Mercruiser 6.2 MPI Back Wash

mercproblem

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Oct 13, 2010
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Hello experts,

I have a question, concerning Mercruiser 6.2 MPI with a Bravo 3 Prop installed in a Larson Senza 226.

Both were bought new 18 month ago, and problem started after 2 month.

During the past 18 month I have had 4 exhaust manifold leaks shifting from one side to the other.
The manifolds have been taken off, cleaned, sealed and flattend by the Mercruiser Service Centre.

On the last boat trip engine overheated, I stopped, shut it down and was towed to shore.
The engine would not crank when it had cooled down.
The boat was delivered to Mercruiser Service Shop and they revealed that the engine
was water filled in cylinders and housing.

Mercruiser say I have experienced "back wash", water coming in through the exhaust manifolds
and into the engine itself. So the damage is not covered by the Mercruiser 2 year warranty.

With this history of manifold work, I wonder i if "back wash" is the real issue here ?

Thanks for any advise,
Magnus
 

TilliamWe

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Dec 21, 2004
Messages
6,579
Re: Mercruiser 6.2 MPI Back Wash

The proper term should have been "water reversion" or "exhaust reversion". Not back wash.
If the exhaust manifold leaks have been where the exhaust manifolds bolt to the cylinder heads, then the two issues are NOT related.

*However, if your exhaust manifold leaks have been at the manifold-to-riser mounting surface, the problems could very easily be related.*

Please tell me that someone got all the water out of your engine right away?
 

JustJason

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Re: Mercruiser 6.2 MPI Back Wash

The other thing you need to check is the water line in relation to the riser height.
 

mercproblem

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Re: Mercruiser 6.2 MPI Back Wash

Thanks for reply, and , no water was not removed ...

It seem the manifolds have been leaking where they bolt on to the cylinder head so maybe not related.

Interesting with this "water line to riser height", it is a big engine for this size of boat it seems, but this was the engine on it when i bought it.

"water reversion", yes, I am now painfully aware of what it is called, thanks for pointing out the correct term.

Once again, thanks for your tips, meeting mercruiser and larson tomorrow.
 

45Auto

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May 31, 2002
Messages
2,842
Re: Mercruiser 6.2 MPI Back Wash

The proper term should have been "water reversion" or "exhaust reversion".

"water reversion", yes, I am now painfully aware of what it is called, thanks for pointing out the correct term.

What makes you think it was reversion and not back wash?

They are not the same thing, there's a big difference between the two.

A leaking manifold is also a different cause of water intrusion then reversion or back wash.

Reversion usually only occurs at idle RPM, and is obvious by the condition of the exhaust valves.

A leaking manifold is not reversion.

This Mercruiser bulletin on Gasoline Engines And Water Intrusion may help you understand the terms:

http://www.boatfix.com/merc/Bullet/01/01_13.pdf
 

mercproblem

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Oct 13, 2010
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Re: Mercruiser 6.2 MPI Back Wash

45Auto, thanks for the link, and confusing me again, will read up on subject :)

the boat was stopped from 30mph in 8 sec according to "engine monitor data", maybe this was to fast "stopping", but after stopping the engine ran on idle with alarm sounding. It was then shut down.

after cooling down, I tried to crank it but engine would not turn.

Thanks again for the tip
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: Mercruiser 6.2 MPI Back Wash

Howdy,



Exhaust "back-wash" can be caused by either turning the key off or pulling the "kill-lanyard" (either on purpose or by accident) while still underway at rather high speed (or well above idle)

8 sec from planing-idle doesn't qualify as an abrupt "slow-down" in my book.


Does this engine have "dry-joint" manifolds and risers? If so, there's NO riser-to-manifold leaks into the exhaust system. (I think all the new Mercruisers use them now)


Does it have riser extensions? They range from 3"-6" (mine has 3")
GLM50310_thumb.jpg


If not, and it had a reversion or backwash event....It may be Larsons problem IF THEY installed the engine/drive combination with insufficient distance between the top of the risers and the resting waterline. (MORE is better)


The Mercruiser installation manual for your engine indicates the minimum dimension.
 

TilliamWe

Banned
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Dec 21, 2004
Messages
6,579
Re: Mercruiser 6.2 MPI Back Wash

The slow down you describe should cause NO issues. If the static line is wrong, that's Larson's issue.
In the meatime, how long has your engine been sitting with water in the cylinders?
 

mercproblem

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Oct 13, 2010
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Re: Mercruiser 6.2 MPI Back Wash

Now I have (maybe) some more details, if I could have your opinion on this it would be great.

We (mercruiser service centre) have looked at the data from the "black box" and it revealse the following :

- engine overheat alarm and low water pressure alarm
- engine stall when thrust lever moved to idle

No cracks or leaking gasgets.

So, I was cruising along, "something" covered the waterintake, the alarm went off.

I redused power, to stop the boat, the engine stalled - and the engine filled up with water.
Or, I redused power, to stop the boat, the engine filled up with water, the engine stalled.

I have had the engine stop priviously when reducing power but it has always started before, I have
also had my Merc Service try to fix this but they never found anything wrong.

Mercruiser warrenty does not cover "water intake" - maybe my insurance will - the engine is damaged
and needs to be replaced according to my Merc Service Centre.

