Temperature Fluctuates - 2015 350 mag mpi ec

[woo102]

Hi. I'm fairly new to the forum. I've done lots of car work in the past and some work on my own boats. I bought my current boat new in 2016. The boat is a 2015 Stingray 225 LR with a 350 mag mpi and a Bravo 3. I mainly boat in brackish water. The boat currently has 275 hours on it. I'd like to say I flush religiously after every trip.....but I flush about 90% of the time. The other 10% of the time I'm lazy and don't flush until a couple days or a week later.....I know....not the best approach.



The boat typically ran around 150-160 degrees (as read by the gauge on the dash) until last season when the temp seemed to slowly creep up to about 170 or so if I was cruising at 40pmh or more. Typically I cruise around 28 mph.



When I winterize, I heat the engine up on a hose, drain the water (take out all the blue drain plugs and the block drains), reconnect everything, then run 5 gallons of RV antifreeze through the engine using a 5 gallon bucket connected to ear muffs. EXCEPT for this past winter. This past winter I just pulled the water lines off both sides of the block then took out 3 blue plastic plugs. Didn't realize there were 2 more in the seawater pump....duh....oh well....the pump appears to have survived.



I took the boat out for the first outing of the season last weekend. I noticed the temp rise up to 200 on the gauge. I immediately brought it back to idle, idled back to the dock, and took the boat home.



The thermostat and seawater pump impeller were original, so I replaced them. The impeller is a mercruiser part and the thermostat is a Sierra part. Went for a test ride today and the temperature was still going up to 200 then cooling back down to 170. Knowing that my cooling 'innards' were just replaced, I kept cruising around 27mph (~2500-2700 rpm) for about 10 minutes. The temperature continued to fluctuate between 170-200 at the gauge. This fluctuation is the same whether I'm at idle or cruising.



I have the mercury vessel view module / app on my phone. I connected to it and saw the temperature fluctuated between 150-160 on the dot (160 degree thermostat) as read by whatever sensor vesselview reads from. I touched the top of my catalytic converters and I could keep my palm on them for about 20 seconds then it was slightly uncomfortable. This is hotter then they were last year, but not scalding.
I started feeling hoses at the thermostat housing. 3 hoses were cool. The large hose that goes to the water circulator pump was warm / hot. I also felt the oil filter and it was hot. Couldn't keep my hand on it for more than a few seconds.
Now finally my question: what the heck is going on? The temperature did not fluctuate like that until this year. What is causing the temperature fluctuations? Why is the large cooling hose feeding the circulator (aka water pump) hot at the thermostat housing while the other 3 are cool? I’m not sure if this is expected or. It. Why are my manifolds / catalytic converters hot to the touch when they weren't before?
All these temperature readings seem like they are still acceptable (except for the fact that my gauge in the dash is showing temps up around 200) but these represent a change from previous years.......and I’m not comfortable taking the boat out until I’m convinced the cooling system is operating properly.


One more piece of information: This is a diagram of my thermostat housing:

https://www.hardin-marine.com/s-2656...d-cooling.aspx



The hose connected to "1" in the diagram is the one getting warm/hot. Not sure if that hose is supposed to get hot or not. Any advice to help me understand the cooling flow of my engine would be appreciated. I tried to find a cooling flow diagram that showed me which hoses were cool water vs which ones were hot, but I had no luck for my particular engine / year.



Any help would be appreciated.

