Overheating exhaust into Vetus mufflers

[Aquastar 33 Ocean Ranger]

Hi, I have a twin engined Aquastar 33 with Perkins Sabre 225Ti engines. All the exhaust systems including the Vetus mufflers have been replaced. The port engine cools the exhaust & muffler perfectly & is 29 degrees at the sensor position. The starboard exhaust sensor alarms at 59 degrees & this happens when I am motoring up a river at 6 knots at 1100 revs. When running at 1400 to 1800 revs the alarm doesn't come on but still runs hotter than the port engine at about 50 degrees. I think I have eliminated any problem with the engine heat exchangers as both engines run at their normal temperatures. As a test I have also swopped over the raw water inlets to the exhaust elbows of each engine. This confirmed that the heat exchangers are working ok because the starboard exhaust still overheated. The overheating seems to be just around the exhaust sensor. I am wondering if the exhaust elbow outlet holes are sufficient because when swopped over the water outlet cooled the port exhaust perfectly. Any ideas?

 

[harvey38]

Hi, so just to recap -

Both engine temp.gauges give a similar, acceptable reading?
Plenty of water being pushed out of the exhausts and similar amount?
Does one exhaust appear to have more steam visible?

Is the exhaust alarm only recently started to occur?

Have you fired an IR thermometer on the exhausts and seen any big differences when reading the same part of the system but other side, ie just before/after the muffler on the port vs starboard?

 

[Aquastar 33 Ocean Ranger]

This has been going on before I bought the boat 2 years ago because the old muffler stub had melted on the top. This was probably due to the fact that there were no exhaust sensors because i fitted them. Like i said in the post the temperatures are different as i have an infrared gauge. I have noticed that the black exhaust pipe is as hot as at the sensor position for about 18”. Strangely it is cooler towards the engine exhaust elbow. I am wondering if the hole spacing of the spray holes inside the exhaust elbow are correct. I have yet to compare it with the port exhaust elbow because that one works perfectly even after i swopped the outlets over. The boat comes out of the water today so hopefully will have a look inside the port elbow to compare. Cheers.

 

[harvey38]

I know the exhaust temps are different but what about the engine temps, are they pretty similar?

Are the exhaust temp senders in exactly the same position on each side and how far away from the engines are they?

Still need answers to -


Both engine temp.gauges give a similar, acceptable reading?
Plenty of water being pushed out of the exhausts and similar amount?
Does one exhaust appear to have more steam visible?

Cheers

 

[Aquastar 33 Ocean Ranger]

Both engine temperatures are the same & the sensors are in the same position. Approximately 1 metre of black pipe from elbow to sensor on each engine. It’s very difficult to say if there is more steam coming from either. The starboard exhaust outlet is cloer to the water than the port one but that I think is because the starboard muffler is on the starboard side of the boat & the port muffler is in the centre of the boat.

 

[Aquastar 33 Ocean Ranger]

Starboard exhaust slightly lower.

 

[burgundyben]

I've seen another of those Vetus silencers melted.

Exhaust gas temp rises with load of course.

I'd consult someone like Halyard.

 

[Aquastar 33 Ocean Ranger]

Yes the starboard one that I removed had the whole top of connection melted away. Up to the sensor position. Since fitting the sensors I have found that it is my first warning of weeds in the raw water intake, which is useful. I presume that is how the previous one had melted because it takes longer for the engine overheating alarm to come on & by then its too late for the mufflers. Last year I serviced the port engine raw water pump because it leaked. I think i may have a look at the starboard one to eliminate that.

 

[trialframe]

I had a similar event on a single engine Nimbus many years ago. Couldn't find the reason. Fitted one of these which possibly helped.

 

[Aquastar 33 Ocean Ranger]

Yes i did see that. I would like to see what the other elbow looks like inside first.

 

[Bandit]

The Sabre 225 TI should rev to 2500 rpm, cruising would be 2200 to 2300, you are running at 1400 to 1800.

