Outdrive Water Pump only cycles water when 'primed'?

[JKolbfleisch]

I replaced the impeller/housing/gaskets and wasn't getting any flow from drive to the thermostat. (Disconnected and observed the direct line hose). After burning up the pump and replacing with yet another unit, I was able to get flow only by 'priming', or pouring water down the hose from the thermostat end towards the Outdrive. Eventually and started gushing and the engine maintained 160' idling

Let the engine cool. Fired it back up .. and no water flow again, at least not until I 'primed' it again. Any ideas why? I can't prime this thing every time I want to use it.

Details.
OMC Cobra 2.3
Brand New Pump
Good water flow thru hoses
Good water flow through pump passageway to screen pickup
Submerged drive into bucket of water and flowed better than hose clamp, but still needs prime

 

[Keyboardman]

If you're trying to run the engine with the outdrive in a tank, it won't work. The outdrive needs to almost fully submerged for the impeller to pump water. It does not have the suction to pull water up from the intake on the bottom end of the lower unit.

 

[HT32BSX115]

Any ideas why? I can't prime this thing every time I want to use it.


Submerged drive into bucket of water and flowed better than hose clamp, but still needs prime

Howdy,

Welcome aboard!



I think Keyboardman hit the nail right on the head!! Since you have already replaced the pump (located on the back of the drive) You know where it's located in relation to water level when the boat is sitting in the lake!

For it to "prime" that part of the drive needs to be completely submerged. Once the engine is running (assuming there's no leaks in the suction line) it will maintain "prime" as long as it's running (even when you're up on a plane.

Once you slow down and stop or at idling speed, the water "level" is above the actual level of the pump so it will always prime.

If the pump is above the level of the water (like in a bucket) or with the boat sitting on a trailer with only the lower part of the lower unit in the water, (water level NOT at pump level) those pumps will usually NOT produce enough suction to self prime.

That's why "muffs" with a pressure water source are required (A flush adapter looks like "ear muffs"!)

Cheers,


Rick

 

[Scott Danforth]

Submerged drive into bucket of water

unless the bucket is big enough to put the whole boat in it, stop.... use the muffs

when a boat is backed into the water, the whole outdrive is under water. this floods the non-self-priming water pump and allows the pump to prime.

then when you are going forward, water is forced up the drive inlet into the water pump at pressure ( 5 psi at 5mph, about 20 psi when you are traveling 20 mph, about 40 psi at 50mph)

attempting to suck water up from a bucket is stupid and results in a burned up impeller.

so now change your impeller again

then use muffs

 

[JKolbfleisch]

Thank you everyone! I should have said that I had both muffs on and it was submerged. Despite that, it still would not reliably cycle water.

That said, I took it out on the river and fully 100% submerged it moved water perfect and maintained 165-170 temps.

I guess I either had very cheap muffs or the OMC design is really picky. Thanks guys!

 

[Scott Danforth]

You most likely did not have the water turned up fully on the hose with the muffs