Best way to quiet my Lehman 120 Exhaust

Hi All:

So I have a pair of 120 Ford Lehmans which currently have a very "droning" exhaust note at most any RPM.

From my engines there is about 6ft of 3.5" wet exhaust hose going to Stainless lift type mufflers which then slope very gradually downhill via more 3.5" hose to straight outlets at the stern.

I bought a Vetus DMP90 muffler and installed it inline on my stbd engine (to see what if any difference it made) and (despite Vetus assurances) it made absolutely no difference at all. The "muffler" would need significantly more water flow (at least 2-3 times IMHO) to make any real difference.

I have ordered and am planning on trying a Vetus LT90 water lift right at the stern on the port engine in a few days in hopes that the mixing right at the transom may make a difference.

Wondering what (if anything) others have done to quiet the exhaust note.

There used to be a company, who's name escapes me at the moment, that made transom mounted exhaust outlet diverters out of heavy rubber that directed your exhaust down into the water. If they are still around you could try those.

Or make one yourself out of hose and a fiberglass 90 deg. fitting.

Are you sure the noise is coming from the exhaust? Non turbo diesels have a lot of noise coming from the air intake and that is fixable.

That sound is pretty common to Lehman's. If it changes to a hollow sound it means you've lost or are loosing raw water flow.

I'm having trouble visualising( what's the audio description of visualising) a droning exhaust note over the shaking and rattling the old girl makes when I start her up.

Rduval said:

...I have a pair of 120 Ford Lehmans which currently have a very "droning" exhaust note at most any RPM...
Wondering what (if anything) others have done to quiet the exhaust note.

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Only thing I can think of is shutting them down. They`re Lehmans.

Our two FL120s make a fair amount of mechanical noise inside the boat. But there is no exhaust noise at all unless one stands on the aft deck right at the transom. We have a custom exhaust system (see photo) with fiberglass lift mufflers feeding the stock exhaust hoses. The mufflers, which have drain fittings at the bottom, and the fiberglass top elbows, were made specifically for our engines and boat by an exhaust shop in Bellingham. The diesel shop we use made the platforms the mufflers sit on and installed the systems using water-cooled manifold elbows from American Diesel. The exhausts themselves are pretty quiet at the transom.

A nice feature of this system is everything but the upper elbows are below the rear of the manifold. So no water can make its way back through the system and into the manifold. This was not the case when we bought the boat. The systems on the boat when we acquired it had the mufflers suspended from the engine room overhead.

Marin said:

The systems on the boat when we acquired it had the mufflers suspended from the engine room overhead.

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Yikes! That is not good.

A couple of years ago I had the unfortunate experience of the muffler box being raised higher than the manifold, when our boat was slipped. That cost about $24,500 and six months off the water. Thank god for insurance.

By the way Marin good to see you around again.

We have a 3.5" exhaust on our stbd engine and a 3" exhaust on our port engine, both 2715e Lees Marine (same engine as Lehman, different marinization). The Lehman manual calls for a 3" exhaust. The 3" exhaust on our port engine has a mellow, fairly quiet sound. The 3.5" exhaust has a throaty sound, much louder than the 3" exhaust. Perhaps your problem is the oversize exhaust and not the muffler.

Capt.Bill11 said:

That sound is pretty common to Lehman's. If it changes to a hollow sound it means you've lost or are loosing raw water flow.

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Funny you should say that Capt Bill, I'm also seeing a lot of steam in the exhaust which I'm told shouldn't be there if there is enough cooling water flow.

Impellers are new 3 months ago, raw water strainers are clear... How do I know if I'm getting enough.

Ski in NC said:

Are you sure the noise is coming from the exhaust? Non turbo diesels have a lot of noise coming from the air intake and that is fixable.

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That's something I've thought about as well but in this case it's definitely exhaust that's the problem but I'm open to suggestions on quieting the intakes as well.

What's the solution to that? I've just got the standard coffee can type screens with foam around them at the moment.

