still cold just starts the road to its ruin.

Running in new and old rebuilt engines?

This can be highlighted in the Perkins 4108 service manual,you can find it in the Cooling pages,they advise that so called Running In of their engines is not required and in fact damage can be done to the rings and cylinders by under using the engine,using too little load.They say further that as soon as water temprature reaches 60c,the engine can be used under full load.


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