I'm not sure if this is the right place to post this, but here goes... My '70 GS455 w/ A/C (not hooked up) cooks me on warm days, even with heat turned off. Hot air is coming from the dash area somewhere, not sure where. Air coming out of vents is not hot, vacuum operated valve for heater hose properly shuts off hot water flow to the heater core. Where is the hot air coming in? I am guessing through the small hole in firewall where wires and vacuum lines pass through, but it's hard to imaginge so much heat can come through a 1 inch hole. Just engine heat seeping through the firewall? I don't know, but even with the windows open on a warm day (75 deagrees or so) I get darn hot inside from this hot air. Any suggestions?
What is your exhaust? Stock diameter, or larger pipes? Larger pipes can sit closer to the floor boards. My header on the passenger side is about 1.5" to 2" away from the firewall, and a section of my carpet actually got brittle and crumbly there once. Are you absolutely sure your heater controls are shutting off flow to the heater core? In my Skylark, even though I have "fixed" the problem maybe a dozen times over the 15 years I've had it, somehow, my heater control creeps forward about a half inch while I drive, and I have a habit of shoving the control over every 15 minutes or so. Is your tranny overheating, maybe?
The cable for the heater should have an adjuster in it near the heater box. Proper adjustment of this cable calls for 1/2 inch of bounce when completely cold. This means that when you slide the lever all the way cold it should bounce back 1/2 an inch. This ensures that the heater door is completely closed. The hole where the vacuum lines runs through should have a big black grommet in it to block hot air. There shouldn't be any big openings between the engine compartment because air will rush in. The air under the hood is slightly pressurized at speed and with the windows open the cabin is slightly de-pressurized so a lot of air will move through a small opening. Close up any holes and put heat insulation under the carpet along the toe boards to block some of the exhaust heat. You can slip aluminum foil under the carpet to see how much heat is coming through the boards. John
With a flush n fill T adapter you can do a heater core bypass. [I do it to both of my cars in the summer] But what is your hood gasket like? If the gasket between the hood n cowl is worn or missing, the fresh air ducts will suck in hot engine air. Even if the AC is not hooked up. Set it to max ac. That will close the fresh air ducts. Seam to be the only way to close them fresh air ducts.
Thanks for the tips! I also thought about the hood seal as I cooked this weekend. It's in fine shape! I disconnected the vacuum line (and plugged it) to the heater control valve which should stop the flow of cooalnt to the heater core. I confirmed this by feeling the temperature of the hoses, and the hose after the valve is not hot, before the valve it is much warmer. Valve seems to be doing its job. I did plug the holes in firewall, didn't seem to help. I have exhuast manifolds, not headers. I'll check the floor insulation under the carpet. I suspect the seal between the A/C evaporator box and firewall is not good, as there seems to be a small gap between these peices. Maybe hot engine compartment air is coming in there? Looks like a big job to remove this and fix it. I think I'd at least have to remove the pass side valve cover in order to remove it. Remove pass side fender too? Yuk.
