Nanni engine overheating

[Gazza]

I'm hoping that someone can give me some pointers as to where I go from here. Our Hunter Pilot has a Nanni 2 50HE 14hp fresh water cooled engine with just over 200 hours shown. It's been fine since we got the boat two summers ago, and has been maintained on schedule. The engine has started overheating - alarm going off as no temp. gauge - after 25 minutes running.

The exhaust elbow was corroded at the water inlet stub pipe, and this looked like the culprit, as it was pretty gunged up, so new elbow fitted, but problem still there.

Inlet Ok
Impellor OK
Water flow from exhaust OK
Thermostat tested and OK
Heat exchanger OK
Oil level OK

Today I took the thermostat out again and retested it - worked at the correct temp., according to my wife's thermometer used for marmalade making. I didn't put the thermostat back in and then ran the engine at 2500 revs in gear , firmly tied to the pontoon,for an hour with no sign of overheating.

My next step is to flush the fresh water system with a flushing agent. If that doesn't work, then the fresh water pump will probably be worth a look at, but I'm wondering if there's anything obvious I've missed.

Any thoughts/experience/advice gratefully received - we should be sailing this week, not grovelling around in the engine compartment!

 

[sailorman]

I'm hoping that someone can give me some pointers as to where I go from here. Our Hunter Pilot has a Nanni 2 50HE 14hp fresh water cooled engine with just over 200 hours shown. It's been fine since we got the boat two summers ago, and has been maintained on schedule. The engine has started overheating - alarm going off as no temp. gauge - after 25 minutes running.

The exhaust elbow was corroded at the water inlet stub pipe, and this looked like the culprit, as it was pretty gunged up, so new elbow fitted, but problem still there.

Inlet Ok
Impellor OK
Water flow from exhaust OK
Thermostat tested and OK
Heat exchanger OK
Oil level OK

Today I took the thermostat out again and retested it - worked at the correct temp., according to my wife's thermometer used for marmalade making. I didn't put the thermostat back in and then ran the engine at 2500 revs in gear , firmly tied to the pontoon,for an hour with no sign of overheating.

My next step is to flush the fresh water system with a flushing agent. If that doesn't work, then the fresh water pump will probably be worth a look at, but I'm wondering if there's anything obvious I've missed.

Any thoughts/experience/advice gratefully received - we should be sailing this week, not grovelling around in the engine compartment!

Faulty sender / alarm meby
contact
http://www.peachment.co.uk/

 

[Malish]

when you say the thermostat 'worked' at the correct temperature what do you mean? Given that no thermostat = engine does not overheat I would be inclined to treat your existing one as suspect and change for new (can't be that expensive?). This may not be the answer as removing the thermostat will by default increase the aperture through which the cooling water flows but I think it is worth a try.

 

[Tropic Cat]

The planned engine flush should take care of things. I've done this in Yanmars with liquid kitchen drain cleaner. It works wonderfully, but keep the thermostat out while flushing.

 

[bendyone]

I had the same engine and problem, it was the sender unit at fault,

 

[vyv_cox]

Check the actual engine head temperature, as it seems likely the alarm sender is faulty. Use your thermometer with a small piece of polystyrene foam outside it, touch on a flat area of the head and hold it for a minute or so. The figure will be accurate to a about a degree and should not be far off the thermostat temperature. Or better still use a contact thermometer if you can get hold of one cheaply.