bajahaha

Hi,
I have a 1996 454 with a Bravo 1 that is overheating. To get a few things out of the way, I've replaced the thermostat, impeller, engine water pump, water intake hose in bell housing, gasket around the plastic hose bib on the inner transom. I have picked out old impeller parts from the coolers as well. From all the testing at this point, it appears that the pump is not sucking water up from the lake (or muffs). As a basic test, I disconnected the seawater intake from the hose bib in the back and stuck it down into a bucket of water. I cranked the engine and it worked fine. I was able to feel very strong suction on the hose while it was in the bucked. When it was connected like this, it worked like a charm. This leads me to believe the problem is between the seawater pump and the lake. I do not believe there are any obstructions in the drive itself because I was able to flow water from inside and out the intake ports on the drive. I believe there is possibly some air entering the system somewhere between the lake and seawater pump. I am suspicious of the plastic hose bib (although it looks absolutely fine), gasket and very ridged intake hose that's inside the boat. We have a huge history with this boat and its overheating. We have are on our 3rd engine. I also thought that maybe there was some way for air (or exhaust) to be entering the system from the drive (perhaps an internal crack). We have been pulling out hair out with this one. I do not have anything really good to go on with the sucking air idea but that's about the best idea I have now.

This trashed our 4th and my birthday is Friday and I would love to take the boat out and have it work.

Any help anyone can provide is greatly appreciated. I would really like to talk with and pay an experienced Mercruiser/Bravo mechanic for some phone time. If anyone's interested and think they might know what's up, please call me 770-856-2277.

Thanks,
Jody

cig1988

Sounds to me that the gimbal housing is corroded where the intake hose seats. There is a black plastic wedge the retains the hose in place. Often when that housing corrodes it will pinch the hose restricting water flow.
Remove the hose housing from the gimbal housing & inspect the opening. It should be completely round.

Is the boat used in salt or fresh water ?

bajahaha

Hi cig1988,

Thanks for the reply. I replced the hose and tapered insert on both ends. The holes are completely round and overall there is very little corrorsion. The boat is currently used in freshwater but it may have been used in salt at one point it its life.

Jody

oldandtired

If all else fails, go with a transom mounted pickup. There is a possibility that the hose has been kinked or worn between the bellhousing and the gimbal housing. The corrosion issue is another. An air leak is relatively unlikey if it happens at idle because almost the entire transom is under water at that time. Have you tried blowing water backwards through the drive (suction side of pump through the transom) to see if the flow seems ok? Just some thoughts.

Rene

jeff32

Make sure you have the right hoses, meaning if you have replaced the hose for cooling water with hoses that don't have kind of metal wire around then but inside the rubber, it may be the hose that collapse or closes on itself from suction pressure. even if you have wires in the hose, make sure they are strong enough... it happened to me...

It may also be the rubber inside the hose that is delaminating and making restrictions on water flow... also happened to me...

Good luck and let us know!

bajahaha

Thanks but no such luck. Is there anything in the drive that could be causing a serious obstruciton or break possibly allowing air to enter the line? I have backflushed the drive and water seems to flow ok but it's kinda hard to say for sure that there aren't any obstructions. I'm pretty sure the hoses for the seawater pump are hooked up correctly but if I recall correctly they are not hooked up the way the diagram on the back of the pump shows. This is a standard rotation engine and the intake for the pump is on the bottom. Does this sound correct? Is there any reason to prime the pump and if so, how would I go about this?

Thanks again!

mtgbiker

clear hose between the out drive an the raw water pump will tell you a lot or between the raw water pump and the t-stat housing to see if air is getting in the cooling system.

Jfever

Just fought an overheat problem w/ my HP500 drove me crazy trying to figure it out. Had good water flow at idle but no pressure when running on plane. It was the pre formed hose running thorugh the gimbal. When you get the r's up a bit the extra suction would collapse the hose and pinch off the water flow.

Thunderstruck

Somebody else chime in because I'm going from memory but I think my standard LH? rotation motors suck in the TOP of the pump and discharge out the bottom. However, as you said there is an arrow on the newer one piece housings that shows motor rotation and the correct hookup. Hook it up accordingly.

bajahaha

Thanks for all the replies. I think the problem may be solved (or close to it). It turns out that although the water pump body had been removed from the pump in the past the impeller had never been removed. I was observing some strange behavior such as the pump working fine if primed but not working at all if it wasn't. For some reason it wouldn't pull suction at all if it wasn't primed. I pulled the impeller and found that the impeller and housing were melted and destroyed (pics to come). I ordered another one but haven't been able to install it yet. I really wanted to get it done for my bday but had plans to visit my mom at Tybee Island, GA for the weekend (I wanted to take it with me to the ocean oh well, I’ll do it next time!)

Before I put this damn thing back together and drag it 45 minutes to the lake and discover whether it’s going to work or not, I have some questions and hopefully someone can point me in the right direction.

1. Does the seawater pump (and ridged intake hose) sit below the water line?
2. If I start the engine while on the trailer with the outdrive in the full down position (with intake ports on the drive fully submerged), how long should it take for the pump to suck water up and create the strong suction it takes to keep the engine cool?
3. Will a little water in the system (it drained while on the trailer) cause any issues?
4. Has anyone had any issues with the Sierra aftermarket pump repair kit?
5. Is there a more bullet proof pump or body I can use to prevent the thing from burning up in seconds like it appears to be doing now?

Thanks!
Jody