454 Bravo One Overheating. Very strange
 

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

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 ?

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

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

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!

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!

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.:)

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.

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.

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

some draining of water while on trailer is no problem----just make sure drive is down at least half when firing it up in the water and fully down when on trailer----put muffs on and run water a few minutes into stern drive before firing up---never ever fire up dry as this will burn impeller in matter of a minute or two---also with muffs on dont go much over idle as the suction increses and will starve the pump---not sure on the aftermarket or heavy duty pumps but id go with factory replacement when available---just thoughts----sorry for the 4th and your b-day----we were grounded too this last week due to a blown coupler and broken skeg-----sux.....:(

good luck with the repairs

1. Yes while stationary
2. instantly
3. no
4. Mine is OK so far
5. Jabsco makes a highly recommended OEM replacement. Don't have part number off hand. Not worth it if your repair kit fixes it for now.

Put some good lubricant in the housing before inserting the new impeller. Run it on a hose so the water gets up into and in front of the pump as well.

bajahaha,
Is yours a fuel/seawater pump combo(like my old '93 454's)?
If not, this is the Jabsco replacement pump, much better than the one piece plastic crap that Merc now uses, it's a bronze housing: I am going to replace the ones on my HP 500EFI's with these units:
http://www.amazon.com/dp/B000O8F1C0/...0&linkCode=asn

Good Luck,
Paul

If you toasted an impellar, Remove the hose from the outlet side of your oil cooler and run water from a hose backwards through the cooler. That will help to flush out any pieces of impellar that came loose.

Thanks again to everyone! We are getting closer to the resolution but still no fix as of yet. I purchased a new pump (impeller and housing) and quicksilver flusher kit. After replacing the pump and hooking up the hoses, we decided to crank it. No water flow anywhere. I pulled the intake hose off the pump (while the water was on full blast) and there wasn't a drop of water at the intake side of the pump. What is going on here? Should there be water at the pump while the flush kit is installed? I would think so. If for some reason there isn't supposed to be, I think my rigid intake hose is worthless because it’s sucking air around the barb. It is very hard and doesn't seal very well around the barb in the back. It looks like the hose is actually fuel inlet hose (extremely rigid) is this correct? I'm ready to purchase a new water hose to see if that works. I'm real curious to know if the flush kit should push enough water through the system for there to be water at the intake side of the pump. Please help. I can't believe or let this freaking boat ruin another summer. I've had it for a year and have spent an incredible amount of time and money on this stupid thing.

Thanks!
Jody

If you pulled the intake side of the pump and did not get any water with the flush kit on, you for sure , have an obstruction. I would concentrate on clearing it. Possible debris? pinched hose? It should flow like the garden hose.



Darrell.

pinched hose in the transom could be it. take your drive off, plug garden hose on the gimball water hose, see what it does, if it does not work, go back wards from inside transon towards gimball. if it works fine, as I said earlier in this tread, I'd check your intake hose! It may not be the problem, but it happened to me and it was the problem!

Good luck again and don't give up. You are maximum an hour away from your problem if you check these 2 things I think!

Let us know what happens!

Remove/replace the flush kit and transom to pump hose. Consider getting the Merc flush attachment. I don't know the part number but it was on somebody's thread not too long ago regarding a 496 water pressure issue.
You sure you had the hoses connected correctly? Was there water coming out of the now-open port on the pump?
Flush kits are known to go bad once in a while. "Theoretically", depending on how much pressure you have at the faucet and where you connect the garden hose, you should be able to push water at least as high as the connection. With just the garden hose cranked up, I can get water out my risers/exhaust.

This is freaking stupid! I purchased a Mercruiser/Quicksilver flush kit, turned the hose on full blast, half blast and everything in between but didn't see a drop of water at the intake side of the seawater pump. I have great water pressure but it didn't make a damn bit of difference. I have backflushed the drive, replaced all hoses between the drive and seawater pump but can't get any water up to the unit while on the flush kit. There is no kink in the hoses and the hoses are all in excellent condition. I am inclined to separate the upper and lower unit to observe the water passage and see if I can spot anything that would be causing this odd ass behavior. Shouldn't I be able to hook up the flush kit and have it push water to the seawater pump without it spewing water everywhere?

Jody

I have the inline flush on the Cig that's "T'ed" into the sea pump. When I turn on the garden hose water comes out of the drive until started. The sea pump works on suction.

Perhaps a little clarification: when YOU say "flush kit", are you talking the ear muffs that go on the drive? Those won't typically push water through the system until the pump is turning.
When I say "flush kit", I'm talking about a T that's installed in the intake hose between the transom and the pump. This gets connected to the garden hose so you're bypassing the transom and drive. My apologies if we are on the same wavelength here.
Also, I re-read your earlier post: the intake hose connects to the pump at the top port, lower port is the pump outlet. Sounds like you have that backwards before?
Back to your issue: if you have the muffs on, and the hoses are connected properly, but you're not getting anything while "the engiine is running", it's possible to have something in the drive; you said you replaced a hose in there? Perhaps an oring gone bad?
Otherwise, the problem is in the transom or the intake hose like said before. You mentioned that you ran the motor with the intake hose in a bucket and all was well (you felt suction). That seems to confirm the transom theory, or drive issue.

I'm glad I found this thread. I just blew the same impeller on my 500 EFI...luckily it happened at the dock just after puttng in.
I installed the new one, but I wasnt aware that the impeller needed to be greased or lubricated....is this true ??? If so, no big deal...it's a 20 min job.

You'll be fine lubed or dry. Lubed helps getting the impellor into the housing abit and prevents a dry start when 1st started. But, remember it's never 'lubed' after the boat has been pulled from the water. Will take a second or 2 to suck water from the drive once back in the lake, which inturn provides the lube. I usually use dishsoap if changing them at home. Otherwise, dry.
Also, no need to worry about the direction of the vanes. They can be in both directions. They will flip the right way the instant the pump is turned. Hard enough to get the little bugger in the housing w/o worrying about the orientation . :)

On the no water topic....

Standard side pickup.
Several yrs ago I was trying to run my motor on muffs. I tried both the standard clamp around type, and the Merc type that used a pin thru the pickup holes. Neither one would supply my motor with water. Have ran it numerous times before with both styles of muffs with no problems. I finally pulled the drive off to check the transom hose.....all OK.
So for chits and grins with the drive on the stand, I hooked up the muffs to check for a blockage in the drive itself. No water would come out the drive itself. There was no blockage. I could see that the passage was free as can be. Water would simply not come up the drives internal passage, the 12" or so even at full pressure. If I held the muffs tight to the drive, no problem. Craziest thing. Put drive back on, to the lake, no problem. Next time on muffs, no problem.

No explanation why it would not work that day.