'95 SN Muffler

[Paublo]

As the part owner (I help with $ and labor) with my daughter and her husband on this boat, I need a little help. It has the GT-40. The engine over heated and will soon be running again with one new head and a valve job on the other one. The dealer says to replace the muffler (for $800), as they go bad when this old and that is what caused it to overheat. Is there any way to check it out? Is there anything inside the muffler beside some baffles? That is only an assumption on my part. Without a better suggestion, I'm about to cut a 2" hole into the side or top and look inside. If everything is ok, then just fiberglass the piece back into place. Any other ideas?
Thanks

[M3Fan]

RE:

There's not much to the invertaflo muffler except baffles. What scares me is that the mechanic thinks the muffler is what caused over heating. Are you sure he didn't say exhaust manifolds?

[Paublo]

No, Sail & Ski in San Antonio looked at the boat and wanted to replace the engine with a new long block and said the muffler had to be replaced too. They said it was getting more common for the muffler to "go" at this age, causing a restriction in the exhaust and then for the engine to overheat.

Based on everyone comments, the basic block and lower end is suppose to be bullet proof on these motors. So, we decided to rebuild the heads (used someone else), but one head was too damaged and is being replaced. I just didn't want to spend the money on a new muffler is if didn't have to be replaced. I assumed that flow thru the muffler is into each end, up and down past a couple of baffles, and out the single outlet. Could a baffle break lose and then block the passage? It seems unlikely to me, but I've been wrong before.

[boatech]

I doubt the muffler is the cause of your overheating problem. the mufflers do go bad offten. i replace them all the time but its always for leaks/cracks/pin holes. and yes they are crazy expensive two questions for you how old is the waterpump/impeller and do you run a sea strainer? oh one more how many hrs. on your boat?

[Paublo]

When it started to run rough and the problem was discovered, the impeller was only 9 months old. The engine has 700+ hours. It is a standard set-up, and I'm not aware of a sea strainer. Does it have one? I assume that your're not refering to the water pick-up or inlet. Sorry to sound stupid about that. And I know what you mean about the pin hole leaks in the muffler. I was going to fill/cover serveral of them with epoxy or resin to buy a few more years.
Thanks for the interest and suggestions.

[Paublo]

Any other ideas? Has anyone seen one of these mufflers opened up? Is it possible for it to fail and cause a significant restriction?

[east tx skier]

To answer a previous question, a sea strainer is an inline metal filter in a removeable plastic housing that keeps debris from the lake out of the raw water cooling system. Isn't this standard on Nautiques after a certain year? If you don't have one, it's a great $40 upgrade from skidim and something you can install in 15 minutes or less.

I'm still running the original mufflers on my 14 year old boat. The only overheats I've seen on other boats were always caused by either (1) an old impeller coming apart (which is no fun as it tends to get stuck downstream in the cooling system and not pump water efficiently at the same time) or (2) lake debris inhibiting water flow usually by either blocking the intake grate hullside or clogging up the screen on the transmission cooler.

Just for grins, pull the hoses on your transmission cooler and look up there with a flashlight. If the impeller's good, then lake debris might tend to be the most likely impliment of blockage. But even without a sea strainer, the stuff that would seem most likely to clog ought to get caught in the transmission cooler or get chewed up by the impeller.

Good luck. Hope it's not the muffler. Didn't realize they were so expensive.

[M3Fan]

Clogging or otherwise preventing water from going OUT of the engine will also cause an overheat condition- so, if water was somehow prevented from leaving the exhaust manifolds or muffler, that would also be an issue, albeit a rare one. If the muffler somehow came apart internally, blocking water flow out of the engine, I'd imagine it would block the exhaust gases too, causing the engine to stop running or something to give. I recall seeing an old "Ship Shape TV" episode where an overheat condition was caused simply by clogged exhaust manifold water jackets.

[slob02]

If water can't get out then neither can exhause gases. This would cause the engine to stall. I also don't see how it caused it to overheat. When the baffle broke on my '97 GT-40, and the exhaust or water couldn't get out, it blew a crack in the front of the muffler so it could get out.

[TRBenj]

To answer a previous question, a sea strainer is an inline metal filter in a removeable plastic housing that keeps debris from the lake out of the raw water cooling system. Isn't this standard on Nautiques after a certain year? If you don't have one, it's a great $40 upgrade from skidim and something you can install in 15 minutes or less.

This may not help with your overheating problem, but your boat should have a raw water strainer. CC started putting them in their boats sometime in the 80's:

[M3Fan]

If water can't get out then neither can exhause gases. This would cause the engine to stall.

... as I mentioned in my post.

[slob02]

Exactally!

[Ultimanta]

I have a 99 Air with a invertaflow muffler. The muffler was removed for patching before last years boating season. Success! I got an additional season out of the muffler before it started to leak in September. I am planning on repatching again this year.
Physically there is nothing 'inside' of this muffler which could cause it to restrict flow. There are two internal baffles: one on inlet side and other on outlet. If the exhaust got so hot that it melted the inlet baffle and forced the melted baffle 'into' the muffler, then I suppose it could choke it off. Take the muffler out for inspection, you will see what I mean. Have you cleaned the water flow passages in the exhaust risers. (Four bolts each side: easy off, easy on, use new gaskets) Depending on how much corrosion/scale there is in the engine cooling system, you may have built up debris and partially blocked the water flow from that side of the engine.

[Paublo]

Great comments and suggestions. For a quick check I connected my leaf blower to the muffler outlet and it seemed to blow thru without a significant restriction. So I've been working on building up and fixing the inlet connections which had some heat damage. I'll check the entire cooling system for restrictions etc. and do the check on the exhaust risers.

That reminded me of another problem I saw once on an I/O engine on a houseboat at Lake Powell. The engine overheated and was replaced with a new long block. The impeller in the outdrive was changed and everything tested ok in the service yard. Put the boat in the water and idleing around the marina all is ok. As soon as the engine speed is raised a little it quickly overheats. Everything is rechecked multiple times. Finally the exhaust manifold is pulled and the passages were restricted by a baked on sand like material. The outdrive picked up sand and silt and it baked onto the hot manifold. It was not enough to run at idle, but too much to run at higher speed.