Heat From Engine Making Cab Hot

[plantmeister]

I'm having a problem with my mustang pushing exorbitant amounts of heat into the cab while running. If it idles, it's even worse, like the heater is on. While driving, the heat still seems to warm my feet and makes it really hot in the cab. The temperature in the car generally stays about half or a little above the half on the gauge, so it's not overheating. Has a stock lx hood.

Note, this car sat for 10 years in storage and I haven't had it for long, so I'm sure it could be anything.

Does anyone have advice of how to fix this, or where to start looking? It was suggested to me that the vent/flap is stuck open and thas why the heat is coming into my cab. Any ideas?

 

[Mustang5L5]

Mustang's are fairly notorious for feeling heat from the exhaust rising up from the trans tunnel hunt. This is normal to a point, but how much is normal, and how much is something else is the big question.

A lot of times, when a carpet is reinstalled without the backing pads, or the inner shifter boot is missing, the heat from the exhaust rises into the trans tunnel and into the cabin. Often times, aftermarket exhaust parts can generate massive amounts of heat as well.

So questions to ask you. What sort of exhaust is on the car? Is the carpet aftermarket and lacking the backing pad? Is the inner shifter boot present. Are you running lean at all?


HVAC draws it's source air from the cowl vent near the windshield, so it wouldn't pull in engine heat.

 

[plantmeister]

As far as I can tell, everything on this car is stock, as far as engine parts go. The mufflers and exhaust system I think is original.

Now, the guy who sold me the car said he replaced the carpet, but I do remember him mentioning something about not having the padding under it. I didn't know it would cause this sort of heat.

Running lean, I'm not sure. The car likes to surge constantly when it's warmed up and idling, and the smell from the car around this time is plasticy/chemical smell. I'm not sure if that's what it smells like when it's running lean, but it does smell very strange around the car when it's hot.

And forgive my ignorance, but I'm not sure what/where the shifter boot is.

 

[Mustang5L5]

Is the car a 5-spd? If so, pull up the shifter trim holding the shifter boot and look under it. Is there a second rubber seal sitting ontop of the shifter? Or can you see the transmission, and the ground under the car?

And yes, not having padding under the carpet saves weight, but that padding is an insulator meant to reduce heat into the passenger compartment.

 

[plantmeister]

The car is an automatic, 5.0. I know there's a piece of trim missing around the shifter, but I'm not sure if that matters as much as what you're talking about.

Okay, great...that means I have to pull up the carpet and have that padding installed right? Is this expensive/tedious to do?

 

[General karthief]

When, not if, you pull the carpet, you can use some dynomat or something similar on the floor pan from the toe board back to the back seat, covering the trans tunnel too, then the padding and carpet.
Not a hard job just time consuming, seats, console have to come out. Don't forget the boot that covers the shifter hole.
I put sound deadener/heat insulation from dynomat from toe boards to tail lights, added about 14 pounds approx. I think it was worth it.

 

[mikestang63]

cheap solution is to get some spray on bedliner or underoating and spray the underneath of the car

 

[plantmeister]

Okay, good suggestions. I do want to put the mat in at some point, but I might be able to get help doing it, so that would be good.
When I got to work this morning, I let it idle and noticed the majority of the heat is indeed emanating from the center console right next to me. So now that's top priority right next to fixing my air conditioner, because this combined with no ac and Florida heat is killer! X(
Thanks for the info!

 

[General karthief]

There is also a boot and metal plate around the base of the steering column or maybe just the plate, can't remember, check that for leaks, also your blend door on the heater maybe leaking hot air but the majority will come through that shifter hole.

 

[Mstng93SSP]

If you have stock exhaust, maybe your cats are clogged and heating up and then heating the floor. With a stock exhaust you should not have a lot of heat around your feet.

 

[plantmeister]

I checked around the steering column, no heat coming from there. I'm starting to think maybe the blend stood is messed up. My windshield fogs up super fast when I use the heater, like it's seeping through the defrost vent.

