Exhaust manifolds - Merc 454

[Joker757]

Hello fellow boaters. I'm new to the site. I have a question regarding the manifold, risers and elbows on my 1999 Maxum 2800SCR. The boat sat for about 8 months and I recently started getting it ready for the season. After changing the oil and filter, thermostat and turning by had a few times I started the engine. I let it idle for about 20mins. I then pushed it up to 3000 RPMs and the temp started going up to about 180 and the alarm eventually went off slightly before 200. I shut down and let it cool down. By the way the boat is on a trailer and I used muffs. I reved it up again and same result. Went back to idle and the temp immediatly went down. From experience this was indicative of a blockage of the exaust cooling passages. I reved it once more and noticed that the water flow out of the stern was now much more volume and about 2 to 3 teaspoons of rust particles ejected. Now when I run it up it stays cool and runs quite and smooth. Just to be safe I decided to pull the risers and elbow. They have some rust inside but aren't blocked. Water jacket walls look don't look thin. These risers and elbows are about 2 years old. Should I clean them or leave them as is? I do plan on replaceing them next year but was hoping to get at least one more season out of them. If I'm to clean them what's the best/safest method? Your thoughts?

 

[Joker757]

Re: Exhaust manifolds - Merc 454

bump

 

[dbric36]

Re: Exhaust manifolds - Merc 454

Running on muffs over 1500 rpms is not recommended. That might be why it is heating up when you rev it up to 3000 rpms.

 

[flargin]

Re: Exhaust manifolds - Merc 454

3k on muffs will make mine get warm, but you might have an impeller going bad, when was the last time it was replaced?

If the impeller is fried, you have to pull the oil cooler and get the bits out of their as well. those impeller blades do a nice job of limiting flow.

 

[flargin]

Re: Exhaust manifolds - Merc 454

oh yea, and welcome to the boards...

these guys really know what is going on, and can usually pinpoint the problem really quickly, but make sure you itemize your year/motors/drive when you post, it saves a lot of time, and helps for improved responses...

 

[Joker757]

Re: Exhaust manifolds - Merc 454

imperller is new. Just replaced a few weeks ago. The overheating and water flow problem is resolved. What I'm asking is what is the
best way to clean the manifolds, risers and elbows. They are two years old and I'm hoping to get at least one more season out of them. The water jacket walls are rusted but still have plenty of meat on them. Thanks.

 

[Joker757]

Re: Exhaust manifolds - Merc 454

oh yea, and welcome to the boards...

these guys really know what is going on, and can usually pinpoint the problem really quickly, but make sure you itemize your year/motors/drive when you post, it saves a lot of time, and helps for improved responses...

Bravo III with 7.4L MPI. Both were replaced in 2004 when I bought the boat.

 

[Bondo]

Re: Exhaust manifolds - Merc 454

They have some rust inside but aren't blocked. Water jacket walls look don't look thin. These risers and elbows are about 2 years old. Should I clean them or leave them as is?
What I'm asking is what is the best way to clean the manifolds, risers and elbows.

Ayuh,... Bolt 'em back together,+ Go boating...