C3 cabin heat

[Bill75]

I'm gaining some headway with the hot air coming out of my duct work but after 3/4 of an hour it slowly starts to build up and the ducts start to get hot. I took a drive today then opened the hood and put a temp probe on the heater/air cond box:240 deg.! Less than two inches away is the exhaust manifold 552 deg.! No wonder these cars get hot inside! With the slightest air movement in the ducts the air inside must gradually work it's way into the cabin. That heater/Air cond box is like a tiny oven.
I doubt even putting foil insulation over it would do much, 250 deg is too darn hot!
I noticed my car is without the foam rubber dam around the bell housing to keep the airflow from the engine compartment going past the bell housing. Is it possible that this would force the airflow to go out of the car in the exhaust manifold area instead of under the car and help create an airflow near the heater box? Sounds a little crazy, I know but something has to get rid of this hot air. I'm even thinking about making some kind of air deflector in front of the heater box to force it down.

Anyone have any thoughts?

 

[M&W's72vette]

Check this product out

http://www.coollizard.com/

I saw this at the SEMA show last year in Vegas, the guy had a coat of his heat barrier product on a griddle and had it turned up to 300 degrees and just a .040 thick layer of it kept ice cubes from melting any faster that the ones sitting on the table. Cool stuff!!

Mike

 

[Bill75]

Hi Mike,

I like your signature! That stuff might be something, pretty thin and it can be painted also, withstands 500 deg. I think I'd even buy the gun if I knew it would work! Thanks for the link.

 

[WayneLBurnham]

I epoxied a layer of aluminum flashing on my box...

...over a patch where the heater box had actually degraded from the heat. It recently fell off.

Next I am going to epoxy a layer of thermotec type fiberglass header wrap stuff like I used to insulate around my rear fiberspring and put a layer of aluminum over it. Alternately, one could use any of the thin ceramic type insulators like the stuff for under the carpets or tape on wire insulation to very effectively reduce heat radiation to the box from the header. If memory serves without going and looking, the involved header pipes are #6 & #8 and you have better than a half inch gap there - that's a lot in the insulation world. You could also wrap just the key 6-12" of pipe on each one to prevent radiation right there. That small amount of header wrap will neither serve as an oil absorbant wick to ignite or a source of warping since it's a long ways from the exhaust port and the union with the other primaries.

I have twin manual heater hose cutoffs (and no auto one - didn't come with the car when I got it.) The most effective thing I've done so far though was to just block off both the wiper tray vent intakes this spring. These were being force fed engine bay air through the no doubt malfunctioning big main duct door. (Just HOW *ARE* you supposed to get to that thing anyhow?)

I will remove these vent intake blocks (on those screen/filter things) when I rig my cowl induction and re-establish the rear hood to wiper tray air seal that, also, was never on the car since I've had it (it's an oversized L88 type aftermarket hood.) When I'm through with that, the center scoop deal from the rear will go only and entirely to the carb and no engine bay air will go to the wiper tray area (or up and over and around the windshield for that matter.)

I also think my perennial through-the-radiator air flow insufficiency feeds directly the air being forced through the engine bay into the cabin. Failure of the air dam system to block air from going under the car and thus coming up in part through the bay (especially my temporary lack of a block of this air at the bottom in front of the crossmember now that I've dumped the fan shroud with my new DeWitts and three Zirgo fan setup) is only increasing the pressure of the air in the bay beyond that which would be expected from the air flow through the radiator into the bay. I'm contemplating a larger blocking sheet or sheets going behind the crossmember - maybe all the way to the engine mount pods or even beyond. I have to figure out what likely impact this will have to prevent building an air pocket under the front of the car though.

I also want to rig a more traditional consumable, flexible or retractible airdam extension to go much closer to the ground. (When my deep, now armored, oil pan is 3" from the ground and the lowest rear pipes are 2.75", there's no reason the front dam shouldn't be 2.5".)

I didn't mean to go off on such a tangent on the aero concerns, but I think the convection effects of the engine heat are probably more important than the simple radiant ones in keeping the heat out of the cabin. As I haven't yet succeeded in fully preventing it (man, was it a LOT less today when I was testing other fixes/problems!), I can't be certain.

 

[Bill75]

Wayne,
I believe if you block off the upper vent 100% you will also block off the water passage from the wiper tray to the ground. Even with the door closed there's a small hole that lets the water drain thru. If you want to remove that vent mechanism, there's two screws thru a bracket that hold it in. You need to have mouse hands to get down in there!!
There's a rubber gasket where the hood seals off the engine compartment at the top of the firewall. If the seal is bad it might be letting in hot air from the engine. I recently discovered missing gaskets on my air conditioner lines where they enter the heater box to the evaporator. That was letting in heat, airflow and exhaust fumes. After plugging them it made a huge difference.

I agree about the radiant heat, the material Mike recommended looks like it might make a big difference, most of the stuff I've run across doesn't have much of an R value, I think the highest was 7 or something. Getting the hot air moving out of the area would also help a great deal, I might make up a simple deflector just for the hell of it and see if it makes any difference. That's assuming there's an airflow across the top of the engine.

