[jasfiveo]

I have the 7.4L 454 Bravo III. I went to the lake today and before I got started I needed some gas. I started the boat and idled with the blower on while I filled up. Approximately four to five minutes later I started out. Immediately the warning buzzer came on. I looked at the gauges and noticed that the temp was rising extremely fast to a dangerous level. All this in five or so minutes with no take off just idle. I cut the motor off and lifted the hatch. I could hear what sounded like boiling water coming from the engine area. The hoses were extremely hot to the touch. As I continued to listen to the boil like sound all of a sudden a whosh (kind of like something was stopped up in a drain pipe and you remove the debris and you could hear the water flow) sound happened and it sounded like everything flushed out. I let the motor cool off and I tried to start it again. All I got was a thud for lack of a better word. I now know that sound was hydro lock. The marina explianed to me that the impellers probably malfunctioned and that water could not flow. He also said that the hydro lock was probably caused by the exhaust flaps melting and everytime I tried to start the motor it was letting water in causing the cylinders to flood. The spark plugs were removed and I fired it up several times to get the water out. I started it back up only to get it back on the trailer. I checked the oil and it has water in it. Can someone help me with what I might be looking at. I am not sure how the internal cooling system, water pumps, impellers, etc work. I sure hope I am not screwed. I don't thing I cracked the head because I did not run the motor and cut it off immediately when I noticed it get hot. Sorry about the long explanation.

[Mark]

Sorry to hear that . But the first thing that would come to my mind is a head gasket. Thats what I would start with. I would ask around how you would do a pressure check on a boat motor. Good luck

[WetWilly]

Hi jasfiveo,

Sorry to hear of your troubles... now lets see if we can get back in the water soon!

Mark has a point, but I think the water in the oil could have come from when you were hydro locking the motor like the mechanic said so I wouldn't worry about the heads or gaskets right now. From your explanation, it sounds like the motor hydro locked near idle so I wouldn't worry about any bent internal parts at this time either.

I would look at performing the follow work first, assuming you had a sea water cooling system (no heat exchanger tank on the top front of the motor) :

1) Change the Impeller ( If your impeller is broken in several pieces, try locating all of them so they don't cause a blockage somewhere else)
2) Change the Thermostat
3) Change the Exhaust Baffles (this will be the most difficult and expensive)
4) Change the Engine oil & filter
5) Check the Exhaust manifolds, the couplers and cooling hoses for any damage.

If your worried about the heads or the gaskets, you can do a dry/wet leak down test on each cylinder and unless you have bad exhaust manifolds or the rare chance the heads or gaskets are bad, this to-do list should get you back playing real soon!

Good luck,
WetWilly

[stereoman405]

Second on WetWilly. Definitely start with sea water pump and move up from there. The hydrolock has me concerned as that is usually a head gasket / cracked head. but being that this happened off idle and not at WOT it might not be that bad. Hopefully head gasket....

[jasfiveo]

From all the reading and the mechanic suggesting the same thing that is the route I will take. Can you share a picture of where the sea water pump/impeller is located? I know where the exhaust flaps and thermostat are. I will get a compression test just to be on the safe side. Will back flushing get all the impeller pieces out? How often should the impellers be replaced? New to all this and need to be educated. I have a complete service book on the way. What is a fair price for this. I have priced the parts and he told me about $70 an hour labor. $35-$40 for the flaps....$15 for the thermostat.....about $100 bucks for the impeller/sea water pump kit. Thanks for the suggestions. Sure wish this happened at the end of the season.

[jasfiveo]

One last thing I forgot to add after reading several other posts about the impeller was that the guy that loads the boats back on the trailer at the end of the day told me that the battery was dead and he had to drag it through the mud that was why my prop and foot were dirty. I did not notice how high the mud level went and if it clogged the water intake on the foot. Could have possibly caused the problem or just coincidence? Had no problems the day before and ran it all day. Just a thought.

[stereoman405]

Here's the best 'How To' out there on sea pump replacement. I just replaced mine on my Chaparral I just sold. My hardest part was getting to the thing, then I realized my rear seat came out really easy. If I had to do it again it would be an easy 1 - 2 hour job. (You'll have to join the site for free to see the pics I bet.)

http://www.speedwake.com/upload/show...light=sea+pump

As far as the mud thing, I guess its possible that if it got really gunked up it could've clogged the inlets, they aren't that big. But I think that would be unlikely. If you pull it apart and there is mud in there then I'd say you have a case to be pissed.

Make sure you get all the impeller pieces you can because it is good to account for all of them. How the system basically works is there is one hose that goes from the out drive into the sea pump, then water is forced out of the pump into another hose that, on my motor, crossed underneath the block and connected to the main water pump housing on the front of the block. I popped that end off while the other end was of the sea pump and used a garden hose to back flush all the debris out.

On the how often, that is pretty debatable. The official advise is once a season just to be safe. (Especially if you're the type with big $$ in the motor.) I myself just keep an eye on temp. If WOT runs tend to creep the temp up then that means the impeller is probably getting worn down (they are made of rubber). I know people that changed them every 5 years with no problem. Also the type of water you're running will affect it. Fresh or salt? Clear or mucky? Do you beach a lot so your drive is prone to sucking up fine sand to chew things up? You get the idea.

All the prices you mentioned sound dead on.

[jasfiveo]

Doing the job this weekend. Quick question about the oil change. Should I change it once than run it for awhile and then change it again. I ask this because I got water in the cylinders and thought it might be a good idea to make sure there is no amount of water in the oil. (don't want to bend internal parts)

[stereoman405]

I'd gauge it by how the oil looks after running it for a few minutes. Any hint of cloudiness and I'd flush it again. Its my understanding that the marine grade Merc oil is designed to "absorb" a limited amount of moisture a little better than standard motor oil, but I still wouldn't feel good with any visible signs of water in there.

[AirNavy]

If it was me, I'd probably change it again if for no other reason than peace of mind. In reality though, once you change the oil and run it up to temp any remaining entrained water would be likely to evaporate pretty quick.