Dave:
Yes, the Deutz diesels are loud. The meter read 96 dB with the rough-cut mower at full chat.
I've run mine less than 50 hours, so I certainly can't answer longevity and maintenance questions from my own experience. Before I bought, however, I checked around a bit and found that Deutz engines generally have a good reputation for reliability, longevity, etc. They are widely used in industrial applications.
Power Trac calls them oil-cooled, which may be more accurate than air-cooled, since mine has a large oil cooler fed by a fan.
I haven't compared power curve specs to other diesels of comparable rated horsepower. The curves are shaped by cam profiles, intake and exhaust sizes and lengths, etc. As with other diesels, the Deutz's are set up to be lower revving than typical gas engines, although in industrial engines that difference is less than in the past. The torque curve is flatter, with the diesels having a bit more low-end torque than a comparable displacement gas engine.
The 45 Hp Deutz is described as "direct injection" with no preheat chamber or glow plugs. Terry Estep at PT told me it can be run dry, filled and started without bleeding anything. I told him I didn't believe that, of course, since part of the diesel mystique is knowing how to bleed the injectors and using the proper swear words to get the ff*&>$@**!! thing making noise again after running it out of fuel.
So far, the Deutz is by far the easiest diesel to start that I have had anything to do with. It invariably fires so quickly that you can turn and release the key and be confident it will be running. (I've only tried it a bit under freezing, since it's been warm since I got it, but it started easily in chilly conditions.)
Some current tractor liquid cooled diesels are also loud. Except for a few dB, I doubt any of us can notice any difference between the Deutz and comparable horsepower Kubota or Yanmar, etc. in operation or maintenance burden. Certainly, I expect it to outlast me without major maintenance or failure.
I like both diesels and gas engines, and have both, but generally take the gasoline side in the economy-longevity debates. I'd love to have my same tractor with a whisper quiet liquid cooled 200+ cu in flat six gas engine, making about 75 HP at 3000 RPM. (Continental? Subaru?)
If I had more time and money, I might try to build such a thing on a Power Trac platform. It wouldn't do anything any better, just would be a kick to try to make it work, and quiet it down. Power Trac might even help. As you can see from their 400 line, they like gas engines, too. I suspect the market would be slim, however, because everyone out there knows the superiority of diesels, even when they cost three or four times as much initially.
(Just for giggles, price a new engine on yours and an 18 to 20 hp diesel of any flavor.)