Feel free to ask me dumb questions because I'm not above making dumb mistakes

 

[alldodge]

You say there are block drains so you should have the 7 point drain system and not the 3 like the one in the link
https://www.hardin-marine.com/s-2651-standard-cooling-system-bravo-air-3-and-7-point-drain.aspx

Use a IR temp gun and get some readings off the thermostat housing. If temp readings indicate close to what your reading from vessel view then your ok. The gauge at the helm and the vessel view are read by two different sensors on the thermostat housing

Impellers should be replaced at least every 3 years, I do mine every 2

 

[woo102]

Ok....so I think this comes down to a dashbaord gauge reading a little high and me being overly cautious / paranoid.
I took the thermostat housing off again to double check my work and get a better understanding of the flow through the housing.
I also read up as much as I could to understand the flow through all the stinkin hoses in this cooling system.
To add another point of comparison, I bought a mechanical temperature gauge and installed it right next to the temperature sender (going to the dashboard gauge) in the thermostat housing.
I also drilled a 1/8" hole in the thermostat (like I would in a closed car cooling system) as an air bleed. I realize I don't have to do that on a boat....but it made me feel better

I put everything back together and ran the boat on the earmuffs in my driveway. Just like when I was out on the water, the engine temp as read by VesselView slowly oscillated between 150 and160 just like one would expect with a 160 thermostat. The dash gauge went between 175-190. The newly installed manual gauge went between 155-165 or so. That gives me more confidance in the VesselView reading. Seems like my dash gauge is drifting off a bit.

I also monitored my manifolds. While idling at full temp, I could put my hand on them for about 2-4 seconds before I had to pull my hand back off. My water hoses going to the manifolds are nice a cool, so I think I have good flow.....and honestly.....I don't really remember how hot those suckers got last year.
Also, the big coolant hose going from the thermostat housing to the water circulation pump is supposed to be hot since it's flowing water that's regulated by the thermostat.

So.....in summary......I don't think I have a problem with the boat.....except for a slightly exaggerating gauge.
I'm going to take it for a long test ride tomorrow and see how it does.
I temporarily mounted the mechanical temp gauge in the engine compartment as a sanity check for the test ride.

If anyone knows how hot those manifolds with catalytic converters should be to the touch, please let me know.

I also made a powerpoint of the water flow through the cooling system and the thermostat housing.
I'll try to post that as a picture.....maybe it will be useful to someone.

 

[woo102]

 

[woo102]

I made some assumptions about the flow through the water distribution assembly. If anyone knows for sure what's inside that thing, I'd love to know.
Also, if I've stated anything that's incorrect in this picture, please let me know, and I'll update it.

 

[woo102]

 

[alldodge]

Nice pics

If anyone knows how hot those manifolds with catalytic converters should be to the touch, please let me know.

Not exact, but they should never get hot enough to burn skin instantly
Temps in the water will be less then on a hose

 

[alldodge]

View attachment 338537

This pic is a bit off. Cold water should go into the thermostat, then out to the exhaust. The valves at the bottom of the manifolds are used for draining only. Water should not be able to go up and in thru those check valves

 

[woo102]

Ok. Thanks.
I'll update the drawing to show the #3 hoses only support flow out of the manifolds for draining purposes (engine off, cooling drainplugs out). I use the dashed, orange-ish-brown arrows for that.

You'll have to help me understand your comment about the flow through the thermostat.
From what I could see, the thermostat housing essentially has 2 separate sections. The thermostat keeps these two sections separate.
The cold section comes in from the seawater pump, through the poppet valve, and out through the top to the manifolds.
The hot section handles the water coming out of the engine (intake manifold) and routs that water back to the water circulation pump. This forms a hot water circuit and allows the engine to reach operating temp..
When the thermostat opens, the water from the cold side can mixes in with the water from the hot side. Hot water from the engine escapes to the manifolds/exit and cold water comes in to cool the engine.
It seems like the cold and hot water just mixes kind of randomly when the thermostat is open.
Is this correct?

This is what I was trying to convey with the thermostat housing pictures, but my powerpoint skills have their limits

 

[alldodge]

I think of the poppet valve as a pressure differential valve, it keeps the pressure to a set limit in the exhaust manifolds. It helps keep the mans with warm water instead of cold. Most of the cold water not used to keep the motor at temp goes straight out the exhaust via items 29 and 20.