So the correct procedure would have been the following,

- Keep going, let the engine protection come in, slow down slowly.
-If "back wash", always carry a sparkplug wrench, remove sparkplus and crank the engine to get water out
- Try to get it started again
- Bring to service centre and se to it they open the engine quickly

Thanks for all the tips
 

Joshua Nichols

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Jun 29, 2009
Messages
1,431
Re: Mercruiser 6.2 MPI Back Wash

All this on a new boat too.. This bites the big one... They fooled around with the manifolds and might of messed something up.. IDK seems fishy
 

TilliamWe

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Messages
6,579
Re: Mercruiser 6.2 MPI Back Wash

If something cover the water intake, then the only way for water to get into the cylinders is for it to have pushed up the exhaust and into the exhaust ports. That's "backwash" I guess.

As far as your insurance coverage, sure turn it in. But you're gonna be in for a long road there. (Partially because of what I am writing below)

In the meantime, if ANYONE had used their head, all they had to do to get the water out was remove the spark plugs and evacuate the water from the cylinders and there would be NO engine damage. Why do people not do the OBVIOUS stuff to save an engine? Why?
 

Bluestream

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Sep 28, 2010
Messages
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Re: Mercruiser 6.2 MPI Back Wash

In the meantime, if ANYONE had used their head, all they had to do to get the water out was remove the spark plugs and evacuate the water from the cylinders and there would be NO engine damage. Why do people not do the OBVIOUS stuff to save an engine? Why?

I think they make more money when they have to replace the whole engine...
 

fossill

Chief Petty Officer
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Jun 20, 2009
Messages
427
Re: Mercruiser 6.2 MPI Back Wash

I thought this type of problem was pretty well engineered out and no longer happened in newer boats. I'd be checking the engine installation against the Merc installation manual specs and diagrams to see where the risers sit in relation to the waterline.
 

tarheelebbtide

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Jul 4, 2008
Messages
94
Re: Mercruiser 6.2 MPI Back Wash

Add me to the growing list of thinking the boat manufacturer probably has some culpability here. If those risers weren't above the resting water line, the engine never had a chance.
 

burp

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Aug 3, 2002
Messages
363
Re: Mercruiser 6.2 MPI Back Wash

How about the exhaust flaps???? Are they installed in the exhaust Y-pipe? Their purpose is to minimize the chance of water intrusion through the exhaust.

The Merc 496 MAG initially didn't have the exhaust flaps, later Merc changed their thought and started installing them. Those folks with the earlier models of the 496 MAG engines were left to fend for themselves. The 6.2L engine could possibly be the same.
 

jaxnjil

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1,368
Re: Mercruiser 6.2 MPI Back Wash

45Auto, thanks for the link, and confusing me again, will read up on subject :)

the boat was stopped from 30mph in 8 sec according to "engine monitor data", maybe this was to fast "stopping", but after stopping the engine ran on idle with alarm sounding. It was then shut down.

after cooling down, I tried to crank it but engine would not turn.

Thanks again for the tip

here is a good link you might profit from reading.http://findarticles.com/p/articles/mi_m0BQK/is_1_8/ai_96379178/?tag=content;col1
the thing i don't understand. if it was a back wash and wasn't shut down but allowed to idle and then rpm brought up slowly why it did clear and dry its self out before shut down.

also in my opinion that was a pretty sudden shutdown. when i first drove a B III i had a tendency to throttle back to fast to be comfortable. you yank these puppy's back and the boat can get a good size wave hit the transom. hence the back wash. they are the best brakes i have seen on a boat.
 

HT32BSX115

Supreme Mariner
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Dec 8, 2005
Messages
10,083
Re: Mercruiser 6.2 MPI Back Wash

when i first drove a B III i had a tendency to throttle back to fast to be comfortable. you yank these puppy's back and the boat can get a good size wave hit the transom. hence the back wash. they are the best brakes i have seen on a boat.
I think it's also a function of how high the risers are.

When I got mine running after the swap from the 460 King to the 454 Bravo III, I did several rapid (idle thrust or neutral) slowdowns to a stop and haven't had a reversion problem yet.

I did also install new shutters which I think will make a difference but more importantly, I have 3" riser extensions which I think makes all the difference.


If you do not have extensions and you have the risers off, you might consider adding them.
 

Don S

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Aug 31, 2004
Messages
62,321
Re: Mercruiser 6.2 MPI Back Wash

Add me to the growing list of thinking the boat manufacturer probably has some culpability here. If those risers weren't above the resting water line, the engine never had a chance.

The manufacturers build the boat for a normal load. If you have a lot of extra weight in the back, like extra batteries, lots of storage of tools, oils, etc. in the bilge, dingies, outboard motors, coolers, gas tanks etc. all added to the back of the boat, along with several people, then you have a lot more load back there than the manufacture intended. It's then YOUR problem, and you need to verify that with YOUR normal load you have the proper riser height. If you don't you need extentions.
 

mercproblem

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Oct 13, 2010
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Re: Mercruiser 6.2 MPI Back Wash

Once again, thanks to all for the tips,
I wish I knew what I have learned from here before the "stopping"

For a "newbie" like myself, when an engine quits and wont crank, things like "backwash", "hydro lock" and "risers" are not on ones mind. It will be an expensive lesson to learn but ".... happens".

It is my first boat and we have had a great time with it (even at the age of 48 learning to wake board) and now we will go the insurance road. Lets see what happens.

One thing for sure, I will follow the posts concerning risers and all, when and if i get a working engine again.

Thanks again
 
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