Exhaust manifold and riser

[lakelivin]

Re: Exhaust manifold and riser

Originally posted by Don S:<br /> You're trying to get me to put a hard fast rule on something that doesn't follow the rules. <br /><br />If you notice the engine is starting to misfire at idle, when you get parked/anchored, check it out. If you can't hardly keep it running at 2000 rpm, shut it off and call for a tow. You have to make a common sense call on this one.<br />It could be bad spark plugs, bad points, bad plug wires or....who knows, maybe even water getting into the cylinders. What I'm trying to say is if you notice something going wrong with the way the engine is running, find out what the problem is. Don't wait for 3 more months till you pull the boat out of the water for a scheduled inspection, or next spring when you have the money. Find and fix the problem, (What ever it is) before it damages something else.

Not looking for hard & fast rules; the answer you provided is very helpful for a real novice like me. Thanks.

 

[Lou C]

Re: Exhaust manifold and riser

Man I can't believe how much some of you guys worry over a couple of hunderd bux vs THOUSANDS for a blown motor. When I got my 88 FW it had the OE 14 year old manifolds but had mostly fresh water use. I changed them to be on the safe side even tho it used the one piece OMC manifolds that cost then 377 a side. Never had a problem, but being a long time shadetree mech, I couldn't stand the idea of getting water in the motor to save a few bux. And you all know how hard it is to get a good rebuilt motor! BTW, on boatered, they only sell Merc rebuilds because not one of the other rebuild companies they used really honored their warrantee. So there you have it, I'd rather maintain and old but good OE motor, than fool around with rebuilds that may never work right, just to save the money on the exhaust.<br />Just part of the cost of having an inboard!!!!<br />If you don't want to bother with exhaust issues get an outboard next time, or a full closed cooled motor.

 

[lakelivin]

Re: Exhaust manifold and riser

Lou,<br /><br />For me (and I imagine a few others), it was more a matter of ignorance about how the manifolds work, danger to the engine associated with one going, etc. I didn't even know that there were different 'chambers' (or whatever the correct term is) inside that carry water & exhaust gases, even though I changed one when it cracked due to freezing years ago (I drained it but didn't realize at the time that the drain holes can plug leaving water inside; sure enough, thats what happened. Now while I drain I use a wire to ream it out). <br /><br />So for many of you these 'discussions' / questions probably seem ridiculous, but I've learned alot from them... Now I know what to look out for & what to do when problems do arise (buy a bottle of Don's $99 magic manifold coating elixir, of course, lol!)

 

[Don S]

Re: Exhaust manifold and riser

As an example, here is the cut away view of a typical exhaust manifold. The red lines I put on it are the webs that seperate the water from the exhaust passages.<br /><br />

 

[lakelivin]

Re: Exhaust manifold and riser

Thanks Don, maybe you could save that picture for the next newbie 'why can't I just...' manifold question that comes along. Bet it would cut down on the text needed to explain the issues (prolly by 1000 words, eh?).

 

[f_inscreenname]

Re: Exhaust manifold and riser

"Bet it would cut down on the text needed to explain the issues (prolly by 1000 words, eh?)."<br /><br />No. They will then say mine is shaped different. <br />

 

[trog100]

Re: Exhaust manifold and riser

yes.. and on the principle that the hotter a part is the quicker it rusts away.. one can see why they go on the inside before they do on the outside..<br /><br />only one thing really interested me thow and it has come to light.. and that one thing is how they fail.. is it a sudden and guaranteed to wreck the engine type failure or is it a slower leak type failure that given reasonably prompt attention will not cause other major engine damage..<br /><br />i have drawn my own conclusion from these interesting and informative "manifold" threads.. i will leave others to draw theirs..<br /><br />trog100

 

[jlinder]

Re: Exhaust manifold and riser

After reading all this I have a question. I have a 1988, 5.0L, cobra drive for about 2 years now.<br /><br />Never gave the exhaust manifolds much thought as I had my hands tied bringing the rest of the boat back into good condition. If it didn't give me problems, and it wasn't on the obvious list (oil, grease, etc) it was out of sight out of mind.<br /><br />Now I have another worry. What preventitive maintenance / checking can I do or should I do.<br /><br />Do I wait until it dies, or should manifolds be pulled every so often to check for possible problems? And if there is something I can do, anyone have a reccomended procedure?<br /><br />Working on that all inclusive winterize/check list of things to do.

 

[Lou C]

Re: Exhaust manifold and riser

The reason why some people will check these every few years and replace, and others may not could have to do with salt water vs fresh. In salt water areas like here, you do hear of motors trashed by bad manifolds quite a bit. So it is seen like a maintenance part on a car, you check/replace every 4-5 years, or sooner if you get symptoms (overheating, hot risers, difficult starting, etc). In fresh water areas it is much less of an issue. When I told my brother who owns a raw water cooled Merc 5.0 in a 97 Glastron about this, he had never really heard of checking risers/manifolds because his boat has always been in fresh water. The OE OMC one piece manifolds must have been pretty good to last 14 years even if it was mostly fresh water. So that is why I looked around for another set, even though I could have converted to the center riser style used in the later models. I like the fact that there is no riser/manifold joint to rust and leak on these.

