Wet Exhaust issue

[LadySea]

I am a new owner of a 1986 Fu Hua(sp?) 34' Trawler with a Ford Lehman 120 diesel. Took it out for my 3rd very short harbor shake down test run. Allowed engine to warm up before leaving the slip and was out for approx 10 minutes, running at about 1500 rpm and reading 180 degrees temperature.

Took it up to 1800 rpm and heard a squealing noise for about 10 seconds and then a bang and squealing noise immediately stopped. The exhaust hose from the exhaust elbow ruptured which was the source of the bang. Immediately dropped back to idle and took it back to the slip. Temperature never exceeded 182 f. The exhaust coming out appeared to be dry?

I removed the exhaust elbow and cleaned it up, it had minor corrosion but still in pretty good shape. Replaced the exhaust hose and checked the raw water impeller which was in good condition. Engine belts are new so now I'm trying to figure out what to do next? Can't find a mechanic so any ideas would be appreciated.

 

[SteveK]

Welcome. I assume the thru hull was open.
The raw water impeller was OK condition but you were getting dry exhaust. You need to check that the impeller is actually turning by removing the cover plate and have someone turn over engine with stop control engaged so it will not start. Just s few turns to rule out the pump assembly.

The squealing sound may have been the fan belt trying to turn the raw water pump.

 

[av8r]

FL 120 raw water pump is gear driven, not belt driven. The early style pump drive was problematic so checking rotation is a good suggestion. A plugged main heat exchanger would diminsh or stop water flow also.

 

[SteveK]

FL 120 raw water pump is gear driven, not belt driven.

I know that. Was thinking too hard on what squealed

 

[Choices]

Squeal could have been a whistle as exhaust hose came off.

Start with water inlet and work back. Lots of places for a blockage on a Lehman.

 

[LadySea]

Thanks for your tips! Interesting thought on the squeal noise? That sounded like fan belts slipping and more like it was coming from the rear than forward where the belts are so I hope that your theory is correct. Raw water pump is confirmed to be operational and working my way back to exhaust, replaced a short hose from pump that had a bulge in it. Other hoses and transmission cooler appear to be clear. Heat exchanger not so much. That looks like it's about 30% plugged with salt deposits and scale so I have elected to buy a new one and refurbish the old one for a spare.

 

[twistedtree]

It seem odd to me that the exhaust was dry, yet the engine wasn’t overheating? If water was getting through the heat exchanger to cool the engine, where did it go afterwards?

 

[LadySea]

Right now I can only guess that there may have been an obstruction at the intake like seaweed or plastic? And I can only assume that the antifreeze coolant in the closed half of the cooling system kept the engine cool. I idled back to the harbor slip (under a mile), so as to avoid overheating the engine. The exhaust hose ruptured in the middle and also lost its seal at the bottom of the exhaust elbow. Because exhaust smoke was leaking into the engine compartment I had the hatches closed and blower on. If there was raw water circulating it may have just ran into the bilge from the bottom of the exhaust elbow? Am having a diver clean the bottom and inspect the intake tomorrow.

I'm also assuming that the exhaust hose ruptured from excess heat caused by too little or no raw water flowing into it. An observer at the stern said there was no water spray visible in the exhaust at the time of the incident.

 

[Comodave]

I have put exhaust alarms on our last 2 boats. They will alarm almost immediately when water flow is cut off. Way sooner that the engine temp alarm. I got them from Borel Mfg. You can add high water alarm and water in fuel sensors too. No affiliation just a satisfied customer.

 

[rgano]

There should not to very much pressure in the exhaust hose after the elbow - just enough to push water up out of the lift muffler, assuming that's what you have. I would be surprised if it would generate enough pressure to cause a whistle and a rupture. Is there something blocking the exhaust hose after the muffler or in the muffler. Got muskrats?

 

[LadySea]

Inspected the muffler when I had the exhaust hose off. Totally clear inside. No muskrats. We did have exhaust coming out of the one way flapper at the stern before the incident. Will have the diver peek in there tomorrow.

 

[Comodave]

I put Hurley muskrat blockers on our last boat, this one had them already.

 

[firehoser75]

I concur with Dave regarding the Borel exhaust hose alarm. It is very inexpensive (from a boating viewpoint of expenses), easy to install, and will warn of a pending engine overheat BEFORE any damage can occur. This is the first place to (usually) show signs of a cooling problem, but without this type of alarm a boater would not know early enough (often) to prevent damage. I also installed an Aqualarm raw water flow alarm between the sea strainer and the raw water pump. This alarm will possibly save impeller damage by warning of closed through hulls, a sea strainer blockage (like a plastic bag, seaweed, etc.), or even other blockages further down the system. IMHO having these 2 alarms greatly reduces the chances of suffering a damaging engine overheat! They are relatively easy to install, and not very expensive. Cheap insurance in my opinion. Not affiliated in any way except as a customer.