Tomas said:

We have a 3.5" exhaust on our stbd engine and a 3" exhaust on our port engine, both 2715e Lees Marine (same engine as Lehman, different marinization). The Lehman manual calls for a 3" exhaust. The 3" exhaust on our port engine has a mellow, fairly quiet sound. The 3.5" exhaust has a throaty sound, much louder than the 3" exhaust. Perhaps your problem is the oversize exhaust and not the muffler.

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That's something I've considered as well. It sure doesn't seem like it would need a 3.5"ID exhaust system but that's what the Lehman mixing elbow is so it's been continued all the way through.

I noticed Marin's photo of his custom exhaust that the outlet looks about half the size of the inlet. Is that that case Marin?

Could it be bad or dried out hardened engine mounts?I know that bad engine mounts can cause a drone thru the hull, that can sound like exhaust noise.

ben2go said:

Could it be bad or dried out hardened engine mounts?I know that bad engine mounts can cause a drone thru the hull, that can sound like exhaust noise.

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Nope, brand new mounts that made the boat MUCH quieter overall. This is definitely the exhaust note.

A 400 cu in old diesel engine is bound to be noisy. I'll bet if you had the engine suspended by magic and not touching the boat the "droning" noise would be gone. You're probably not getting the "rumrumrumrum" noise directly from the engine.

The engine shakes the boat and lots of parts of the boat shake at various frequencies and those parts in turn shake other parts at frequencies not the same as the original exciter frequency. A bulkhead may be resonant to 1100 rpm and your reduction gear provides that frequency through the propeller shaft and prop.

Whenever you have two frequencies vibrating at close to the same frequency another vibration and frequency emerge called the "beat frequency" in electronics. It's frequently a low frequency like the drumming of a twin engined boat or airplane w the engines not synced. It's usually called a "harmonic" frequency.

Look for something like a bulkhead or other flat panel that "drum". Feel all around for things other than the engine that are vibrating. It will probably feel like the vibration is coming and going. A fix is to attach something solid to that thing vibrating and not in the center is best.

Another thing to consider is the exhaust hose shaking things. Exhaust hose is frequently very stiff and will pass shaking to another boat part ... like a plywood platform that a lift muffler is attached to.

Rduval said:

That's something I've considered as well. It sure doesn't seem like it would need a 3.5"ID exhaust system but that's what the Lehman mixing elbow is so it's been continued all the way through.

I noticed Marin's photo of his custom exhaust that the outlet looks about half the size of the inlet. Is that that case Marin?

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It does look that way. But it shouldn't be. Might just be the way the picture makes it look. That is pretty much the standard exhaust set up on a GB.

Rduval said:

Funny you should say that Capt Bill, I'm also seeing a lot of steam in the exhaust which I'm told shouldn't be there if there is enough cooling water flow.

Impellers are new 3 months ago, raw water strainers are clear... How do I know if I'm getting enough.

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When was the last time you boiled out your coolers? And how old is you mixing elbow? Is it SS or stock steel?

Many good suggestions, especially quieting the intakes. I'll add consider sound insulation under the deck. Feeling for vibrating items is a good idea. There is an app for iPhone called Db meter you can point your phone at something to see if sound is coming from there.

Steam usually means insufficient water flow. Water quiets exhaust.

Is the Sind more apparent outside at the stern.

Call me crazy but I guessing this guy knows the difference from a sound made by vibration and the sound his exhaust is making at the transom.

Capt.Bill11 said:

Call me crazy but I guessing this guy knows the difference from a sound made by vibration and the sound his exhaust is making at the transom.

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Thank you Bill, yes I do; but I still appreciate all the input though... "no stone unturned"...

If I lean over the transom the "droning" gets louder so I know it is exhaust. If it was coming from inside the boat it would get quieter with the transom between my head and the cabin. I guess it's possible that some noise may be generated through the hoses to the transom thru-hulls but I doubt it. There's 8 feet of hose from the lifts to the transom.

I did have an issue before I changed the motor mounts that was the cabin sole vibrating as described (like a drum) but that's taken care of and this droning is only noticeable the farther (further?) aft you go and esp on the flybridge.