 

[lakelivin]

Re: Exhaust manifold and riser

Jack,<br /><br />my take after reading these manifold threads (note i don't have any expertiese personally) is that theres not much checking you can do since the real issue is if a problem develops INSIDE the manifold. (If I misssed something and there's a practical way to test, say the integrity of the inside chamber, someone please correct me.) <br /><br />I'm gonna follow Don's advice above:<br /><br />"If you notice the engine is starting to misfire at idle, when you get parked/anchored, check it out. If you can't hardly keep it running at 2000 rpm, shut it off and call for a tow. You have to make a common sense call on this one.<br />It could be bad spark plugs, bad points, bad plug wires or....who knows, maybe even water getting into the cylinders. What I'm trying to say is if you notice something going wrong with the way the engine is running, find out what the problem is. Don't wait for 3 more months till you pull the boat out of the water for a scheduled inspection, or next spring when you have the money. Find and fix the problem, (What ever it is) before it damages something else."<br /><br />I'm also going to start paying more attention to how much rust & scale is coming out of my manifolds when I drain them (using a wire to ream them out while they drain, of course).

 

[Lou C]

Re: Exhaust manifold and riser

Lake-- you have the same one piece units that I have on mine. The thing to do is remove them every few years (fortunately OMC used studs and nuts to hold them on, so you can spray penetrating oil to get the nuts free, and are less likely to break a bolt as used on other styles) and look at the rear of the riser section. You will see the big exhaust opening in the center, and four smaller openings around the periphery of the outlet. Those are the water outlets, if they are clear, you probably don't have that much internal rust, but if they are getting plugged with rust (and you would probably noitce some higher speed overheating) then you have to decide, do you want to take a chance by reaming them out with a coat hanger, or realize that the rust is particles of the inside that has flaked off, making it thinner, more likely to rust through. <br />As Clint Eastwood once said..."do ya feel lucky?"<br />BTW, if you do take them off be careful they weigh almost 50 lbs each! You have to loosen the clamps for the exhaust hose first, then remove the nuts holding them to the head. Don't forget to get new gaskest for the mani to head joint.

 

[Cool It]

Re: Exhaust manifold and riser

Hey guys , I saw a 400.00 figure thrown out there is that a ball park on just the parts or would that include labor? if not what do you think the total with labor should run on a 1988 5.0 Mercruiser. I have not had a overheating problem but the manifolds and risers do seem slightly hot to the touch. boat ran great last season. Dont know when or if manifolds/Risers and should you include the elbows have been changed. Just starting to think about what will need to be done for this coming season-- Cant Wait!!!<br /><br />Thanks<br />Cool It

 

[Don S]

Re: Exhaust manifold and riser

The $400 figure would get you parts only for one side of your Mercruiser V8, $800 for both sides. (List price, including gaskets.)<br />Labor would depend on the condition of the bolts that have to be removed to get the manifold off the head. I have had them so rusty that I had to use a torch and cut the heads off the bolts. Something I DO NOT do while the engine is in the boat.<br />Even if they are not all rusty, it also depends on access. Some boats the engine compartment is so small you can't even get to the bolts.

 

[trog100]

Re: Exhaust manifold and riser

i think some good advice is to listen to how your engines sound.. get used to what they should sound like when they are running sweet.. if they dont sound right investigate and find out why dont just ignore it till your next service.. i think its been generally agreed that manifold leaks start small and if put right quickly enough are not likely to cause expensive engine damage.. whether u replace em on a time basis or keep a carefull ear open is up to the individual and his circumstances i think..<br /><br />from what i read V 8 engines have more of a problem than simple four cyliner jobs.. twice as many manifolds to fail.. cost twice as much to replace.. far easier to not notice a misfire on one or two cylinders.. harder to get at.. <br /><br />water getting into a cyliner in any quantities will cause a misfire at least.. cos it will short the plug out.. the plug tip will be wet when removed and with the plug removed it will also splutter out the plug hole when u crank the engine over on the starter..<br /><br />damage caused by long term but small amounts of salt water getting into the exhaust manifold gas area would probably be rusted valve stems and seats and perhaps rusty cylinder walls..<br /><br />gonna hazard a guess here and say that salt water corrodes things at least three times quicker than fresh water does.. replace every four years is a saltwater thing.. that tends to suggest that ten years or more isnt an unreasonable expectation manifold life-wise on freshwater boats..<br /><br />course with a diesel engine assuming it has the same water cooled exhaust arrangement the danger from hydro-locking would be a thousand times worse..<br /><br />trog100

 

[Uncle Dave]

