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Thread: Crossover corrosion.

  1. #1
    Join Date
    Feb 2006
    Posts
    185

    Default Crossover corrosion.

    I'll try to post pictures of what I found today on my exh. crossover. My boost press. had gone from 13 psi to 8 psi at WOT and was slowly decreasing. I noticed I was rolling the coal also at WOT. Checked fuel pressure with a gauge taped to the windshield at WOT and it dropped to about 1 psi. From what I understand this is sufficient at WOT. Checked all the ducting from the compressor outlet through the intercooler to the intake and was sure there were no leaks. Finally noticed when I got under the truck with it idling I could feel an exh. leak below the driver's side manifold. Took the crossover off and the pictures tell the story. I had wrapped the crossover with header thermal wrap about 8 yrs. ago when I put the mandrel bent one piece on the truck. I remembered there was a discussion concerning wrapping the crossover on either this forum or one of the others several years ago, but I couldn't find that again. The gist of it was that there was a disagreement about the thermal wrap on the crossover. Most said it was a good idea, but the detractors said it would cause the pipe to corrode. Which the attached pictures reflect and the detractors had a good point. I put on a new 2 piece Diamond Eye crossover today after giving it 3 coats of VHT and then wrapping it with new thermal header insulation. I'm a retired airline mechanic and on the Boeing, Douglas and Airbus ships, the GE, Rolls Royce and Pratt and Whitney large turbofan engines all have thermal blankets on the turbine sections. To maintain efficiency is what I understood, not for cowling protection. I've also seen large Caterpillar diesel generator sets with blankets on the exhaust feeding the turbine of the turbocharger. If it's good enough for those engineers, it's good enough for me. Just my opinion and worth what you're paying for it. At my age, if the crossover corrodes through again, I'll be long gone. Truck is a '93 C2500, mech. inj. pump.
    Attached Images Attached Images

  2. #2
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

    Default

    Yes, wrapping the pipe is to help maximize efficiency. Heat is energy, and retained heat before the turbine is retained energy. After the turbine however, heat should be shed as rapidly as possible to decrease resistance (gas contraction), which also helps to maximize efficiency. Unfortunately, pipe wraps have a drawback. They retain moisture and corrosive materials, and remain out of sight. Rust belt salt and chemicals make it worse, added to heat cycles that shed carbon from the steel. The pipe becomes a sacrificial, consumable part. 8 years isn't bad, so consider the cost over time as a maintenance item.

    An alternative to wrapping the pipe is coating. Ceramic and others can help to retain heat, but don't have the same drawback of moisture/material retention. Road salt/chemicals can be rinsed away as needed.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  3. #3
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
    Posts
    3,081

    Default

    Thanks for sharing your experience!

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  4. #4
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,057

    Default

    Quote Originally Posted by 56pan View Post
    on the Boeing, Douglas and Airbus ships, the GE, Rolls Royce and Pratt and Whitney large turbofan engines all have thermal blankets on the turbine sections.
    Now you'll have to institute a hot section inspection interval...
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  5. #5
    Join Date
    Feb 2006
    Posts
    185

    Default

    Quote Originally Posted by JohnC View Post
    Now you'll have to institute a hot section inspection interval...
    I've got a cheapo HF borescope. I'm sure that would be okay with the FAA.

  6. #6
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,057

    Default

    I'll ask my PMI...
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  7. #7
    Join Date
    Feb 2000
    Location
    Montana
    Posts
    11,382

    Default

    Run some tests looking for a measured difference in turbocharger boost/spoolup with and without crossover wrap. My guess... hard to impossible to measure a difference (performance benefit) in these low boost apps.

    I know that people will use wrap in other apps to help control heat that could damage or negatively affect something close by. That would be my motivation for using wrap.... Just mulling it...

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