 

[cardude01]

I put Hurley muskrat blockers on our last boat, this one had them already.

I thought you were jacking around with us at first but then looked it up.

I learn something everyday on this site. ?

 

[Comodave]

We have a weasel or a muskrat that lives under our boardwalk on the river. I don’t want to chance that it decides to live in our exhaust instead of under the boardwalk. The PO next door though it was cute so he fed it and nw it won’t leave. The Hurley guards are cheap insurance.

 

[Steve1.0]

I thought you were jacking around with us at first but then looked it up.

I learn something everyday on this site. ?

Sounded like a joke to me also. After looking at hurley's web page, it appears the little darlings have a taste for rubber and silicone hose as well!

 

[Comodave]

They can absolutely sink the boat. The Hurley devices are easy to install and worth every penny if you have them around.

 

[koliver]

A better known phenomenon is mice eating the insulation off your electricals under the hood on your car. Seems in the production of plastic used in that application something mice like to chew is used. Yes, personal experience.
Same?

 

[Steve DAntonio]

I would strongly consider installing a wet exhaust temperature alarm, it may have alerted you to this problem before the failure. Regardless, these alarms have saved countless engines and wet exhaust systems from overheating, they will sound within about 30 seconds of the exhaust losing cooling water, long before an engine can overheat.

Among the worst raw water hose failures I've seen are those that carry seawater to the injection elbow. If that fails, the engine will not overheat, raw water will be pumped into the vessel by the engine, sometimes setting off the high water alarm, and the rubber, fiberglass or plastic components used in the exhaust system are all exposed to hot exhaust gasses, which can be as high as 900F. It's often a mess at best and a fire at worst. Well worth the cost, I tell one manufacturer of these alarms they don't charge enough. More here https://stevedmarineconsulting.com/onboard-alarms-part-i/

In Taiwan

 

[Bmarler]

I a huge fan of exhaust temp alarms too. I really like the blue seas one as it has actual temp readouts on it. My exhaust runs about 95 degrees, so I set the alarm to 105.
Use the other three channels for genset exhaust, tranny cooler temp, and genset block temp. Each has their own alarm set points so you can customize based on how they normally operate.

 

[rgano]

I second or third Steve's recommendation for exhaust temp alarms, and if I was redoing it now, I would go with the Blueseas model mentioned by Bmarler. I installed overheat alarms on each of the three exhausts of my trawler, and installation on the main and genny of this MS Pilot was on my mind when the rubber elbow coming out of the raw water pump of my 315 HP Yanmar blew one day while we were bowling down the bay at 3400 RPM. It puts out 35 gallons a minute at that speed. I was alerted by two lighted and audible alarms to the issue, high bilge and coolant overheat. Looking down at the gauges I saw a pegged temperature needle as I was pulling the shifter to neutral and pressing the engine stop button and looking back and the black exhaust smoke, all in a tenth of the time it takes to read this sentence. The engine luckily survived ok, and exhaust alarms were strapped in place before either main or genny were ever restarted!

 

[sunchaser]

Aside from the good advice already received, warming up your engine at the dock can lead to glazing issues. Best to start engine, slip the lines and depart.

BTW, did you check that water was leaving exhaust after starting engine?

 

[firehoser75]

+1 on not idling your diesel!! Start up and ensure all is well (gauges read correctly, alarms off, raw water flowing, etc.) slip the lines and depart. Warm up consists of warming up (while underway) under a small load (~1000 RPM or less) motoring out of the marina or anchorage. Wait until you reach close to operating temp before running at normal RPM. Diesels don't like long periods idling in neutral.

 

[TJM]

I am looking for the Blue Seas exhaust alarms as I like the ability to see a number in degrees F°. Is it the M2 OLED unit with the 1821 Temp senders ?
Great info here.

 

[Bmarler]

I am looking for the Blue Seas exhaust alarms as I like the ability to see a number in degrees F°. Is it the M2 OLED unit with the 1821 Temp senders ?
Great info here.

yes, that's what i use. the kit i bought came with two 1820, and two 1821 sensors. two are submersible, two are not. there's different temperature ranges for them as well, so plan ahead. i took i/r readings so i knew what i was looking for and was reasonably confident the sensors were in range.
also, i was a bit confused about the relay output when going through the manual. i thought it was for powering the alarm buzzer or bell. it really can be used for almost anything. there is already a buzzer built in to the display that is plenty loud for me.
it takes a few minutes to program it, and each of the four channels run independently as far as how they react to the settings. highly recommend.