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Old 08-03-2015, 02:55 AM   #41
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The yard can't seem to find the energy to get involved to complete this thing and I'm ready to kill them. You'd think they'd want to get paid.
I'm to the point where I need to deal with these items myself and get my boat the hell out of there before i get arrested for assault (or worse).
I've felt this pain several times now. My last repair was supposed to take less than a week. After six weeks, I was nearly homicidal. I just don't get these guys.
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Old 08-03-2015, 07:01 AM   #42
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If I increase RPM up to 2000 while in neutral is there enough exhaust pressure between the turbo and the elbow to check for a leak?
If "between the turbo and the elbow" you mean the turbocharger exhaust side and an elbow that connects the turbo to the downstream exhaust system, the answer is a qualified yes.

The backpressure developed in an exhaust system has a minimum level that is a product of the size of the tubing, the number and angle of the fittings, the level of water in a lift muffler if one exists, and the overall length of the system from the turbine outlet to the atmosphere. The lowest pressure is developed at idle, the highest at maximum power.

Using a generator as an example since we can easily see the difference created by load changes that occur at the same rpm, a system might have a no load backpressure of 13 or 14 inches of water column (~34mB) to a full load backpressure in the high 20 inches (~70mB) or even higher with a poorly designed system.

Even 13 or 14 inches of water is usually enough to determine if exhaust fittings are leaking.

Don't be so hard on the mechanics. They want to replace the insulation blanket because if you took the boat and ran without it and had a fire that could be shown to be the result of leaving it off, they would be liable. Let them put it on and if you want it off, you take it off so there is no doubt exactly who created what might be a hazard in your engine room.
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Old 08-03-2015, 08:16 AM   #43
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Turbo's generally do not develop positive pressure unless under load...Reving in neutral will not accomplish that.
My observations from years of experience with Audi gas Turbos and VW Diesel turbos with accurate boost gauges..
I can understand this on turbocharged car and truck engines as they would have a by-pass of some kind to get rid of unwanted boost pressure. Is a bypass or waste-gate a normal feature on turbo marine diesels?
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Old 08-03-2015, 08:34 AM   #44
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On my Cummins with boost gauges there is no pressure until the engine is in gear and rpm up to about 1400. Out of gear no pressure no matter the rpm.
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Old 08-03-2015, 09:03 AM   #45
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I can understand this on turbocharged car and truck engines as they would have a by-pass of some kind to get rid of unwanted boost pressure. Is a bypass or waste-gate a normal feature on turbo marine diesels?

A Bypass (either a diverter valve or blow off valve) is in a car system to de-pressurize the inlet system when the throttle plate slams shut as in a shift to a higher gear.. Without it you'd have a high build up of pressure in the inlet tract that could stall the turbo. Not good for performance (or turbo's). No need in a marine application as there is no rapid change in throttling in high torque ranges, and most are very low pressure systems..A few PSI maybe, where cars I've owned have approached 25PSI
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Old 08-03-2015, 09:49 AM   #46
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On my Cummins with boost gauges there is no pressure until the engine is in gear and rpm up to about 1400. Out of gear no pressure no matter the rpm.
Do your boost gauges give accurate load readings? Thinking of using them instead of Fuel flow meters.
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Old 08-03-2015, 11:42 AM   #47
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On my Cummins with boost gauges there is no pressure until the engine is in gear and rpm up to about 1400. Out of gear no pressure no matter the rpm.

No boost because it is unnecessary to achieve RPM you select. More load requires more fuel and therefore creates more exhaust and boost.. Diesels are fuel limited engines not air limited.
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Old 08-03-2015, 12:09 PM   #48
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No need in a marine application as there is no rapid change in throttling in high torque ranges, and most are very low pressure systems..A few PSI maybe, where cars I've owned have approached 25PSI
That reads as if you have never heard the turbo on a large marine diesel "bark."

They most certainly do experience compressor stall and the charge air pressure on a marine diesel can exceed 45 psig. That is why rapid power changes are not recommended because the pressure differential across the compressor will lead a a stall and can damage the turbo and inlet ducting.

All of this is of course irrelevant since the OP asked if he could find an exhaust leak by running the engine at high idle. He didn't ask if he could find a charge air leak.
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Old 08-03-2015, 01:57 PM   #49
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Maybe you said already and I missed it but am curious...what year are the engines and are they TI or TA turbos ? I think TA was available after about 1988 or so. I guessing from the heat blankets they are TI ? If so has the boat ever lived in salt water ?
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Old 08-03-2015, 02:59 PM   #50
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On the turbo 6-71 the air charge is being cooled between the turbocharger and the blower, thus all are intercooled (TI).
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Old 08-03-2015, 03:15 PM   #51
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On the turbo 6-71 the air charge is being cooled between the turbocharger and the blower, thus all are intercooled (TI).
I asked as I was seriously interested in an older Hatteras that had 8v92TI's in FL and one engine surveyor told me he was now refusing to survey the TI engines as the salt water can corrode things to the point the salt gets into the engines. Might survey great one day and engine ruined a week later and the buyer comes complaining to surveyor about not catching the issue.

At least on the TA versions the salt water is cooling fresh water so not as risky to core engine components. Having said that, if OP's boat always in fresh water not likely the issue.
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Old 08-03-2015, 09:25 PM   #52
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At least on the TA versions the salt water is cooling fresh water so not as risky to core engine components. Having said that, if OP's boat always in fresh water not likely the issue.
It's a TI with a closed cooling system. The boat is a fresh water as well. But this has no bearing on my query.
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