 

[M&W's72vette]

I have a daytona style hood on my car, my thinking was to have the vents in the hood to get rid of some hot air from under the hood. When I did my turbo setup I could have hooked back up to the original exhaust pipes under the car but I went with sidepipes instead to see how much difference it made to the heat issue inside the car. The headers I used to have on the car were too close to the body in the collector area and kind of cooked the floorboards a little and it would get very hot on your feet. The exhaust pipes that go from the engine to the turbos arent even close to the floorboards now and the car is alot cooler inside. I am giong to use a vintage air setup so I can have a/c again as I had to remove the stock heater a/c setup to make room for the passenger side turbo and I am giong to put the non a/c vents in the car so you can get some fresh air in by your feet. I am doing a C-4 suspension conversion in a year or so and while I have the body off the frame I am going to spray the lizzard skin product everywhere under and inside the car to make it cooler and hopefully quieter too....gotta keep mama happy, if mama aint happy, nobodys happy...lol

 

[Grizzly]

Underhood Air Movement

Does anyone know if someone has tried to force air out the fender vents with something like radiator fans? Do people who have fans on their radiators find that in town driving is cooler in the car because of the increased air flow at slow speeds?

Just about baked this weekend and I know that I need some kind of AC, but it would seem to me that you still need to control the underhood temperatures.

 

[vmrod]

I always thought that fender vent-fans would be a 'cool' and functional add-on. Never actually made one though.

 

[WayneLBurnham]

In the C4 forum & site lead in fender fans were

mentioned on an alternator thread.

I've been interested also in relocating tranny and oil coolers (and perhaps future a/c condensor and "futurer" intercooler) to the upper fenders, adjacent to the hoods, above the wheels and such, to free air access to the main radiator. I hadn't thought of bay-to-wheel well fans until that thread earlier tonight - great idea (also might help cool brakes faster!)

 

[WayneLBurnham]

Yeah, mine's never had that...

There's a rubber gasket where the hood seals off the engine compartment at the top of the firewall. If the seal is bad it might be letting in hot air from the engine.

Never had one at all on this one. I'm sure when they replaced the hood they didn't bother. (I suspect I have the '82 style nose, ass, aftermarket hood and original lack of some interior parts - like rear interior quarter panels - are from a front-to-rear "sammich" hit, probably from sitting at a stop light babbling on a cell phone...)

I believe if you block off the upper vent 100% you will also block off the water passage from the wiper tray to the ground. Even with the door closed there's a small hole that lets the water drain thru.

I only blocked it with foil I spray painted black - it leaves leak room at the bottom. You know, I also wonder what role that wiper tray finish thing I bought performs to limit some of that hot air flow....it cracked so I took it out until I fix it.

If you want to remove that vent mechanism, there's two screws thru a bracket that hold it in. You need to have mouse hands to get down in there!!

I assumed there was no way in there other than with the fender off. I put the steel backing plate for my MSD 6AL on the driver side version of that. It was a lot of fun - I used some Harbor Freight Special "LongAss Brand" cheapy needle nose to hold those nuts once I had epoxied the backing plate to that wall. I dropped those nuts 478.219 times each, on average. :ugh (Then again, I was super pleased at how nicely that ignition fit there - I can even change the pills easily by hand!)

Hey, if I remove the mechanism, can I repair, rebend, regasket, respring, rewhatever the whole assembly and reinstall? Does it come out through the bottom or top or, may all the gods of fiberglass forbid, through the passenger compartment?

 

[Bill75]

Vent Removal

Wayne,

The whole mechanism will come out from the outside of the car. Remove the screen then the two bolts holding the mechanism. You'll have to move it around inside the duct until you find the right position and it'll come right out. I had mine out last year to fix a pinched line.

Bill

 

[Bill75]

Coollizard

I called Coollizard yesterday and had a really informative talk about their stuff. .040 thick and very flexible. The guy claims he can coat a piece of aluminium and bend it 90 deg and then back without harming the coating adhesion or cracking it. Also it can be painted any color after it's dried with a urethane paint as long as it has at least 12% elongation. The material streaches and shrinks with the base material it's been applied to so it doesn't crack. Has alot of documented cases of people being really happy with it. It's also fireproof and will stop a fire from spreading he claims.
Bad side is you need a special gun to spray it because of the large particle size and it costs $178 I think. It's probably well worth it though if it does the trick.

I think it would be a good addition but the real benifit would be to allow air to circulate in that area to get the hot air away from the firewall. I brought home a piece of aluminium last night to make up a model and give it a try.

 

[Bill75]

Wayne,

Why did you block off the vent 100% with tape? I know the answer might be "to keep out the hot air", but I found on my car that the top vent was open all the time when I got the car and was forcing air continually thru the duct work. According to the vacuum schematic for our cars, the top vent is supposed to be CLOSED with the control in the "OFF" position preventing fresh air from entering. When I removed the top vent actuator I found a small vacuum line pinched under the mounting bracket that was preventing the actuator from working. It had been installed that way from the factory! I replaced the small piece and the actuator and door work as designed now. Might want to investigate. You cannot see the small line unless you remove the actuator and door.
Also, that gasket at the top of the firewall is really important, if it's missing on your car the engine compartment air will really contaminate the fresh air seeping into the car around the wiper area and fresh air door.
Bill

 

[Bob Chadwick]

One of the ways you can control the engine heat going into the vent is by making sure that the rubber seal on the back of the hood is good.

