Exhaust manifold rusted at engine port.

[beruken]

I removed my 6 season exhaust manifold and risers off to inspect over the winter and have now just gotten to it. The boat is used about ten times a year in saltwater and usually flushed after each use. I noticed the two engine ports on rear of the 4.3 v6 are carbon coated while the other 4 ports have some level of rust as depicted in the following images. Also the manifold in the exhaust section has a fair amount of rust.

The first port shows the clean port rear of engine while the second two show both the engine side and manifold side ports rusted respectively. I will note the flappers were replaced with the manifolds and still appear to work.I realize it's probably time to replace the manifold while it is not breached from what I can see, I am concerned with whether this is normal for salt corrosion to reach this part of the manifold or even the engine? I would certainly expect all the ports to have the same level of corrosion or at least some.

Any thoughts or experience with this? I do not recall how the ports looked when I did the manifold the first time and are concerned with possible corrosion around the valves or even further.

Ken

 

[Lou C]

No it’s not normal and its time to replace at least the elbows if not the manifolds as well. Post up pics of the mating surfaces of each. You likely have the older style wet exhaust joint which is prone to this problem. You can test the manifolds by filling them up with acetone when propped up level. Careful because it’s flammable but it will find leaks that water won’t leak thru till it gets hot. If it passes and there is not a lot of flaking rust in the cooling passages they can be re used IF the mating surfaces can be cleaned up flat and level and not pitted. You absolutely should replace the elbows, they usually rust worse. If it were me I replace the whole system. My engine has had 3 exhaust systems over 15+ years of salt water boating, 2 sets of OMC batwing one piece units and last is the 2 piece center riser style.
you can do it now or try to get a few more seasons out of them but that could cost you an engine. A bad risk I say.

now if this boat has those horrible one piece Merc batwings dump them NOW before they destroy the engine!

 

[beruken]

Thanks. I did soften some of the mating surfaces already and acetone point well taken. Extreme amount of flaking which I cleaned up. Was hoping to get another season out of these as I couldn't chisel through the thinnest points I had access too or at least get the boat running since I rebuilt carb. Couldn't get image size small enough to post but will try again later. Hopefully this will be a good knowledge base post for others.

 

[Lou C]

OK here's a pic when I put the last set of OMC batwings on in 2011, notice the exhaust ports are nice and grey no rust there, your manifold exhaust ports should look the same. What you have shows salt water getting in the engine. In this pic those manifolds I took off were in use 6 seasons in salt water...so I tossed them and installed my last set of those (NLA) that I had. Then in 2017 converted it to the center riser style used on later OMCs (91 and up) and all Volvos (94 and up)...

 

[tank1949]

No it’s not normal and its time to replace at least the elbows if not the manifolds as well. Post up pics of the mating surfaces of each. You likely have the older style wet exhaust joint which is prone to this problem. You can test the manifolds by filling them up with acetone when propped up level. Careful because it’s flammable but it will find leaks that water won’t leak thru till it gets hot. If it passes and there is not a lot of flaking rust in the cooling passages they can be re used IF the mating surfaces can be cleaned up flat and level and not pitted. You absolutely should replace the elbows, they usually rust worse. If it were me I replace the whole system. My engine has had 3 exhaust systems over 15+ years of salt water boating, 2 sets of OMC batwing one piece units and last is the 2 piece center riser style.
you can do it now or try to get a few more seasons out of them but that could cost you an engine. A bad risk I say.

now if this boat has those horrible one piece Merc batwings dump them NOW before they destroy the engine!

Boater may need to replace shutters! I am not familiar with V6 exhaust systems or Batwings. Chevy v8s have them inside the the tops of their y pipes. Chevy V8s and their exhausts that are used in salt water need constant monitoring where I live. Although there are some so-called MC experts on this forum that that will say that the boater did something wrong over his boat's life and brag that they have gotten 20 + years riser/exhaust usage in salt water, we here along the Florida Gulf coast have been fighting this crap for decades. Cast iron and saltwater hate each other and iron will eventually lose. We typically get 4-6 years out of risers (elbows) and a little longer with exhausts. About 8-10 years on a block. If constant flushing, a little longer. Sorry, but I have replaced them too many times as well. That's the main reason why I went to closed cooling. I only need to test the risers with acetone.

