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Started By
Message
Yamaha OX66 250 HP issues - loss of water pressure/cavitation
Posted on 6/24/13 at 11:29 am
Posted on 6/24/13 at 11:29 am
The boat is a 30' Scarab with twin 250 hp Yamaha OX66's. Over the winter we took the boat in to the mechanic to get annual maintenance. Turned out that the starboard motor lower unit was on its last leg and needed replacing. We also had water pumps replaced in both motors.
Now we are having an issue with the starboard motor cavitating and losing water pressure (eventually getting hot and alarm sounding) when running above 4500 rpms or around sharp curves. This happens whether the motor is all the way down or trimmed up in its running position. It seems to me that once the water pump loses prime, it doesn't recover. Ideally, I would take the boat back to the mechanic to get it looked at, but its down at the camp and its not the easiest task. Looking for some suggestions on what the issue might be and if it is something I can try and tackle myself.
Now we are having an issue with the starboard motor cavitating and losing water pressure (eventually getting hot and alarm sounding) when running above 4500 rpms or around sharp curves. This happens whether the motor is all the way down or trimmed up in its running position. It seems to me that once the water pump loses prime, it doesn't recover. Ideally, I would take the boat back to the mechanic to get it looked at, but its down at the camp and its not the easiest task. Looking for some suggestions on what the issue might be and if it is something I can try and tackle myself.
2
Posted on 6/24/13 at 11:34 am to lsufishnhunt
I would think it has to do with the new water pump. I'm not familiar with Yamahas. I would take it back he may have install it wrong or left parts out
This post was edited on 6/24/13 at 11:35 am
Posted on 7/1/13 at 3:55 pm to offshoretrash
Anyone else with any ideas? I really don't want to have to bring it back to the tech if it can be avoided.
Posted on 7/1/13 at 3:58 pm to lsufishnhunt
If nothing else has changed and you can't see anything wrong, pull that water pump and check it.
Do it yourself. You'll save a ton of money instead of pulling that big bastard to a shop
Do it yourself. You'll save a ton of money instead of pulling that big bastard to a shop
Posted on 7/1/13 at 4:26 pm to DownshiftAndFloorIt
Sounds like a water pump issue. Pull your water pump off & make sure that all the parts are there. could be something simple like a missing part of some grass hung up in it.
If that doesn't work, sell the yamaha's & buy 2 new mercs... Problem solved
If that doesn't work, sell the yamaha's & buy 2 new mercs... Problem solved
Posted on 7/1/13 at 4:47 pm to lsufishnhunt
you probably have a plugged passageway in the cooling system.
the foot needs to be pulled and check pump.
If all is good there pull thermostat and check for small pieces of rubber from old pump.
I would prob pull themostat first, cause its easy.
If you see rubber you need to blow out and blow through the piss hole
the foot needs to be pulled and check pump.
If all is good there pull thermostat and check for small pieces of rubber from old pump.
I would prob pull themostat first, cause its easy.
If you see rubber you need to blow out and blow through the piss hole
Posted on 7/1/13 at 4:51 pm to greasemonkey
I was thinking along these lines for a while... but the cavitating has me confused. This past weekend we were running through some sloppy seas and the motor would cavitate pretty regularly, then totally lose water pressure. I'd have to come back down to idle before it would pick back up. A clogged passageway wouldn't do this, would it?
Posted on 7/1/13 at 4:55 pm to lsufishnhunt
no that sounds more like a hub slipping...
might have 2 diff problems
might have 2 diff problems
Posted on 7/1/13 at 5:05 pm to greasemonkey
Will a hub randomly slip? I've always thought that once a hub slips, its done.
Sorry for all the questions, just trying to figure this out. The more I read, I'm starting to be a little more concerned that its a fuel/VST Filter/O2 Sensor issue combined with a water pump issue. Thoughts?
Sorry for all the questions, just trying to figure this out. The more I read, I'm starting to be a little more concerned that its a fuel/VST Filter/O2 Sensor issue combined with a water pump issue. Thoughts?