Another area this is supposed to introduce a lot of hot air into the system is the area where the heater hoses go up to the heater core. I haven't had a chance to do it but have been told that it can be sealed up prtetty well with gasket material glued into place.

 

[Bill75]

I had some electrical putty that they use around the cable entrance to the service box and used it to seal the heater pipes on mine last week. I was really getting alot of exhaust in the car thru the unsealed air conditioner pipes where they enter the heater/air cond box. Man what a difference when I sealed those up.

I made a deflector shield out of aluminium positioned in front of the heater box. Therory is to move the air past the manifold and out of the car. It made a very big difference by not getting the heater box as hot. I could actually put my hand on it, after a similar ride without the shield it was 240 deg!! Truthfully though, I can't say it was due to air movement or just the fact that the 550 deg manifold was shielded from the heater box. The back of the AL shield was really hot. Aluminium transfers heat really well.

I did remove the right hand splash guard behind the front of the rocker panel and behind the front wheel. I was thinking it might increase the area where the air could flow out of the car. It opens it up big time to the outside world but it's hard to tell if it's making a difference yet. Maybe this weekend I'll go for a longer ride but it's easy to try, 4 bolts and it's out.

Bob, how's you paint job coming along? Same color?

Bill

 

[Bob Chadwick]

Bob, how's you paint job coming along? Same color?

Thanks for asking Bill. Dropped it off at Paintdaddy's last Sunday. Same color. I like the blue and it's cheaper since the door jambs, etc. don't have to be painted.

I'm going back and forth on a couple of Viper style parallel racing stripes. Today I think so. Ask me again tomorrow.

 

[WayneLBurnham]

Yeah - this was a spur of the moment thing

Wayne,

Why did you block off the vent 100% with tape? I know the answer might be "to keep out the hot air", but I found on my car that the top vent was open all the time when I got the car and was forcing air continually thru the duct work.

Also, that gasket at the top of the firewall is really important, if it's missing on your car the engine compartment air will really contaminate the fresh air seeping into the car around the wiper area and fresh air door.
Bill

Yeah, I know that door is open for some reason - whether malfunctioning from the mechanism or just bad seals. I've always know the lack of a rear gasket was the main motive force for the flood of 150+ degree air coming into the cabin. I had never removed the mech and will try it soon.

Now I don't have the problem with the hose introduction areas like you and Bob mentioned, although when I swap the current hose for the flexible metal line I'll double check.

I know a lot of my problem will end when I make the cowl air system (which mainly includes a rear hood seal the previous owners deleted.)

 

[Bill75]

Puzzled even more!

This heat coming thru the AC vents is really frustrating. I finally got the time and courage to remove the heat/ac box and the heater core expecting to find the gasket bad on the temp door. I even ordered a new one (that didn't even come close to being right) but the gasket was perfect. My hand is holding the box right where it bolts to the firewall and that open duct is the passageway to the A/C condenser. The door to the right is the acess to the heater core, when the temp indicator is moved, the door starts to open and allows air to pass thru the core to the other duct and closes off the A/C duct (I think that's right :crazy )
Anyway, there has to be a slight amount of air somehow getting into the condensor box allowing enough air movement to gradually pass thru the A/C ductwork. As the box heats up the air inside gets hotter. Just a guess. Maybe up thru the condensate drain??????

 

[Chas]

when i had this apart on my 73 to replace the core, i took the pin out and installed a small rubber O-ring between the assy....i had a rattle when i bought it, and while i was working on the housing out of the car , i noticed where the rattle came from within at the door ..this stopped it completely and didnt hamper the operation of the door...i wish i had taken pics of it so i could show it here like you have...nice work...ironic thing i had happen , in my effort to battle the heat in the car,i made it really sound proof! my flowmasters made it hard to hear the radio , let alone the passenger...now its a nice low rumble compared to the roar i had inside at speed..and the rattles are gone..still gets hot , just takes longer to work its way thru the layers... Chas

This heat coming thru the AC vents is really frustrating. I finally got the time and courage to remove the heat/ac box and the heater core expecting to find the gasket bad on the temp door. I even ordered a new one (that didn't even come close to being right) but the gasket was perfect. My hand is holding the box right where it bolts to the firewall and that open duct is the passageway to the A/C condenser. The door to the right is the acess to the heater core, when the temp indicator is moved, the door starts to open and allows air to pass thru the core to the other duct and closes off the A/C duct (I think that's right :crazy )
Anyway, there has to be a slight amount of air somehow getting into the condensor box allowing enough air movement to gradually pass thru the A/C ductwork. As the box heats up the air inside gets hotter. Just a guess. Maybe up thru the condensate drain??????

 

[Bill75]

Hi Chas,
That's a good trick thanks, I'll check mine over while it's apart, man I'm not anxious to do this again! I put insulation on the floor of mine last year and it made mine quiter also.
Bill