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2004 merc 350 mag mpi high temps on new dry joint manifolds, one thing after another with this boat

stang32

Regular Contributor
have an issue where this boat has readings on new manifolds and riser of over 180 degrees,
back story ,the boat was overheating terribly and the previous owner had another mechanic run tests where he pulled the thermostat and "allegedly" pulled the risers for inspection. which he said were fine. i stepped in after that point., running the boat found that there was no water coming out of the transom when running on muffs the boat went into overheat, raising the idle speed caused the hose to blow off of the elbow from the water distribution housing, when the hose blew off, the temp went back to normal. further inspection found the manifolds and risers terribly corroded with rust.. (original from 2004) now fast forward to now, i replaced the manifolds and risers, and all seamed well, until i was called and informed the boat temp did not raise above 100 degrees. tests with infrared heat gun found the entire system did not go above 100 degrees including the manifolds. i found that the thermostat was removed and not in the system( which the PO said was replaced) and installed the correct one. after that this issue has arrised.
the PO had the seapump impeller replaced when the overheat started happening. once i got involved, the boat was out of the water

anyways, i replaced the manifolds/risers and ran the boat on muffs and it cooled nicely and the water flowed out the exhaust. i did notice the temp was not climbing but i felt the reason was because it was on muffs and the water coming from the house was very cold and pressured. it wasnt until the boat was in the water and we saw the temp still didnt go up that i found the thermostat was missing.
do you think the impeller can be bad even though the engine temp is staying within range?

the hose routing looks to be correct.
i think based on all the other inacurate information i have been fed, it may be possible this impeller was not changed as the said it was

i just don;t see why the engine will be within range if the impeller is bad and how does the engine stay @165 when the manifolds are climing to close to 200 degrees.
this boat is one issue after another, after the thermostat was installed one of the hose clamps going to the lower manifold fitting broke and caused the bilge to fill with water up to the middle of the water circulator pump pulley. this because the bilge pump screen was clogged and stopped the pump from disposing of the water. i immediatly pumped out the bilge and found that the p/s pump took on water. further inspection found the the exhust tubes both melted holes in them and the shutters were gone. on the port side of the engine. i replaced all these parts and found the manifolds were getting extremely hot. so now i need to figure out why this is heating up so much yet keeping the engine temp within range.i am puliing the boat tomorrow to remove the drive and inspect the bellows for water due to this issue.
 
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There are three different types of gaskets available for dry joint elbows... Two for raw water cooled manifolds, and one for "fresh water" cooled manifolds. The difference is in cooling water flow into the elbows... It sounds as if you have raw water cooled manifolds and elbows.

The purpose of the thermostat in any engine is to make sure the engine runs WARM enough.

Re: Shutters gone.... often pieces lodge in the drive passages and restrict water flow.
 
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it has the right restrictor gaskets that is for sure.
yes i know what a thermostat does, and its doing its job,
thats 1 thought, and why i am pulling the drive later today i will check for the plates.
thanks for the reply.
 
ok, update time, today i replaced the raw wter impeller, the manifolds still overheated, then while the engine was off, i removed the drain plug from the thermostat housing and the amount of pressure behind this thing was ridiculous. so much water came out. i then restated the boat and water was shoting out of this point. i pulled one of the hoses that come from the thermosta housing to the manifold with the engine running and no water came out of it. note: there should be water backfeeding up the hose frm the manifold from the supply hose that connects to the lower fitting.
the boat is out of the water now so i looked and saw no water exiting the transom.
i pulled the small hoses that go to the lower fittings on the manifolds and heavy water came from them. 'i pulled those fittings and the check valve is just flopping around and when i blow into it hard, the flow shuts down. so i think i have solved this issue. parts will be here on tuesday so i will follow up.
 
