Low water PSI..Mercruiser 5.0 MPI with Bravo 3

[pbuzz3323]

My 2003 searay 240sd for the past 2 years has not seemed to be getting a really good flow of water through the engine from the outdrive and transom.. I have the searay smartcraft gauge that was showing me low water pressure. Finally took boat in this past month and found the sending unit was not functioning properly so it was replaced. get a reading in the 2.5 to 3.0 PSI range when it should go to around 9-12 im told. The boat has never overheated on me and when this happened I did the risers over, circ pump and seawater pump. still low numbers. I was told its in the transom and probably calcium buildup. was told to pull the outdrive..(By the searay tech) and use marykate on off hull cleaner...To put it in a bucket with hose and put hose in transom water jacket and start it and let it suck it in and let it soak and that may clear it up. Searay told me they do it quite often and it breaks up alot of crap but im afraid to enter that into my system. was told that if that didnt work a thru hull fitting in bottom of boat could be done to suck up raw water and by pass the transom. Only thing is it may require an engine lift because its tight space in there.. Anyone have any dealings with this cleaner inside the engine or ever hook up a thru hull pick up??? Im not sure which way to go but I figure to atleast use the cleaner and if an engine lift isnt required I will have the thru hull installed...Im told it will solve the flow problem. Has anyone had this problem? Also wondering if this is something I can do myself..all I need to do is run the thru hull hose to the seawater pump pickup hose correct? this way it will get transom and thru hull water. Just gotta figure which is inlet and which is outlet right?

 

[Bt Doctur]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Forget the WP gauge and just watch the temp gauge.If your rwc, you actually want a low reading .nothing restricted, water in = water out .Bravo does have a corrosion issue where the transom hose is. Most have a clamp, bravo uses an insert. corrosion builds up between the outside of the hose and the casing crushing the hose.

 

[45Auto]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Is the 3.0 PSI at idle or at speed? My 2003 Bravo shows 3.0 PSI at idle and 15 PSI at about 2500 RPM.

There's not much to the pick-up system except a piece of hose between the outdrive and transom shield. When's the last time you changed the u-joint bellows? If it's the 7 year old original, it's about time for a change. You can easily replace the pick-up hose when the bellows is replaced.

 

[pbuzz3323]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Didnt get it back but tech says its staying constant at around 3.0 both idle and accellerating. I never have changed the u joint bellows..Not sure how to do that yet either. and if the wp gauge keeps getting lower doesnt it mean my flow is becoming restricted? I have to pay attention to it dont I??

 

[Don S]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Do you have a serial number for your engine handy? Mercruiser lists NOTHIHG by year. Which sea water pump do you have? The one with the plastic pump housing or the one with the brass pump housing. Have you done a pump output test yet?
Assuming you have the dry joint type exhaust, do you have an air actuated drain system on your engine? Or, which drain system do you have? Do you have a raw water cooled system, or a closed cooling system.
Here is a link to the service manual for your engine,
http://www.4shared.com/document/UA6kxFEY/Service_Manual_31.html
Section 6 has the output test, and pump id and other info for your cooling system.

 

[pbuzz3323]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Don..My serial Numbers are Drive #OM157978, Transom# OM571152 and engine # is OM624941. I dont believe I have the Brass seawater pump and The impeller was done at the beginning of last year...I have never done a Pump output test and its the 3 point drain system..Not air. System is totally raw water cooled also. I did Buy the Full Manuals on line a few years back..Not the chinsey ones but the real Mercruiser manuals.

 

[Don S]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

You do have the brass pump.
I think the first thing I would do would be to check the pressure with and actual gauge. Replace the water pressure sender with a fitting and hook up a gauge. Then you will know what you really have. For it to stay at exactly 3 psi at all rpm's just isn't right.
This also has to be checked "In the water", not on muffs.

Do you have manuals 31 and 37?

 

[pbuzz3323]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

It was tested in the water also and the reading stayed the same..yes..I have both manuals. Just hook up gauge to engine and run it normally? Guess I have to get 1.

 

[pbuzz3323]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

well..Searay called..Decided to go through with the Thru Hull installation for water pick up..another 900. They say it will solve the low water pressure problem in the cooling system..Cant take the chance of causing engine damage for 900.00 Then Im really screwed

 

[Don S]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Ahhh Yes, the old "Throw money at it till it works" method of boat repair.

It worked fine from 5 years when suddenly it needs a $900 thru hull pickup system to make it work. I really have problems understanding how that could suddenly happen.

