Exhaust component inspection due to slight overheating

[Skidude17]

My Mercruiser 5.7L MCM SN 0F598365 got a little hot this summer most of the times I ran it. It never overheated, but it was definitely in the hot range. I have a closed cooling system, and I replaced the impeller and housing at the beginning of the season. I just took off the exhaust risers, and they seem to be in good condition, and since I did that, I went ahead and took a look at the flappers. The flappers look like they need to be replaced, but I don't think that would cause the slight heating. I've already drained and refilled my coolant at the end of the 2021 season. I should probably check my thermostat. What else should I check / do to figure out why my engine is running about 40 degrees hotter than it should be?
How bad are these flappers? I will be replacing them, but I'm trying to figure out if these are the worst ever, or if I'm changing them about the correct interval.
Do my exhaust risers look okay? The gaskets didn't appear to have any holes or excessive wear. I'm about to start rambling. The riser gaskets appeared to have some kind of orange gasket sealer on them. Is it common to use a gasket sealer here? If so, what type? A little bit of coolant leaked over into the exhaust manifolds. I don't think this would be a big issue, but after reading all of the posts, it makes me worry about getting any water-based fluids back into the engine. How important is it to replace the all of the pipe clamps? I don't store my boat in the water.

 

[alldodge]

If motor is actually running hotter I would look for air bubbles coming from the raw water pump to the thermostat housing. Use a shot piece of clear hose to see what's happening.

Don't see the flappers causing the issue, and many have used high temp gasket sealer. Most times its not needed but also doesn't hurt

 

[dubs283]

Flappers are toast

Good on the impeller replace

WAG is there is a blockage before/after the raw water pump

Is this a salt water boat?

 

[Skidude17]

Flappers are toast

Good on the impeller replace

WAG is there is a blockage before/after the raw water pump

Is this a salt water boat?

This is a saltwater boat. I'm not sure what you mean by WAG.

 

[Scott06]

WAG is wild azz guess

what about ps cooler on back of engine did u check it for debris or blockage

did you open heat exchanger and rod out passages

 

[Lou C]

WAG=Wild a-s-s guess
Flappers don’t cause overheats they get damaged due to running too hot (not enough water exiting to keep them cool). Do the clear hose test also if the elbows are more that 5 seasons used I’d change them. Is the boat kept in salt water? If so your water intakes might be clogged with marine growth, that has to be cleaned out. If the closed system has been in use a long time the heat exchanger may need to be cleaned out as well. Have you removed & tested the thermostat?

 

[Lou C]

Looking closer at pix flappers look overheated & warped but Elbows look good however I’d hook ‘em up to a water hose to see how they flow make sure they aren’t clogged. Lastly check for bubbles in the AF use clear hose to see if exhaust gas is getting into the coolant (leaky head gaskets). If you find that change the oil right away could have glycol getting into the motor oil as a result of leaky head gaskets.

 

[Skidude17]

WAG is wild azz guess

what about ps cooler on back of engine did u check it for debris or blockage

did you open heat exchanger and rod out passages

I don't think it's the power steering cooler. I'm pretty good about cleaning it out every year. I don't think there's much I can open on the heat exchanger. I've never cleaned out the seawater pump since I've owned the boat (2019), and I'm not sure if the previous owner did. I think that's my next step. I went out in the boat today, and according to the dash gauge it's running about 172 degrees (12 degrees above what it should be). I'm sure the seawater pump needs cleaning, and if it's not super dirty, then I'll test the thermostat.

 

[nola mike]

I don't think it's the power steering cooler. I'm pretty good about cleaning it out every year. I don't think there's much I can open on the heat exchanger. I've never cleaned out the seawater pump since I've owned the boat (2019), and I'm not sure if the previous owner did. I think that's my next step. I went out in the boat today, and according to the dash gauge it's running about 172 degrees (12 degrees above what it should be). I'm sure the seawater pump needs cleaning, and if it's not super dirty, then I'll test the thermostat.

Verify your temp with an IR thermometer.

 

[Skidude17]

Verify your temp with an IR thermometer.

Are the $20/$30 thermometers on amazon any good, or should I opt for a better one? I don't have a lot of use for one outside of this. Where should I measure the temperature?