Hi, may I ask what you replaced and if it made a difference? ... i have a quite similar problem...
cheers from austria
 
though with me temps are as follows:
manifolds (both sides) 200-250°F (cruising over 3000rpms) and riser (both sides) can go to over 400°F (!!!!!!) ...but then the knee is cold (by cold i mean as cold as the lakewater)
The boat has been in a professional garage (licensed mercury dealer) with parts of the BravoIII replaced...thus engine was out (summer 2023)), both impeller AND waterpump, among other stuff have been replaced, the engine temp seems to be ok, it really is just the manifold and knee... I am convinced that the problem did only occur AFTER the mechanics went to work.... i mean you could "smell" and feel (when opening the "hatch" that the temps were to high additionally when stopping the engine you can hear the water boil in manifold/riser at stern side ...though I don´t want to point fingers just now...as so often it may be a coincidence...but you may keep that in mind, when trying to think of problem location.
Furthermore, parts of the bravoIII underwent maintenance after the gearoil was clouded with water....new seals etc. (spring 2023)
I checked the plastic-distributor pipe (which feeds the fuelpump and the starboard manifold) going from the impeller (black hose) to the thermostat housing (?) and made sure neither there nor in the fuel pump are any restrictions/blockades etc etc
it is a sea ray 240 with mercury 350 mag mpi(2007 or so)

thank you so much!
 
If the manifolds & elbows were clogged I wonder if the water distribution housing is too; I’d check it for clogs. Also did you measure raw water volume flow? How about Bravoitis? They are known for a fitting in the transom mount that restricts raw water intake.
 
raw water cooled...
the water temp shown on the gauge is exactly where it is supposed to be, the IR thermometer (actually two diff. makes, just to make sure) show water temps in hoses/pipes/ engine(as far as one can tell) just according to the specs, oil temp (measured at the filter) is ok too.
the exhaust system looks good to me (manifold/riser/ellbow), the ellbows (knees?) are cold (as cold as the lake water), how ever the riser get insanely hot (over 400°F if you go for it) and the manifolds get considerably hotter (200-300°F) than they should
i´ll give them a more thorough inspection tomorrow, same goes for the water distribution housing, but at first inspection i could not see any clogging or debris that could lead to clogging

i have not measured the flow volume yet, but will so so tomorrow as well.... am i right to measure the volume coming out of the impeller housing?
...will earmuffs with 0,5inch hose and a good water pump do? or will the propeller have to be in/under water?...
---> the transom mount was replaced this summer (by a authorized mercury/mercruiser dealer), that is when the drama took its course... the reason for the change was considerable steering play...personally I am convinced that it is related to this ...the dealer sees it quite differently of course...
again, i don´t want to point fingers before i am certain, as it may very well be coincidence...how ever, as nothing has worked so far, it has to be taken into account...
thank you for your fast and thoughtful replies...that "bravoitis" sounds like a possible....
i ll give you a heads up tomorrow or the day after :)
 
if the exhaust manifolds are getting that hot, I'd suspect the wrong gaskets were used between the top of the manifolds and the elbows...if adequate water volume can't flow out of the manifold, it will get very hot...
 
If you DM me your email address, I email you the applicable (cooling systems) chapter of the OEM shop manual ( 20meg) as well as the Dry Joint specific addendum (Service Manual 37 ) also 20 meg... Not only is it important to have the correct gaskets on the dry joints, they need to be installed only one way... hence offer to send manual sections.
 
if the exhaust manifolds are getting that hot, I'd suspect the wrong gaskets were used between the top of the manifolds and the elbows...if adequate water volume can't flow out of the manifold, it will get very hot...
there are two gaskets manifold- gasket- riser- gasket with restricted flow- elbow
they seem to be the right gaskets and also correctly installed
 
what bogs me, is the fact that the elbows are perfectly cool, but the manifolds/risers are too hot ...gaskets could be a reason, and i have suspected this too, how ever, they seem to be in right order (restriction btw riser and elbow + "looking" into the direction of travel)...
so since the hoses from the coldwater supply to the balljoints /manifolds actually do come first and only than comes the water-distributor-plastic-thing which will bring cold water to the elbows, i do suspect the balljoints to be faulty, but why would they fail on both sides with the stern-sided one being (together with the manifold) brand new.
 
