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Author Topic: Lister STW watercooled thermostat  (Read 3024 times)
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« on: April 12, 2011, 02:56:07 PM »

goodday all,

Currently overhauling a Lister STW3 lifeboat engine which is, directly (sea)watercooled.
Whilst inspecting the thermostat housing I noticed previous owner installed a Waxstat thermostat that will open at about 74 degreed C.
Personally I think this is to hot for a direct raw water cooled engine, probably causing a lot of scale.

Anyone of you got experience with Waxstat, or thermostat suppliers in general? What do you think should be the right temperature?

best regards
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« Reply #1 on: April 13, 2011, 07:36:41 AM »

Firstly Hello and welcome to the forum.

The STW3 is a fine engine, and when coupled with the Lister hydraulic gearbox is a hard to beat combination. However if you have a Lister STW3 running with a raw seawater cooling system, scaling is not going to be a high priority issue for you.

Firstly I would investigate the condition of the sacrificial Anodes that this engine should already be fitted with, secondly in the longer term I would suggest that you investigate some other form of cooling ie keel cooling, or an indirect system via a heat exchanger. As raw water cooling will inevitably cause coolant jacket corrosion, which is greatly accelerated if the water jacket is left empty of sea water for extended periods of time, ie during layups in the boatyard.

I have seen the SRW [from which the STW was derived from]  engines corrode from the inside out, and the top water rail is usually the first to go, closely followed by the water cooled exhaust manifold, in addition because of the rather unique cylinder block / headgasket design [ due to the STW engine being derived from an aircooled design] corrosion can and does take place between the cylinder head studs and cylinder block. Making removal of the cylinder blocks very difficult.

From a thermostat perspective I would fit the hottest thermostat you can get, as these engines will carbon up rapidly if they are being run to cool.
Hero Member
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« Reply #2 on: April 13, 2011, 09:27:40 PM »

goodday all,

Personally I think this is to hot for a direct raw water cooled engine, probably causing a lot of scale.

What do you think should be the right temperature?

best regards

  With 50/50 coolant. 195F minimum, 210F is better. Hot engines run cleaner and last longer.
  Don't mix up a hot running clean efficient  engine and an overheated engine that is boiling over.
  Somehow people get thinking if too hot is bad than colder is better. Ain't so.
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