Mystery Cooling Problem - NEED HELP!

[dmeals]

1988 OMC Cobra, 5.7 GM. Runs on hose ok but overheats very quickly drawing lake water. Shut down at approximately 200 degrees. Let cool and pulled intake hose coming from transom at the therm housing. No waterflow! Details follow:

- New pump housing, cup, gaskets, o-ring & impeller (Sierra)
- Checked direction of impeller - OK
- Checked pump hsg for cracks, deformation - OK
- Pulled drive, checked intake grates, back-flushed from intake through upper - no debris good flow
- Back-flushed hose from cooler through copper watertube - no leaks, no debris
- Checked gimbal housing hose - no debris, no delamination
- New drive mounting gasket & o-ring on gimbal hsg
- Pulled cooler - no debris
- Pulled hose from cooler to therm housing, some water in hose - no debris, no delamination
- All clamps tight

So, why won't it pump water from the lake and cool properly???

I am dumbfounded! Any suggestions appreciated!!

 

[Levinz11]

Re: Mystery Cooling Problem - NEED HELP!

Is the vent hose on the impeller housing clear?

 

[Idlespeedonly]

Re: Mystery Cooling Problem - NEED HELP!

is the impeller burnt up each time?
Your checklist is pretty thorough and complete.

 

[Howard Sterndrive]

Re: Mystery Cooling Problem - NEED HELP!

is the impeller turning? there's some sort of splined shaft in there to turn it? (I'm not much of a Cobra guy)
I'd pop the cover off and bump the starter if you haven't already verified that.

 

[dmeals]

Re: Mystery Cooling Problem - NEED HELP!

is the impeller turning? there's some sort of splined shaft in there to turn it? (I'm not much of a Cobra guy)
I'd pop the cover off and bump the starter if you haven't already verified that.

New impeller, no is is not damaged. Yes, the bleed line, vent line is unobstructed.

Split the drive to check the gearcase water passage and housing. May have found the problem. The water tube guide and grommets melted. I suspect it was sucking air.

Forgot to mention in my original post that the boat had an extreme overheat and melted the y-pipe connetor boots, exhust boot, etc. That is what started this repair.

Have a new seal kit coming in a few hours. Will reassemble, test run and advise outcome.

Thanks for the input.