Tuesday, April 6, 2021

Exhaust Wrap

In my last post, I wrote about removing the bumper and exhaust in order to install a tow hitch. While I had the exhaust out, I figured I would apply the exhaust wrap I had sitting in my garage. Exhaust wrap is one of those religion things that gets some folks all fired up, so we'll go there first.

Why Exhaust Wrap Rocks
I'll start with why so many people think exhaust wrap is a good idea. Exhaust wrap is basically a fiberglass cloth. Like the fiberglass insulation in your house, this wrap holds the heat inside your header or pipes. This is supposed to bring specific benefits. First, the higher heat inside the pipe is supposed to help the exhaust gasses exit the tail pipe faster. I don't know where there is research proving that, but let's assume that there is some. The folks at CoolIt seem to believe it. The folks who do ceramic coatings do too.

Second, by keeping the heat inside the pipe, it is not escaping into your engine compartment. This reduces overall heat, making your intake air cooler, and I suppose, in theory, making everything in the engine compartment a little happier, and operate a little cooler. In the case of Hapy, the engine compartment is located under the rear-most third of the bed. So, any heat that builds inside the compartment eventually radiates up into the main cabin. In the Summer, when we are driving in the Central Oregon high-desert, the main cabin gets pretty hot without the extra heat from the engine. So, it is for this reason that I am exploring the exhaust wrap.

Why Exhaust Wrap Sucks
For every positive, there is a negative. The counter-argument to the holding the heat inside the pipe is that if you apply too much insulated wrap (or any at all, according to some), you could contain too much heat and damage your header or exhaust pipe. That would be bad, especially if there isn't any real research to prove that higher temperature exhaust gasses travel faster. My Google-fu may not be working these days as all my efforts to find hard evidence were fruitless. I did, however, find this image that shows a crack or split in a pipe that appears to have been previously wrapped, and it was posted by someone who does ceramic coatings, so s/he probably knows a few things about heat management.

The second big negative for exhaust wrap is that the exhaust wraps absorb moisture and cause your exhaust to rust out. This might be true, but I would think that the outside of a correctly installed exhaust wrap is still going to be over 100*C when in use, causing any moisture to vaporize. I suspect that the real cause of the destroyed exhaust is overly-aggressive wrapping causing too much heat to be held in, destroying the pipe. Many fellow internet'ers have shot their wrap with exhaust paint afterwards to prevent water absorption. That will not prevent moisture appearing between the wrap and the pipe during cool-down if the ambient air is below the dew point (like it is here in NW Oregon practically every night). For that, I would expect that standard exhaust paint on the pipes before applying the wrap would suffice.

The last negative could be the heat being held in, and rather than helping exhaust gasses escape (and reducing Exhaust Gas Temp -EGT at the head), the trapped heat actually increases EGT. I have not been able to find research to demonstrate this, however. Quite the contrary, actually. So, this is probably not a thing, but I felt it was still worth mentioning.

Where I Landed
My searching for evidence of the viability of applying exhaust wrap to a turbo-charged diesel engine has actually pointed in the direction of doing it. Many large truck owners running Cummins turbo diesels wrap the turbo as well as the downpipe straight to and past the catalytic converter. Some owners painted the wrap with exhaust paint to protect it against the risk of water absorption. Overall, the consensus appears to be that it is a pain to do, but worth doing if you are okay with putting in the time: the temps in the engine compartment feel lower, the engines seem to be running as well or a little better. The cost-to-value to pay someone else to do it, however, isn't there. It may not even be worth your own time, depending on your reason for considering it and how much you intend to do. In my case, the heat radiating into the main cabin is sufficient reason for me to look for ways to contain some heat. I wanted a larger bore exhaust (2.5" versus 2") when this one was built, so if the exhaust starts to fail because of the wrap, I will have (a) proven these can cause damage and (b) forced my way into the bigger exhaust I wanted. So, even though this may cause my exhaust pipe to fail, I am doing it anyway because I just want to know.

