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Cat DH8

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Joined: 03 Aug 2012
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PostPosted: Fri Aug 03, 2012 9:43 am    Post subject: Cat DH8 Reply to specific post Reply with quote

I am using a friends Cat D8H Dozer and the last few hours of operation it has been losing power and smoking black. Air filters are clean, fuel is fresh. There is a small exhaust leak where the two piece exhasut manifold meets, but I sealed it up and didn't change the power. The turbo sounds like it is working. I am told the engine was rebuilt two years ago.. Any ideas where to start?
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Tractor Guru

Joined: 20 Jun 2007
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PostPosted: Fri Aug 03, 2012 11:07 am    Post subject: Re: Cat DH8 Reply to specific post Reply with quote

Even though it can be a PITA to check, and the turbo 'sounds; like it is working, that's where I'd start looking. I just replace a turbo on a customers machine a few months back that 'seemed to be working' and spun freely by hand and didn't appear to drag when spinning. Still my gut told me it was the problem and when the turbo shop tore it down they found the thrust bearings were shot and had been dragging causing the turbo to slow down instead of reaching full speed. Even a few thousand RPM'on the turbo can make a huge difference in the performance of the engine. Too, turbo seals leaking too much to the cold/suction side of the turbo can cause an excessive amount of oil to get drawn into the combustion chamber. A small leak will often go unnoticed as the oil will typically get burned off, but a larger leak will, in effect, flood the engine and will create black smoke due the amount of unburned fuel (oil and diesel) caused by the flooding. Either way the turbo would be my first choice to look at. Good luck.
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PostPosted: Fri Aug 03, 2012 11:41 am    Post subject: Re: Cat DH8 Reply to specific post Reply with quote

Get a hose and a low pressure gauge into the intake manifold and check the boost under load.
Look for 10 to 15 PSI(not exact spec) but will give you an idea on turbo without tearing it down.
Later Bob
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PostPosted: Sat Aug 04, 2012 7:30 am    Post subject: Re: Cat DH8 Reply to specific post Reply with quote

Are the fuel filters clean/new? Check for fuel flow after the filter.
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Richard Maurer
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Joined: 28 Jul 2012
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PostPosted: Sun Aug 05, 2012 8:35 pm    Post subject: Re: Cat DH8 Reply to specific post Reply with quote

Is there any water in it? It won't matter now, it's already too late.
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