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Risers Manifold Longevity

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alparmer

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I’ve pretty much have gone through my 2007 Larson with dual 2007 MPI 5.0 Bravo III. The only thing that worries me and do not know about is how to determine the status of the raw water cooled components. This is my first raw sea water boat. It does not have closed loop cooling. The engines have 330 hours and from what I can tell the PO didn’t bother with maintaining much. The engines ran great for many hours while relocating the boat and did not overheat at all.

I’m trying to educate myself on how the cooling system works in these engines. I’m going to replace the raw water pumps as soon as it comes out of the water for bottom paint. As far as I know the pump draws water from the hull then pushes it all through the block, heads, and then the exhaust manifold?!? Risers??? I was told one tell tale sign the manifold and risers are rusting out is that it will start overheating. I’m running normal temps. . I was also told that when they go out, it’ll hydrolock the engine which means replacing the entire thing. Is there any way to avoid a hydrolock.

I was also told that it’s a good idea to install a flush kit. I have had them in fresh water engines but not sure it makes sense on a sea water engine that will always be in water.

Thanks in advance for any input.
 
OK Here's my personal philosophy regarding used boats:
Unless you have log books that document every maintenance item, you're best off starting from scratch. It's not going to be cheap, but hey boating is not a poor man's hobby no matter how you slice it.
Let's start with fluids. Change everything...oil, steering, hydraulic, outdrive lube, whatever. New filters as needed.
Rubber. All new hoses, belts, fuel lines, and if needed engine mounts
Tune up: plugs wires cap rotor timing and fuel adjustments

When you have all this done, put it in a book or spreadsheet so that you know when you have to do it next.
 
Have pretty much replaced or repaired most components. Replaced both cool fuel pumps, ouch, because when I went to replace the filters I couldn’t believe my eyes. The bottom pre filter was black and the main filter fell apart. All four pumps were noisy and the top cover bolts were welded by rust and snapped off. New idle pulleys, belt, and soon the raw water pumps. I need to also replace the t stat and the weird T cooling pipe with the plastic white balls. I also have most electronic sensors for backup, senders, cap rotor, etc. I don’t like surprises. I also had to rebuild the trim pumps. Pulling it out of water soon to service the bravo 3s
 
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alparmer said:
I’m trying to educate myself on how the cooling system works in these engines....................As far as I know the pump draws water from the hull then pushes it all through the block, heads, and then the exhaust manifold?!? Risers???
The seawater pump supplies cooling water to the T-stat housing.
Once there (depending on engine cooling demands), most all of it is sent to the exhaust system.
The engine's thermostat dictates how much seawater enters and leaves the engine for actual engine cooling demands.
Once the seawater leaves the engine via the T-stat housing, it too is then delivered to the exhaust system.

I was told one tell tale sign the manifold and risers are rusting out is that it will start overheating. I’m running normal temps. . I was also told that when they go out, it’ll hydrolock the engine which means replacing the entire thing.
If the seawater can find it's way into an open exhaust port..... yes, that is possible.

Is there any way to avoid a hydrolock.
Be pro-active and replace the exhaust components.
If your system incorporates back-flow-prevention flappers, make sure that they are in tact.

I was also told that it’s a good idea to install a flush kit. I have had them in fresh water engines but not sure it makes sense on a sea water engine that will always be in water.
Salt water corrosion never sleeps. Once it has begun, it is very difficult to arrest it.
A Flushing Kit may help.
Click to expand...


By the way, your exhaust elbows will be more prone to failure than the Spacers/Risers will be.


 
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alparmer said:
Have pretty much replaced or repaired most components. Replaced both cool fuel pumps, ouch, because when I went to replace the filters I couldn’t believe my eyes. The bottom pre filter was black and the main filter fell apart. All four pumps were noisy and the top cover bolts were welded by rust and snapped off. New idle pulleys, belt, and soon the raw water pumps. I need to also replace the t stat and the weird T cooling pipe with the plastic white balls. I also have most electronic sensors for backup, senders, cap rotor, etc. I don’t like surprises. I also had to rebuild the trim pumps. Pulling it out of water soon to service the bravo 3s
Click to expand...

According to your description, you have Gen 3 fuel coolers. Did you change the whole unit out or just replace the bad parts? Mercruiser would have supplied the parts at no cost. If the coolers were bad, you will need to have the injectors cleaned professionally to avoid and lean condition damage.

No need to change fuel lines or water hoses unless they have scars on them.

As for the exhaust manifolds, elbows and riser spacers(if equipped) They are 12 years old. Replace them. Purchase OEM parts. They are just a few dollars more than crappy aftermarket parts.



FYI, the 5.0 is a terrible engine, we see about 5 years of service out of them in a well used 29 Amber Jack style boat.
 
The cool fuel assemblies didn’t have any paint delamination. I decided to replace all four pumps because I knew the low pressure pump was bad on one engine. Most of the pump cover bolts were welded and snapped off. Not wanting to drill and use helicoils I decided to buy refurbished pumps with new components and the newer barb water inlets. The original snap on style with one nut were in bad shape also. Got two refurbished pumps for the price of one. Not sure if any junk got passed the pump to the injectors as it idles great and runs strong at wide open. Probably not a bad idea to get them cleaned anyway.