It should be open most the time but depends on rpm. As the rpms increase the valve will also open more

 

[woo102]

Does any cold water from the seawater pump ever go through the water distribution assembly and into the water circulation pump via hoses 11 & 12?
.....or is that path exclusively for drainage?

 

[Lou C]

Ok I’m not familiar with this new fangeled Merc cooling system with the quick drain and all the extra hoses to do the same thing normal drain plugs and only 5 or so hoses and no plastic stuff to crack would do, but:
Remember any raw water cooled system is not pressurized and depends on a good flow of cool water in and warm/hot water out to keep temps normal. So I’d first pick up an IR temp gun and use it to take readings at the base of the intake manifold right under the thermostat housing this will tell you temps very close to the stat itself and also measure temps of the elbow portion of the cat converter exhaust. I would probably pull out the stat and test it with a pot of hot water and a radiator temp thermometer. Make sure it opens at the rated temp all the way and closes when the water cools off. If not replace with an O.E. unit. Lastly in brackish water your cooling passages in the manifolds/elbows could be clogging if they are made of cast iron like conventional exhaust. Normally in salt water you have to replace the elbows every 5-7 years. Might be worth a look. Hot water has to freely exit the engine and the first gate valve is the thermostat the last ones are the actual cooling ports in the manifolds/elbows. On my old OMC one piece units by 5 seasons one of the ports would be clogged with rust, you can see this in the pic. I replaced these with the OMC/Volvo style 2 piece exhaust about 4 years ago and the cooling ports are much larger but still I will check them the same way. Probably replace the elbows after 7 years in salt. In the pic of the new manifolds you can see how much larger the cooling ports on these are. The engine does run cooler with the new style exhaust.

 

[alldodge]

Does any cold water from the seawater pump ever go through the water distribution assembly and into the water circulation pump via hoses 11 & 12?
.....or is that path exclusively for drainage?

IF its working correctly, there should be no water go up thru the check valve, its only used for draining. That said, if its not working correctly then it could.

 

[Searay205]

Wow excellent effort!!! I have a 5.0 mph with the catalyst crap. No I cannot hold the top of my hand on the exhaust elbow/riser but can lay it there for 10-20 seconds. Don't forget their is a catalyst element in their at about 1000F. Ok I lied, I removed the catalyst element so yes I can but I assume your catalyst are still installed.

PartVu has the best price on manifolds with free shipping. I am not saying you need them just FYI. I bench 200lbs 5 times and I struggeled to move the giant box ONE manifold came in, lol. They are heavy and packaged to be drug behind the delivery truck. LOL.

 

[Lou C]

So I guess they are cast iron not aluminum alloy then lol!
Normal pre cat exhaust is about 50 lbs per side

 

[Lou C]

Get an IR temp gun no need to burn fingers etc. My OMC/Volvo center riser exhaust runs at a cool 100* at idle and a max of 135* after coming off plane, I'm not sure what's normal for that Merc system.

 

[Searay205]

get a Rinda. You have temp sensors in your exhaust risers. You can see ECT, EMT etc. Mine usually ran about 159F, which is close enough to engine coolant at 160F BUT you always have ambient seawater hitting the manifolds in addition to the engine water. As far as weight exhaust manifold 69lbs not including riser. Riser probably 10-15 lbs. I have no idea how the manifold bolts don't shear under the weight they carry, but they don't.

You also have some pipe plugs on the top of your manifolds used for closed cooling. Pull one out does it look plugged?

 

[woo102]

I took the boat out this weekend. I compared the temperature sensor reading (via Vessel View), temperature sender reading (via the dashboard gauge), and the reading from the mechanical temp gauge I just installed. Vessel View and the mechanical gauge were within 5 degrees of each other just as they were on the hose. Max temp for these gauges was 163 (vessel view) and 168 (mechanical gauge). Cruised around for an hour or so then did some higher speed runs.....temp was solid....everything looking good. All in all, I put 4 hours on the engine, no issues. I was able to keep my hand on the manifold / cat housing for about 4 seconds at all time.
The dashboard gauge reached a max of about 200. I think my dash gauge is going goofy on me.
I have a DVOM with an IR sensor. I forgot it on this trip. I'll bring it next time and report my manifold temps on idle and after cruising around.

