Nanni Diesel running cold

[Marc1]

Hi there!
Recently bought a pocket cruiser, little 22' powered by a Nanni diesel N4.50 ... 50 hp with MG360 twin disk transmission. Engine has 320 hs

The engine runs faultlessly and at 1900 revs, it pushes the boat at 7 knots.
I have some experience with diesel engines, mainly larger units running big generators and we always had them running at 180 to 185F
Now this little Kubota, runs at 160, if I slow down at 1600 1500 revs it goes even colder.

So my first thought was, someone pulled the thermostat out, so bought a new one and the gasket, a bit of goe and armed with a siphon a bucket and socket, I proceeded to take a few litres of coolant out, undo the thermostat housing only to find a perfectly good thermostat in there.

Oh well, since I am here, in goes the new thermostat, new gasket, fill up the coolant, and after a bit of chuffing around, realised that I had wasted my time since the engine runs at exactly the same temperature as before.

I did try to run the little Kubota faster mainly to see how the hull behaves, but as expected at 2800 rpm, the top speed of the engine, the poor boat pushes a mighty wave but can not go over it. Predictable.

And the temperature climbed to 180 and after a while 190 and as it seem to want to get hotter, I decided to stop the experiment.

The water pump">raw water pump was leaking, so I changed the impeller and seals. The exhaust elbow had a crack so I replaced it. The new one weights half what the old one does, I assume from the rust accumulated in it and not from making the cast lighter. Hopefully. The new one has also a neat little anode.

But back to the temperature, it seems that 160 is all it does. Running cold is not good for any engine, but of course between the two evil cold is better than hot. Should I just run it this way? Nanni Diesel agent is no much help, to any technical question they say "I am not an engineer, I work in an office and sell parts" ...

Nanni, Beta and Westerbeke are almost identical engines marinized by different little outfits, and the cooling system is designed not by Kubota but by them. I did notice that the thermostat fits in the housing in a way that the coolant circulation is never completely shut. There is a generous gap between the end of the valve and the housing. The one I bought and the one that was in there are identical so no chance of it being the wrong one.

If someone has experience with Nanni, maybe you can comment, or if you run Beta or Westerbeke, what temperature do you run your engine?

[sailormed]

.....There is a generous gap between the end of the valve and the housing......
Maybe experiment with a less generous gap and see what temperature you get.

[sailormed]

.....There is a generous gap between the end of the valve and the housing......
Maybe experiment with a less generous gap and see what temperature you get.

Sorry for double post, have whacky internet here in Bali.

[Chardonnay]

It sounds like you are overpowered. 50hp seems excessive for a 22'. Beta tells me that a 38 (37.5 hp) is all I need for my 38' cruiser. Diesels want to work at around 80% rpm and load, yours is basically idling at or near the boat's hull speed. In the long term, this is not good for your engine. It's not getting hot enough so you don't get complete fuel burn, leads to carbon deposits, uneven cylinder heating, etc.

[Sailmonkey]

Our phasor (marinized kubota) runs @ 165 with our 165 thermostat.

[a64pilot]

You never said what the thermostat was rated at.
If it’s a 160 thermostat, then that is what the engine should run, any hotter and you have a cooling system problem, which you did.
If you want it to run hotter, install a hotter thermostat.
However I wouldn’t, I’d leave sleeping dogs lie.

[jls095]

As a data point, our Beta 43 (Kubota V2003) runs consistently at 165 regardless of engine speed or temperature of the water.

[bluenoser613]

Your boat is over-powered. You only need something like 20 HP for that size of boat.

[jls095]

The people responding that the OP is overpowered do realize that the engine has no idea how big the boat is, right? Engine loading is a function of prop size and pitch, not length or displacement.

[Marc1]

Thank you for the many replies.
To the suggestion to use a hotter thermostat ... Nanni Diesel the only supplier of parts I have in Sydney, only gives me one choice. And it is not even graded so I don't know what I have in there.

As for the boat being overpowered, you are correct to a point.
This is a Steber Persuader, made by Stebercraft in Australia. It is a family business that used to be run by a member of the family who was fond of slow boats. He built this boat with little 25 HP saildrives and 32 HP shaft drive. Mine is a bit of an oddity with the 50 hp Nanni.

When the current owner took over the business he started to power this same hull with Yanmar 125 HP in order to take the hull to plane. It is a planing hull after all and their "offshore" version does 22 knots with the little 2L Yanmar turbocharged. it planes at 12 kn and cruises at 16kn comfortably.