 

[nola mike]

Are the $20/$30 thermometers on amazon any good, or should I opt for a better one? I don't have a lot of use for one outside of this.

yeah, they're fine.

 

[Scott06]

I don't think it's the power steering cooler.

would take the hose off and see

I don't think there's much I can open on the heat exchanger.

you should be able to take ends off and see if tubes are clogged

I went out in the boat today, and according to the dash gauge it's running about 172 degrees (12 degrees above what it should be).

172 isnt hot. My boat with 160 stat runs about 170 normally. Would rule out gauge inaccuracies as Nola suggested.

 

[Lou C]

If you have a 160 stat, anytime there is a load on the engine it should run slightly hotter than 160. The hottest I ever get on mine (raw water cooled in salt) is approx 175 and that's after coming off plane, it will cool down to about 165 after idling for a few min.

Judging by the flappers you might not be getting enough raw water flow through you heat exchanger.
As far as measuring temps...I will check the intake manifold right under the stat housing, I find that is about 10* cooler than the dash gauge, then I will measure the tops of the elbows, and also the 90* down pipes between the elbow and the Y pipe.
I get usually 145-150 on the intake, 100* tops of the elbows, about the same on the down pipes. Right after coming off plane the tops of the elbows will be about 135*, same with the down pipes. You could measure the big hose at the top of the stat housing to see how hot the coolant is exiting the engine and also the one at the bottom of the front circulating pump to see how hot the coolant is exiting the heat exchanger. Finally you can measure the hoses feeding the manifolds (if a half system) or the elbows (if full) where they connect to the heat exchanger, this will give you an idea how hot your exiting raw water is. If your manifolds are on the closed system (full system) they will probably be about the same temp as the engine, maybe a little hotter because they get flow from the coolant exiting the engine after the stat opens, then that coolant returns to the heat exchanger. Some pics of how the system is plumbed would be helpful. Looking at your pix again, it looks like you have a full sytem, because I see the elbow has a feed hose leading to it and the manifold has a top exit for a hose, that usually means a full system where coolant enters the bottom of the manifold from the stat housing, then flows through the manifold, and exits the top to return to the heat exchanger.

 

[tpenfield]

It's a little hard to tell from the pictures, but it looks like you have a FULL closed cooling system. (as opposed to a HALF system) Flappers won't matter on overheating. They usually last a couple of years before they are toast.

My 'SWAG' is . . . I would be checking the raw water side. Salt water can mean marine growth inside the outdrive water intake duct and piping, or stuff gets stuck at one of the oil coolers. BTDT . . . Not sure if you've kept the boat in the water previously. . .

As for the exhaust manifolds, hoses, etc. Make sure your exhaust manifold gaskets are in good shape - install new ones and inspect the mating surface of Manifold-to-Riser/elbow. You should have the full block-off gaskets with full closed cooling. Make sure hose clamps are tight.

Post more pictures of the engine, outdrive, etc. if you can.

 

[tank1949]

My Mercruiser 5.7L MCM SN 0F598365 got a little hot this summer most of the times I ran it. It never overheated, but it was definitely in the hot range. I have a closed cooling system, and I replaced the impeller and housing at the beginning of the season. I just took off the exhaust risers, and they seem to be in good condition, and since I did that, I went ahead and took a look at the flappers. The flappers look like they need to be replaced, but I don't think that would cause the slight heating. I've already drained and refilled my coolant at the end of the 2021 season. I should probably check my thermostat. What else should I check / do to figure out why my engine is running about 40 degrees hotter than it should be?
How bad are these flappers? I will be replacing them, but I'm trying to figure out if these are the worst ever, or if I'm changing them about the correct interval.
Do my exhaust risers look okay? The gaskets didn't appear to have any holes or excessive wear. I'm about to start rambling. The riser gaskets appeared to have some kind of orange gasket sealer on them. Is it common to use a gasket sealer here? If so, what type? A little bit of coolant leaked over into the exhaust manifolds. I don't think this would be a big issue, but after reading all of the posts, it makes me worry about getting any water-based fluids back into the engine. How important is it to replace the all of the pipe clamps? I don't store my boat in the water.

how old is boat and or risers. They are good for 4-7 years in salt water. I'd pull and examine water passage as best as I can. If they are old, replace. Sierra told me NO GASKET sealer. If an Alpha, how old is water pick up impeller?