Nanni 14 Underheating

This is what i found listed as the thermostat

Double ported thing like many car ones where as the main port opens the bottom flap closes the by pass

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Diagram I found in a manual shows how it will work

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Perhaps the OP could confirm that his stat is a dual-port one and looks like the one found by Vic?

If it is then I suspect that there is something wrong with the dimensions or fitting of the stat or it's a single port version and it is not closing the flow to the H/E such that coolant is always partly flowing around the H/E, although that's a bit difficult to visualise as these errors would usually cause overheating rather than over-cooling. :confused:

You can still check this as described above by blocking off the port to the H/E with some plastic around the stat although it might be a bit more complicated that just popping the stat in a plastic bag. Actually, thinking about this, you only need to close off the valve to the H/E in the thermostat which is the upper one in Vic's photo so it should be exactly the same as blanking off a single-port stat. A piece of plastic film over the pointed end on the stat and trapped around the flange but not long enough to flap down and get in the way of the lower bypass valve should work fine, assuming that the lower disc is the bypass valve in your engine. This would normally be the case.

I'm sure you will find that once it is only the bypass that is open then engine will soon get up to temperature.

If you have good access you might be able to take some measurements of the spacing of the ports and compare those to the dimensions of the stat to see if it is closing the H/E port when the engine is cold.

Richard
 
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Thank you to all who have contributed here.
Yes I can confirm that my stat is a dual port job like the one pictured and inside the housing there is a port which will get closed off by the bottom plate of the stat as it opens. I tried to show this in my diagram. I'm about as certain as one can ever really be that the stat is okay as it's new and I tested it in a pan of water before fitting. When it went in it was closed and seated neatly in its hole, and the housing has never been anywhere near hot enough to get it to open. The stat is a real pain to get at because the exhaust elbow has to come off first. An anode has been added to the elbow, presumably an attempt to reduce the rampant corrosion that seems to consume it, and its housing blocks access to the stat cover bolts.

Today I ran the engine with the calorifier pipes disconnected. The temperature levelled out at about 55-60 on the guage, which appears to be accurate.

I think that what I have here is just a case of poor design. The heat exchanger/exhaust manifold is a substatial aluminium casting wirh one chamber full of sea temperature water and one full of coolant, probably separated by a metal wall of perhaps 10mm thckness. Allowing the full coolant flow through even when the stat is closed is bound to result in heat leaking away and longer warm up/ poor calorifier performance/ underheating. Maybe with a big engine it would be fine, but a little 14HP just doesn't seem to produce enough heat to deal with cold winter river water. I notice that the Beta engines use a more conventional, car like stat set up.

The heat exchanger is very different to the one shown by ianc in his pics and there's no port on a machined surface that can be blanked easily. Perhaps I should fill the casting with expanding foam! Ha.
I can't think of anything else to try so I think I'll just leave it and wait till I can get the boat seaworthey and out to sea. Perhaps it will be fine in slightly warmer water.
 
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