Looking at the spec sheet RPM to L/hr for each engine if correctly propped: 1400=7L/hr, 1800 =14L/hr, 2200 = 27L/hr and 2500= 40L/hr, fuel burnt equals engine heat needing cooling. your boat should be able to run at 2200 or 2500 for extended periods and not over heat.

I think you should go back to first principles.:
Never assume sensors and gauges to be functioning correctly, cross check by swapping over engines to sensors to gauges if you can
Are your seawater uptakes blocked or restrained in any way or sucking air into the system
Are the impellers in good condition
Are your engines seawater systems partly blocked, shredded impeller debris at the coolers, calcification. seaweed or debris in the seastrainer or cooler stack
When was the last time you inspected the water injection bend after the turbocharger , they do corrode up very quickly, I am replacing mine about every 7 years see pictures, Blocked injection bends will lead to high back pressure and low water flow.

The pictures below show a very restricted injection bend probably less than 50% and a new one , the top of the picture is the lowest part of the bend which is blocked and will lead to a very uneven spray pattern and hot spots.

 

[Aquastar 33 Ocean Ranger]

Like I’ve said before i swopped over each water injection pipe to the other engine & the starboard water flow cooled the port exhaust muffler perfectly. The starboard muffler was still hot even when it was cooled from the port engine. This makes me think that it maybe the configuration of the spray holes in the exhaust elbow. I need to see if the port elbow is a different design. The pictures are of the starboard elbow after it was repaired at the flange position because it cracked.
The overheating only occurs when the engine is at about 1100 revs pottering down the river. At 1800 revs there is more water flow & the alarm goes out but it is still hotter than the port engine at similar revs. I never run the engines at 2400 for very long because I would be flat out burning a massive amount of diesel. I do run them flat out occasionally to keep them nice & clean.I have found that 1800 is plenty fast enough & feels more comfortable.

 

[QBhoy]

did she have those vetus units in the exhaust as built new ?

 

[Aquastar 33 Ocean Ranger]

Who knows? The boat was built in 1994 & we bought her 2 years ago last August. The previous owners owned the boat for 15 years. We replaced both exhaust systems completely as the starboard inlet muffler connection was melted away on top. We fitted the exhaust alarms which saves the mufflers if there is weed in the water inlet. If the engine overheated alarm comes on it’s too late for the mufflers so the exhaust alarms are the first warning of weed in the inlet filter.

 

[burgundyben]

I'd talk to Halyard, they are experts.

 

[Aquastar 33 Ocean Ranger]

Yes thanks, someone else mentioned them. I’ll ring them today.

 

[Bandit]

If you have clear plastic lids on your seastrainers you will see if there is an air leak into the cooling seawater upstream of that but not after.

 

[Aquastar 33 Ocean Ranger]

i don’t think there is any problem with the water flow because i swopped over the outlet feeds into the mufflers & the starboard engine cooled the port muffler perfectly & the starboard one still overheated. I’m inclined to think that it is the design of the spray holes in the s/s exhaust elbow. Now the boat is ashore i will take the port engine elbow off & compare it to the one in the picture.

 

[harvey38]

I'm getting confused with of this this -

So theere is no issue with the engines overheating but the muffler is melting on one engine?

How far away from the exhaust elbow is are the mufflers, are they equidistant and where in the system are the exhaust sensors?

Most Aquastars had straight through exhausts, we're mufflers an after fit and are they correctly placed and specced for your engines?

"We replaced both exhaust systems completely as the starboard inlet muffler connection was melted away on top. We fitted the exhaust alarms which saves the mufflers if there is weed in the water inlet. If the engine overheated alarm comes on it’s too late for the mufflers so the exhaust alarms are the first warning of weed in the inlet filter"

I'd be more concerned about the engines overheating than the mufflers in the event of a blockage.

 

[Aquastar 33 Ocean Ranger]

Interesting that you say they were straight through exhausts.! However there is no problem on the port engine which makes me think that it is the design of the spray holes in the starboard elbow. By the time the engine overheats, the exhaust muffler would have melted which is why the sensors are doing a good job. I will try & remove the port elbow soon to compare.
I have just replaced what was there when we bought the boat 2 years ago.