mercruiser manifolds - lifetime

[julians]

Hi All,

Do the newer style dry joint exhaust manifolds on mercruiser 5.0 mpi's have a longer life than the older style ones?

Mine are coming up to 5 years old, So i'm probably going to take them off and inspect for corrosion and replace if necessary.

Can anyone explain what I'm looking for? And is it likely that the risers and elbows will also need replacement or will any significant corrosion be limited to the manifolds?

The boat lives in saltwater 365 days of the year, it only comes out of the water for the yearly service.

 

[tinkicker0]

Hi All,

Do the newer style dry joint exhaust manifolds on mercruiser 5.0 mpi's have a longer life than the older style ones?

Mine are coming up to 5 years old, So i'm probably going to take them off and inspect for corrosion and replace if necessary.

Can anyone explain what I'm looking for? And is it likely that the risers and elbows will also need replacement or will any significant corrosion be limited to the manifolds?

The boat lives in saltwater 365 days of the year, it only comes out of the water for the yearly service.

What you are looking for is a new set of manifolds.

 

[AndieMac]

Hello and welcome.

Agree with TK, if you are not doing regular inspections and are in the salt all year, don't hesitate, go for new ones.
The consequences of water ingress will be serious.

 

[julians]

I'm going to inspect them this winter, but what should I be looking for ?

So I take it the dry joint manifolds dont last any longer than the 'wet joint' manifolds?

Is it just the manifolds that are likely to need replacement or will the elbows etc also need replacing?

Also, If i do need new manifolds, is it best to go for aftermarket manifolds or proper mercruiser manifolds? If aftermarket, which aftermarket brand is best?

Sorry for all the questions....the boat seems to be going through a moneypit stage of its life.

 

[lovezoo]

When I asked this question on iboats re my 2001 4.3EFI this is what I was told:

Manifolds and risers usually fail in 2 ways. They start corroding inside and the rust fills the passages and the engine starts running warmer, usually noticed by an engine that normally runs at 170° running at 175° to 180° consistantly.
That's when they should be replaced.
THe other failure is actually easier to notice. You start the engine and it's only running on 4 or 5 cylinders till it runs for a while and clears out. This is where people loose an engine is it's sitting with salt water in it. What happens is the gasket surface area of the exhaust manifold and riser corrode away and allow water to leak from the water section of the manifold to the exhaust port and enters the cylinder through an open valve. If that gasket surface is thin or turned into a black carbon substance, it will leak.

 

[julians]

Thanks lovezoo, thats useful information, it implies that its the gasket failing that leads to the water in the cylinders which can cause the big bills, but because I have the dry joint manifolds , they cant fail in this way, and the only way they could fail is by the passages in the manifolds becoming blocked by rust and causing a slight overheat.

Does anyone agree or disagree with that big presumption above, or have any first hand experience with the newer dry joint manifolds?

I have contacted mercruiser for their view, I will update here with any info.

I have also contacted Key parts for their opinion, they say they havent had to supply many of teh newer style dry joint manifolds and the ones they have supplied have been needed due to frost/ice damage rather than corrosion.

Any way, all information is gratefully received, keep it coming please.

Thanks

 

[MapisM]

Does anyone agree or disagree with that big presumption above, or have any first hand experience with the newer dry joint manifolds?

First of all, welcome to the madhouse.

No first hand experience on these manifolds - actually I wasn't even aware that the newer ones have the dry joint system!
Do you know since when they introduced it?
I've seen many V8 blocks, both small and big, but in none of them the stock manifolds had dry joints.

Anyhow, I agree with your presumption.
In fact, dry joint manifolds have been used since ages in all performance exhausts, because indeed the water passages shown also in the drawing posted by lovezoo are a weak link by design.
In stainless steel performance exhausts, it is often recommended to pressure check them regularly, because they can crack and leak where the tubes are welded, leading to water reversion problems.
This has killed a number of the otherwise excellent 525 Mercury engines.
But on cast iron manifolds with dry joints (as I guess yours are, correct me if I'm wrong), probably a pressure check is a waste of time.
All in all, as long as the engine and BOTH the exhausts run as cool as they should, I don't think you have reasons to worry.
Btw, if you leave your boat in the water because you regularly use her, that's not too bad for the whole raw water circuit. Much better for instance than leaving the boat unused on the hard for long periods without rinsing it with fresh water.

 

[julians]

I understand that mercruiser switched to dry joint manifolds in 2002.

The boat lives on a mooring all year round, only coming out of the water for a couple of days per year for a service etc, and then going straight back in.