 

[Lou C]

Closed cooling is definitely the way to go in warm salt water; if/when I repower this boat for sure that and a remote oil filter mount are must-haves. Having said that in our salt water up here in LI you can get 15-20 years from a block the heads start getting questionable at about 15 yrs; I replaced mine 3 years ago to buy some time. Most inboard mechanics I’ve spoken to say it’s rare for a block to rust thru here....

 

[tank1949]

Closed cooling is definitely the way to go in warm salt water; if/when I repower this boat for sure that and a remote oil filter mount are must-haves. Having said that in our salt water up here in LI you can get 15-20 years from a block the heads start getting questionable at about 15 yrs; I replaced mine 3 years ago to buy some time. Most inboard mechanics I’ve spoken to say it’s rare for a block to rust thru here....

Maybe the cold weather mitigates the rust/cancer. I got about 8 years from a block. Heads cancered and hydro locked motor. You will like the remote oil kits!

 

[Lou C]

Yep we have cooler water temps and boats are stored for 6 months out of the year here. When I winterize it I fill the engines and manifolds with either -100 marine AF or I mix up a batch of Sierra no tox AF, this is supposed to help and Mercury actually has recommended it for years.

 

[beruken]

Boater may need to replace shutters! I am not familiar with V6 exhaust systems or Batwings. Chevy v8s have them inside the the tops of their y pipes. Chevy V8s and their exhausts that are used in salt water need constant monitoring where I live. Although there are some so-called MC experts on this forum that that will say that the boater did something wrong over his boat's life and brag that they have gotten 20 + years riser/exhaust usage in salt water, we here along the Florida Gulf coast have been fighting this crap for decades. Cast iron and saltwater hate each other and iron will eventually lose. We typically get 4-6 years out of risers (elbows) and a little longer with exhausts. About 8-10 years on a block. If constant flushing, a little longer. Sorry, but I have replaced them too many times as well. That's the main reason why I went to closed cooling. I only need to test the risers with acetone.

8 -10 years on a block? Is your season year round?

K

 

[beruken]

Thanks for the posts. Already purchase some new manifolds and risers. From what I can see I assume the engine is in working order despite the rust leading into the ports. It had been running fine just prior to winterizing. What's a good manner to check if the block is about fail?

 

[Bondo]

What's a good manner to check if the block is about fail?

Ayuh,...... from internal rust,..??..?? No real practical way to do such,.....

 

[tank1949]

8 -10 years on a block? Is your season year round?

K

Some do year round. 8-10 year life if MC powered boat is stored wet in salt water and totally sea water cooled. MC owners that I know either went closed cooling or OBs. I trailered my last three MC powered boats. Flushing with fresh water helps. Good luck! My best fishing buddy is a retired Merchant Marine sea captain. All his diesel powered boats were closed cooled.

 

[Lou C]

Thanks for the posts. Already purchase some new manifolds and risers. From what I can see I assume the engine is in working order despite the rust leading into the ports. It had been running fine just prior to winterizing. What's a good manner to check if the block is about fail?

There isn't really. The only way you'd know it's rusted through is water in the oil or cyls. A good rule of thumb is the heads will rust through sooner, usually behind a valve seat. When I took mine apart 3 years ago, the block passages looked good as far as I could see, the heads were replaced because of cracks due to a previous overheat. However, even if they were not cracked, the machinist felt the cooling passages were getting eroded and they would not seal well on the new head gasket, and that erosion is due to salt water corrosion. Up here in the northeast I've had a lot of friends with raw water cooled Mercs or Volvos and no one that I know, had a block rust through. So it depends on your conditions. The problems I have seen, most common is exhaust systems not replaced on time, causing water in cyls and rusted exhaust valve stems, leaky bellows causing rusted gimble bearings and ujoints, or engines cracked due to improper winterization. All preventable with proper maintenance. But if I were in Fla, I'd have only outboards.

 

[tank1949]

Closed cooling is definitely the way to go in warm salt water; if/when I repower this boat for sure that and a remote oil filter mount are must-haves. Having said that in our salt water up here in LI you can get 15-20 years from a block the heads start getting questionable at about 15 yrs; I replaced mine 3 years ago to buy some time. Most inboard mechanics I’ve spoken to say it’s rare for a block to rust thru here....

My catastrophic failure was when head "cancered" through and cause hydro locked. I suspect other head was like the "cancered" head. I had to pull head to identify failure. I looked inside water cavity of block and saw a bunch of rust/ flakes. I didn't want to take any additional risks trying to salvage old motors. I replaced both.