Cobra not pulling up water?

[Bigdaveaz]

The Pain in the butt OMC i have been fixing problems on Daily has sprouted a new one, will not pump water by the new impeller. It runs at temp with the earmuffs, but when put in the tank will not pump. Back flushed and is clear. 87 4.3 What is special about the Cobra. Took the hose off the t-stat housing and ran engine, no flow? Dave.

 

[Bigdaveaz]

Re: Cobra not pulling up water?

Forgot to add,it will flow some at 2krpm, none at idle? Dave

 

[Bt Doctur]

Re: Cobra not pulling up water?

And just how deep is this tank?And how far is it immersed?

 

[Bigdaveaz]

Re: Cobra not pulling up water?

Just up to the upper and lower case separation,back in tank at boat shop. Dave

 

[Bigdaveaz]

Re: Cobra not pulling up water?

Am thinking,could I have a "break,separation,leak" at the water hose/fittings from the impeller to the t stat? How to test? Dave. Once again, thanks for all your time! Dave

 

[Bt Doctur]

Re: Cobra not pulling up water?

May not be deep enough in the tank .Might be sucking air here

 

[Bigdaveaz]

Re: Cobra not pulling up water?

Have stearn drive in water to the separation and a little above,(upper and lower gear case). I have checked all pathways for obstructions,none. Iam beginning to suspect maybe drawing air between intake and impeller. no water flow below 2k rpm! If I have to separate upper and lower,what is involved,do I first remove drive from boat,or can i just remove lower Gear case to access the connections to water from pick up to impeller? Dave.

 

[Boatin Bob]

Re: Cobra not pulling up water?

If the water is just over the "separation" the pump is sitting in the air, normally in the lake it's under water.

If your going to separate the upper/lower you MUST remove the drive from the boat, there is a shift rod that you have to turn before splitting otherwise you will bend it. You really should have a manual to do this.

 

[Bigdaveaz]

Re: Cobra not pulling up water?

On a Cobra the pump is located at the back on the top gear case near the top, will never be underwater! Dave

 

[Gary H NC]

Re: Cobra not pulling up water?

As easy as the impeller is to get to pull it back out and inspect it.Was it a Sierra part? Was it pumping normal with the old one?

 

[Boatin Bob]

Re: Cobra not pulling up water?

On a Cobra the pump is located at the back on the top gear case near the top, will never be underwater! Dave

I know where the pumps are as I have twin Cobra's, on my boat the water comes right up over the top of the drives (over the oil dipstick) so I know my pumps are under water all the time unless trimmed very high.

 

[bruceb58]

Re: Cobra not pulling up water?

When the boat is on plane, the pump will be out of water.

 

[Bigdaveaz]

Re: Cobra not pulling up water?

Thank you Gary, impeller is new,had boat tech install it! I got the boat not running,so there prob.was a engine heating problem. I have cleared all passages, checked all connections that i can get to,am running out of ideas,just will not pull water below 2k rpm~!

 

[Gary H NC]

Re: Cobra not pulling up water?

If it were me i would pull the cover off the impeller and take a look.New ones have been known to break blades or the brass hub spin in them.It would be an easy check anyway.The housing gasket may have got out of place or about anything.
I would also call the Tech that installed it and ask if pieces of the old one was missing,maybe blocking the flow some where.
Also look at the big rubber hoses that connect to the exhaust manifolds,it you see bubbles in the rubber then the engine was run hot before.

 

[Gary H NC]

Re: Cobra not pulling up water?

Look at this Dave,good investment!

http://cgi.ebay.com/ebaymotors/1987...62QQcategoryZ26453QQihZ024QQitemZ370032377600

 

[Bigdaveaz]

Re: Cobra not pulling up water?

May have to break down and get that, don't know if i will keep the boat though! Is the seal between the drive and the intermediate an "airtight" seal, I keep thinking my problem is one of loosing vacuum,drawing water up to the impeller! How critical is the depth of the lower pick up in the water, had it in the "tub" at the boat store,maybe not deep enough? Dave

 

[Boatin Bob]

Re: Cobra not pulling up water?

When the boat is on plane, the pump will be out of water.

True enough Bruce but I really meant when I normally start mine in standing still position, the pump is submerged.

For Bigdave...I've had problems with brand new and almost new impellers and have had to change them to get water flow, yet by visually looking at them you just can't see anything wrong with them, maybe get another one from a different supplier (worst case is you'll have a spare)

 

[bruceb58]

Re: Cobra not pulling up water?

True enough Bruce but I really meant when I normally start mine in standing still position, the pump is submerged.

Bob, I agree.

Been a few years(and beers) since I had my Cobra but remember having a similar issue. I would really want to put it in the water and run a test there at the dock if you could. Run it up to 1000 RPMs and pull the hose that enters the thermostat and see what flow you have. Then run it at other RPMs. Don't leave the hoseoff very long or you will burn up the hoses that leave the exhaust riser.

 

[Bigdaveaz]

Re: Cobra not pulling up water?

Thanks, Bruce,i'm about out of ideas. Do you remember what was the outcome of your Cobra go-round? 2nd new impeller,Dave.

 

[bruceb58]

Re: Cobra not pulling up water?

It ended up being fine and I was paranoid for no reason.