cooling issue

I have a powerboat with twin engines in a staggered configuration.

the boat uses external water pickups and both flow water at the same rates through the sea strainers (under pressure) so I know there are no obstructions (or at least equivalent parasidic drag).

the forward engine runs hotter under heavy load than the rear (non staggered) engine.

I also noticed at idle the forward engine appears to flow less water through the strainer than the rear engine.

the impeller is fine in the forward engine sea water pump and there are no obstructions in the engine or oil cooler either because both engines allow the same flow of water under pressure.

I have noticed that the forward engine sea water pump does not prime at idle like the rear engine... I have to run the engine at about 1,200 rpm for 10 seconds before it will prime and start sucking water through the strainer. The rear engine primes immediately. I have switched sea water pumps between engines so I know it's not the pump.

do you think that the height of the sea water pump on the forward engine being higher relative to the water line as opposed to being closer to the water line, like the rear engine water is; is the cause of my problems running hotter and lack of priming at idle?

thanks in advance.

 

Not an expert on boats but have worked as a pump specialist. Certainly as your suction lift increases, so too does the performance. From the information that you provide I would think that the suction lift on the pump on the forward engine may not be vertical enough. Pumps don't like sucking sideways as the line is prone to air pockets, hence the problem with priming. If you could keep the suction line below the waterline as much as possible and have it rise as vertical as possible into the pump this may help.

All I can think of. You did indicate that the pumps have seperate inlet lines.

Poida