exhaust temperature higher on port side

[Specjay]

Hello,
I own a 2008 SN with an Excalibur 330 engine (GM 5.7L small block).

This summer, we were hearing a clicking noise, it was coming out of the port side exhaust. So I had to replace the exhaust manifold gaskets and the riser gaskets.

Since then, I've noticed that the port side riser is much hotter than the starboard one. I replaced the water pump impeller and also the thermostat. The problem is still there. I removed the two 3-1/2" flexible hoses at the riser outlets to push water from the two hoses coming from both side the thermostat, and the manifolds don't seem to be blocked. Then, I plugged one side of the two 3-1/2" hoses going to the muffler and pushed compressed air into the one on the other side. I noticed that there's a kind of stainless steel flap at the muffler outlet that doesn't seem to open. I then reconnected everything use a garden hose directly before the strainer and tested it with water. I noticed that water eventually came out of the muffler, but only around this stainless steel plate. How does this valve work? It seems like water is collecting in the muffler and is suddenly expelled out, is this normal? I have attached a picture of the muffler outlet where we can see the flap or exhaust valve..

Also, I tried to clamp the hose at the outlet of the thermostat housing, which goes to the starboard side, and the temperature of the port-side riser immediately dropped. There must be a restriction somewhere; could it be my muffler?

If I am not clear, let me know because english is not my primary language.

Thanks
Jeremy

[JayG80]

I'm not much help to you, but one question. Did you position the riser gaskets with the blocked water passage port end facing the exhaust outlet?

[Specjay]

Yes, I remember to put it the right way.

[SilentSeven]

Trying to help, let me see if I follow.

- The primary problem you are working is that your left (port) side manifold is running hotter than the right (starboard) side manifold.
- You have done some recent work including 1 / replacing riser gaskets 2 / thermostat and 3 / raw water pump impeller.
- You have some questions about how the muffler might effect your manifold temperatures including a possible valve in the muffler.

Does this sound correct?

Here's a few thoughts and suggestions.

Regarding the manifolds not being an equal temperature, I have observed the same thing on both my GT-40 (prior boat) and my current Excalibur 330 but have never measured the side to side variance. Not sure you have a problem here unless the left manifold is exceptionally hot. By this I mean you are seeing paint smoking or are having heat problems with the exhaust hose. Some data would help - any chance you can use a laser thermometer to measure the surface temps of each manifold and report back?

It's possible you might have some water obstruction issues with the left manifold feed. Is the boat run in salt water? Salt water accelerates scale in the manifold. Also, if the raw water pump impeller disintegrated at some point, you may have rubber pump bits stuck in the feed line. You typically will see pump bits around the thermostat but it's not impossible you have some bits blocking the manifold feed line. Consider pulling the feed line and inspecting the line and manifold port for blockage.

It's possible you may have low water output from the raw water pump. The most common reason for low output are air leaks on the intake line of the raw water side. Tighten all your hose clamps and make sure your strainer o-ring is in good condition and is snug.

This boat has the two inlet / one outlet muffler, correct? I have never heard of any valve or stainless flap in the muffler. To the best of my knowledge they are all fiberglass construction and have no valve. There have been occasional reports of a baffle coming loose inside the muffler and partially obstructing the exhaust path but that seems to be quite rare. The behavior you describe of the exhaust system taking some time to push water out or coming out in spurts is pretty consistent with what I've seen in the past - especially if the boat exhaust water is drained by towing up a hill or something like that.

Bottom line - unless your left manifold is running excessively hot, what you're observing sounds like expected behavior.

[Specjay]

Hi Steven,

You're spot on with my question. You're also right about the parts I replaced, except that I also replaced the water pump impeller, and the old one was in good condition.

I have an infrared thermometer, so I'll measure the difference this weekend. The boat is a 2008 and I've had it since 2020. I've never paid attention to the risers temp except since the engine started ticking (broken manifold gasket also replaced).

I'm going to buy some clear hose to get an idea of the flow rate going to the manifolds. I think the way the water enters the thermostat housing contributes to the manifold (port) being hotter, but that's just a theory.

The boat is not running in salt water so there is no exchanger. There's a single raw water inlet and two air/water outlets that join in the muffler. I also think what I'm seeing in the muffler is actually a baffle.

thank you for your response
Jeremy

[SilentSeven]

I think the way the water enters the thermostat housing contributes to the manifold (port) being hotter, but that's just a theory.

This is the common working theory - the manifolds don't get the same volume of water. Will be curious what your measurements show.

As a note - even with a closed cooling system/ heat exchanger, the water used to cool the exhaust system exhaust is raw water.

Do check your inlet feed line clamps and strainer oring - any air leak means you are not drawing the maximum water.

[Specjay]

Good evening guys,

I feel bad but I have to admit my mistake, I must have been working too quickly and installed the port riser gasket on the wrong side. This is not the kind of mistake I used to make, a sign that I'm not getting any younger.

Thank you very much for taking the time to respond. Sorry for your wasted time.

Jeremy

[Rednucleus]

But it helps everyone here not do it to ourselves!!

[SilentSeven]

Glad you found it. We've all been there.