I looked into repowering with the yanmar but after a lot of inquiries, decided against it. It would cost almost what I paid for the boat, and would leave me with a faster boat yet with everything else the same, and this boat, designed to cruise at 7 knots, has a serious visibility problem with the shallow windscreen, not to mention a puny 60L fuel tank

Their new version uses the same hull but a shorter cabin, higher hardtop and the windscreen is twice the size.

After some more search on the internet, it seems that I am not the only running a nanni cold. There was another thread from a sailing boat with a 14HP nanni that runs cold. The comment was that the marine engine contrary to the tractor engine, can not shut the coolant off until it reaches running temperature because it needs to cool the manifold. In the case of small engines or small load, that bit of coolant is enough ergo the cold temperature.

Not saying this is the case, only what they were saying. The way the thermostat housing is built, there is an opening under the thermostat that is only shut when the top valve opens pushing the piston down and closing the bottom gap. So there is a designed double circulation. One for when it's cold and one for when it is hot, and the thermostat diverts this flow. There is no permanent shut when cold.

I suppose I could increase the pitch of the propeller to increase the load, however my running experience told me the prop is correct since it was running at 2800 rpm at WOT.
Then again, overpowered so I could over prop it ... (?)

[Painted Skies]

Originally Posted by Marc1

After some more search on the internet, it seems that I am not the only running a nanni cold. There was another thread from a sailing boat with a 14HP nanni that runs cold.

We installed a 50hp Nanni in our 41-ft Tartan (9T displacement) last year. During its first 145 hours of operation, we have yet to see the temperature above 165 degrees during normal running at 2000 rpm (regardless of air or sea temperatures).

[a64pilot]

A marine engine can’t shut off the raw water cooling flow, just as the same engine in a tractor can’t shut off the radiator fan, or very few can.

However it’s irrelevant within realistic examples the thermostat controls the fresh water coolant temp, and that is the temp your seeing.

[a64pilot]

What you have not told us is what it the temp setting of the thermostat?
If it’s a 195 thermostat and your only running 160, well then something is wrong.
However if it’s a 160 or so thermostat and that is what your running, then that is what is to be expected.

Now the fact that it runs much hotter and seems to continue to run hotter when run hard is indicative to an inadequate cooling system, your heat ex is too small or more likely there is a flow restriction somewhere.

That is why in my opinion that everyone should have a temp gauge and should run their engines at full throttle for five minutes every once in a while. Pushing the limits of your cooling system is a very good way to detect declining efficiency of the system, before it fails when your in a tough spot.

I’ve not yet seen a Marine Diesel that runs as hot as 195 myself, I believe the reasons terrestrial engines do has a lot to do with emissions as anything else.

[TFM]

For what it's worth, I just finished up baffling series of events with respect to a 600+ hour Westerbeke 30C3 - 25 hp diesel. It started out with an overheating event where I did all the usual things from checking exhaust volume, grass or other foreign matter at the intake, replacing the thermostat with a new one, draining all the cooling fluid from the engine and replacing with new, replacing the impeller (which was missing a blade), reaming out the heat exchanger, etc. I tested the boat's 170 degree thermostat with a new one in boiling water and both opened at about 175, slowly rising to about 190 and fully open at 212 as expected. Everything went back together in proper sequence and a test run followed, with the temperature climbing quickly to 190+, so reversed course and crawled back slowly to the dock, frustrated after a long day being a mechanic, which I'm not. Puzzled and not wanting to quit, when things cooled off I poked around in the engine compartment and finally noticed a petcock, which I opened; it gurgled and coolant came out in dribbles before flowing smoothly. For a short while after that, everything was normal, but mysteriously the overheating occurred again and bleeding the petcock would not help. The boat had to be moved to the boatyard for other work, so the thermostat was removed, gutted of its innards and replaced. Now the temperature gauge stays around 165 degrees Fahrenheit in Florida Gulf Coast waters.
My question is the same as Marc 1's - does it do any harm? And if it does, what do I need to do to get my engine back to "normal"?

[Marc1]

I don't know the temperature setting of the thermostat. It is not written on it and it came wrapped in bubble wrap so no box.
Inadequate cooling system, yes, I run the engine at wot before I discovered the exhaust elbow cracked and full or rust and a leaking raw water pump. Addressed both issues but have yet to run another wot experiment.

My guess is that I will probably be able to run at wot and the engine will not overheat within a reasonable amount of time. Not much I can change in that department anyway.

What do you think about increasing the pitch of the prop? The gearbox is 2:1 but i don't know the size of the prop. It is a 3 blade and at a guess 16"or 17" x may be 18 or 19, not sure.

PS ... on a side note. If I type ... raw water pump ... I get something different when I post it. Strange.