Those Ball joints are poppet valves most likely, they probably have springs behind them and work when most of the pressure forces them open.

If thats what they are, they need inspection to make sure they move freely both in and out and spin easily. If there are deep grooves worn in where they spin tbey can be reversed to the round side.
 
Those Ball joints are poppet valves most likely, they probably have springs behind them and work when most of the pressure forces them open.

If thats what they are, they need inspection to make sure they move freely both in and out and spin easily. If there are deep grooves worn in where they spin tbey can be reversed to the round side.
I believe those ball and spring valves in the T restrict raw water flow to the elbows. They let some raw water by to cool the exhaust when thermostat is not open. If they don’t close or restrict water flow enough engine will overheat as too much raw cooling water goes to the exhaust bypassing the engine
 
I believe those ball and spring valves in the T restrict raw water flow to the elbows. They let some raw water by to cool the exhaust when thermostat is not open. If they don’t close or restrict water flow enough engine will overheat as too much raw cooling water goes to the exhaust bypassing the engine
I know exactly what they do as I have them in my own boat and many others I service.

At cold start up the water pressure being diverted due to the thermostat being closed, opens the poppet balls to allow max flow to the elbows as you said to cool exhaust. Once Thermostat opens and that pressure is reduced, the poppets close to some point as the main water pressure is now flowing through the rest of the cooling system and up through the manifolds up through the elbows and out to cool exhaust.

Because many who winterize there boats by way of alternative methods as compared to MANUALLY draining and using RV Antifreeze and MANUALLY adding it to removed hoses (two of which are the ones going to the elbows) they NEVER look to see if the poppet balls look good/function properly (meaning not stuck or spring is bad or groves have worn into balls as they spin). Seen it all......

I have not worked on the Dry joint system yet. all my clients have older product and that's why they bring it to me as i am older...lol.
It seems to me that Mercruiser fixed something that did not require fixing with 50+ years of no prior issues unless it has to do with EPA related crap.
 
I'm guessing that Merc changed the exhaust to the dry joint exhaust because leaking manifold to elbow gaskets was a common source of water in a cyl. Maybe not a big problem in freshwater but in salt water it can be. So they separated the water flow and the exhaust gas flow with that new design. As long as the elbows don't rust through, you are not likely to get water in a cyl like what can happen with wet joint exhaust from a defective gasket, or even bolts not torqued properly.
I have only had the OMC with the OMC/Volvo style exhaust, no poppet balls or anything like that, and have not had any troubles with the exhaust running too hot, and I have had the original OMC one piece exhaust (Just like what Merc tried on the V6) and the later style 2 piece wet exhaust joint that Volvo used till they were forced to add the dreaded cat converter exhaust.
What it seems like to me from an engineering perspective is this, Merc tried to do 2 things, one is to separate the cooling water and exhaust gas (actually a good idea), and also keep the manifolds hot enough to prevent condensation in the manifolds (warm manifold vs cold manifold systems). Also a good idea, but seems more trouble prone. OMC & Volvo never had a warm manifold system, but they used a higher temp thermostat (160*) on just about all their engines, to avoid condensation in the exhaust. Even so, the manifolds on mine run very cool at idle, like 100*. The hottest they ever get is approx 140* after coming off plane.
I would look carefully at how Merc says the gaskets should be oriented if you have spacers and elbows. It may be that with spacers and elbows, the gaskets between the manifold & spacer should be open but the ones between the spacer and the elbow should have the restrictor on one gasket.
 
thank you for your thoughts,

the gaskets are/were installed according to the manual , eventhough i sometime wonder why that front piece has to be restricted that much.
i´ll inspect those t-fittings more closely tomorrow (even though one of them is new), i´ll also change the impeller (eventhough it has just under 20hrs on it), just to make sure
then i ll reassemble and test it

so:
NO bravoitis
NO blocked fuel cooler/pipe
NO blocked water distributor
NO blocked t-stat/t-stat housing
NEW Impeller (no prior impeller ever cracked or fell apart)
NEW Waterpump
Engine was replaced 4 yrs ago, flushed with antifreeze every fall and NO salt water
any more thoughts?
 