I know many cars have a heat shield of some kind on underside of their hood (bonnet for my UK readers). I may explore that whether this exhaust wrap experiment pans out or not. Truth told, with all the other changes going on (ECU chip and new injectors with bigger nozzles) I will probably not be able to separate out the impact of the exhaust wrap.... unless the wrap causes the pipe to fail.

Some manufacturers and some folks on the web describe soaking the exhaust wrap in water before applying it. I think the theory is that getting the wrap wet for application ensures that it gets super-tight on the pipes. Sounds plausible. So, I pull out this long roll of exhaust wrap and I can tell right away there is way more than I need. But, how to figure out how much you need without just doing it? So, I started applying the wrap as tightly as I could, twisting it tighter every time I went around. I made sure my overlap was no more than 1/4" (manufacturer directions) and in about 20 minutes I had my exhaust wrapped from the plate that mounts to the turbo to the leading edge of my muffler. But, its dry. I asked myself: should I unwrap what I just did to get the wrap soaking wet and then try to get it on even tighter? That seemed silly. Besides, some manufacturers (Design Engineering, the folks who made the wrap I was using) clearly state that soaking it in water to install is unnecessary. So, I left it as-is. I put on a pair of stainless steel cable ties (from Harbor Freight) at the muffler end, where the wrapping stopped. I cinched down the end near the turbo with only one, making sure to put the clip nowhere near where fingers might catch during install. 

Clear Coat
Once the wrap was on, I really liked how the pipe looked. Before, it was plain looking. The black high-temp VHT paint had chipped off in spots, leaving bare silver steel showing. With the wrap, it looked like it was now dressed in tweed. Suddenly, it had some class. Sure, the inevitable small oil leak or kicked up gravel from the road will savage this tweed outfit eventually. So, to delay that, I bought and shot it with some clear exhaust paint. I didn't know they even sold it, but for $12US at AutoZone, I found it among all the assorted colors. The additional upside to shooting clear is that I didn't need complete deep coverage for it to look good, or look the same. Folks who shoot black or a color match for their engine need to apply multiple coats to cover up the tan/tweed. I shot liberally, but there was no way to know how well it covered because the tweed still looks like, well, tweed.

I will need to keep an eye on how much oil appears on the wrap, however. The pipe was a little grimy before. I know that I have a recurring issue with oil leaking from the turbo-charged air near the rear of the engine. This is very close to where the exhaust is. I may have just created a big towel for the oil to soak into.... a towel around a very hot exhaust pipe. Truth-be-told, this experiment may end fairly soon if I see oil leak evidence on the wrap.

Exhaust Installed
closed hanger
I let the clear coat cure overnight, and re-installed the exhaust after work the next day. As I did, I noted and changed a few things. First, I paid handsomely for a "custom" exhaust however many years ago. The muffler they used can be found on the internet for $18US today, which tells me the quality chosen back then. The plain steel pipe has 3 90* turns in it before the muffler and a 90* turn afterwards through a crappy tailpipe. When I decide to revisit this, I will not be going to Ed's Mufflers again (looks like that location is gone anyway). Ironically, I went to them because I thought they would do something better than Midas or Meineke. Midas built a custom dual exhaust on my old '78 F250 20+ years ago that was way better than this. Lesson learned.

Anyway, one of the other disappointments of the install was that they welded the body-side of the exhaust hanger closed, so the rubber bit could never be replaced. Not the best plan. After wrestling this exhaust in and out around that a few times, it continues to be a reminder that Ed's didn't do what I asked. 

The exhaust attaches to the turbo with 1 13mm nut and 2 13mm bolts. In the past, I would wrestle the rear hanger on first. This time, it popped on without gymnastics, almost like it knew it was approaching its final days. Then, I hung the exhaust on the one stud and rotated the exhaust until one of the bolts slid through. Finger tighten, torque etc. Everything fit fine (nothing touching, but close) with the tow hitch in place. Of course, now I need to remove the hitch so I can attach the bumper correctly. But, that's another post.

Thanks, as always, for following along.

No comments: