Hi Folks! My name is John and I own a C3. Over on the C3 General page we are trying to resolve the interior heat issue with some C3s. My 74 C3 T-top gets so hot around the floorboards that you can hardly keep your foot on the gas pedal after 45 minutes or so. This is a pretty common problem on C3s, and it got me wondering if this was a problem in the C2 community. It does not seem to matter what configuration the exhaust system uses, whether headers or stock manifolds, side pipes or standard exhaust, cat or no cat.

So, my question to all of you is: Can you drive your car for an hour at normal road speeds comfortably, or does the heat drive you out?

Feel free to check out the Interior Heat thread in the C3 General page for a thorough explanation of what we are dealing with and what has been done so far to try to resolve the situation.

Thanks for any insight you can provide,

John

 

My 65 has side pipes and I do not have any problems with engine or exhaust heat in the cabin. An earlier 65 I had had a replacement front end that had not been sealed well on the fender sides of the firewall and it felt like the heater was blowing hot air all the time around the door panels. Not so with original seal.

 

I think you'll find that unwanted heat in the cabin is a frequent complaint of C2 owners as well, witness the dynomat discussions we have here from time to time. The fiberglass floor pan, combined with the standard jute padding under the carpet and what little insulation the General provided back in the day, are certainly not in keeping with modern expectations. First order of business, however, is to seal up any holes or missing grommets, etc. Then consider higher performing insulation. I've revisitted the boots around my clutch rod, accel rod, patched up a hole left by Bubba, etc. and it really helped; a layer of Dynomat on the driver and passenger front floorboard also helped, for me. I note that I have sidepipes; I think it's just heat coming off the engine and the exhaust manifolds.

By the way, the #1 offender of unwanted heat in my C2 is (was) the heater box, which runs hot coolant through it 100% of the time. When I saw my little girl (who loves to ride in my 65 with Daddy) holding her legs up during one of our rides, I knew it was time to do something - I went ahead and put a shut off valve on the incoming coolant hose to the heater box, kinda near where the battery sits (I didn't invent this, I saw it detailed here on the C1/C2 section) and THAT made a huge difference.

 

I have a 68 L-79 and have had issues with heat. The 68 has shields under the floor that extends up to the firewall. There is also a heat shield on top of the transmission. That said, I added a heat wrap on each exhaust pipe from the exhaust manifold to the crossmember. I did this about 15 years ago and have not had a problem with rust from trapped water. It made a difference. I would also use ThermoTec under the carpet on the cabin floor. Jerry

 

I have used Dynamat Extreme in my 65 and in a few C1's.
Helps reduce cabin heat and quiets the interior of the car.
I'm getting ready to install it in my 57 Gasser.

 

my 62 floor gets so hot that i can't comfortably hold my hand on the bare floor, i have recorded 150*....

i read once-upon-a-time that there was a 'horse collar' shaped piece of insulation used on C3s between the firewall/transmission tunnel and the bellhousing to keep hot air from flowing down thetransission tunnel
Bill

 

Side exhaust made a big diff in my 63 coupe. So does side vent windows turned all the way out...oops.

Louvered splash pans? Had a 74 coupe but don't recall a heat problem.

Wonder if as an experiment you ran the car with the hood popped. Early cars do that to keep the engine cool, wonder what affect it would have oin the interior?

Missing any firewall plugs?

 

Funny, since I have a BB hood on my 65 and since I never (intentionally) drive it in the rain, I removed the rain shields from the hood vents some time ago and thus made them quite functional. Noticed a little cooler operating temps on the gauge, but didn't notice an appreciable decrease in firewall-floorboard heat, but that's a seat of the pants observation.

 

My 67 coupe is very hot inside. I have factory A/C too. A great deal of the heat is from a torn shifter boot but it still gets hot inside. I have a towel wrapped around the shifter to keep exhaust and heat out. When I take it for a spin in the summer, (I'm in Texas so summer is 9 months of the year) when I get out, my jeans and shirt are soaked with sweat. Girlfriend doesn't like riding in it most of the year. I was thinking about some Dynomat or Refectix type shielding for it.

The undisputed king of unbearable heat though, was my C3 74 convertible with Hooker sidepipes. That one was so hot in the floor boards, that it melted a guys tennis shoes because they touched against a steel rod under the dash or something. I was in college at UT Austin, and when I would go from Fort Worth to Austin, I would often have a 12 pack of Cokes in the passenger seat. If they sat in the floor board area, I would hear a high pitched "ping" a number of times during the 3 hour trip. When I got to Austin, I would find that all of the cans were deformed from the heat and carbonation trying to explode. On two occasions, one or more of the cans would explode and get a pressurized pin holes spraying Coke out into the cab.

On the 74, I even had a thick amount of the pink Owens Corning fiberglass under the carpet. I had so much under there, that the carpet was squishy and puffy. Girls had to wrap their legs with towels so that they wouldn't burn from the heat coming from the footwells. That was the hottest car I could ever imagine but it was such a chick magnet and so much fun!....

 

just did my floor and tranny/ console with thermotec...
do the research and you will see the differnce.
I used the product that called heat and sound barrier.
1/16 of inch thickness. self-adhesive backing
2000 f made a nice differnce. still warm,but not hot.
49 bucks a roll 60x36 inches at summit

 

Buy the thermal barrier kit from Wilcox along with new rubber backed jute padding. The foil faced thermal barrier is pre-cut and needs to be glued down for the install. The jute padding gets glued down over the thermal barrier and there's no problem with the carpet install. Very very easy and it works. Just finished a 550 mi round trip up beautiful Coast Hwy 101 in California with outside air temp of 82 degrees. Some stop and go traffic getting out of L. A. with the A/C on and the whole floorboard was cool and the cabin was very quiet. So quiet that now I hear the wind noise through the doors weatherstrip which will need replacement and adjustment. Project creep. I'm used to it.
Tom

 

Thermal insulation under the carpet was worth every penny. It's added two months to my driving season here, as in its otherwise too dang HOT in July, August and September to drive it (no AC). Now I can drive until mid-May and start again in late Sept. (Yeah Diablo thinks I'm a wuss....lol)

 

I used a product a few years ago called Mighty Mat I believe. It's foil backed fiberglass that was developed for the restaurant industry. It's very light and easy to work with. It was also very reasonable.

 

I've done all of the above suggestions with the exception of the heat barrier on the floor which I will be doing this winter when I re-carpet. Little by little it all adds up to a more comfortable car. Personally, I'd start with the heater shutoff valve. It was the most effective, easiest and least expensive thing I've done to reduce interior heat.

 

I would like to thank everyone that has given responses. You have been very helpful, and confirmed my feeling that the C3 community was not alone in battling this problem.

Thanks a million!

John

 

I recently sold my 69 big block. It was a 427/400 HP with factory side exhausts.

I had all the shields in place, i.e., the underbody metal shields and the plastic "toe board" shields. Had all the foam shields too.

The floor boards would get so hot after an hour or so that you could burn your feet....

My 63 does not have that problem.

Chuck