Overheated..Please help!
 

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.

Re: Overheated..Please help!
 

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

Re: Overheated..Please help!
 

Re: Overheated..Please help!
 

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....

Re: Overheated..Please help!
 

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.

Re: Overheated..Please help!
 

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.

Re: Overheated..Please help!
 

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.

Re: Overheated..Please help!
 

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)

Re: Overheated..Please help!
 

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.

Re: Overheated..Please help!
 

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.

Re: Overheated..Please help!
 

Started working last night and got to the exhaust shutters. The plastic was completely melted and the only thing left was the stainless steel plate. I got the updated version which does not require the metal rod and grommets on both ends. I pulled the thermostat housing and looked at the thermostat. Does anyone know what degree it is....140...160..etc.. Does anyone have a part number? The impeller is next up and pulling the oil. Should I change the plugs since they had gotten wet. Everything will still spark up fine and start. Thanks.

Re: Overheated..Please help!
 

It should be a 160. Here's one of the best places I have found so far to get parts: http://www.marinepartsplus.com/ . They have a nice fiche layout and pretty good prices as well. If nothing else, the fiche is nice to get part numbers from so you can call arround locally to see who has what in stock. If the plugs are old, change them (again, peace of mind if nothing else). If they are pretty new, pull them and inspect the ceramic insulator to make sure they didn't crack.

Re: Overheated..Please help!
 

I pulled the sea water pump and opened up the housing and what do you know a shredded impeller. I think all of the pieces were still in the housing. I will backflush just to be safe. I pulled off the exhaust elbows and bellows (not fun) and found the exhaust shutters. They were completely melted. The only thing left was the 1/8 inch stainless steel plate the plastic was molded onto. The thermostat looked fine but changed it anyway. I pulled the oil (not fun when you can't heat the engine up) and going to change it and test run it with muffs once the parts are in. I will probably change it again if all is fine because I could not pull it all out with the oil being cold. I want to post some pics of the destroyed parts. Can someone point me to the thread on posting pictures. Thanks

Re: Overheated..Please help!
 

Re: Overheated..Please help!
 

Thanks....ran the boat in the lake this weekend and all went well. Temp stayed about 150-160 when running about 3000rpm. Did some tubing and never got over 175. I sure wish they would have put the impeller in a better place (i.e. take a hint from an inboard). Especially an item that needs to be replaced every few years. Anyway...new impeller...new thermostat....new exhaust shutters....and two oil changes later I am back out on the water. Cost about $160 for parts and some free boat rides for my buddies that helped me fix it. Thanks for the info from you guys.

Re: Overheated..Please help!
 

Good to hear. Glad you got it fixed for cheap. :wink_thumbup: