riser manifold replacement

[scoflaw]

Own a 10 year old merc 305. Previous owner replaced the risers and manifolds in 07 after overheating issues and water in motor. Is there any way to know when to replace these items other than letting them fail? Salt water boat that sits at a slip all season, no flushing.

 

[Philster]

Re: riser manifold replacement

Flush 'em by using a flush kit that cuts off raw water flow and sucks from fresh water hose w/ engine running. They don't have to sit in salt all the time. You can't flush the outdrive, but you can flush the engine and pieces.

Remove, inspect, replace and you get new gaskets if they check out fine.

Or... plan on expensive maintenance every couple of years.

 

[full stringer]

Re: riser manifold replacement

yes you should still flush the engine hook a hose directly up to the thermostat housing intake or put muffs on the outdrive intakes under water. But that wasn't his question he wanted to know when to replace his manifolds. the answer is when you cant hold your hand on them when engine is at proper running temp. sometimes one will be real hot and the other side cool because all the water is flowing with less resistance through the unrestricted side the other is clogged. there is a product called salt away i use it every flush it removes the salt and provides a coating to prevent salt from embedding into the pores of the engine passages and manifold passages as well as the risers

 

[legoman67]

Re: riser manifold replacement

i work at a marina, and general rule of thumb is every 2-3 years. of course if you fresh flush after every use then your time goes up substantially

 

[westportfish]

Re: riser manifold replacement

If possible on that style of manifold, fresh water cool them. My big block Chevy manifolds are cooled with the engine coolant and only the risers see any salt water. I have been running the same manifold log for 15 years and have changed the risers twice.

 

[JoLin]

Re: riser manifold replacement

If possible on that style of manifold, fresh water cool them. My big block Chevy manifolds are cooled with the engine coolant and only the risers see any salt water. I have been running the same manifold log for 15 years and have changed the risers twice.

Converting an engine that old to fresh water cooling isn't recommended. There's too much junk in it that will clog the system.

The poster didn't state where he boats. If in salt water, folks in my area look at 5-6 years as the replacement interval. The fresh water flush recommended above is a good idea and might extend that.

My .02

 

[Philster]

Re: riser manifold replacement

I just replaced manis/riser/elbows. The general consensus amongst me, my surveyor, my merc tech and merc manager was, "Hmmmm.... maybe...".

I couldn't get myself, or anyone to get any further than that, because it's sometimes a tough call. When I finally decided and just did it, I sucked it up and decided I didn't like being in limbo. I said, "Replace the whole shebang."

Next day: My neighbor comes by and asks me about the boat. I tell him it's getting X am't of maintenance done right now. He tells me about his Crowline's 454 Merc that hydro-locked when water got back into the engine (exhaust water leak). He's boatless this season and is selling the hull. Can't drop the cash for an engine.

It's one hard, tough piece of maintenance, but salt water forces the issue. You can fend it off a few years with dedicated flushing. Get a flush kit installed.

Unfortunately, you are gambling your whole engine on these pieces.

 

[CayugaCobalt]

Re: riser manifold replacement

Sorry to ask a stupid question, but...

Is engine cooling system flushing as you have discussed at all relevant to a boat run only in freshwater with an open system, whereby the lake water is sucked in and spit back out?

I have such a boat that is overheating and have eliminated all potential sources except "clogged" manifold/exahust riser and possibly blown head gasket.

 

[Philster]

Re: riser manifold replacement

Fresh water setups can last decades. Generally, no need to flush.

What sources have you eliminated?

 

[CayugaCobalt]

Re: riser manifold replacement

I have eliminated the water tube at the transom that is known to sometimes corrode and suck air.

I have eliminated raw water impeller, thermostat and oil cooler. I have also checked hoses twice for any leftover bits of impeller.

Boat maintains 170F precisely and indefinitely at idle type speeds. So only on plain at speed it overheats.

The boat is a 2001, I bought it in 2007 with 85 hrs on it and it was perfect in 2007, 2008 and half of 2009 when out of the blue one day cruising down the lake it overheated. I did not suck up weeds or a plastic bag.

I now recall the previous owner, who was very anal with the boat, did have the boat in brackish water. Toms River NJ area.

I am now trying to figure out if manifolds are clogged or hot exhaust is bubbling in. I think I can use clear vinyl tubing to look for these bubbles.

I used clear vinyl upstream of thermostat to ensure I was not sucking air.

 

[Ronzai]

Re: riser manifold replacement

Is your system half raw water and half block closed side antifreezed? Anychance of air on the antifreeze block side? Air in any hydraulic circuit can interupt flow and sometimes stop it completely. I have a 1989 Searay with a 454 and Bravo drive, and I have been battling a temperature spike on acceleration. 140* farenheit while idling, and hit the gas, and it spikes within seconds to 180*f. Previous years that I used the boat, I could go wide open for extended periods of time and the highest it went was 150*f. I did make the mistake of paying a mechanic and not watching him, he blocked off, with solid gaskets between my riser and exhaust manifolds. I found this out by removing my risers after I overheated all summer and allmost ruined my motor. He told me I had to "Trust Him". Be careful who works on your boat and don't be afraid to watch! I am finishing up on my own after that.