High Water Pressure Merc 700 SCI
#1
"Unregistered Gun"
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High Water Pressure Merc 700 SCI
Helping a buddy troubleshoot his high water pressure issue, the boat has low water pickups and staggered Mercury 700 SCI’s. It has Hardin two stage sea water pumps, boat pumped water on the hose with no issue. Backed it in at the ramp and it wouldn’t pump any water. Pulled it out and pulled the pumps apart. Both impellers were fine and no missing vanes, replaced both impellers with new and put back in the water and pumped fine. Took the boat out for a spin and now it has high water pressure, both mechanical gauge and water pressure sensor readings are the same. About 45 mph the water pressure is pushing 35 psi and have read up to 45 psi on smartcraft. Checked the relief valve in the strainer and the dump lines, all is clear and relief valve appears to be working. Boat ran flawless in the past, any ideas?
#3
"Unregistered Gun"
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Thanks!
#4
Registered
Have you tried back flushing from the headers? Cap stbd side at jumper outlet with a bar stool rubber foot or something similar, pump in from port header jumper outlet and watch what comes out the sea pump hose, disconnected from sea pump obviously.
#5
Platinum Member
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The Hardin 2 stage has been on the boat for some years with no issue, it has a Whipple stage 2 kit I think. It has stainless marine strainers with the relief valve built into the lid, he spoke to them yesterday and they recommend using a newer design lid they offer. Will see how that goes!
Thanks!
Thanks!
#6
"Unregistered Gun"
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Thanks!
Last edited by Jim Diesel; 06-29-2022 at 05:10 PM.
#7
Platinum Member
Platinum Member
Ok, my 2 stage pumps have a -20 inlet from the strainer then a -16 to the engine / headers and a -12 to the intercooler............why is there only 1 outlet on the two stage pump ? agree the valve might be the issue if all the other line are clear
#8
"Unregistered Gun"
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“One of many of Hardin Marines latest cooling innovations in a new two stage sea pump for the popular Mercury Racing HP525, 600SCI, 662SCI, and 700SCI engines. Engine builders have been pleading for a solution to the lack of water that the factory sea pump delivers and Hardin Marine rose to the occasion with the development of this product. Finally an answer to failed headers from water starvation and detonating engines from under supplied intercoolers.
This pump is designed to retrofit to all Mercury Generation 5/6 engines equipped with a sea pump mounted fuel pump. This pump accepts the OEM factory mechanical fuel pumps that are integrated components in the OEM fuel system and provide additional priming support to the factory EFI system. On the supercharged engines this unit is perfect to solve the cooling system short comings of the factory single stage sea water pump system that splits the single water supply to feed the factory intercooler.”