Re: Exhaust manifold and riser

A BIG thanks to all who gave such good advice and a little humor along the way on this thread. <br /><br />It has made me an "expert" on manifolds and risers. <br /><br />Thanks again<br />Uncle Dave

 

[Bondo]

Re: Exhaust manifold and riser

only one thing really interested me thow and it has come to light.. and that one thing is how they fail.. is it a sudden and guaranteed to wreck the engine type failure or is it a slower leak type failure that given reasonably prompt attention will not cause other major engine damage..<br />

Even a Slow Minor Leak Can Destroy your motor........................<br /><br />With a Catastrophic Failure, You're running at mid-high RPMs, There'll be No Damage, Until you throttle back....<br />Running fast, the exhaust gases will carry the water out.....<br />When you throttle back, there'll be reversion,+ the water will be Sucked into the motor.........<br /><br />With a Slow Leak, You'll be out boating without a care in the world........ <br />You get to the dock, or on the trailer,+ Then the manifold unloads All it's water into the Cylinders...........<br />Next time you go boating, The motor's hydrolocked,+ the base has water in it........<br />By then, You'll need Manifolds,+ Potentially a New Motor..................<br /><br />So,..................<br />A Little Bitty Leak has Much More of a chance to Destroy your motor than a Catastrophic Failure...................<br /><br />Boating is Not an Inexpensive pass time....<br />The Choice is Yours,<br />Pay a little Before it happens...........<br />Or,<br />Pay Alot After it's Really an Issue............

 

[trog100]

Re: Exhaust manifold and riser

yes anything is possible.. but i assume u mean the next time i try to start my engine.. i could be wrong but i am pretty sure that hydrolocking during cranking aint gonna damage anything neither is a small amount of water in the oil during this period.. basically the engine would just refuse to turn over.. conrods dont bend that easy..<br /><br />but i could envisage a situation assuming the boat has been stood a while.. is in a salt water environment that small unnoticed leaks could perhaps cause a valve or two to rust solid in their guides and bend the odd pushrod or two when the engine is cranked over as seems to have happened in another current thread.. pushrods probably do bend that easy.. he he..<br /><br />i bought a sixteen year old boat dude..cheap.. its a gamble.. i could make it far less of a gamble by throwing an immediate ten grand at it no doubt.. there are far more "maybes" than just my manifold.. <br /><br />i replace my engine cos by all reconings its past its sell by date and might fail at any moment.. i replace my outdrive on the same prinicple.. the list goes on and on and so does that "hole in the water" that some would have me throw my money into.. and many do just that no doubt..<br /><br />i do everything on the cheap.. i am an expert at it.. i am pretty certain my way aint gonna cost me any more money than it has to.. my one extravagance so far is treating the poor old boat to a new $1500 camper canopy.. i could keep the old one but its an eyesore..<br /><br />maintainance and how u go about it is up to the individual and his circumstances.. i know mine and act accordingly.. others should do the same..<br /><br />i also dont question for one minute the basis of good sound preventative maintainance.. a few quid spent wisely can save much money later.. but when it aint spent wisely it can and does cost an arm and a leg..<br /><br />and please dont try and tell a guy who spent twenty years running a taxi business without going broke how to save money on mechanical maintainance.. boat.. car.. or whatever.. cos u aint gonna succeed he he..<br /><br />course one lesson i might learn from all this is that i really cant afford a boat and that proverbial "hole in the water" u have to throw oodles of money into is an unavoidable "fact".. if so i will leave boats to the rich and amuse myself some other way more suitable to my means.. he he<br /><br />i also have the problem of living in the UK.. any new merc parts i buy will cost at least double what u guys pay for em.. again part of my circumstances.. and my cheap sixteen year old boat cost me £3600 nearly $7000 dollars which by american standards probably aint that cheap either.. he he<br /><br />there is one lesson i have already learned.. if i had have read this forum in depth before buying my boat.. i would probably would not have bought it.. he he he<br /><br />make of that last comment what u will..????..<br /><br />trog100

 

[chuck in WA]

Re: Exhaust manifold and riser

Where have you guys found a $400 manifold? I recently priced this stuff for my 1985 MerCruiser 140 and found $600 for the manifold and $300 for the riser - ouch!!! Time to search the junkyards?

 

[chuck in WA]

Re: Exhaust manifold and riser

Never mind, just saw another thread on the same subject with a link. Thanks all - this site is great!!!

 

[Lou C]

Re: Exhaust manifold and riser

Makes you realize that the only way to go for inboards in salt water is a full closed cooling system, that way only the risers are in question, and to pull them off every 3-4 years to replace is no big deal. I will probably get an outboard next time anyway since it is hard to find straight inboards in the size boat I can have (20' or so). I like Shamrocks with the Keel Drive system, since all the running gear is protected by the keel. But they are tough to find and expensive used, like a Whaler. No outdrives to maintain!!!