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HELP - I need some OSO experience!!

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Old 06-04-2003, 09:40 PM
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Unhappy HELP - I need some OSO experience!!

With all the knowledge and experience on OSO, I know someone has the answer I need! Pleeeeeeease!!

Some of you may remember that last year I had trouble getting my boat to pick up enough water for the motors. I run a Cobra cat with two steps in the hull. It has stock HP500 carb motors with Bravo outdrives. The X-dimension is set so that the center of the prop shafts are even with the lowest point of the sponsons. My drives are mounted on the transom with no extension boxes.

It was originally equipped with transom mount pick-ups that would go "dry" at some speeds, especially in turns. I modified them to run deeper which helped, but do to the limited room on my transom, their location interfered with the nose cones on the outdrives when trimed in.

Over winter I pulled both motors to perform some thorough maintenance as well as to clean up the bilge, wiring, etc. While the motors were out I installed adjustable thu-hull pick-ups about mid way between the last step and the transom. Through testing I found that even with the pick-ups adjusted to their maximum depth, they ran "dry" above about 80 mph. I figure the step was causing so much turbulence that the pick-ups were not in "solid" water.

On to Plan "B" - I removed the thru hulls and sent my lower units to Bob's Machine Shop to have low water pick-ups installed. I figured problem solved, right? Wrong! Now it runs great at 50 and above, but apparently loses water when cruising at low to medium speeds.

Running at about 35, we ran it with the motor cover open and you could see water coming thru both sea strainers, but the temp gauges started bouncing all over the place. The gauges never rose above 170 - 180, but the alarm eventually went off and I shut one motor down and idled back.

I installed new 140 degree thermostats with the same results. Next I removed the thermostats and the motors ran very cool until the gauges started bouncing from 100 - 150 degrees and again eventually the alarm went off.

Questions:
[list=1][/list=1]
  • Could I be getting steam pockets in the intake manifold below the thermostat housing and would this cause the gauge/alarm indications? This is where both temp sending units are mounted (in the factory positions).
  • Would crossovers in place of the recirculating pumps help?
  • Do my drives need to run deeper below the transom?
  • If so, what size drive extensions should I try, 1/2", 1", more?
  • Does anyone have any extentions that I could try before I buy?

Sorry for making this so long, but I'm at the limit of my experience. Any help that anyone can give will be appreciated.

Jeff
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Old 06-04-2003, 09:58 PM
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I'm just guessing but it's possible you're picking up aerated water due to the hull steps at those speeds.
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Old 06-05-2003, 07:30 AM
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Crazy - I agree. The question is how to solve it. I'm leaning toward trying some drive spacers to drop the LWP's down into the water further. Thanks!
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Old 06-05-2003, 07:59 AM
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I agree that airation is most likely the root of your problem. It would be my recommendation to try spacers first. Don't go to far to fast. You want to keep the drives from going to deep. The deeper you go, the harder the load on the drive on re-entry. If you can borrow a set and test that would be your best bet. Good luck and keep us posted.
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