As for the mufflers, how can I check for clogs? I was in thick traffic the other day, and had been sitting for a while, and I heard a loud noise and felt it in my car. I had to look around because I thought somebody might have hit me, very lightly. I assume it might have been a backfire? Is this caused by the clogged mufflers?

 

[Mustang5L5]

My windshield fogs up super fast when I use the heater, like it's seeping through the defrost vent.

That might be a sign of a leaking heater core.

 

[General karthief]

Take out you thermostat and test it on the stove, fill a small pan with water, just don't tell the cook, they usually get testy about using one of their cooking tools for automotive testing, with a meat thermometer see where the stat opens, I test new ones this way and have found several to be faulty. I'd buy one anyway and test it for accuracy.
Do you still have the factory puke tank?

 

[mikestang63]

trust me you would know if your cats were clogging- the car would run like crap and you might have some overheating issues.
Regarding the heater box going- can you smell antifreeze or mold inside the car. Is the passenger side carpet by the firewall damp. Are you needing to top off the radiator or overfill? Those are signs along with your windshield fogging up., If your vents are stuck on defrost that is normall an easy fix- there is a hard plastic line running across the top of the firewall from the vacuum tree marked with A/C to a vacuum fitting in the passenger side corner. Often this line gets brittle and breaks. Just replace it with some normal vacuum tubing. There is also another hard vacuum line from another tee in the passenger corner going inside the car- that one is more complicated to repair if it broke inside the car but 99% of the time its the first vacuum line I spoke about.

 

[plantmeister]

trust me you would know if your cats were clogging- the car would run like crap and you might have some overheating issues.
Regarding the heater box going- can you smell antifreeze or mold inside the car. Is the passenger side carpet by the firewall damp. Are you needing to top off the radiator or overfill? Those are signs along with your windshield fogging up., If your vents are stuck on defrost that is normall an easy fix- there is a hard plastic line running across the top of the firewall from the vacuum tree marked with A/C to a vacuum fitting in the passenger side corner. Often this line gets brittle and breaks. Just replace it with some normal vacuum tubing. There is also another hard vacuum line from another tee in the passenger corner going inside the car- that one is more complicated to repair if it broke inside the car but 99% of the time its the first vacuum line I spoke about.

No overheating, mold or antifreeze smell. Just terrible fogging whenever I use my heater. Sounds like it might be that vent/hose.

As for the cats, I think you might be right. It runs fine, except it tries to die when I shift from park to drive or reverse, the oil pressure has dropped recently, and it idles rough. Oil burn smell when I gun it, etc, but no loss of power. I'm sure there are interconnected problems through this car, but I don't think it's the cats causing those particular problems with it running bad. That's a whole other animal haha

 

[vristang]

Did you figure this out?

I wouldn't be so quick to rule out the cats... they can get incredibly hot if even partially plugged, and can cause an engine to stall at low speed...
It sat for a while too, right?

Do you smell antifreeze in your coolant? If it's straight water, you won't smell antifreeze from the heater core.

 

[plantmeister]

Did you figure this out?

I wouldn't be so quick to rule out the cats... they can get incredibly hot if even partially plugged, and can cause an engine to stall at low speed...
It sat for a while too, right?

Do you smell antifreeze in your coolant? If it's straight water, you won't smell antifreeze from the heater core.

Not yet-- a couple of pressing matters came up on the Mustang that I had to focus on first, so the heat has been put on the back burner. It may all be connected though, if it is the cats. But the fuel system really needs work, too. The guy I bought it from said the fuel tank was rusted out, so he replaced it and the pump, but NOT the filter. *face palm*. Along with the gaskets being rotted and bolts missing on the filler neck that I can't figure out what size to replace them with, it's a big mess.

Anyway, I've checked the passenger floorboard for dampness and I don't smell any antifreeze in the cab. The reservoir looked like it had antifreeze in it, but I'll check to be sure.

Yea, it sat in storage for 10 years, apparently. And it definitely shows.

 

[Mustang5L5]

As for the stalling issue when going from D to R, search for "Mustang idle reset procedure" and follow that.