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post #5 of Old 03-10-2016
Beyond The Pale
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Re: Turbo diesels

In my opinion, modern, auto-based, high-rpm Turbodiesels don't belong in smaller Sailboats. Who needs that much added power? Anyway, they aren't common. Bog-Standard non-Turbo Marine Diesels are still the most common kind, by far.
As to whether a Diesel will run with a frozen Turbo- it depends.
A friend of mine bought a Mercedes 300TD with a frozen Turbo. It still ran, but slowly, and smokily. He replaced the Turbo, and the Car ran again as well as it ever would. After a couple of years, I bought it from him, and put another 100K miles on it. Oil, a couple of lamps, wiper blades, and tires were all that I replaced. And then a tree fell on it...
My current 300TD has over 350K original miles on the clock...
The 30 year old Volvo Diesel on my boat is also original, but it isn't Turbocharged. It runs like a top- tickle the manual fuel pump lever a few times, and it starts right up.

(Those old MB Diesels were _heavy_; the 300TD 125HP Turbo series engines weighs something like 1,100 pounds. I've lifted a couple, with much mechanical assistance.)

"If the engine can run without a turbo what does that do to the engine?"
Again, it Depends.
Mechanical Fuel Injection pumps were calibrated for Turbo use, and would dump too much fuel into the cylinders at higher engine RPMs if the Turbo froze, leading to Smoke in the exhaust, and engine Coking. This could also cause Glow Plugs to burn out.
Older Diesel fuels were only fair lubricants, (Sulfur...), but raw Diesel getting past the rings could lead to cylinder scoring on starting when cold.
If you are talking about modern EFI Diesels, with modern low-Sulfur Diesel fuel, you have to be a bit more specific. I have no idea what each manufacturer has in the way of Exhaust Sensors and Sensing. It's all very Proprietary these days.

Someone else commented:
"If the turbocharger locks up so that the shaft won't turn, no, the engine won't run."
Simply. Not. True. Turbochargers are not displacement pumps, like piston pumps or Roots Blowers. At low or no RPM, enough exhaust gas gets past the vanes to allow the engine to start and run. Turbocharging depend on high Turbo RPM to work at all. A frozen or weary Turbo just adds back-pressure to the exhaust system, and messes with Injection settings.
(BTW- the Failure Mode is the Turbo bearings. Lack of oil or very dirty oil is Death to them. The bearings either get frictiony, they freeze up after being run hard and shut down too quickly, or they fail spectacularly, causing vanes to hit what's around them that they shouldn't hit. I've rebuilt more than a few, but with this distinction- they were made by Varian, and they weren't used in boats, that I know of.)

"Now virtually all recent boats have small turbo diesels... You would have difficulty even spec'ing a new boat with a naturally aspirated engine."
Volvo, Yanmar and most other manufacturers still offer naturally aspirated Diesels, from one to four cylinders, I just checked, and Catalina, Hunter and Beneteau offer them; I just checked again. Where did you come up with that claim? (You may have something if you are talking about custom >$500K Mega yachts, but since you didn't make that claim, I am assuming that you aren't.)

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