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Generator exhaust- are you kidding me?

greg.hahn

greg.hahn

So I've got a Kohler 60KVA diesel generator that needs a new exhaust. Got a quote from a reputable company that wants $5700 to replace the exhaust system. $2700 is for the muffler alone! :eek: :eek: :eek:

I've Googled the same muffler online and found it for $900. That still seems rather steep, but a huge improvement.


The part quoted is: 352646 Silencer, Critical

Reckon this is a super silent muffler for city use? Look...this generator is way back in a field in the middle of nowhere. It doesn't even NEED a muffler. But why is this one so expensive?

Why can't I have the local muffler or diesel tractor shop fabricate an exhaust system for this?
 
If you want to get within a 100 feet of it while it's running without ear protection you'll appreciate a muffler.
City/County/State code may require a "silencer" muffler regardless how close it is to habitable dwellings.
 
This size generator usually uses a medium sized truck engine. 60kW is relatively small. A semi truck muffler or even a large farm tractor muffler may well suffice.
 
I suspect the original muffler was an engineered silencer and not just a muffler. The Db rating is probably much less than what conventional mufflers are rated at. That and it probably isn't a thin sheetmetal arrangement, but a heavy-duty unit. It may also have to incorporate a spark-arrestor to keep from setting any surroundings on fire as well. Many newer diesels also have particulate filters in the exhaust system too.

Lastly, it also is probably made by only one manufacturer and in very limited numbers.
 
And remember the engine is designed to expect a certain amount of back-pressure from the muffler...if you mess around with no muffler or jury-rig something else to the engine, you may risk performance problems or long-term damage (overheating pistons, valves, etc.)

Sticker shock is common on big genny parts for reasons already mentioned by nocomradio. Had a $2K radiator replacement on a big Onan rig a few years ago.
 
Find out the make and model of the engine, then google the engine to see what it was used in. Then, you can look for mufflers that will work for that engine.
 
Kmagrill said:
Find out the make and model of the engine, then google the engine to see what it was used in. Then, you can look for mufflers that will work for that engine.
Click to expand...

You will need to keep in mind however that an engine used in a truck or moving piece of equipment may have had a vastly different exhaust system than a stationary engine. A stationary engine, in this case a generator, would tend to run a considerably higher exhaust temperature because it is running at somewhere near its maximum RPM and its enclosed in a box keeping airflow to a minimum around the hot exhaust parts. There may be more heat shielding involved in the more expensive muffler that this unit requires.
 
The heat radiated by any engine, running in a properly designed system, is governed by the thermostat. Certainly, a loaded engine produces more heat energy than an idle engine, but the job of the cooling system is to shed the excess energy to maintain an optimal engine temperature at all times. If the cooling system cannot maintain a stable temperature at any load and at any RPM, then there is a problem, either one of improper design, or a defect/failure. Even under differing loads, the exhaust temperature should not be significantly different between the different engine configurations, except when a different temperature thermostat is used. That said, the exhaust ports may be somewhat hotter in a loaded generator than on an idle truck, however, trucks and tractors often have to pull heavy loads at low speeds and are designed to handle this condition without damage.
 
Kmagrill said:
The heat radiated by any engine, running in a properly designed system, is governed by the thermostat.
Click to expand...

The heat RADIATED by an engine is probably only governed in a very minor way by the thermostat. The thermostat is charged with keeping the coolant within the engine at a desired temperature. The thermostat has no knowledge of how much heat is being RADIATED... only how much heat is being retained in the cooling system.
 
GRC's explanation is a very good one. The exhaust system temperature can vary wildly depending on load and engine RPM. I have a 2.5 ton diesel truck. In the dash is a pyrometer which is inserted into the exhaust manifold where it dumps into the front exhaust pipe approximately 6-8 inches from the last exhaust port on the engine. At idle, the exhaust temp is around 400 degrees. Normal driving up the road will give you around 800-1000. Put it under load, (i.e. more fuel applied) and it will easily climb to near 1200-1400 degrees, which if kept there long will cause a piston to melt.

In a stationary engine, such as a large generator, the alternator on that unit puts a large load on that engine, and the exhaust temperature could very easily be pushing the upper limits of the engine design. When you contain all that inside a large insulated box, you tend to compound the issue and therefore need a specially designed exhaust system that has to be well insulated and more free-flowing too. If this is a turbo diesel, then the problem is even greater, because by compressing the intake air stream it heats that air charge up and drives the temperature up much faster yet. One way that many diesels counteract this high exhaust temperature is to add an intercooler in front of the radiator. In a stationary application, this then requires a very large fan to keep things cool up front since you don't rely on ram-air from the front of the vehicle moving through the air stream.

Not trying to say that the exhaust system probably isn't overpriced, but there was a significant amount of engineering that had to go into it to fit, work with the rest of the components in the generator unit, and do that without risk of a very expensive and potentially dangerous meltdown. In other words: a muffler ain't just a hole to get the exhaust out of the engine and do it quietly.
 
I agree that the exhaust gets much hotter under load. What I am saying is that the air temperature around the manifold is, primarily, a function of the core engine temperature combined with the fan-derived air temperature passing through the radiator. As the engine radiates more core heat energy, this is wicked away to the radiator and exchanged to the air at a faster rate. Once the engine reaches its normal operating temperature the temperature inside of the enclosure will stabilize at some value well below 200 degrees F. If you leave a piece of paper pinned to the engine (not on the exhaust system itself) it won't be scortched after you have run the engine because the cooling system regulates the core engine temperatures. All of the exhaust systems, whether on the generator or a truck, have to be capable of dealing with the high output of heat generated under load, but it isn't as if the exhaust system had to operate surrounded by ambient air that's hundreds of degrees already.
 
greg.hahn said:
So I've got a Kohler 60KVA diesel generator that needs a new exhaust. Got a quote from a reputable company that wants $5700 to replace the exhaust system. $2700 is for the muffler alone! :eek: :eek: :eek:

I've Googled the same muffler online and found it for $900. That still seems rather steep, but a huge improvement.


The part quoted is: 352646 Silencer, Critical

Reckon this is a super silent muffler for city use? Look...this generator is way back in a field in the middle of nowhere. It doesn't even NEED a muffler. But why is this one so expensive?

Why can't I have the local muffler or diesel tractor shop fabricate an exhaust system for this?
Click to expand...

Is this inside or outside? Recently received quote for about 10K for same on 180 kW unit. Inside units are now blanketed exhaust turbo can reach 900 degrees f. Pipe and muffler not quite as hot but way on up there!

Best regards,

w/
 
Watt Hairston said:
greg.hahn said:
So I've got a Kohler 60KVA diesel generator that needs a new exhaust. Got a quote from a reputable company that wants $5700 to replace the exhaust system. $2700 is for the muffler alone! :eek: :eek: :eek:

I've Googled the same muffler online and found it for $900. That still seems rather steep, but a huge improvement.


The part quoted is: 352646 Silencer, Critical

Reckon this is a super silent muffler for city use? Look...this generator is way back in a field in the middle of nowhere. It doesn't even NEED a muffler. But why is this one so expensive?

Why can't I have the local muffler or diesel tractor shop fabricate an exhaust system for this?
Click to expand...

Is this inside or outside? Recently received quote for about 10K for same on 180 kW unit. Inside units are now blanketed exhaust turbo can reach 900 degrees f. Pipe and muffler not quite as hot but way on up there!

Best regards,

w/
Click to expand...


It's outside. And by the way, I got a quote from a Kohler dealer for $3300 to do the same job. It still seems high, but it's over $2100 less than the first one.
 
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