I think everything is working fine except for my dashboard gauge.
Thanks to everyone for the advice / info.

 

[Ploring]

I've been reading threads like this vigorously trying to figure out if I need to replace my exhaust (and my CATS) -- I have a 2013 Monterey SY 340 with Merc 377 Mags. It's raw water cooled in salt water with CATS and the Dry Joint original exhaust. I've been getting guardian faults off an on on both engines since buying in 2020 but it's getting more consistent. Starboard engine had the latest with it triggering guardian mode. I was at a loss until I bought a Rinda and finally plugged it in. It's now clear to me that the Port side Exhaust Manifold Coolant Temp (EMCT) Sensor seems to be the issue. Fault history showed 220 degrees which is I'm sure too high. Like most people who have researched the Merc Dry Joint exhausts, I'm hearing very little in the way of a maintenance schedule for replacement. One person on this forum @Searay205 advised that he removed manifold and they were spotless inside. I think it's crazy that my exhaust could be 9 years old and still good. However, my mechanic (who is all but retired but coaches me for free on the phone) says he has never seen them fail on the inside before failing on the outside. He suggested that I swap the sensors to see if they give the same readings from the opposite side. I did that on my Starboard engine and the Port side EMCT is still running 50 degrees higher at low rpms on the dock. Also when I swapped it, the port side was dry (unexpected), but the starboard side drained some water (expected). To me this means that the flow of water is getting plugged up in the Port side 4" elbow. I'm pretty much ready to bite the bullet on the expense, but finding people who work on Sterndrives seems to be VERY difficult right now. Now my question -- Is there a way to inspect the inside of the manifold without removing it? I think there may be some plugs build into it. I'm handy, but I'm not a mechanic so trying not to do any harm.

 

[Ploring]

I've been reading threads like this vigorously trying to figure out if I need to replace my exhaust (and my CATS) -- I have a 2013 Monterey SY 340 with Merc 377 Mags. It's raw water cooled in salt water with CATS and the Dry Joint original exhaust. I've been getting guardian faults off an on on both engines since buying in 2020 but it's getting more consistent. Starboard engine had the latest with it triggering guardian mode. I was at a loss until I bought a Rinda and finally plugged it in. It's now clear to me that the Port side Exhaust Manifold Coolant Temp (EMCT) Sensor seems to be the issue. Fault history showed 220 degrees which is I'm sure too high. Like most people who have researched the Merc Dry Joint exhausts, I'm hearing very little in the way of a maintenance schedule for replacement. One person on this forum @Searay205 advised that he removed manifold and they were spotless inside. I think it's crazy that my exhaust could be 9 years old and still good. However, my mechanic (who is all but retired but coaches me for free on the phone) says he has never seen them fail on the inside before failing on the outside. He suggested that I swap the sensors to see if they give the same readings from the opposite side. I did that on my Starboard engine and the Port side EMCT is still running 50 degrees higher at low rpms on the dock. Also when I swapped it, the port side was dry (unexpected), but the starboard side drained some water (expected). To me this means that the flow of water is getting plugged up in the Port side 4" elbow. I'm pretty much ready to bite the bullet on the expense, but finding people who work on Sterndrives seems to be VERY difficult right now. Now my question -- Is there a way to inspect the inside of the manifold without removing it? I think there may be some plugs build into it. I'm handy, but I'm not a mechanic so trying not to do any harm.

PS - Feels like I already wrote a book but in addition to the above.. One of my catalysts is kicking a failure error on the Port engine Port Side (the same side that's getting hot). So it's pretty clear it needs to be replaced. I'm very interested to understand how people are dealing with this as well. Seems like I may be able to buy something that eliminates the rear O2 sensors.