Manifolds, risers, and engine temp

[Nicholas Del Rio]

Hello all!

Boat owner for about a month now and interested in your feedback regarding the condition of my exhaust risers (feel like I’m drinking from a fire hose trying to take in all the info about a marine vehicle). I’m waiting for a response from the guy I bought it from regarding his maintenance schedule, but in the meantime I thought I’d share some pics of the risers and manifolds *externally* and see if the pools of rust at the joints might be indicative of a leak or if it’s just typical rust. It’s a 2003 4.3 MPI engine and has only been used in fresh water lakes, so based on the year and structure of the components I’m assuming they’re dry joint risers that hopefully have a decent lifespan, although I’m keen to replace to avoid engine failure. My thought is just to continue the season and then check before winterization or pre-season 2023.

*** sorry for funky orientation of images, not sure about the image size and ratio expectations for this site ***


Also, my engine runs just under 160 degrees on slow speeds but climbs as high as 173 under sustained throttle at around 40 mph. Reduces steadily back down to 160 when I back off throttle. Seems like normal engine behavior?

 

[Gallf1]

Saltwater guy here....I just did my manifolds, risers and elbows as part of regular maintenance. I can tell you from experience that the only way to verify condition is to remove and inspect the elbow and you can look down into the riser and part of manifold....if it all looks good then it cost you just the cost of new gaskets and some time. If they are bad, you may have saved yourself a new engine cost!

If you dont have solid maintenance records, I would proactively replace the raw water impeller so at least you know that it is good.

 

[scoflaw]

Looks good, those parts can last a very long time in fresh water

 

[Nicholas Del Rio]

Saltwater guy here....I just did my manifolds, risers and elbows as part of regular maintenance. I can tell you from experience that the only way to verify condition is to remove and inspect the elbow and you can look down into the riser and part of manifold....if it all looks good then it cost you just the cost of new gaskets and some time. If they are bad, you may have saved yourself a new engine cost!

If you dont have solid maintenance records, I would proactively replace the raw water impeller so at least you know that it is good.

thanks for your response. The previous owner had the boat professionally serviced every fall. But it seems as if the mechanic only checked things like bellows, belts, fluids, etc, and so previously owner was not sure whether the risers and manifolds were checked as part of routine inspection/maintenance. So I guess I’m flying blind with regards to the state of the exhaust components.

should I check asap, or something I can wait till fall or early spring?

 

[Nicholas Del Rio]

Looks good, those parts can last a very long time in fresh water

Good to know! I think I’ll take a deeper gander at the end of the season. Doesn’t seem too difficult to remove and check the state of these components.

 

[thomas d millett]

2002 Mercruiser MCM 496 magnum Smartcraft engine guardian system kicked in after 30 minutes of running at 2500 rpm on a hot day. Engine temp never got over 170 degrees, which is what it usually runs. We got back in on limited engine power at idle speed.

Mechanic says he detected overheated port exhaust and suggests new manifold, riser and elbows on both sides (says Mercruiser suggests this every 5 or so years). New manifold assemblies were installed in April 2019, a month before I bought the boat. I have not put more than 50 hours on it in each of the 3 1/2 seasons that I have had it. The boat is on a mooring in salt water for 6 months per year.

I have no choice but to spend the $5,500 to do the job, but does this make sense, and is there something I could have done (or as part of my mechanic's winterization) that could have given the assembly a bit more life?

 

[scoflaw]

No doesn't make sense, probably bravoitis. Dig deeper

 

[superwa]

About manifolds in salt water, 4 years brings failure rate down to 25%. 45% at 5 years. At 3 years is 0.5%
I had one fail at 4 years. It does happen. Just think that at 5 years you are almost at 50/50 chance of failure. Not worth a new engine.

https://www.boatus.com/expert-advice/expert-advice-archive/2012/july/exhaust-manifolds

 

[Pirate Lady]

No doesn't make sense, probably bravoitis. Dig deeper

I had Bravoitis. Will idle all day at 170 but 5 mins on plane, not 30 and she is cooking.
If he can run 30 mins at 2500, it’s not Bravoitis.

 

[Gallf1]

2002 Mercruiser MCM 496 magnum Smartcraft engine guardian system kicked in after 30 minutes of running at 2500 rpm on a hot day. Engine temp never got over 170 degrees, which is what it usually runs. We got back in on limited engine power at idle speed.

Mechanic says he detected overheated port exhaust and suggests new manifold, riser and elbows on both sides (says Mercruiser suggests this every 5 or so years). New manifold assemblies were installed in April 2019, a month before I bought the boat. I have not put more than 50 hours on it in each of the 3 1/2 seasons that I have had it. The boat is on a mooring in salt water for 6 months per year.

I have no choice but to spend the $5,500 to do the job, but does this make sense, and is there something I could have done (or as part of my mechanic's winterization) that could have given the assembly a bit more life?

Personally, I flush my engines with fresh water and Salt Away after EVERY outing. I run the mix thru a 13 gallon bucket with a suction hose tee'd into the raw water hose between the closed sea cock and strainer. When I see the suds come out the exhaust, I know it has worked its way thru the raw water side. I leave the freshwater mix in the system.
You can do this at a mooring by just filling a 13 gallon bucket from your fresh water tank system.

https://www.amazon.com/EZ-Stor-Container-Bucket-Gallon/dp/B00LUZV0EY