I'm guessing that Merc changed the exhaust to the dry joint exhaust because leaking manifold to elbow gaskets was a common source of water in a cyl. Maybe not a big problem in freshwater but in salt water it can be. So they separated the water flow and the exhaust gas flow with that new design. As long as the elbows don't rust through, you are not likely to get water in a cyl like what can happen with wet joint exhaust from a defective gasket, or even bolts not torqued properly.
I have only had the OMC with the OMC/Volvo style exhaust, no poppet balls or anything like that, and have not had any troubles with the exhaust running too hot, and I have had the original OMC one piece exhaust (Just like what Merc tried on the V6) and the later style 2 piece wet exhaust joint that Volvo used till they were forced to add the dreaded cat converter exhaust.
What it seems like to me from an engineering perspective is this, Merc tried to do 2 things, one is to separate the cooling water and exhaust gas (actually a good idea), and also keep the manifolds hot enough to prevent condensation in the manifolds (warm manifold vs cold manifold systems). Also a good idea, but seems more trouble prone. OMC & Volvo never had a warm manifold system, but they used a higher temp thermostat (160*) on just about all their engines, to avoid condensation in the exhaust. Even so, the manifolds on mine run very cool at idle, like 100*. The hottest they ever get is approx 140* after coming off plane.
I would look carefully at how Merc says the gaskets should be oriented if you have spacers and elbows. It may be that with spacers and elbows, the gaskets between the manifold & spacer should be open but the ones between the spacer and the elbow should have the restrictor on one gasket.
Merc has several designs including ones similar to OMC which I have worked on many.
My poppet valve syatem is 1987 and all original fresh water use only. Works perfectly.

One thought,
Using infared heat guns does not always point to a problem.
I say this with a lot of caution but,
If the rubber exhaust boots are not getting hot enough to smell or melt, you may not have a problem.

Typical exhaust temps coming out of chamber is around 1200-1300* F.
So by the time it mixes with block temp water and exits the elbow it will be close to 200* f or higher...but not hot enough to melt rubber...
The water flowing thru elbows make the castings cooler.

Again my lack of experience with dry joint I cannot explain your issue directly.
 
mh,at some point i was thinking about hunting a ghost too...but i had a cracked manifold as a likely consequence of the heat problem (actually it cracked twice ...see below), in different forums I read of temps below boiling temperature on the manifolds, risers, elbows, mercury itself has no temp-ranges stated and doesn´t know of any, neither do my mechanics (licensed mercury dealer), i ll give you a short overview of my boat (´s problems)

up until 2019 regular services and check-ups...mostly and regularly by merc-dealers

2019 new engine + manifolds (when i was abroad for a year, my father incorrectly "winterized" the boat which led to cracked manifolds and cylinders (only towards the outside)...i still used it for 50+ hrs, but he wanted it changed nevertheless.
2020 new impeller housing

the whole next thing is a bit odd, last winter (2022), we had the bravo III partially serviced (oilleak/water in gearlube), but i don´t think it is related, as problems would likely have began sooner... the next 20-30 hrs boat worked well except for hot-start issues...with a bit of throttle all was well (see manual)
then in summer break 2023 (motorboats are banned from the lake in jul/aug), we had the transom thing changed due to considerable play in steering (so the engine was out), including impeller service, idle sensor (?) and quite a few other things and THAT is when the problems began...the mechanic told me, that when he test started, the engine felt funny the first few turns, with him suspecting water in the cylinders...so he checked and found a cracked manifold... his guess was leaking injectors, so he replaced two of them (I was doubtful back then, and it obviously wasn´t the root of evil) and he replaced the gaskets of both sides (back in 2019 i reused the old gaskets supplying hightemp-silicone which has worked fine for the time being.
When i got the boat back, it "felt like" the engine compartment was - at high rpms - hotter than normal and there was also a funny smell, but all gauges showed ok water-/oil temps, oil smelt fine etc., then after a week of boating, the engine started to be a bit rough on idle and the next day the engine wouldn´t even turn due to water in the cylinders... so back to the mec´s, replacing the manifold yet again (+new gaskets, new spark plugs...), they thought it maybe a warranty thing, as according to mercury there has been a faulty series of manifolds.

