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Old 31-08-2016, 01:15   #1
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Hot Nanni! (4190)

So my 43hp Nanni diesel is getting hot..... It has brand new impeller in water pump">raw water pump..... and Raw water pumps gloriously out of the Raw water Pump.

The old impeller still had all its vanes on, so don't think they are blocking downstream.....

Whilst the hose was off the outlet of raw water pump, I gave that a good blow, and it seem free flowing to me..... to accept the water from the raw water pump......

Running at low Revs, water coming out of Exhaust is nice and cool, all seems well..... but I can't help thinking there is not quite enough raw water coming through the system (checked feed to Raw water pump.... plenty)

Boat (yacht) hasn't been used for a while.... you can feel the build up on the prop when you put it in gear...... but in my previous experience, this just slows the boat down..... doesn't heat it up.... but boat does overheat above about 1100rpm in gear........ so....

Checked it in neutral too..... boat will over heat in Neutral if left to run 1500rpm.....

When boat is hot..... white.... (steam) comes out of wet exhaust.... so surely this means not enough raw water??

You could use the boat all day long @ 800rpm..... but that's not the plan!

Any ideas my fellow sailors?
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Old 31-08-2016, 03:53   #2
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Re: Hot Nanni! (4190)

It could be a clogged heat exchanger, over time they get a nice coating of crud that reduces the cooling efficiency. Also could be a thermostat issue.

Is the heat exchanger getting hot on the outside , or is it staying pretty cool, while the engine block is getting hot? I guess it could also be a blocked exhaust outlet. Or a FW pump issue.

If this is the issue it's easy enough to drain the coolant, remove the end caps and the exhaust mixer from the heat exchanger, inspect the tube stack and also check the thermostat in a pot of water at the same time. You might want the fancy expensive nanni o rings to reseal the heat exchanger ends back on.

Curious to see what it ends up as. Possibly its a combination of things all conspiring with the weeded prop to cause the overheating. When you have it fixed get a infra red thermometer and get some baseline readings. Also time how long it takes to fill a bucket of water out from the exhaust at idle rpm, and a few other engine revs.
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Old 31-08-2016, 03:54   #3
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Re: Hot Nanni! (4190)

Also might just be a clogged raw water intake...

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Old 31-08-2016, 04:13   #4
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Re: Hot Nanni! (4190)

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Originally Posted by Snowpetrel View Post
Also might just be a clogged raw water intake...

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Raw water comes into a Cleaner with basket..... if you take the top off even with the engine running at speed, water pours over the sides......... so I'm assuming there is more than enough raw water available.....

Thanks for all your ideas though... I'll sure try some!!
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Old 31-08-2016, 05:13   #5
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Re: Hot Nanni! (4190)

You're getting hot water/steam out the exhaust when she runs hot, so heat transfer is occurring. But, are you getting enough for higher RPM? It still sounds like not enough raw water coming through the system - heat exchanger working, but exhaust getting hottter rather than the modest increase you'd expect. How much heated raw water is making it out the exhaust end? I'm with Snowpetral on blocked exit or weak raw water pump.
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Old 31-08-2016, 07:16   #6
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Re: Hot Nanni! (4190)

Have you looked into the coolant (fresh water) flow? Check coolant level? Do you have a water heater connected to the engine? Change any hoses recently? Could be an air lock, run the engine at idle for a couple of minutes with the pressure cap off to allow any air to escape, then shut down and check coolant level. If you need to add coolant that's good, means the air lock has broken.

Could also be a stuck thermostat (probable) or broken water pump (unlikely).

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Old 31-08-2016, 07:49   #7
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Re: Hot Nanni! (4190)

What about a clogged exhaust elbow? This can seriously interrupt the seawater flow.


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Old 31-08-2016, 14:24   #8
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Re: Hot Nanni! (4190)

I have checked the coolant..... it is full, and I do have a water heater that appears to be working fine..... as far as I know, the COOLANT pump does not have any replaceable parts.

I will run without cap on this morning to see if there are any airlocks......

There is a 45 degree exhaust Elbow at the rear of the heat exchanger...... this was replaced with a brand new one just two years ago, So I can't believe this is causing a back up in the Raw water...... but it definately seems like a Raw water Flow problem to me, so I'll take it off and check it out.....a nd take out the heat exchanger and check that out too.....

Thanks for all the ldeas........ keep em coming!
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Old 31-08-2016, 14:47   #9
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Re: Hot Nanni! (4190)

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as far as I know, the COOLANT pump does not have any replaceable parts.
They can be rebuilt. Its a possibility but do the heat exchanger, thermostat and mixing elbow first
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Old 01-09-2016, 04:38   #10
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Re: Hot Nanni! (4190)

We had overheating problems with our engine. It turned out to be the exhaust elbow coking up and choking the flow of cooling water. By the time I had discovered this I had replaced the water pump impeller and given the heat-exchanger an acid bath, heh.
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Old 01-09-2016, 21:03   #11
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Re: Hot Nanni! (4190)

OK, so I had a bit of a play with it all today...... definitely plenty of raw water..... I took BOTH the end caps of the heat exchanger off and checked that out...... all good...... As I mentioned earlier, the Elbow is only 2 years old..... I didn't have a new gasket for that, so I didn't remove it. When I put all the raw water system back together...... it seemed to work perfectly. Even when I got the block & heat exchanger hot, you could still happily touch the heat exchanger caps, the Elbow, and even the water coming out of the exhaust of the boat was only just warm......... SO

Problem MUST be on coolant side of the set up...... but I didn't get a chance to play with it..... surely VERY FIRST THING TO CHECK MUST BE THERMOSTAT?..........

That said, I'm not entirely sure where it is........ I'm guessing here??

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Old 01-09-2016, 21:46   #12
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Re: Hot Nanni! (4190)

Quote:
That said, I'm not entirely sure where it is........ I'm guessing here??
Yep, that's where it is on our 43 hp Nanni.

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Old 01-09-2016, 22:52   #13
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Re: Hot Nanni! (4190)

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Originally Posted by Weyalan View Post
We had overheating problems with our engine. It turned out to be the exhaust elbow coking up and choking the flow of cooling water. By the time I had discovered this I had replaced the water pump impeller and given the heat-exchanger an acid bath, heh.
I hear ya.... but replaced that just two years ago... Surely it can't be coked up already?...... i might buy a new gasket and take it off and check anyways.....

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Old 01-09-2016, 22:58   #14
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Re: Hot Nanni! (4190)

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Originally Posted by tkeithlu View Post
You're getting hot water/steam out the exhaust when she runs hot, so heat transfer is occurring. But, are you getting enough for higher RPM? It still sounds like not enough raw water coming through the system - heat exchanger working, but exhaust getting hottter rather than the modest increase you'd expect. How much heated raw water is making it out the exhaust end? I'm with Snowpetral on blocked exit or weak raw water pump.
That's exactly what I thought..... but brand new impeller in raw water pump... both ends of heat exchanger checked/cleaned, and nearly new elbow...... I'm starting to change my mind......
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Old 01-09-2016, 23:02   #15
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Re: Hot Nanni! (4190)

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Originally Posted by DeepFrz View Post
They can be rebuilt. Its a possibility but do the heat exchanger, thermostat and mixing elbow first
Checked Heat Exchanger...... looks good..... mixing elbow only two years old... seems to be working OK....... will buy a new gasket though, so I can take it off and check it again.....

I'm going with THERMOSTAT.... can I take it out and run it without it??..... will this confirm it is the issue??
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