Posted on 7/1/13 at 5:11 pm to lsufishnhunt
I have seen them randomly slip but it usually gets worse pretty quick.
dont see how that would make it cav but not really sure.
def believe you have 2 seperate probs..
try a search for clogged water pass on your model.
swap props around to see if prob changes on cav
quote:
Sorry for all the questions, just trying to figure this out. The more I read, I'm starting to be a little more concerned that its a fuel/VST Filter/O2 Sensor issue combined with a water pump issue. Thoughts?
dont see how that would make it cav but not really sure.
def believe you have 2 seperate probs..
try a search for clogged water pass on your model.
swap props around to see if prob changes on cav
Posted on 7/1/13 at 5:13 pm to greasemonkey
quote:
swap props around to see if prob changes on cav
Easy now. He may be counter-rotating with twins.
Posted on 7/1/13 at 5:14 pm to Jester
quote:
dont see how that would make it cav but not really sure
It sounds like a cav... but i guess it could be surging, which might sound like a cav.... ???
quote:
Easy now. He may be counter-rotating with twins.
This.... Can't swap them around.
This post was edited on 7/1/13 at 5:16 pm
Posted on 7/1/13 at 5:19 pm to lsufishnhunt
quote:
Easy now. He may be counter-rotating with twins.
This.... Can't swap them around.
glad you caught that.
surging sould seem dif than cav but it might would be hard to tell the dif for the non greasemonkey
Posted on 7/1/13 at 5:21 pm to greasemonkey
quote:
surging sould seem dif than cav but it might would be hard to tell the dif for the non greasemonkey
I would've thought the same thing, but now i'm really questioning myself. I'm definitely no greasemonkey, but I like to think that I could tell the difference in a cav and surge, but who knows at this point.
Posted on 7/1/13 at 5:21 pm to greasemonkey
Meh
He should be able to tell the difference in cavitation and blowing a hub out. Cavitation sounds wayyyy different than just surging an engine.
He should be able to tell the difference in cavitation and blowing a hub out. Cavitation sounds wayyyy different than just surging an engine.
Posted on 7/1/13 at 5:26 pm to DownshiftAndFloorIt
I've been on cav all along, but the talk of a possible hub slip brought me HERE and made start to question if it was a surge instead of cav...
Posted on 7/1/13 at 5:28 pm to DownshiftAndFloorIt
quote:
He should be able to tell the difference in cavitation and blowing a hub out. Cavitation sounds wayyyy different than just surging an engine.
I kige this
OP
cavitation revs higher than a surge would, like revin in neutral.
Posted on 7/1/13 at 5:30 pm to greasemonkey
When running at 35-3600 RPMS, it'll jump up to about 42-4400 Rpms...
Posted on 7/1/13 at 5:30 pm to lsufishnhunt
Idk howconfident you are with yourself but if you're a boat guy and feel like its cavitating its probably cavitating. As to what's causing it, 
Cavitation is caused by aerating the prop, so you have to look for what's allowing it to suck air. Is ANYTHING different with the port and starboard back end of the boat?
Cavitation is caused by aerating the prop, so you have to look for what's allowing it to suck air. Is ANYTHING different with the port and starboard back end of the boat?
Posted on 7/1/13 at 5:36 pm to lsufishnhunt
I read some of your link and I guess on twins one biting harder than the other could make it hard to diagnose.
I would def do the vst filter and o2s if they havent been done recently.
I dont believe its a hub.
Have the fuel press checked,or google it and rent gauge from parts store and do yourself
I would lean more to surge and do tune up stuff such as filters plugs and o2s if they havent been changed
I would def do the vst filter and o2s if they havent been done recently.
I dont believe its a hub.
Have the fuel press checked,or google it and rent gauge from parts store and do yourself
I would lean more to surge and do tune up stuff such as filters plugs and o2s if they havent been changed
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