Crossover corrosion.

[56pan]

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.

[DmaxMaverick]

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.

[arveetek]

Thanks for sharing your experience!

Casey

[JohnC]

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...

[56pan]

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. :)

[JohnC]

I'll ask my PMI...

[More Power]

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...