AD41's getting hot at High RPM since prop change

I

Ian MacAulay

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Evening

Just after a quick bit of info.. Been looking at a boat that had replacement duo props and on outing its buzzer went off as the temp slowy rose

Also at this point it was noticed the engines were turning 4100-4200rpm

Now I know the engines rpm is a bit high at WOT but just a few hundred rpm cause them to overheat?? Props are Volvo duo A7

Thanks

Ian
 
Thanks mate...

I understand 3900. Is Max but being 300rpm over would that be enough to cause the overheat?

Also to bring down 300 rpm what sort of adjustment in pitch will they need ..


Thanks

Ian
 
It's probably two separate problems.

4100 is over propped, but should not cause overheating, which could be furred-up heat exchangers, blocked exhaust elbow, poorly pump, etc.

Going up one prop size would drop max rpms by 300 if it's only one size over propped.
 
Last edited:
FlowerPower said:
4100 is over propped, but should not cause overheating
Click to expand...
Why not?
The OP didn't tell us how long it took to overheat while running at WOT above the rated max rpm, but I surely wouldn't expect any engine (let alone a light duty/high speed one) to run forever in such conditions without overheating...
 
It's possible, but unlikely, I think. If running 300rpm over causes an overhead, then that cooling system is a bit "marginal".
 
FlowerPower said:
It's possible, but unlikely, I think. If running 300rpm over causes an overhead, then that cooling system is a bit "marginal".
Click to expand...

I think the water flow is more or less proportional to the engine rpm's when the cooling system is working ok so I would also start with the heat exchanger, bad pump, or blockage approach. Quite common on older engines having these issues so unless its been cleaned, checked recently it needs to be done.
 
the heading says since prop change and the implication is the op is looking to buy the boat.

Hence the. Overheat since prop change is just a claim by the seller ?

Why were the props changed. ? Grounding ? Heat exchanger full of sand?

This aside I would never consider running an engine over it max rated rpm. It is not a car with a few seconds over the red line but producing high power. If run at 3900 does it over heat ?
 
Thank you all for help and answers.

So firstly it needs the new props increasing. These were replaced as the old ones were to heavy worn and claims the numbers were unable to be seen so that's why the new ones are incorrect..

So can duo props be re pitched??

So it also sounds like there is maybe a cooling system issue.. He has only used it plodding about so maybe blocked up.. Is the heat exchanger and cooling system easy to flush?
He informs me the tempature slowly increased and then buzzer went off at 190°

Thanks Ian
 
Engines were serviced yesterday and starboard engines water pump was in a right state.... wonder if thats the issue


Been reading and some say to slightly under prop to reduce stress on gears and engine.. is this correct?


thanks


ian
 
Evening all


I have done a fair few jobs on her including rydlyme in the exchangers and coolant flush on both engines.

Today I had a chance to test properly for my self. Port engine still runs about 5° hotter and when opened up alarm sounds first then few seconds later starboard engine alarm sounds and they sit around 90° on both

But the previous owner said she got high rpm to over heat.......

My testing with 4 people full fuel and water and heavy ish lugguage got me a poor 31mph at WOT of just 3500 and buzzers off at this ....

Now are these engines working g to hard and getting hot and the lack of rpms affecting my water flow or any other ideas. Also I have A7 duo props and how much will I need to go to get me to my desired 3900 rpm?

Thanks

Ian
 
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