I just found a company online that makes inline mufflers called GGB Exhaust that are only a couple of hours away from me. He said they've sold their inlines to a few diesel customers with the same complaint. He said that they will NOT change the DB level much but they should all but eliminate the droning, at least that has been their experience in the past. They should arrive tomorrow or Wednesday. For $226cdn delivered for a pair (I got a bit of a discount), they're worth a try.

Now, on the water flow... Boiled out the coolers???? Please explain.... Never knew I had to do that or how. Also, bear in mind (if it makes a difference) this boat has been in fresh water it's whole life....

I meant no insult but determining sound source is often not easy.

Boiling is what radiator shops did to clean them. IIRC it was actually an acid bath that bubbled away.

IN any event to find the source of a water restriction a systematic inspection of every part from seacock to mixer is better than random attack, IMO.

bayview said:

I meant no insult but determining sound source is often not easy.

Boiling is what radiator shops did to clean them. IIRC it was actually an acid bath that bubbled away.

IN any event to find the source of a water restriction a systematic inspection of every part from seacock to mixer is better than random attack, IMO.

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No Insult taken...

Not sure how often the coolers need to be boiled? and which ones? Oil? Transmission? Even in fresh water or is it a salt water thing?

Ah, I did not catch you were a fresh water boater. My bad. In that case since your strainers are clean and your impellers new I'd check and make sure there are no old blades or junk trapped in the first cooler down stream of the pump. Then use a IR temp gun to see if you can find any hot spots along the flow of the raw coolant water.

Rduval said:

T

I noticed Marin's photo of his custom exhaust that the outlet looks about half the size of the inlet. Is that that case Marin?

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The photo was taken with a wide-angle lens, so I'm sure that accounts for some of it. The water-cooled elbow on the manifold is a stock item from American Diesel. The exhaust hose that the fiberglass lift muffler feeds is the stock exhaust hose for this boat and these engines. The hose run from the cooled elbow to the muffler is larger in diameter than the exit pipe out the top of the muffler, but I don't know the comparative diameters of the various components. As Capt. Bill says, this is a pretty common setup for twin-engine GBs with these engines, at least around here.

There is steam and there is steam. Our engines steam some during the winter simply because of the ambient temperature and humidity conditions. They don't steam enough to be noticeable during the warmer months.

However, when they do steam, one exhaust steams more than the other. I asked our diesel shop about this (the one that installed the new exhaust systems) and they said that there are several factors affecting the presence and amount of steam out an exhaust. The difference in the length of the exhaust run between the port and starboard engines can do it, for example.

I have seen boats cruising in the fall and spring here with the entire back end of the boat enveloped in steam. On the one or two times I had an opportunity to ask the operators about it, they said that's just the way it's always been.

If your coolant and transmission temps are correct, if there's no coolant getting into the oil, if all indications are that the engine or engines are running just fine, the chances are that if there's steam, that's just the way it is.

Now if they didn't steam before and now they do and you haven't changed anything like the exhaust system or whatever, then there would be cause for concern.

We make it a practice to watch the exhaust ports when the engines are started, and once or twice during a run I'll wander back and watch the exhausts for a bit. If everything looks like it always does at startup and underway, then no worries.

IMO coolers are least likely cause ,plugged shower head holes, bad impeller, junk or impeller parts blocking something would be my bet before doing anything like "boiling"

Louder or changed sound of exhaust is a sure sign of water flow reduction .

The post above makes a good pint. If it has been this way since new I would be less concerned.

I have boated in snow storms, fl summer , pacific cold water and never see anything except for a few wisps of steam .

Plugged shower head????

Rduval said:

Plugged shower head????

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Ditto. What is this "shower head" that you speak of?


1983 Present 42 Sundeck
Twin Lehman 135's

I had a dock neighbor (fresh water) that would go to Sam’s and buy a case or two of cheap white vinegar. He would fill a 5 gallon bucket with it, close the through hull, take the hose off going to the strainer and put the end into the bucket of vinegar, start the engine and run it till all 5 gallons were run into the engine. The vinegar was left in the system for 24 hours. He felt that it would clean out the raw water system. He never had a overheating problem, but this might be because he was a meticulous about his maintenance,etc…

Vinegar.... Not a bad thought if it was done regularly. Not sure if it would be strong enough to get old crap out though....