IO-390 Exhaust Contacting Cowling Causing Hot Spot – Experience with Thermo-Tec Heat Wrap?

[Carlosanlley]

I’m currently dealing with an issue where my Vetterman Exhaust is making contact with the cowling at one specific point, creating a hot spot. We discovered it after doing some ground engine runs. At this point, the engine probably hasn’t run more than about 20 minutes total, and the only higher power setting we used was around 2,000 RPM for less than 5 minutes just to cycle the prop. I’m attaching photos of the hot spot.


At one point we saw an IO-390 installation that had a heat shield wrap/sock covering the entire exhaust, and we initially thought about doing the same thing on ours. However, after speaking with Vetterman Exhaust, they told us they do not recommend it because the exhaust could fail. They did not go into much detail, but I assume it is because the wrap prevents the exhaust from dissipating heat properly, increasing the temperature of the entire exhaust system. At the time of that discussion, we were talking about wrapping the full exhaust system.


Now that I’m specifically dealing with this hot spot on the cowling, I’m considering applying heat shield wrap only on the section that is contacting the cowling — probably no more than about 3 inches — as a temporary solution. Longer term, I’m planning to modify the cowling to achieve at least 1/2" clearance between the exhaust and the cowling at the interference point.


Has anyone dealt with something similar? Also, does anyone have experience using heat shield wrap in this kind of application? The product I purchased is Thermo-Tec.

 

[Toobuilder]

Yes. I have cowl clearance issues too, and I use short sections of header wrap to prevent burning. In my experience, it’s an effective solution.

That said, it looks like you have physical contact. That’s not good, no matter what you wrap it with. Suggest you to add a blister on the cowl before flight.

 

[Carlosanlley]

Yes. I have cowl clearance issues too, and I use short sections of header wrap to prevent burning. In my experience, it’s an effective solution.

That said, it looks like you have physical contact. That’s not good, no matter what you wrap it with. Suggest you to add a blister on the cowl before flight.

Thanks for sharing your experience. How many flight hours have you flown with the wrap installed?

Also, in your opinion, what could be the short-term impact of the exhaust remaining in contact with the cowling, even with the wrap installed?

 

[jdabney]

I’m currently dealing with an issue where my Vetterman Exhaust is making contact with the cowling at one specific point, creating a hot spot. We discovered it after doing some ground engine runs. At this point, the engine probably hasn’t run more than about 20 minutes total, and the only higher power setting we used was around 2,000 RPM for less than 5 minutes just to cycle the prop. I’m attaching photos of the hot spot.
View attachment 117698View attachment 117699

At one point we saw an IO-390 installation that had a heat shield wrap/sock covering the entire exhaust, and we initially thought about doing the same thing on ours. However, after speaking with Vetterman Exhaust, they told us they do not recommend it because the exhaust could fail. They did not go into much detail, but I assume it is because the wrap prevents the exhaust from dissipating heat properly, increasing the temperature of the entire exhaust system. At the time of that discussion, we were talking about wrapping the full exhaust system.
View attachment 117701

Now that I’m specifically dealing with this hot spot on the cowling, I’m considering applying heat shield wrap only on the section that is contacting the cowling — probably no more than about 3 inches — as a temporary solution. Longer term, I’m planning to modify the cowling to achieve at least 1/2" clearance between the exhaust and the cowling at the interference point.
View attachment 117700

Has anyone dealt with something similar? Also, does anyone have experience using heat shield wrap in this kind of application? The product I purchased is Thermo-Tec.

Yes, if the wrap touches the cowl, the vibration will chafe through the wrap in an hour or two of flight. The only safe solution is to eliminate the contact.

 

[Toobuilder]

Thanks for sharing your experience. How many flight hours have you flown with the wrap installed?

Also, in your opinion, what could be the short-term impact of the exhaust remaining in contact with the cowling, even with the wrap installed?

I have several hundred hours with my wrapped sections.

Looking more closely at your burn point, It appears that the insulation on the cowl side is “pillowy”. Is that the case? Is it possible that you do not have hard contact with the cowl itself? If you have positive clearance without that pillowy insulation I suggest removing a section of the blanket insulation - say a 3 inch diameter circle - and replace it with one layer of aluminum speed tape. If there is no physical contact then the speed tape combined with header wrap should be adequate. I have some frighteningly close gaps in my airplane and this combo is pretty effective. It’s worth a try before you add a blister.

 

[DanH]

I’m currently dealing with an issue where my Vetterman Exhaust is making contact with the cowling at one specific point,

Something is mounted funny or the pipe isn't right. Track down the root cause, skip the bandaid.

 

[Carlosanlley]

Something is mounted funny or the pipe isn't right. Track down the root cause, skip the bandaid.

Well, one thing to mention is that we went with a Lycoming IO-390 instead of the IO-360, so a lot of things that came in the FWF kit did not fit quite right, and on top of that, we went with the Showplanes cowling.

 

[DanH]

Carlos, I put a 390 in an RV8 starting near 20 years ago...and had the exhaust system modified to get the cowl clearance I wanted.