Exhaust Heat

The exhaust on my truck exits just in front of the rear wheels. The mufflers are almost directly below the seat. I get a lot of heat inside, most noticeably as it comes through the gap between the back and bottom of the seat. I've looked at various insulation solutions but can't decide what might work best. I have a wood floor so an adhesive-backed sheet on the bottom side won't work. Should I insulate inside? Wrap the mufflers? Other solutions? Please give me any suggestions you have on how to solve the heat problem.

I've had heat issues as well, but perhaps on a smaller scale.

When I first got my shop truck, it had a superwhamadyne high performance carburetor installed, and the fuel line tested the effects of gravity as the line ran over top of the air compressor.....


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I replaced the carburetor with a 2 bbl Holley, and ran the fuel line under the air compressor bracket, installing a fuel filter on the fender well.


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This worked fairly well for the limited putzin around I do with it, normally only a few miles at a time. Then came last Tuesday and the forcast of 100+ degrees weather. Got in my daily driver to head to work, and the PSD's starter had given up the ghost after 170,000 miles. Can't complain too loud about that. Still needed to make it to work, so I fired up the beast and it made the 20 minute drive without issue. ........until the return trip that afternoon. Temps were around 105 degrees, cowl vent barely helped, and the first substantial hill came after about 5 minutes of driving, so it was good and warmed up. I barely made it up the hill, the engine was spitting and snotting, and luckily for the impatient drivers behind me, there was a paved shoulder to the road. I finally inched to the top, found a safe place to pull over, and surveyed beneath the hood. I felt the fuel filter, which at this point, and considering the proximity to the exhaust manifold, was too warm to keep your hand on it. The worst hill behind me, I did manage to make it home, using the paved shoulder for most of the trip. Changed out the starter on the diesel dually that night, and decided to address my fuel line on the F7 the following night. Removed the fuel filter from the heated area, and installed a steel line in place of the rubber hose....


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This still left the line in close proximity to the infamous Y block crossover pipe. To help protect it from as much heat as possible, I made a stop by my buddy's motorcycle shop for some used HD (sportster, I think) heat shields........


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....and after many fittings and trimmings.....hey, this is the shiniest thing on this truck...


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....which helped out considerably. On your truck, the muffler is a major heat source but also a heat sink. There is quite a bit of metal there to hold the heat, so naturally it will dissipate for some time afterward. I don't know that a heat shield would be the optimal solution, I think my first inkling would be to get the mufflers out from under the cab to move that heat source elsewhere. If that is not a feasible solution for you, then perhaps a shield over top of the muffler would help to keep some of the heat off the bottom of the cab.. A racing buddy uses asbestos wrap on headers that may be another solution around the muffler..

I'll be the smart arse and say simply this......DRIVE FASTER...... then the airflow under the truck will get sucked the heat out quicker..

I used a thermal/acoustic blanket from EZ Cool - EZ Cool Automotive Insulation heat barrier and noise reduction for cars, trucks, classic cars, street rods and much more It's a lower cost alternative to DynaMat, and if you take time to read some of their technical backup and testing it's a pretty amazing product. Installed on the inside, beneath the carpeting.

It makes the most sense to start at the heat source (the muffler) and insulate it. Header wrap tape would be my choice. I've used it in a couple of places where an exhaust pipe comes too close to the starter or power brake diaphragm. If more insulation is needed, insulate the floor, right above the muffler.

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Originally Posted by daveS53

It makes the most sense to start at the heat source (the muffler) and insulate it. If more insulation is needed, insulate the floor, right above the muffler.

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Personally I'd opt for a heat shield before I tried insulation on the mufflers, but that's just me....

What is your concern pertaining to gluing a thermal pad to the floor?

Are you worried about moisture, or adhesion?

A sheet of polished stainless screwed to the bottom of the floor would certainly make a difference. Wrapping the mufflers will help significantly, but the wrap is delicate and will be hanging in tatters the first time you scrub. A heat shield with an air gap welded to the tops of the mufflers should also work well.

I'm concerned about adhesion to the wood. All the products I've looked at either say or imply they won't adhere to wood. The stainless steel plate is something I hadn't thought of.

Thanks for the thoughts so far, although it kinda leaves me where I already was.

I installed Dynamat under the carpets. But I also just ordered a 21 x 24" piece of Boom Mat to install under the floor just above the mufflers. I'll cut it in half and install a piece over each muffler.

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Originally Posted by Al G

I'm concerned about adhesion to the wood. All the products I've looked at either say or imply they won't adhere to wood. The stainless steel plate is something I hadn't thought of.

Thanks for the thoughts so far, although it kinda leaves me where I already was.

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If you simply seal the wood with Spar urethane you can glue anything you want to it. I do it all the time with speaker boxes.

Heat shields do not wrap a muffler, they are only on the top half. Heat shields will give the biggest bang for the buck. They set up off the muffler about an inch, this does two things. First the shield itself acts as a heat sink absorbing heat quickly and dissipating it. Second the air gap between the shield and muffler allows air flow to cool the heat that is radiating from the muffler.

Notice the way the shields for the header pipe is made post # 2. Go look under a pick up to get the full idea. Very common, could get one or two at a junk yard. Cut bend and fit if the mufflers on your hotrod truck are smaller then a stock truck.

If it is feeling hot in the winter you are in for a sauna come summer. I also suggest you consider sealing any leaks in the cockpit floor. Wood is not the best heat transfer material, radiates more then dissipates.

Had a 74 vette that had shields installed from the factory to the fiberglass floors.

If you're going to use a heat shield, note that aluminum is a much better conductor of heat than stainless steel.