Cold Outside Air Through Firewall

[Herewego]

Hey Everyone,
I have searched for an answer to this question to no avail. I appologize if it has already been discussed. My 09 has a lot of cold air blowing through ( I Think) the firewall when driving down the road. The heater/Blower is working fine, but its getting mixed with this cold outside air. I have not located any openings, but im 6'5" and not very flexible. Is there any common area that air leaks through? Hopefully its as easy as stuffing Rags/Insulsulation in. Its getting pretty cold in NY.

Thanks in advance

 

[richingalveston]

Make sure the rubber around your floor vents are good and that the vents are closing good, the two largest holes are where the speedo cable and the glow plug cables go through the fire wall. The rubber graumets for these come out pretty easy.

 

[jw4x4]

Sounds to me like the side vent(s) are open.

 

[Barrman]

I second the kick panel vent door seal. I pulled a set off a truck the other day that had 1/4-1/2 inch gaps all around each door. No way is air going to be held by by that. Replacement doors are $29.99 each at LMC. Try putting duct tape on both housings and see if it stops.

 

[Herewego]

Side vents are both closed. I will check for gaps tho. I can feel the air blowing through with my hand. It seams to be more to the center of the firewall. Very close to where the hot air blows out.

 

[jw4x4]

I am at a loss to explain that one. Perhaps when its dark, have someone get under the truck and shine a flashlight toward the area and look for gaps from the inside?

 

[jw4x4]

Transfer case shifter boot?

 

[Herewego]

Good idea with the flash light! If I find anything interesting ill let you guys know. Thanks

 

[o1951]

Extra hole someone made for cable to equipment removed?

All else fails- you can do what I did once. Connect shop vac hose to shop vac exhaust. Open a window enough to get hose thru. Seal with cardboard and duct tape.
Fire up vac. Go around outside and under truck and feel/ see air blowing out. R/R as necessary.

 

[richingalveston]

right above your vent box is where the glow plug harness wires come through for your diagnostic port. It is a 2 inch hole. from the outside, it is just below the resistor and towards the pasenger side about 4 to 6 inches from center. you can follow the diagnostic port wires to the hole from the inside or look for the flat plug just behind the trans dipstick to find the hole. The other issue might be the seal around the heater core box. It is two pieces, one inside and one outside and the two peices have foam weatherstripping around them to seal each side against the fire wall.

 

[MarcusOReallyus]

All else fails- you can do what I did once. Connect shop vac hose to shop vac exhaust. Open a window enough to get hose thru. Seal with cardboard and duct tape.
Fire up vac. Go around outside and under truck and feel/ see air blowing out. R/R as necessary.

Them's good thinkin's!


To add to that, if you still can't find it, add some smoke to the process. It's probably easiest to reverse the flow, and move your source of smoke around the firewall, etc. to see where it gets pulled in. Obviously, you need to do this in a sheltered area.

 

[Warthog]

Are you sure the heater vent flap is closing all the way? With it open fresh air will come in.

 

[Herewego]

Update. So while looking at a friends M1009 today I noticed a piece on his lower heater duct assembly that I do not have on my vehicle. This could be the solution to my problem, and so the hunt begins. I pointed the piece out in the picture. Note....The picture is from google and just shows the part I'm missing.

 

[richingalveston]

that is just a diverter that blows air three directions, will have nothing to do with the cold air issue. it is either your vent flap, side vents or a hole open behind the dash
look at the diagnostic harness that goes through the firewall behind your trans dipstic to make sure the stopper is there. also check your heater core box gaskets.

 

[Vhyle]

right above your vent box is where the glow plug harness wires come through for your diagnostic port. It is a 2 inch hole. from the outside, it is just below the resistor and towards the pasenger side about 4 to 6 inches from center. you can follow the diagnostic port wires to the hole from the inside or look for the flat plug just behind the trans dipstick to find the hole. The other issue might be the seal around the heater core box. It is two pieces, one inside and one outside and the two peices have foam weatherstripping around them to seal each side against the fire wall.

This. The grommet on this exact harness on my truck was out of the firewall, and I didn't even know it until I had the air cleaner and GP resistor removed. Pulled on it and popped it back in place. How long will it stay? I guess we'll see.

 

[pbrstreetgang]

Where is the vent flap located
i have same issues
replaced with origjnal copper heater core, sealed, insulated heater box, cleaned all vents out completely, had two mechanics
look at system, put card board in grill, replaced two or three radiator caps, and four or five thermostats, all 190 temp and tested in pot on stove before installation
still have warmish/coldish air

 

[Skinny]

Yeah, I get outside air from everywhere except where a piece of glass exists. Start going through all connections on the firewall with sealer. Open up your door panels and make sure the plastic barrier if it has one isn't ripped. These are 30 year old bare bone trucks. The nice thing is in the winter, the hot air blowing off the engine comes up through my transfer case shifter hole and keeps me warm

You may be replacing all weatherstrip and rubber seals on the cab to solve this problem.

 

[pbrstreetgang]

What does it mean if i just get cold air when the fan blows
as if i had ac in the truck.

The heater hoses are cool after truck has been running for a hour

 

[richingalveston]

your heater core is stopped up, if the water does not flow, the hoses will stay cold. take both of them loose and see if you can flush some water through.

 

[Hasdrubal]

Sounds like your thermostat.