Gen VI 7.4L Bravo New Raw water pump fail on initial start up! Why?

[mr300z87]

So today I installed a new Impeller and pump housing on my 7.4L. This is the engine mounted pump with the fuel pump mounted to it. I started this morning by removing the entire assembly so I could change the gear oil in the fuel pump cam area. I then install brand new Mercrusier parts with a little bit of dish soap as lube to assist with install the impeller and prevent dry start up. At first everything seemed ok and I had water coming out the drive as it should. After a warm up I did an oil change, then a run just to check for leaks. This is when I notice a whining noise like a belt slipping so I got some soapy water to spay the belts to figure out which one, none were the noise. Then I notice the engine was getting hot and no water discharge out the drive. I shut it down immediately and after some cool down time I removed the pump housing, thankfully this can be done on this engine without removing the whole pump assembly from the engine. This is what I found


This is not my first impeller change but have never had this happen before. I am baffled as to why it failed, After re installing the old one 2.5 years and maybe 60 hours run time and it runs perfect. BTW at no time was the engine run without the hose connected and turned on. Before I shell out an another $100 for a new one I need to know what would cause this and if I did anything wrong. Manual says to use soapy water mixture but maybe some 2-4-C merc grease would be better. As always any advice is greatly appreciated. Mike

 

[Bt Doctur]

K-Y is a better choice, or soapy dishwasher mix

 

[Grub54891]

I've seen that happen, the owner had the pickup and discharge hoses reversed. But you had water flowing through the drive....so not sure.

 

[eric102]

Could getting one or more of the vanes bent over the wrong direction during the install cause it?

 

[mr300z87]

Thanks for all the replies,

Grub, the hoses were on correct.

Eric, all the vanes were the correct direction as I installed the impeller the same way as the old one was.

I am still a little baffled by this and lost a good nigh sleep over it. With that said I am going to pick up a new kit and try again this time using much more soapy water or might try petroleum jelly as a pre start lube. My fear is that the last time I had a pump failure on different boat it wasted the engine.

 

[eric102]

Just noticed you have the same boat and engine, mine's a 91 250 DA with Bravo 2 which I purchased new in 91. Have changed that dam impeller and pump body parts at least a dozen times, probably more! Never could do it without removing the entire assembly and working on it at a bench.

 

[mr300z87]

Eric, My other boat was a 20ft cuddy with a B-1 drive and it was a total nightmare to change the pump, and i have done that one a few times. On that one I could barely get my hand on the hoses to remove them. Since this one has the fuel pump attached to the water pump I need to remove the entire assembly to service the fuel pump gear oil. While is was sitting in the bilge crying and staring at the pump I realized that the pump hosing bolt were accessible. With both hoses off and a half inch socket on my ratchet the pump housing was off in 5 minutes. My local Merc dealer has the parts in stock and I will be picking up a new one while off from work later this week. I am still hoping to get her splashed this Saturday.

 

[Bondo]

I am still a little baffled by this and lost a good nigh sleep over it.

Ayuh,...... 2 thoughts,...... With a Bravo motor mounted pump, if there's a vacuum leak 'tween the pump, 'n the sea water pickup,...
There's No water to the pump,......

2nd is Bravoitis, where the through transom point corrodes closed,.....
Again, No water to the pump,.....

 

[QBhoy]

Hi

the issue with the bravo and engine driven pump is that even with the best of muffs (for running on the trailer) aren’t anything like as effective as it being in the water with a good head of pressure on it. Always hard work for the pump to pull the water up.
If you have an air gap between the drive and pump it’s hard going.
Good chance the mechanical internal pump is air locked too. Make sure it’s pumping too.

 

[mr300z87]

Thanks for looking and responding, in my original post I stated that after re-installing the old pump I ran it for 15 minutes with no issues. As for Bravoitis the engine was installed a few years back and only 60 hours since, at which time a new water hose was installed. See Signature file I have run this engine many times on the hose never having a issue in the past. Also of note is I have confirmed the hose from the pump to the engine is clear. One thing that just popped into my head that I did not think of is the engine was completely dry from winter storage (air don't freeze) since I did not start it before water pump service. Could this have caused a longer than normal time with minimal water in the pump caused by no back pressure from water being in the hoses and engine. It was also a couple hours from time of assembly until start time caused by having to wait for help installing the drive. The dish soap I used as lube could have completely dried up. When I install the new one later this week I will make sure there is plenty lubricant (was thinking petroleum jelly) in the pump housing before for first start plus the engine is already full of water. Things like this really mess with my head, I know I am and pride myself a good mechanic. This install is not new to me and should not have gone like this. Going to chalk this up to a bunch of small issues that could have caused a much bigger one, and move forward. Install new pump and go boating all summer!!!!!!!!!!! I am off Thursday and Friday so 5 day weekend with the holiday, still pushing for a Saturday 5/25 splash. Have a great night.