My manifolds are cast iron not stainless, so hopefully less issues with cracking due to expansion etc

I'll speak to mercruiser direct , as at the moment its looking like the 5 year replacement life that has historically applied might well only apply to the old wet joint manifolds.

 

[lovezoo]

Thanks lovezoo, thats useful information, it implies that its the gasket failing that leads to the water in the cylinders which can cause the big bills

I don't think that is the case. Its the gasket surfaces of the manifolds/risers rusting that causes the problems. First thing to do really is take the risers off and see what they look like. Any sign of rust and I would replace them, especially if you are planning to keep the boat for a few years.

 

[spannerman]

If the engine is cooling properly and the manifolds and risers are not getting too hot to touch , then there is no reason to replace, wait until they show signs of restricted circulation this will manifest itself as slightly higher running temp as water can't exit so easily, but its not going to happen overnight.
If you are concerned then drain off the manifolds with the blue plug at the bottom and remove the riser to inspect the joint, they should only leak externally in principle evidenced by white salt deposits.
I would buy two new blue drain plugs as I've had both fail this year on my motor which is fresh water cooled and under higher pressure admittedly, but they seem to weaken after being removed a couple of times.

 

[julians]

So the catastrophic mode of failure where it ended up leaking water into the cylinders and potentially destroying the engine has been pretty much removed by the new dry joint manifolds?

Therefore precautionary replacement of the manifolds is no longer necessary (as the risk and consequences of failure are significantly lower), and its ok to wait until you see higher than normal engine temps before replacing?

Sounds great to me.

I will also speak to mercruiser and let you know what they say.

 

[MapisM]

I would buy two new blue drain plugs as I've had both fail this year on my motor which is fresh water cooled and under higher pressure admittedly, but they seem to weaken after being removed a couple of times.

Interesting. My 496 is also fresh water cooled, but I don't see why this could lead to a higher pressure on the raw water which circulates in the manifolds. Could you elaborate? Ta!

 

[MapisM]

I understand that mercruiser switched to dry joint manifolds in 2002.

Thanks, either all the engines I've seen were older, or I never noticed the connection hose which surely the dry joint versions must have.

 

[phockit]

Still worth removing and checking everything, for instance the flaps that prevent back wash which can get stuck or just disintegrate over time (I assume these still exist on the MPi engine).

Paul

 

[tinkicker0]

When I asked this question on iboats re my 2001 4.3EFI this is what I was told:

Thanks LZ, I learned something new. Is this the normal failure mode?

I always presumed that the corrosion was through to the ports from the water jacket internally, not the outlet water ports and along the riser gasket face. Easy to check if so and cheaper to run "on condition" than changing as a time expired item.

 

[lovezoo]

Thanks LZ, I learned something new. Is this the normal failure mode?

I always presumed that the corrosion was through to the ports from the water jacket internally, not the outlet water ports and along the riser gasket face. Easy to check if so and cheaper to run "on condition" than changing as a time expired item.

I don't know what the normal failure is, but it seems that if the engine is running at the right temperature, running ok on startup and there is no evidence of corrosion if you take the risers off then they don't need to be changed - which is good news given the cost of replacements.

As they are cast-iron parts, they are going to rust, but the rate at which they go will depend entirely on how they are treated, so I can't see how you can have a set time interval for replacement.

My engine has always been flushed with fresh water after use and doesn't have that many hours on it - obviously a boat with more hours and salt-water use only will need changing sooner. Its always worth being on the safe side though as a new engine will cost quite a bit more than a set of new manifolds and risers.

 

[julians]

And if you have the dry joint manifolds that mode of failure (ie corrosion in the area where the water flows between manifold and riser) should never happen because the water flows through a seperate pipe, so if this started to fail you would just see water flowing to atmosphere (rather than into your cylinders).

This picture here (from trickett marine) shows the dry joint connection quite well.

http://www.trickettmarineproducts.co.uk/images/P1190057.JPG

 

[MapisM]

You might find also the schematic below of some interest, if you're going to remove and check the exhaust.
I had to look at how these new manifolds are made, 'cause they made me curious.
And I must say that it looks clever, with the raw water passage practically integrated in the manifold and elbow.
Very different from the separate pipe used in stainless exhausts.
And almost unnoticeable - now I see why it never catched my eye.

 

[lovezoo]

And if you have the dry joint manifolds that mode of failure (ie corrosion in the area where the water flows between manifold and riser) should never happen because the water flows through a seperate pipe

I guess that is why Mercruiser changed to that type of riser - shame they didn't do it a year or two earlier as my boat is a 2001.

 

[julians]

I imagine you could retrofit the dry joint manifolds and risers to an older engine....I guess it would be cost effective if you were looking at replacing manifolds and risers anyway?