I’m going to go ahead replace the exhaust and risers to be safe.

I’ve been told the MPI 5.0 is a great engine as long as it’s serviced at the right intervals. This is the first time I hear it’s not a good engine. They currently have 330 hrs and will be happy if I get 1k hrs From them. When it’s time to replace I’d like to see what options are available. More power? Diesel? Volvo? or just rebuild and keep going.

Thanks for the reply
 
Looked at the parts diagram for my engine 0W678681 and it looks like I have 3,500 just in parts for the exhaust manifolds, elbows, and risers. Is that right? Is there a kit that includes all parts. Wife is going to kill me, just spent a small fortune getting everything else up to par.
 
5.0 will treat you fine,,had one in a boat and only reason I changed it was because a low hour 350 mag came my way cheap and my buddy took my 5.0 and used it till he sold them boat and it maybe running still.

As for the exhaust manifolds, are they dry joint style? If so those seem to last much longer, if you don't know look on this site for the comparison between all the styles. That price for exhaust sounds way high, if OEM is out of the budget I have had good luck with Barr marine products, stay away from GLM. I love Eddie marine but that was back in my go fast days and those were pricey.

If boat has always been fresh water you could have them pressure tested, but they are pushing 12 years, now my uncle who is a 40 year marine service owner says salt water 3-5 years, fresh 5-10 and if low hour well cared for, properly flushed and winterized 15 years , I have 2 sets of the dreaded 1 PC manifolds that are 19 years old. I recommend the new dry joint style of it isn't already equipped.
 
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fastjeff said:
How much better did your boat run with the 5.7 (vs. the 5.0)?

Jeff (5.0 boat owner)
Click to expand...

Replaced a 5.0 MPI with a new complete 350 mag MPI in front of an Alpha drive on a 23 Crownline BR. Had to go up two pitch on the prop and it burns half the fuel.

We only see about 5 years out of a well used 5.0 in a heavier boat. Especially the 29 Amber Jacks with twins and B3 drives.
 
Thanks for the replies. I can’t hide any expenses from wifey because she is a CFO and counts every penny. LOL

I don’t know if I have dry or wet joints. It’s all OEM 2007 Mercruiser MPI 5.0 B3s.

The prices I found was all parts individually and most of them made by Sierra. Do all parts have to be changed? Risers, manifold, and elbows. I wish I knew if the Previous owner had them replaced at one point. 12 years old and runs great but don’t know if I have one more run or years left until they go. I remember reading somewhere that on this model there was an improvement which made them last longer. I’ll have to search again.

I’m taking the boat out of the water next week and will ask the mechanic about the risers etc. I just wanted to know a little more before they try to get more money out of me. I don’t know anything about the marina so don’t know if they are honest or not.
 
If you have a 2007 it should be the dry joints and that's why they are more expensive. Dry joint came on line in 2002 if I recall right. The problem with predicting manifold and elbow life is that it is a guessing game. Unless you take them apart and check you have no idea how they are holding up inside. The outside can look great and the inside could be close to putting water in a cyl. I used Barr aftermarket on my OMC one piece V6 conversion and it worked out well. Cast in USA good quality. Tell your wife replacing the exhaust while expensive will avoid a much more expensive engine replacement due to water in cyls, stuck exhaust valves and rusted cyl walls. I would prefer Barr to Sierra if you can get em. Try Lighthouse Marine or Partman in Riverhead Long Island. Where I got mine.
 
alparmer said:
I don’t know if I have dry or wet joints. It’s all OEM 2007 Mercruiser MPI 5.0 B3s.

.
Click to expand...


Note auxiliary water passages ("C" passages) bypassing the exhaust path flange at bottom i.e dry joint
Dry Joint Elbow.jpgOn a dry joint elbow, the water passages are external and not cast as slot passages beside the exhaust flow.
 
merc dry joint elbows after 4.5 years in salt water.jpg
These are dry joints, check out the one on the left.....even though the dry joint design is definitely better than the wet joint as you can see in this pic this engine could still have had water ingestion due to the rotted area you see on the left one. So like I said, unless you take em off and check you will never know until its too late. My engine originally had OMC one piece batwings and I replaced those every 5-6 seasons, by the 6th season they had corroded enough that one of the elbow water exits was getting clogged. Never had water in the engine on that schedule of replacement and they were not cheap...approx. $450 a piece. I changed to the Barr 2 piece style used on later OMCs and Volvos since the batwings had long ago become NLA. I had to buy some V/P exhaust pipes & hoses that fit between the elbow and the Y pipe, with these it all fit like factory. The cost of the manifold/elbow kit with the gaskets and bolts is approx. $720 or so. But expect the Merc dry joint to cost more....I do think it is a better design...I would have adapted it to my engine but the angle of the elbow is different from OMC/Volvo to Merc so I was not sure it would line up.
 
I put 2500 hours on my 5.0, lost compression on two cylinders and replaced motor with a new 5.7. Much quicker out of the hole, same top speed.
 
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