 

[45Auto]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

You'd be much better off spending the $900 to get all your bellows and hoses replaced, but hey, ya gotta do what ya gotta do!

 

[pbuzz3323]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Don...this has been a problem for the last 3-4 years..very low water pressure reading and its been getting gradually lower and lower..Do you not agree with this repair? Im told this will fix the problem as the restriction is in the transom..another way would have been to pull the engine to clear clog...Maybe im being naieve but they said its a common thing they do in this situation...but they also are in a business to make money.... Im sick to my stomach over this..I know you havent look at my boat but really what other option do I really have? Im not meaning to sound snippy or rude either...just frustrated. Kinda trusting what hes telling me..Real dangerous.

 

[DC20]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

pbuzz,
My low water pressure was traced back to a worn brass pump housing like you have. I think what Don and others here are trying to tell you is Mercruiser doesn't need there stuff redesigned, there is a problem that needs to be fixed.

 

[45Auto]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

It's not a complicated system.

Water enters through the intakes on your outdrives and travels through the hose labeled "C" below:

Hose C from above is connected to Hose 1 in the picture below. Your PSI sender is on the opposite side of the water pump from Hose 1.

Temporarily replace the PSI sender with a mechanical guage to verify the readings.

Only place you can have a restriction is in Hose 1, Hose C, or the sterndrive intake itself. None of them are difficult to check or replace.

Hose 1 can be removed without removing the engine. Access to Hose C requires the outdrive bellhousing to be removed, which has to be done to replace the bellows which should be done every 5 years anyway.

 

[pbuzz3323]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

I see what you mean..so its a fairly short run from where water first enters the outdrive to where the sending unit is located..They did say they checked where the connections are for a plug in the line and it wasnt in the line,,Thus leaving the transom as the culprit..They do need a better design to this system then if that area is a problem...The one thing I do feel better about is that this thru hull setup will increase the water flow..now seeing it will bypass the drive and transom

 

[45Auto]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

They do need a better design to this system then if that area is a problem

In over 30 years of boating and almost 10 years on this forum, you're the ONLY one I've ever seen who thinks they have a problem with it. Don't hold your breath waiting on a re-design anytime soon .......

 

[GLENN M]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

the bigger the restriction the higher the psi,no restriction no psi. you need to check flow,i dont think youve found your problem.iam with Don i would test until i could deduce actual problem forget guessing or assumeing.l can hear marinas next statement {'well it was a problem and did help,but you have more problems']

 

[redjmp]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

removed

 

[redjmp]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

Well I don't think calcium build up is your problem as you live in NY which has cold water. Calcium buildup to my knowledge is usually a tropical problem because the high water temp/low oxygen content facilitates the build up.

If you think it is calcium, you can try some CLR...

But with that in mind, theres only 2 options in my mind.

1) Zebra mussels if you boat in fresh water
or
2) Barnacles if you boat in salt water.

Markykate is an excellent product for removing these!

Why don't you take their advice and try some?

It may indeed etch exposed metal a little because of the acids but you don't need to leave in there very long so it wont really do any damage if flushed thoroughly.

It will also take care of calcium or algae or any other thing that has decided to grow in there.

I am not familiar with the bravo drives and I am not sure if you are able to take the boat out of the water but if you can, try removing the lower unit and inspecting for barnacles etc.
Maybe you can try to plug the inlet at the leg and feed some Marykate from the seawater intake from inside the transom and letting it sit for a few minutes.

At least this way you don't have to worry about it running through your engine.

I just can't see the logic nor agree with paying $900 to drill a hole in the bottom of a perfectly good hull.

What are you going to do when the barnacles start congregating on the inside of the thru hull?

Just my 2 cents...

 

[45Auto]

Re: Low water PSI..Mercruiser 5.0 MPI with Bravo 3

the bigger the restriction the higher the psi,

False statement there. It depends on where the restriction is.

You really think that plugging the intakes on your boat so the pump can't get any water at all would give you high water pressure?

A restriction on the INTAKE side of the pump will lower PSI, a restriction on the DOWNSTREAM side of the pump will raise PSI.

For example, if an impellor has come apart and plugged the power steering or fuel cooler, a new impellor will cause HIGH water pressure because the pieces of the old impellor are causing a restriction on the downstream side of the pump.

Barnacles or a collapsed hose on the INTAKE side of the pump will lower PSI because the pump can't get the flow (volume) of water required.