anyway, that was when i started to check the temps with an IR-thermometer and again, as soon as you´d go "faster" than moderate cruising speed (like over 3500rpms), the manifolds would go up to +/-300°F (+/- 150°C) and the risers well above 400°C (well over 200°C), water inside the manifolds/risers (port side) would even begin to boil (!!!) though both side have almost similar temps.
again, the elbows are perfectly cold.
since the waterpump made slight squeaking noises the mec´s changed it too, but to no avail.
--> i have run the boat only for short testdrives (check temps etc.) since... high rpms (like over 3500 or so) lead to increased manifold/riser temps
idle/harbor speed there are no probs, moderate cruising speed (like 2800rpm) still is sort of ok, soon as you go from high rpms to idle, the manifold/riser temps go back to almost normal .

things next in line:
-nethertheless replace the impeller,
-block the t-fittings draining hose (the almost veritcal ones), as at least with moderate water flow, the ball/spring thing won´t close...if my mec´s described the design of these t-fittings correctly...with water flow from the t-stat-housing side hoses the ball-spring-thing should be pushed down and the water flow down towards the water dirstributor should be blocked, and with no pressure the ball should be up and allow drainage?!
--> this would imply a different functionality as you guys have discribed above though.
-i have descaled the riser and t-stat housing
- inspect the exhaust flaps
- reassambly and methodically check water flow volume from impeller to the end and if necessary backwards -- thank you ALL for your thoughts and great support!
 
Well for some reason it appears that your exhaust elbows are getting enough water but the manifolds & risers aren’t. IIRC on this Merc warm manifolds system the elbows always get water but the manifolds don’t get flow till the thermostat opens. So the elbows will feel cool but the manifolds will be hotter than the engine water temp because the water exiting the stat housing has already been heated to about 160* and now picks up more heat from the manifolds. The question is how hot is too hot? I would think about 200* is about the hottest they should be. The idea was to keep them above 120* because below that temp is where you can get condensation in the exhaust.
 
So I have disassembled the whole water system, i could not find any obstructions, water flow seems to be ok in risers and elbows and everywhere else too. after reassembly i built a "tank" to test the water yet again and especially test the impeller. i checked water flow and it seems to be alright. to give you an idea, ive uploaded 3 videos. the water flow on the elbows (hose) is pretty much the same as on the manifolds (hose from t-stat housing) and the water being pushed out of the elbow (once the hose is disconnected is still considerable, though less then coming in from the hose (no wonder... most of it will still be running down the ellbow´s outlet.)
the thing now ist (with NO -stat installed): everything all temps are fine at idle, the risers will go up to around 180-190°F at 1500rpms
the manifolds stay at around 100°F (remember, no T-stat, so that should rise with the tstat reinstalled).
Now at 3200rpms the riser temp goes up to 230°F HOW EVER: the temps are taken from the center of the risers ...if i am not mistaken there is NO watercooling there (unlike older models)...so naturally temps will be higher there...
what do you think of the water flow (and the reflow)

for the water flow please check the youtube links.
 
Ok, so this may be a beginners question:
should there be exhaust gases/ water coming out of the propeller on my bravo III... because there are neither water nor exhaust fumes coming out...
I cannot remember if there ever was, since i am also servicing our life-guard boat with a Honda BF135....so it may only be the honda with water coming out of the propeller.
The Bravo III was serviced by said mercury dealer/mechanic in spring 2023 because of water in the gearlube.
 
Usually you will not see much water if any at all coming out of the prop at idle speed when you're running it on a water hose on land, but for sure you will see water coming out of the idle relief ports which are under the transom mount.
 
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