Blowing Out the Turbos

[kelpy]

It isn't about just getting the engines up to temperature, it is getting them to designed operating conditions to keep the oil seals loaded, the air boxes clean of water and oil, the exhaust manifolds and, if equiped, turbos, free of unburned fuel (and oil from the unloaded/worn seals), the injector tips clean, etc.

[Photolomy]

It all boils down to temperature. If the engine runs too cool for long periods of time, the cylinder walls can become glazed. Normally (ideally), the cylinder walls are bare metal with the remnants of the honing pattern still on them (after break in). That pattern consists of microscopic ridges that are necessary for oil to coat the walls and yet also allow the rings to slide by ON that film of oil. That texture allows the surface of metal to hold the oil. When the engine is run cool for long periods of time, that oil will turn to something like a hard and permanent varnish, filling in those ridges. Without the ridges, the lubrication is less effective and more oil will also be pushed ahead of the rings and burned. When the engine is run hot enough, this does not occur.

All that being said, if your coolant temps are 165 or greater, then you should be fine. I know some say 170 deg or greater, but when you look at the applications that DD put these engines in, I don't think they need to be run hotter than what DD says they need to be. However, it would take my engines quite a long time to get to 165 deg at 900 rpm, even though DD does say that 900 is the minimum RPM for an 8v71TI. For economy, I run mine at 1100. But, I often get impatient.

I also do a high rpm run at the end of the day, but I pretty much believe that does nothing in terms of what this discussion is about, but it does tell me if something else might be going on, like dirty bottom, clogged fuel filters, clogged strainers, etc.

[Photolomy]

I also want to add - if DD recommends 900 rpm as the minimum, then why are we discussing this? Isn't running these things at idle (~600 rpm) for a long time the real (and only) No-No? well, and also don't run them at 190 degrees. It seems to me, and I could be wrong, that DD's original recommendations have been altered and exaggerated over time, by the internet. Like what happens with gossip.

[luckydave215]

Food for thought - these engines were designed to turn military generators - at 1800 rpm. From that we may infer that the design intent was that all parts of the engine (internal clearances, combustion heat flow, turbine inlet temperature, lubricant temperature, oil pressure, combustion gas flow patterns ad nauseum) would be optimized for steady 1800 rpm running, all other speeds are less than optimum.
Of course we care about fuel burn, engine life, etc. but the engines don't know that, they just know they were designed for 1800.

[Jubilee]

Three mechanics have advised that the engines should be run up about every 4 to 5 hours. They further stated that most turbos kick in at about 1850 RPM and that the run up should exceed the 1850. I have followed this procedure for 22 years and have had no trouble.

[Passages]

Three mechanics have advised that the engines should be run up about every 4 to 5 hours. They further stated that most turbos kick in at about 1850 RPM and that the run up should exceed the 1850. I have followed this procedure for 22 years and have had no trouble.

How long should they be held at 1850?

[Boatsb]

Exactly 65,000 revolutions.

[luckydave215]

Anyone had to replace a turbo because they ran them too easy?

I have.

[luckydave215]

Loading the engine is to burn off the soft soot in the cylinders that comes from prolonged light load operation. The turbos aren't really affected by that

.

Not true, the hot side of the turbos are affected by carbon deposits (one of mine stuck on the hot side from not running hard enough).
The hot side of the turbo sees very high temps, as the exhaust pressure is held up until then (that's how turbo charging recovers energy from waste heat)

[Passages]

Exactly 65,000 revolutions.

So 35 minutes, 8 seconds. Got it!