I
iwanlane
Guest
" Hi,
I'm stumped, please
" Hi,
I'm stumped, please help.
Old outboard was given to me. Took it for a test run. Ran fine for a few minutes then stalled. Starter very hard to pull. Left motor to cool down for several hours. Started motor again but couldn't see any water coming out of anywhere. With some investigation, we realized that in fact, there is no facility to observe water comming out. Cooling water is pumped straight back into lower unit. I drilled 3mm hole in cooling channel just before the water discharges into the lower unit so that I could tell if water is pumping fine.
This worked well and now I can observe operation of cooling system.
Problem symptoms:
1. At lower to medium revs, water pumps fine.
BUT at high revs, water stops altogether and verocious air bubbling occurs around propeller.
2. With propeler shaft horizontal or pointing slightly upwards towards sky, water pumps fine.
BUT with propeler shaft pointing slightly downwards towards sand, water stops altogether.
3. When motoring boat straight forward or turning to port(i.e. motor pointing right), water pumps fine.
BUT when motoring boat to starboard(i.e. motor pointing left), water stops altogether.
Impeller seems new and undammaged. Intake screen not clogged. No obvious blockages.
Questions:
Could the combustion exhaust pressure at higher revs be high enough to force the water back through the cooling system?
What kind of water pumping pressure should I be expecting?
Do the symptoms indicate any water leakages between pump and discharge?
Could it be that at the higher revs, the water is pumping so fast that none exit at the hole I drilled?
Sorry for being so long winded.
Any help would be greatly aprreciated.
Thank you.
Iwan "
I'm stumped, please
" Hi,
I'm stumped, please help.
Old outboard was given to me. Took it for a test run. Ran fine for a few minutes then stalled. Starter very hard to pull. Left motor to cool down for several hours. Started motor again but couldn't see any water coming out of anywhere. With some investigation, we realized that in fact, there is no facility to observe water comming out. Cooling water is pumped straight back into lower unit. I drilled 3mm hole in cooling channel just before the water discharges into the lower unit so that I could tell if water is pumping fine.
This worked well and now I can observe operation of cooling system.
Problem symptoms:
1. At lower to medium revs, water pumps fine.
BUT at high revs, water stops altogether and verocious air bubbling occurs around propeller.
2. With propeler shaft horizontal or pointing slightly upwards towards sky, water pumps fine.
BUT with propeler shaft pointing slightly downwards towards sand, water stops altogether.
3. When motoring boat straight forward or turning to port(i.e. motor pointing right), water pumps fine.
BUT when motoring boat to starboard(i.e. motor pointing left), water stops altogether.
Impeller seems new and undammaged. Intake screen not clogged. No obvious blockages.
Questions:
Could the combustion exhaust pressure at higher revs be high enough to force the water back through the cooling system?
What kind of water pumping pressure should I be expecting?
Do the symptoms indicate any water leakages between pump and discharge?
Could it be that at the higher revs, the water is pumping so fast that none exit at the hole I drilled?
Sorry for being so long winded.
Any help would be greatly aprreciated.
Thank you.
Iwan "